ALBERT

Description: Imperfect scaling in distributions of radar-derived rainfall fields Hydrology and Earth System Sciences Discussions, 10, 11385-11422, 2013 Author(s): M. J. van den Berg, L. Delobbe, and N. E. C. Verhoest Fine scale rainfall observations for modeling exercises are often not available, but rather coarser data derived from a variety of sources are used. Effectively using these data sources in models often requires the probability distribution of the data at the applicable scale. Although numerous models for scaling distributions exist, these are often based on theoretical developments, rather than on data. In this study, we develop a model based on the α-stable distribution of rainfall fields, and tested on 5 min radar data from a Belgian weather radar. We use these data to estimate functions that describe parameters of the distribution over various scales. Moreover, we study how the mean of the distribution and the intermittency change with scale, and validate and design functions to describe the shape parameter of the distribution. This information was combined into an effective model of the distribution. Finally, the model was fitted to data from numerous storms, and the resulting parameters were compared to investigate the change in scaling behavior through time.

Description: Spatially resolved information on karst conduit flow from in-cave dye-tracing Hydrology and Earth System Sciences Discussions, 10, 11311-11335, 2013 Author(s): U. Lauber, W. Ufrecht, and N. Goldscheider Artificial tracers are powerful tools to investigate karst systems. Tracers are commonly injected into sinking streams or dolines, while springs serve as monitoring sites. The obtained flow and transport parameters represent mixed information from the vadose, epiphreatic and phreatic zones, i.e., the aquifer remains a black box. Accessible active caves constitute valuable but underexploited natural laboratories to gain detailed insights into the hydrologic functioning of the aquifer. Two multi-tracer tests in the catchment of a major karst spring (Blautopf, Germany) with injections and monitoring in two associated water caves aimed at obtaining spatially and temporally resolved information on groundwater flow in different compartments of the system. Two tracers were injected in the caves to characterize the hydraulic connections between them and with the spring. Two injections at the land surface, far from the spring, aimed at resolving the aquifer's internal drainage structure. Tracer breakthrough curves were monitored by field fluorimeters in caves and at the spring. Results demonstrate the dendritic drainage structure of the aquifer. It was possible to obtain relevant flow and transport parameters for different sections of this system. The highest mean flow velocities (275 m h −1 ) were observed in the near-spring epiphreatic section (open-channel flow), while velocities in the phreatic zone (pressurized flow) were one order of magnitude lower. Determined conduit water volumes confirm results of water balances and hydrograph analyses. In conclusion, experiments and monitoring in caves can deliver spatially resolved information on karst aquifer heterogeneity and dynamics that cannot be obtained by traditional investigative methods.

Description: On the lack of robustness of hydrologic models regarding water balance simulation – a diagnostic approach on 20 mountainous catchments using three models of increasing complexity Hydrology and Earth System Sciences Discussions, 10, 11337-11383, 2013 Author(s): L. Coron, V. Andréassian, C. Perrin, M. Bourqui, and F. Hendrickx This paper investigates the robustness of rainfall–runoff models when their parameters are transferred in time. More specifically, we studied their ability to simulate water balance on periods with different hydroclimatic characteristics. The testing procedure consisted in a series of parameter transfers between 10-yr periods and the systematic analysis of mean-volume errors. This procedure was applied to three conceptual models of different structural complexity over 20 mountainous catchments in southern France. The results showed that robustness problems are common. Errors on 10-yr-mean flows were significant for all three models and calibration periods, even when the entire record was used for calibration. Various graphical and numerical tools were used to show strong similarities between the shapes of mean flow biases calculated on a 10-yr-long sliding window when various parameter sets are used. Unexpected behavioural similarities were observed between the three models tested, considering their large differences in structural complexity. While the actual causes for robustness problems in these models remain unclear, this work stresses the limited transferability in time of the water balance adjustments made through parameter optimization. Although absolute differences between simulations obtained with different calibrated parameter sets were sometimes substantial, relative differences in simulated mean flows between time periods remained similar regardless of the calibrated parameter sets.

Description: The Chemistry CATT-BRAMS model (CCATT-BRAMS 4.5): a regional atmospheric model system for integrated air quality and weather forecasting and research Geoscientific Model Development, 6, 1389-1405, 2013 Author(s): K. M. Longo, S. R. Freitas, M. Pirre, V. Marécal, L. F. Rodrigues, J. Panetta, M. F. Alonso, N. E. Rosário, D. S. Moreira, M. S. Gácita, J. Arteta, R. Fonseca, R. Stockler, D. M. Katsurayama, A. Fazenda, and M. Bela Coupled Chemistry Aerosol-Tracer Transport model to the Brazilian developments on the Regional Atmospheric Modeling System (CCATT-BRAMS, version 4.5) is an on-line regional chemical transport model designed for local and regional studies of atmospheric chemistry from the surface to the lower stratosphere suitable both for operational and research purposes. It includes gaseous/aqueous chemistry, photochemistry, scavenging and dry deposition. The CCATT-BRAMS model takes advantage of BRAMS-specific development for the tropics/subtropics as well as the recent availability of preprocessing tools for chemical mechanisms and fast codes for photolysis rates. BRAMS includes state-of-the-art physical parameterizations and dynamic formulations to simulate atmospheric circulations down to the meter. This on-line coupling of meteorology and chemistry allows the system to be used for simultaneous weather and chemical composition forecasts as well as potential feedback between the two. The entire system is made of three preprocessing software tools for user-defined chemical mechanisms, aerosol and trace gas emissions fields and the interpolation of initial and boundary conditions for meteorology and chemistry. In this paper, the model description is provided along with the evaluations performed by using observational data obtained from ground-based stations, instruments aboard aircrafts and retrieval from space remote sensing. The evaluation accounts for model applications at different scales from megacities and the Amazon Basin up to the intercontinental region of the Southern Hemisphere.

Description: Antecedent flow conditions and nitrate concentrations in the Mississippi River Basin Hydrology and Earth System Sciences Discussions, 10, 11451-11484, 2013 Author(s): J. C. Murphy, R. M. Hirsch, and L. A. Sprague The influence of antecedent flow conditions on nitrate concentrations was explored at eight sites in the Mississippi River Basin, USA. Antecedent moisture conditions have been shown to influence nutrient export from small, relatively homogenous basins, but this influence has not been observed at a regional or continental scale. Antecedent flow conditions were quantified as the ratio between the mean daily flow of the previous year and the mean daily flow from the period of record ( Q ratio), and the Q ratio was statistically related to nitrate anomalies (the unexplained variability in nitrate concentration after filtering out season, long-term trend, and contemporaneous flow effects) at each site. Nitrate anomaly and Q ratio were negatively related at three of the four major tributary sites and upstream in the Mississippi River, indicating that when the previous year was drier than average, at these sites, nitrate concentrations were higher than expected. The strength of these relationships increased when data were subdivided by contemporaneous flow conditions. Five of the eight sites had significant negative relationships ( p ≤ 0.05) at high or moderately high contemporaneous flows, suggesting nitrate that accumulates in these basins during a drought is flushed during subsequent storm events. At half of the sites, when flow during the previous year was 50% drier than average, nitrate concentration can be from 9 and 27% higher than nitrate concentrations that follow a year with average daily flow. Conversely, nitrate concentration can be from 8 and 21% lower than expected when the previous year was 50% wetter than average. These relationships between nitrate concentration and Q ratio serve as the basis for future studies that can better define specific hydrologic processes occurring during and after a drought, which influence nitrate concentration, such as the duration or magnitude of low flows, and the timing of low and high flows.

Description: Contribution of snow and glacier melt to discharge for highly glacierised catchments in Norway Hydrology and Earth System Sciences Discussions, 10, 11485-11517, 2013 Author(s): M. Engelhardt, T. V. Schuler, and L. M. Andreassen Glacierised catchments significantly alter the streamflow regime due to snow and glacier meltwater contribution to discharge. In this study, we modelled the mass balance and discharge rates for three highly glacierised catchments (〉50% glacier cover) in western Norway over the period 1961–2012. The spatial pattern of the catchments follows a gradient in climate continentality from west to east. The model uses gridded temperature and precipitation values from seNorge ( http://senorge.no ) as input which are available at a daily resolution. It accounts for accumulation of snow, transformation of snow to firn and ice, evaporation and melt. The model was calibrated for each catchment based on measurements of seasonal glacier mass-balances and daily discharge rates. For validation, daily melt rates were compared with measurements from sonic rangers located in the ablation zones of two of the glaciers and an uncertainty analysis was performed for the third catchment. The discharge contributions from snowmelt, glacier melt and rain were analysed with respect to spatial variations and temporal evolution. The model simulations reveal an increase of the relative contribution from glacier melt for the three catchments from less than 10% in the early 1990s to 15–30% in the late 2000s. The decline in precipitation by 10–20% in the same period was therefore overcompensated resulting in an increase of the annual discharge by 5–20%. Annual discharge sums and annual glacier melt are strongest correlated with annual and winter precipitation at the most maritime glacier and, with increased climate continentality, variations in both glacier melt contribution and annual discharge are becoming stronger correlated with variations in summer temperatures.

Description: δ 18 O water isotope in the i LOVECLIM model (version 1.0) – Part 1: Implementation and verification Geoscientific Model Development, 6, 1481-1491, 2013 Author(s): D. M. Roche A new 18 O stable water isotope scheme is developed for three components of the i LOVECLIM coupled climate model: atmospheric, oceanic and land surface. The equations required to reproduce the fractionation of stable water isotopes in the simplified atmospheric model ECBilt are developed consistently with the moisture scheme. Simplifications in the processes are made to account for the simplified vertical structure including only one moist layer. Implementation of these equations together with a passive tracer scheme for the ocean and a equilibrium fractionation scheme for the land surface leads to the closure of the (isotopic-) water budget in our climate system. Following the implementation, verification of the existence of usual δ 18 O to climatic relationships are performed for the Rayleigh distillation, the Dansgaard relationship and the δ 18 O –salinity relationship. Advantages and caveats of the approach taken are outlined. The isotopic fields simulated are shown to reproduce most expected oxygen-18–climate relationships with the notable exception of the isotopic composition in Antarctica.

Description: δ 18 O water isotope in the i LOVECLIM model (version 1.0) – Part 3: A palaeo-perspective based on present-day data–model comparison for oxygen stable isotopes in carbonates Geoscientific Model Development, 6, 1505-1516, 2013 Author(s): T. Caley and D. M. Roche Oxygen stable isotopes (δ 18 O) are among the most useful tools in palaeoclimatology/palaeoceanography. Simulation of oxygen stable isotopes allows testing how the past variability of these isotopes in water can be interpreted. By modelling the proxy directly in the model, the results can also be directly compared with the data. Water isotopes have been implemented in the global three-dimensional model of intermediate complexity i LOVECLIM, allowing fully coupled atmosphere–ocean simulations. In this study, we present the validation of the model results for present-day climate against the global database for oxygen stable isotopes in carbonates. The limitation of the model together with the processes operating in the natural environment reveal the complexity of use the continental calcite-δ 18 O signal of speleothems for a global quantitative data–model comparison exercise. On the contrary, the reconstructed surface ocean calcite-δ 18 O signal in i LOVECLIM does show a very good agreement with the late Holocene database (foraminifers) at the global and regional scales. Our results indicate that temperature and the isotopic composition of the seawater are the main control on the fossil-δ 18 O signal recorded in foraminifer shells when all species are grouped together. Depth habitat, seasonality and other ecological effects play a more significant role when individual species are considered. We argue that a data–model comparison for surface ocean calcite δ 18 O in past climates, such as the Last Glacial Maximum (≈ 21 000 yr), could constitute an interesting tool for mapping the potential shifts of the frontal systems and circulation changes throughout time. Similarly, the potential changes in intermediate oceanic circulation systems in the past could be documented by a data (benthic foraminifers)-model comparison exercise whereas future investigations are necessary in order to quantitatively compare the results with data for the deep ocean.

Description: Bias correction can modify climate model-simulated precipitation changes without adverse affect on the ensemble mean Hydrology and Earth System Sciences Discussions, 10, 11585-11611, 2013 Author(s): E. P. Maurer and D. W. Pierce When applied to remove climate model biases in precipitation, quantile mapping can in some settings modify the simulated trends. This has important implications when the precipitation will be used to drive an impacts model that is sensitive to changes in precipitation. We use daily precipitation output from 12 general circulation models (GCMs) over the conterminous United States interpolated to a common 1° grid, and gridded observations aggregated to the same scale, to compare precipitation differences before and after quantile mapping bias correction. The change in seasonal mean (winter, DJF, and summer, JJA) precipitation between different 30-yr historical periods is compared to examine (1) the consensus among GCMs as to whether the bias correction tends to amplify or diminish their simulated precipitation trends, and (2) whether the modification of the change in precipitation tends to improve or degrade the correspondence to observed changes in precipitation for the same periods. In some cases, for a particular GCM, the trend modification can be as large as the original simulated change, though the areas where this occurs varies among GCMs so the ensemble median shows smaller trend modification. In specific locations and seasons the trend modification by quantile mapping improves correspondence with observed trends, and in others it degrades it. In the majority of the domain the ensemble median is for little effect on the correspondence of simulated precipitation trends with observed. This highlights the need to use an ensemble of GCMs rather than relying on a small number of models to estimate impacts.

Description: Can we determine what controls the spatio-temporal distribution of d-excess and 17 O-excess in precipitation using the LMDZ general circulation model? Climate of the Past, 9, 2173-2193, 2013 Author(s): C. Risi, A. Landais, R. Winkler, and F. Vimeux Combined measurements of the H 2 18 O and HDO isotopic ratios in precipitation, leading to second-order parameter D-excess, have provided additional constraints on past climates compared to the H 2 18 O isotopic ratio alone. More recently, measurements of H 2 17 O have led to another second-order parameter: 17 O-excess. Recent studies suggest that 17 O-excess in polar ice may provide information on evaporative conditions at the moisture source. However, the processes controlling the spatio-temporal distribution of 17 O-excess are still far from being fully understood. We use the isotopic general circulation model (GCM) LMDZ to better understand what controls d-excess and 17 O-excess in precipitation at present-day (PD) and during the last glacial maximum (LGM). The simulation of D-excess and 17 O-excess is evaluated against measurements in meteoric water, water vapor and polar ice cores. A set of sensitivity tests and diagnostics are used to quantify the relative effects of evaporative conditions (sea surface temperature and relative humidity), Rayleigh distillation, mixing between vapors from different origins, precipitation re-evaporation and supersaturation during condensation at low temperature. In LMDZ, simulations suggest that in the tropics convective processes and rain re-evaporation are important controls on precipitation D-excess and 17 O-excess. In higher latitudes, the effect of distillation, mixing between vapors from different origins and supersaturation are the most important controls. For example, the lower d-excess and 17 O-excess at LGM simulated at LGM are mainly due to the supersaturation effect. The effect of supersaturation is however very sensitive to a parameter whose tuning would require more measurements and laboratory experiments. Evaporative conditions had previously been suggested to be key controlling factors of d-excess and 17 O-excess, but LMDZ underestimates their role. More generally, some shortcomings in the simulation of 17 O-excess by LMDZ suggest that general circulation models are not yet the perfect tool to quantify with confidence all processes controlling 17 O-excess.

Description: Assimilating water column and satellite data for marine export production estimation Geoscientific Model Development, 6, 1575-1590, 2013 Author(s): X. Yao and R. Schlitzer Recent advances in satellite retrieval methodology now allow for estimation of particular organic carbon (POC) concentration in ocean surface waters directly from satellite-based optical data. Because of the good coverage, these data reveal small-scale spatial and temporal concentration gradients and document the evolution of surface water POC as well as the underlying driving biogeochemical processes throughout the seasons. Water column nutrient data also reveal biogeochemical activity. However, because of the scarcity of data, the deduction of temporal changes of particle production and export is not possible in most parts of the ocean. Here we present first results from a new study combining both data streams, thereby exploiting the high spatio-temporal resolution of surface POC concentrations from satellite optical sensors with water column nutrient data having sparser coverage but providing information throughout the entire water column. We use a medium-resolution global model with steady-state 3-D circulation that has been optimized by fitting to a large number of hydrographic parameters and tracers, including CFCs and natural radiocarbon. Production and export of POC is allowed to vary monthly, and the magnitudes of the monthly export fluxes are determined by fitting the model to satellite POC data as well as water column nutrient data using the adjoint method. Two cases have been investigated: (1) the production rate of POC is set to be proportional to export production (EP) and the seasonal changes are assumed sinusoidal (meridionally varying amplitude and phase), and (2) the POC production rate is linked to primary production rates (literature). Both cases were run with the same initial state and model settings, and show total cost function decreases of 12 and 95%, respectively. The POC misfit term alone decreased by 75 and 99.8%. The integrated annual global POC exports of the two cases are 9.9 and 12.3 Gt C yr −1 , respectively. Overall, the remaining POC and phosphate misfits of both solutions are considered too large, and the difference fields still exhibit significant systematic geographical patterns. This indicates that the present model runs are too simplistic and do not fully explain the data. Further, more refined model setups are needed.

Description: The effect of training image and secondary data integration with multiple-point geostatistics in groundwater modeling Hydrology and Earth System Sciences Discussions, 10, 11829-11860, 2013 Author(s): X. He, T. O. Sonnenborg, F. Jørgensen, and K. H. Jensen Multiple-point geostatistic simulation (MPS) has recently become popular in stochastic hydrogeology, primarily because of its capability to derive multivariate distributions from the training image (TI). However, its application in three dimensional simulations has been constrained by the difficulty of constructing 3-D TI. The object-based TiGenerator may be a useful tool in this regard; yet the sensitivity of model predictions to the training image has not been documented. Another issue in MPS is the integration of multiple geophysical data. The best way to retrieve and incorporate information from high resolution geophysical data is still under discussion. This work shows that TI from TiGenerator delivers acceptable results when used for groundwater modeling, although the TI directly converted from high resolution geophysical data leads to better simulation. The model results also indicate that soft conditioning in MPS is a convenient and efficient way of integrating secondary data such as 3-D airborne electromagnetic data, but over conditioning has to be avoided.

Description: Multi-decadal river flows variations in France Hydrology and Earth System Sciences Discussions, 10, 11861-11900, 2013 Author(s): J. Boé and F. Habets In this article, multi-decadal variations in French hydroclimate are investigated, with a specific focus on river flows. Based on long observed series, it is shown that river flows in France generally exhibit large multi-decadal variations on the historical period, especially in spring. Differences of means between two 21 yr periods of the 20th century as large as 40% are indeed found for many gauging stations. Multi-decadal spring river flows variations are associated with variations in spring precipitation and temperature. These multi-decadal variations in precipitation are themselves found to be driven by large-scale atmospheric circulation, more precisely by a multi-decadal oscillation in a sea level pressure dipole between western Europe and the East Atlantic. It is suggested that the Atlantic Multidecadal Variability, the main mode of decadal variability in the North Atlantic/Europe sector, controls those variations in large-scale circulation and is therefore the main ultimate driver of multi-decadal variations in spring river flows. Multi-decadal variations in river flows in other seasons, and in particular summer, are also noted. As they are not associated with significant surface climate anomalies (i.e. temperature, precipitation) in summer, other mechanisms are investigated based on hydrological simulations. The impact of climate variations in spring on summer soil moisture, and the impact of soil moisture in summer on the runoff to precipitation ratio, could potentially play a role in multi-decadal summer river flows variations. The large amplitude of the multi-decadal variations in French river flows suggests that internal variability may play a very important role in the evolution of river flows during the next decades, potentially temporarily limiting, reversing or seriously aggravating the long-term impacts of anthropogenic climate change.

Description: Enhancing the representation of subgrid land surface characteristics in land surface models Geoscientific Model Development, 6, 1609-1622, 2013 Author(s): Y. Ke, L. R. Leung, M. Huang, and H. Li Land surface heterogeneity has long been recognized as important to represent in the land surface models. In most existing land surface models, the spatial variability of surface cover is represented as subgrid composition of multiple surface cover types, although subgrid topography also has major controls on surface processes. In this study, we developed a new subgrid classification method (SGC) that accounts for variability of both topography and vegetation cover. Each model grid cell was represented with a variable number of elevation classes and each elevation class was further described by a variable number of vegetation types optimized for each model grid given a predetermined total number of land response units (LRUs). The subgrid structure of the Community Land Model (CLM) was used to illustrate the newly developed method in this study. Although the new method increases the computational burden in the model simulation compared to the CLM subgrid vegetation representation, it greatly reduced the variations of elevation within each subgrid class and is able to explain at least 80% of the total subgrid plant functional types (PFTs). The new method was also evaluated against two other subgrid methods (SGC1 and SGC2) that assigned fixed numbers of elevation and vegetation classes for each model grid (SGC1: M elevation bands– N PFTs method; SGC2: N PFTs– M elevation bands method). Implemented at five model resolutions (0.1°, 0.25°, 0.5°, 1.0°and 2.0°) with three maximum-allowed total number of LRUs (i.e., N LRU of 24, 18 and 12) over North America (NA), the new method yielded more computationally efficient subgrid representation compared to SGC1 and SGC2, particularly at coarser model resolutions and moderate computational intensity ( N LRU = 18). It also explained the most PFTs and elevation variability that is more homogeneously distributed spatially. The SGC method will be implemented in CLM over the NA continent to assess its impacts on simulating land surface processes.

Description: Teleconnection analysis of runoff and soil moisture over the Pearl River basin in South China Hydrology and Earth System Sciences Discussions, 10, 11943-11982, 2013 Author(s): J. Niu, J. Chen, and B. Sivakumar This study explores the teleconnection of two climatic patterns, namely the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), with hydrological processes over the Pearl River basin in South China. The Variable Infiltration Capacity (VIC) model is used to simulate the daily hydrological processes over the basin for the study period 1952–2000, and then, using the simulation results, the time series of the monthly runoff and soil moisture anomalies for its ten sub-basins are aggregated. Wavelet analysis is performed to explore the variability properties of these time series at 49 timescales ranging from 2 months to 9 yr. Use of wavelet coherence and rank correlation method reveals that the dominant variabilities of the time series of runoff and soil moisture are basically correlated with IOD. The influences of ENSO on the terrestrial hydrological processes are mainly found in the eastern sub-basins. The teleconnections between climatic patterns and hydrological variability also serve as a reference basis for inferences on the occurrence of extreme hydrological events (e.g. floods and droughts).

Description: Hydrological functions of sinkholes and characteristics of point recharge in groundwater basins Hydrology and Earth System Sciences Discussions, 10, 11423-11449, 2013 Author(s): N. Somaratne, K. Smettem, J. Lawson, K. Nguyen, and J. Frizenschaf Karstic limestone aquifers are hydrologically and hydrochemically extremely heterogeneous and point source recharge via sinkholes and fissures is a common feature. We studied three groundwater systems in karstic settings dominated by point source recharge in order to assess the relative contributions to total recharge from point sources using chloride and δ 18 O relations. Preferential groundwater flows were observed through an inter-connected network of highly conductive zones with groundwater mixing along flow paths. Measurements of salinity and chloride indicated that fresh water pockets exist at point recharge locations. A measurable fresh water plume develops only when a large quantity of surface water enters the aquifer as a point recharge source. The difference in chloride concentrations in diffuse and point recharge zones decreases as aquifer saturated thickness increases and the plumes become diluted through mixing. The chloride concentration in point recharge fluxes crossing the watertable plane can remain at or near surface runoff chloride concentrations, rather than in equilibrium with groundwater chloride. In such circumstances the conventional chloride mass balance method that assumes equilibrium of recharge water chloride with groundwater requires modification to include both point and diffuse recharge mechanisms.

Description: An efficient method to generate a perturbed parameter ensemble of a fully coupled AOGCM without flux-adjustment Geoscientific Model Development, 6, 1447-1462, 2013 Author(s): P. J. Irvine, L. J. Gregoire, D. J. Lunt, and P. J. Valdes We present a simple method to generate a perturbed parameter ensemble (PPE) of a fully-coupled atmosphere-ocean general circulation model (AOGCM), HadCM3, without requiring flux-adjustment. The aim was to produce an ensemble that samples parametric uncertainty in some key variables and gives a plausible representation of the climate. Six atmospheric parameters, a sea-ice parameter and an ocean parameter were jointly perturbed within a reasonable range to generate an initial group of 200 members. To screen out implausible ensemble members, 20 yr pre-industrial control simulations were run and members whose temperature responses to the parameter perturbations were projected to be outside the range of 13.6 ± 2 °C, i.e. near to the observed pre-industrial global mean, were discarded. Twenty-one members, including the standard unperturbed model, were accepted, covering almost the entire span of the eight parameters, challenging the argument that without flux-adjustment parameter ranges would be unduly restricted. This ensemble was used in 2 experiments; an 800 yr pre-industrial and a 150 yr quadrupled CO 2 simulation. The behaviour of the PPE for the pre-industrial control compared well to ERA-40 reanalysis data and the CMIP3 ensemble for a number of surface and atmospheric column variables with the exception of a few members in the Tropics. However, we find that members of the PPE with low values of the entrainment rate coefficient show very large increases in upper tropospheric and stratospheric water vapour concentrations in response to elevated CO 2 and one member showed an implausible nonlinear climate response, and as such will be excluded from future experiments with this ensemble. The outcome of this study is a PPE of a fully-coupled AOGCM which samples parametric uncertainty and a simple methodology which would be applicable to other GCMs.

Description: GAPPARD: a computationally efficient method of approximating gap-scale disturbance in vegetation models Geoscientific Model Development, 6, 1517-1542, 2013 Author(s): M. Scherstjanoi, J. O. Kaplan, E. Thürig, and H. Lischke Models of vegetation dynamics that are designed for application at spatial scales larger than individual forest gaps suffer from several limitations. Typically, either a population average approximation is used that results in unrealistic tree allometry and forest stand structure, or models have a high computational demand because they need to simulate both a series of age-based cohorts and a number of replicate patches to account for stochastic gap-scale disturbances. The detail required by the latter method increases the number of calculations by two to three orders of magnitude compared to the less realistic population average approach. In an effort to increase the efficiency of dynamic vegetation models without sacrificing realism, we developed a new method for simulating stand-replacing disturbances that is both accurate and faster than approaches that use replicate patches. The GAPPARD (approximating GAP model results with a Probabilistic Approach to account for stand Replacing Disturbances) method works by postprocessing the output of deterministic, undisturbed simulations of a cohort-based vegetation model by deriving the distribution of patch ages at any point in time on the basis of a disturbance probability. With this distribution, the expected value of any output variable can be calculated from the output values of the deterministic undisturbed run at the time corresponding to the patch age. To account for temporal changes in model forcing (e.g., as a result of climate change), GAPPARD performs a series of deterministic simulations and interpolates between the results in the postprocessing step. We integrated the GAPPARD method in the vegetation model LPJ-GUESS, and evaluated it in a series of simulations along an altitudinal transect of an inner-Alpine valley. We obtained results very similar to the output of the original LPJ-GUESS model that uses 100 replicate patches, but simulation time was reduced by approximately the factor 10. Our new method is therefore highly suited for rapidly approximating LPJ-GUESS results, and provides the opportunity for future studies over large spatial domains, allows easier parameterization of tree species, faster identification of areas of interesting simulation results, and comparisons with large-scale datasets and results of other forest models.

Description: Climate information based streamflow and rainfall forecasts for Huai River Basin using Hierarchical Bayesian Modeling Hydrology and Earth System Sciences Discussions, 10, 11559-11584, 2013 Author(s): X. Chen, Z. Hao, N. Devineni, and U. Lall A Hierarchal Bayesian model for forecasting regional summer rainfall and streamflow season-ahead using exogenous climate variables for East Central China is presented. The model provides estimates of the posterior forecasted probability distribution for 12 rainfall and 2 streamflow stations considering parameter uncertainty, and cross-site correlation. The model has a multilevel structure with regression coefficients modeled from a common multivariate normal distribution results in partial-pooling of information across multiple stations and better representation of parameter and posterior distribution uncertainty. Covariance structure of the residuals across stations is explicitly modeled. Model performance is tested under leave-10-out cross-validation. Frequentist and Bayesian performance metrics used include Receiver Operating Characteristic, Reduction of Error, Coefficient of Efficiency, Rank Probability Skill Scores, and coverage by posterior credible intervals. The ability of the model to reliably forecast regional summer rainfall and streamflow season-ahead offers potential for developing adaptive water risk management strategies.

Description: A spatial bootstrap technique for parameter estimation of rainfall annual maxima distribution Hydrology and Earth System Sciences Discussions, 10, 11755-11794, 2013 Author(s): F. Uboldi, A. N. Sulis, C. Lussana, M. Cislaghi, and M. Russo Estimation of extreme event distributions and depth-duration-frequency (DDF) curves is achieved at any target site by repeated sampling among all available raingauge data in the surrounding area. The estimate is computed over a gridded domain in Northern Italy, using precipitation time series from 1929 to 2011, including data from historical analog stations and from the present-day automatic observational network. The presented local regionalisation naturally overcomes traditional station-point methods, with their demand of long historical series and their sensitivity to very rare events occurring at very few stations, possibly causing unrealistic spatial gradients in DDF relations. At the same time, the presented approach allows for spatial dependence, necessary in a geographical domain such as Lombardy, complex for both its topography and its climatology. The bootstrap technique enables evaluating uncertainty maps for all estimated parameters and for rainfall depths at assigned return periods.

Description: Overview of the first HyMeX Special Observation Period over Italy: observations and model results Hydrology and Earth System Sciences Discussions, 10, 11643-11710, 2013 Author(s): R. Ferretti, E. Pichelli, S. Gentile, I. Maiello, D. Cimini, S. Davolio, M. M. Miglietta, G. Panegrossi, L. Baldini, F. Pasi, F. S. Marzano, A. Zinzi, S. Mariani, M. Casaioli, G. Bartolini, N. Loglisci, A. Montani, C. Marsigli, A. Manzato, A. Pucillo, M. E. Ferrario, V. Colaiuda, and R. Rotunno During the first Hymex campaign (5 September–6 November 2012) referred to as Special Observation Period (SOP-1), dedicated to heavy precipitation events and flash floods in Western Mediterranean, three Italian hydro-meteorological monitoring sites were activated: Liguria-Tuscany, North-Eastern Italy and Central Italy. The extraordinary deployment of advanced instrumentation, including instrumented aircrafts, and the use of several different operational weather forecast models has allowed an unprecedented monitoring and analysis of high impact weather events around the Italian hydro-meteorological sites. This activity has seen the strict collaboration between the Italian scientific and operational communities. In this paper, an overview of the Italian organization during the SOP-1 is provided, and selected Intensive Observation Periods (IOPs) are described. A significant event for each Italian target area is chosen for this analysis: IOP2 (12–13 September 2012) in North-Eastern Italy, IOP13 (15–16 October 2012) in Central Italy and IOP19 (3–5 November 2012) in Liguria and Tuscany. For each IOP the meteorological characteristics, together with special observations and weather forecasts, are analyzed with the aim of highlighting strengths and weaknesses of the forecast modeling systems. Moreover, using one of the three events, the usefulness of different operational chains is highlighted.

Description: Correcting basin-scale snowfall in a mountainous basin using a distributed snowmelt model and remote sensing data Hydrology and Earth System Sciences Discussions, 10, 11711-11753, 2013 Author(s): M. Shrestha, L. Wang, T. Koike, H. Tsutsui, Y. Xue, and Y. Hirabayashi Adequate estimation of the spatial distribution of snowfall is critical in hydrologic modeling. However, this is a well-known problem in estimating basin-scale snowfall, especially in mountainous basins with data scarcity. This study focuses on correction and estimation of this spatial distribution, which considers topographic effects within the basin. A method is proposed that optimizes an altitude-based snowfall correction factor ( C fsnow ). This is done through multi-objective calibration of a spatially distributed, multilayer energy and water balance-based snowmelt model (WEB-DHM-S) with observed discharge and remotely sensed snow cover data from the Moderate Resolution Imaging Spectroradiometer (MODIS). The Shuffled Complex Evolution – University of Arizona automatic search algorithm is used to obtain the optimal value of C fsnow for minimum cumulative error in discharge and snow cover simulations. Discharge error is quantified by Nash–Sutcliffe efficiency and relative volume deviation, and snow cover error was estimated by pixel-by-pixel analysis. The study region is the heavily snow-fed Yagisawa Basin of the Upper Tone River in northeast Japan. First, the system was applied to one snow season (2002–2003), obtaining an optimized C fsnow of 0.0007 m −1 . For validation purposes, the optimized C fsnow was implemented to correct snowfall in 2004, 2002 and 2001. Overall, the system was effective, implying improvements in correlation of simulated vs. observed discharge and snow cover. The 4 yr mean of basin-average snowfall for the corrected spatial snowfall distribution was 1160 mm (780 mm before correction). Execution of sensitivity runs against other model input and parameters indicated that C fsnow could be affected by uncertainty in shortwave radiation and setting of the threshold air temperature parameter. Our approach is suitable to correct snowfall and estimate its distribution in poorly-gauged basins, where elevation dependence of snowfall amount is strong.

Description: Attribution of hydrologic forecast uncertainty within scalable forecast windows Hydrology and Earth System Sciences Discussions, 10, 11795-11828, 2013 Author(s): L. Yang, F. Tian, Y. Sun, X. Yuan, and H. Hu Hindcasts based on the Extended Streamflow Prediction (ESP) approach are carried out in a typical rainfall-dominated basin in China, aiming to examine the roles of initial condition (IC), future atmospheric forcing (FC) and hydrologic model uncertainty (MU) in the streamflow forecast skill. The combined effects of IC and FC are explored within the framework of a forecast window. By implementing virtual numerical simulations without the consideration of MU, it is found that the dominance of IC could last up to 90 days in dry season, while its impact gives way to FC for lead times exceeding 30 days in the wet season. The combined effects of IC and FC on the forecast skill are further investigated by proposing a dimensionless parameter ( β ) that represents the ratio of the total amount of initial water storage and the incoming rainfall. The forecast skill increases exponentially with β , and varies greatly in different forecast windows. Moreover, the influence of MU on forecast skill is examined by focusing on the uncertainty of model parameters. Two different hydrologic model calibration strategies are carried out. The results indicate that the uncertainty of model parameters exhibits a more significant influence on the forecast skill in the dry season than in the wet season. The ESP approach is more skillful in monthly streamflow forecast during the transition period from wet to dry than otherwise. For the transition period from dry to wet, the low skill of the forecasts could be attributed to the combined effects of IC and FC, but less to the biases in the hydrologic model parameters. For the forecasting in dry season, the usefulness of the ESP approach is heavily dependent on the strategy of the model calibration.

Description: A conceptual model of check dam hydraulics for gully control Hydrology and Earth System Sciences Discussions, 10, 11901-11941, 2013 Author(s): C. Castillo, R. Pérez, and J. A. Gómez There is little information in scientific literature regarding the modifications induced by check dam systems in flow regimes in restored gully reaches, despite it being a crucial issue for the design of conservation measures. Here, we develop a conceptual model to classify flow regimes in straight rectangular channels for initial and dam-filling conditions as well as a method of estimating efficiency in order to provide guidelines for optimal design. The model integrates several previous mathematical approaches for assessing the main processes involved (hydraulic jump HJ, impact flow, gradually varied flows). Its performance was compared with the simulations obtained from IBER, a bi-dimensional hydrodynamic model. The impact of check dam spacing (defined by the geometric factor of influence c ) on efficiency was explored. Eleven main classifications of flow regimes were identified depending on the element and level of influence. The model produced similar results when compared with IBER, but led to higher estimations of HJ and impact lengths. Total influence guaranteed maximum efficiency and HJ control defining the location of the optimal c . Geometric total influence ( c = 1) was a valid criterion for the different stages of the structures in a wide range of situations provided that hydraulic roughness conditions remained high within the gully, e.g. through revegetation. Our total influence criterion involved shorter spacing than that habitually recommended in technical manuals for restoration, but was in line with those values found in spontaneous and stable step-pools systems, which might serve as a reference for man-made interventions.

Description: Senstitivity of water balance components to environmental changes in a mountainous watershed: uncertainty assessment based on models comparison Hydrology and Earth System Sciences Discussions, 10, 11983-12026, 2013 Author(s): E. Morán-Tejeda, J. Zabalza, K. Rahman, A. Gago-Silva, J. I. López-Moreno, S. Vicente-Serrano, A. Lehmann, C. L. Tague, and M. Beniston This paper evaluates the response of stream flow and other components of the water balance to changes in climate and land-use in a Pyrenean watershed. It further provides a measure of uncertainty in water resources forecasts by comparing the performance of two hydrological models: Soil and Water Assessment Tool (SWAT) and Regional Hydro-Ecological Simulation System (RHESSys). Regional Climate Model outputs for the 2021–2050 time-frame, and hypothetical (but plausible) land-use scenarios considering re-vegetation and wildfire processes were used as inputs to the models. Results indicate an overall decrease in river flows when the scenarios are considered, except for the post-fire vegetation scenario, in which stream flows are simulated to increase. However the magnitude of these projections varies between the two models used, as SWAT tends to produce larger hydrological changes under climate change scenarios, and RHESSys shows more sensitivity to changes in land-cover. The final prediction will therefore depend largely on the combination of the land-use and climate scenarios, and on the model utilized.

Description: Global and regional sea surface temperature trends during Marine Isotope Stage 11 Climate of the Past, 9, 2231-2252, 2013 Author(s): Y. Milker, R. Rachmayani, M. F. G. Weinkauf, M. Prange, M. Raitzsch, M. Schulz, and M. Kučera The Marine Isotope Stage (MIS) 11 (424–374 ka) was characterized by a protracted deglaciation and an unusually long climatic optimum. It remains unclear to what degree the climate development during this interglacial reflects the unusually weak orbital forcing or greenhouse gas trends. Previously, arguments about the duration and timing of the MIS11 climatic optimum and about the pace of the deglacial warming were based on a small number of key records, which appear to show regional differences. In order to obtain a global signal of climate evolution during MIS11, we compiled a database of 78 sea surface temperature (SST) records from 57 sites spanning MIS11, aligned these individually on the basis of benthic ( N = 28) or planktonic ( N = 31) stable oxygen isotope curves to a common time frame and subjected 48 of them to an empirical orthogonal function (EOF) analysis. The analysis revealed a high commonality among all records, with the principal SST trend explaining almost 49% of the variability. This trend indicates that on the global scale, the surface ocean underwent rapid deglacial warming during Termination V, in pace with carbon dioxide rise, followed by a broad SST optimum centered at ~410 kyr. The second EOF, which explained ~18% of the variability, revealed the existence of a different SST trend, characterized by a delayed onset of the temperature optimum during MIS11 at ~398 kyr, followed by a prolonged warm period lasting beyond 380 kyr. This trend is most consistently manifested in the mid-latitude North Atlantic and Mediterranean Sea and is here attributed to the strength of the Atlantic meridional overturning circulation. A sensitivity analysis indicates that these results are robust to record selection and to age-model uncertainties of up to 3–6 kyr, but more sensitive to SST seasonal attribution and SST uncertainties 〉1 °C. In order to validate the CCSM3 (Community Climate System Model, version 3) predictive potential, the annual and seasonal SST anomalies recorded in a total of 74 proxy records were compared with runs for three time slices representing orbital configuration extremes during the peak interglacial of MIS11. The modeled SST anomalies are characterized by a significantly lower variance compared to the reconstructions. Nevertheless, significant correlations between proxy and model data are found in comparisons on the seasonal basis, indicating that the model captures part of the long-term variability induced by astronomical forcing, which appears to have left a detectable signature in SST trends.

Description: Hydrologic impact of climate change on Murray Hotham catchment of Western Australia: a projection of rainfall-runoff for future water resources planning Hydrology and Earth System Sciences Discussions, 10, 12027-12076, 2013 Author(s): S. A. Islam, M. A. Bari, and A. H. M. F. Anwar Reduction of rainfall and runoff in recent years across South West Western Australia (SWWA) has drawn attention about climate change impact on water resources and its availability in this region. In this paper, hydrologic impact of climate change on Murray Hotham catchment in SWWA is investigated using multi-model ensemble approach. The Land Use Change Incorporated Catchment (LUCICAT) model was used for hydrologic modelling. Model calibration was performed using (5 km) grid rainfall data from Australian Water Availability Project (AWAP). Downscaled and bias corrected rainfall data from 11 General Circulation Models (GCMs) for Intergovernmental Panel on Climate Change (IPCC) emission scenarios A2 and B1 was used in LUCICAT model to derive rainfall and runoff scenarios for 2046–2065 (mid this century) and 2081–2100 (late this century). The results of climate scenarios were compared with observed past (1961–1980) climate. The mean annual rainfall averaged over the catchment during recent time (1981–2000) was reduced by 2.3% with respect to observed past (1961–1980) and resulting runoff reduction was found 14%. Compared to the past, the mean annual rainfall reductions, averaged over 11 ensembles and over the period for the catchment for A2 scenario are 13.6 and 23.6% for mid and late this century respectively while the corresponding runoff reductions are 36 and 74%. For B1 scenario, the rainfall reductions were 11.9 and 11.6% for mid and late this century and corresponding runoff reductions were 31 and 38%. Spatial distribution of rainfall and runoff changes showed that the rate of changes were higher in high rainfall part compared to the low rainfall part. Temporal distribution of rainfall and runoff indicate that high rainfall in the catchment reduced significantly and further reductions are projected resulting significant runoff reductions. A catchment scenario map has been developed through plotting decadal runoff reduction against corresponding rainfall reduction at four gauging stations for observed and projected period. This could be useful for planning future water resources in the catchment. Projection of rainfall and runoff made based on the GCMs varied significantly for the time periods and emission scenarios. Hence, considerable uncertainty involved in this study though ensemble mean was used to explain the findings.

Description: Upscaling of evapotranspiration fluxes from instantaneous to daytime scales for thermal remote sensing applications Hydrology and Earth System Sciences Discussions, 10, 7325-7350, 2013 Author(s): C. Cammalleri, M. C. Anderson, and W. P. Kustas Four upscaling methods for estimating daytime evapotranspiration (ET) from single time-of-day snapshots, as commonly retrieved using remote sensing, were compared. These methods are based on the assumption of self-preservation of the ratio between ET and a given reference variable over the daytime hours. The analysis was performed using eddy covariance data collected at 12 AmeriFlux towers, sampling a fairly wide range in climatic and land cover conditions. The choice of energy budget closure method significantly impacted performance using different scaling methodologies. Therefore, a statistical evaluation approach was adopted to better account for the inherent uncertainty in ET fluxes using eddy covariance technique. Overall, this approach suggests that at-surface solar radiation is the most robust reference variable amongst those tested, due to high accuracy of upscaled fluxes and absence of systematic biases. Top-of-atmosphere irradiance was also tested and proved to be reliable under near clear-sky conditions, but tended to overestimate the observed daytime ET during cloudy days. Use of reference ET as a scaling flux did not perform as well as the solar radiation method, but similarly had errors with little seasonal dependency. Finally, the commonly-used evaporative fraction method yielded satisfactory results only in summer months, July and August, and tended to underestimate the observations in the fall/winter seasons from November to January at the flux sites studied.

Description: Global isoscapes for δ 18 O and δ 2 H in precipitation: improved prediction using regionalized climatic regression models Hydrology and Earth System Sciences Discussions, 10, 7351-7393, 2013 Author(s): S. Terzer, L. I. Wassenaar, L. J. Araguás-Araguás, and P. K. Aggarwal A Regionalized Climatic Water Isotope Prediction (RCWIP) approach, based on the Global Network for Isotopes in Precipitation (GNIP), was demonstrated for the purposes of predicting point- and large-scale spatiotemporal patterns of the stable isotope compositions of water (δ 2 H, δ 18 O) in precipitation around the world. Unlike earlier global domain and fixed regressor models, RCWIP pre-defined thirty-six climatic cluster domains, and tested all model combinations from an array of climatic and spatial regressor variables to obtain the best predictive approach to each cluster domain, as indicated by RMSE and variogram analysis. Fuzzy membership fractions were thereafter used as the weights to seamlessly amalgamate results of the optimized climatic zone prediction models into a single predictive mapping product, such as global or regional amount-weighted mean annual, mean monthly or growing-season δ 18 O/δ 2 H in precipitation. Comparative tests revealed the RCWIP approach outperformed classical global-fixed regression-interpolation based models more than 67% of the time, and significantly improved upon predictive accuracy and precision. All RCWIP isotope mapping products are available as gridded GeoTIFF files from the IAEA website ( www.iaea.org/water ) and are for use in hydrology, climatology, food authenticity, ecology, and forensics.

Description: Water displacement by sewer infrastructure in the Grote Nete catchment, Belgium, and its hydrological regime effects Hydrology and Earth System Sciences Discussions, 10, 7425-7467, 2013 Author(s): D. Vrebos, T. Vansteenkiste, J. Staes, P. Willems, and P. Meire Urbanization and especially impervious areas, in combination with wastewater treatment infrastructure, can exert several pressures on the hydrological cycle. These pressures were studied for the Grote Nete catchment in Belgium (8.18% impervious area and 3.89% effective impervious area), based on a combination of empirical and model-based approaches. The effective impervious area, combined with the extent of the wastewater collection regions which do not coincide with the natural catchment boundaries, was used as an indicator for the urbanization pressure. Our study revealed changes in the total upstream areas of the subcatchments between −16% and +3%, and in upstream impervious areas between −99% and +64%. These changes lead to important inter-catchment water transfers. Based on simulations with a physically-based and spatially-distributed hydrological catchment model, profound impacts of effective impervious area on infiltration and runoff were found. The model results show that the changes in impervious areas and related water displacements in and between catchments due to the installation of the wastewater treatment infrastructure severely impacted low flows, peak flows and seasonal trends. They moreover show that it is difficult, but of utmost importance, to incorporate these pressures and artificial processes in an accurate way during the development of hydrological models for urbanized catchments.

Description: Virtual water trade and development in Africa Hydrology and Earth System Sciences Discussions, 10, 7291-7324, 2013 Author(s): M. Konar and K. Caylor A debate has long existed on the relationships between human population, natural resources, and development. Recent research has expanded this debate to include the impacts of trade; specifically, virtual water trade, or the water footprint of traded commodities. We conduct an empirical analysis of the relationships between virtual water trade, population, and development in Africa. We find that increases in virtual water imports do not lead to increases in population growth nor do they diminish human welfare. We establish a new index of virtual water trade openness and show that levels of undernourishment tend to fall with increased values of virtual water trade openness. Countries with small dam storage capacity obtain a higher fraction of their agricultural water requirements from external sources, which may indicate implicit "infrastructure sharing" across nations. Globally, increased crop exports tends to correlate with increased crop water use efficiency, though this relationship does not hold for Africa. However, internal African trade is much more efficient in terms of embodied water resources than any other region in the world. Thus, internal African trade patterns may be compensating for poor internal production systems.

Description: An interdisciplinary swat ecohydrological model to define catchment-scale hydrologic partitioning Hydrology and Earth System Sciences Discussions, 10, 7235-7290, 2013 Author(s): C. L. Shope, G. R. Maharjan, J. Tenhunen, B. Seo, K. Kim, J. Riley, S. Arnhold, T. Koellner, Y. S. Ok, S. Peiffer, B. Kim, J.-H. Park, and B. Huwe Land use and climate change have long been implicated in modifying ecosystem services, such as water quality and water yield, biodiversity, and agricultural production. To account for future effects on ecosystem services, the integration of physical, biological, economic, and social data over several scales must be implemented to assess the effects on natural resource availability and use. Our objective is to assess the capability of the SWAT model to capture short-duration monsoonal rainfall-runoff processes in complex mountainous terrain under rapid, event-driven processes in a monsoonal environment. To accomplish this, we developed a unique quality-control gap-filling algorithm for interpolation of high frequency meteorological data. We used a novel multi-location, multi-optimization calibration technique to improve estimations of catchment-wide hydrologic partitioning. We calibrated the interdisciplinary model to a combination of statistical, hydrologic, and plant growth metrics. In addition, we used multiple locations of different drainage area, aspect, elevation, and geologic substrata distributed throughout the catchment. Results indicate scale-dependent sensitivity of hydrologic partitioning and substantial influence of engineered features. While our model accurately reproduced observed discharge variability, the addition of hydrologic and plant growth objective functions identified the importance of culverts in catchment-wide flow distribution. The results of this study provide a valuable resource to describe landscape controls and their implication on discharge, sediment transport, and nutrient loading. This study also shows the challenges of applying the SWAT model to complex terrain and extreme environments. By incorporating anthropogenic features into modeling scenarios, we can greatly enhance our understanding of the hydroecological impacts on ecosystem services.

Description: On the parallelization of atmospheric inversions of CO 2 surface fluxes within a variational framework Geoscientific Model Development, 6, 783-790, 2013 Author(s): F. Chevallier The variational formulation of Bayes' theorem allows inferring CO 2 sources and sinks from atmospheric concentrations at much higher time–space resolution than the ensemble or analytical approaches. However, it usually exhibits limited scalable parallelism. This limitation hinders global atmospheric inversions operated on decadal time scales and regional ones with kilometric spatial scales because of the computational cost of the underlying transport model that has to be run at each iteration of the variational minimization. Here, we introduce a physical parallelization (PP) of variational atmospheric inversions. In the PP, the inversion still manages a single physically and statistically consistent window, but the transport model is run in parallel overlapping sub-segments in order to massively reduce the computation wall-clock time of the inversion. For global inversions, a simplification of transport modelling is described to connect the output of all segments. We demonstrate the performance of the approach on a global inversion for CO 2 with a 32 yr inversion window (1979–2010) with atmospheric measurements from 81 sites of the NOAA global cooperative air sampling network. In this case, we show that the duration of the inversion is reduced by a seven-fold factor (from months to days), while still processing the three decades consistently and with improved numerical stability.

Description: Inclusion of ash and SO 2 emissions from volcanic eruptions in WRF-Chem: development and some applications Geoscientific Model Development, 6, 457-468, 2013 Author(s): M. Stuefer, S. R. Freitas, G. Grell, P. Webley, S. Peckham, S. A. McKeen, and S. D. Egan We describe a new functionality within the Weather Research and Forecasting (WRF) model with coupled Chemistry (WRF-Chem) that allows simulating emission, transport, dispersion, transformation and sedimentation of pollutants released during volcanic activities. Emissions from both an explosive eruption case and a relatively calm degassing situation are considered using the most recent volcanic emission databases. A preprocessor tool provides emission fields and additional information needed to establish the initial three-dimensional cloud umbrella/vertical distribution within the transport model grid, as well as the timing and duration of an eruption. From this source condition, the transport, dispersion and sedimentation of the ash cloud can be realistically simulated by WRF-Chem using its own dynamics and physical parameterization as well as data assimilation. Examples of model applications include a comparison of tephra fall deposits from the 1989 eruption of Mount Redoubt (Alaska) and the dispersion of ash from the 2010 Eyjafjallajökull eruption in Iceland. Both model applications show good coincidence between WRF-Chem and observations.

Description: Technical note: Method of Morris effectively reduces the computational demands of global sensitivity analysis for distributed watershed models Hydrology and Earth System Sciences Discussions, 10, 4275-4299, 2013 Author(s): J. D. Herman, J. B. Kollat, P. M. Reed, and T. Wagener The increase in spatially distributed hydrologic modeling warrants a corresponding increase in diagnostic methods capable of analyzing complex models with large numbers of parameters. Sobol ' sensitivity analysis has proven to be a valuable tool for diagnostic analyses of hydrologic models. However, for many spatially distributed models, the Sobol ' method requires a prohibitive number of model evaluations to reliably decompose output variance across the full set of parameters. We investigate the potential of the method of Morris, a screening-based sensitivity approach, to provide results sufficiently similar to those of the Sobol ' method at a greatly reduced computational expense. The methods are benchmarked on the Hydrology Laboratory Research Distributed Hydrologic Model (HL-RDHM) model over a six-month period in the Blue River Watershed, Oklahoma, USA. The Sobol ' method required over six million model evaluations to ensure reliable sensitivity indices, corresponding to more than 30 000 computing hours and roughly 180 gigabytes of storage space. We find that the method of Morris is able to correctly identify sensitive and insensitive parameters with 300 times fewer model evaluations, requiring only 100 computing hours and 1 gigabyte of storage space. Method of Morris proves to be a promising diagnostic approach for global sensitivity analysis of highly parameterized, spatially distributed hydrologic models.

Description: PORT, a CESM tool for the diagnosis of radiative forcing Geoscientific Model Development, 6, 469-476, 2013 Author(s): A. J. Conley, J.-F. Lamarque, F. Vitt, W. D. Collins, and J. Kiehl The Parallel Offline Radiative Transfer (PORT) model is a stand-alone tool, driven by model-generated datasets, that can be used for any radiation calculation that the underlying radiative transfer schemes can perform, such as diagnosing radiative forcing. In its present distribution, PORT isolates the radiation code from the Community Atmosphere Model (CAM4) in the Community Earth System Model (CESM1). The current configuration focuses on CAM4 radiation with the constituents as represented in present-day conditions in CESM1, along with their optical properties. PORT includes an implementation of stratospheric temperature adjustment under the assumption of fixed dynamical heating, which is necessary to compute radiative forcing in addition to the more straightforward instantaneous radiative forcing. PORT can be extended to use radiative constituent distributions from other models or model simulations. Ultimately, PORT can be used with various radiative transfer models. As illustrations of the use of PORT, we perform the computation of radiative forcing from doubling of carbon dioxide, from the change of tropospheric ozone concentration from the year 1850 to 2000, and from present-day aerosols. The radiative forcing from tropospheric ozone (with respect to 1850) generated by a collection of model simulations under the Atmospheric Chemistry and Climate Model Intercomparison Project is found to be 0.34 (with an intermodel standard deviation of 0.07) W m −2 . Present-day aerosol direct forcing (relative to no aerosols) is found to be −1.3 W m −2 .

Description: Skill and reliability of climate model ensembles at the Last Glacial Maximum and mid-Holocene Climate of the Past, 9, 811-823, 2013 Author(s): J. C. Hargreaves, J. D. Annan, R. Ohgaito, A. Paul, and A. Abe-Ouchi Paleoclimate simulations provide us with an opportunity to critically confront and evaluate the performance of climate models in simulating the response of the climate system to changes in radiative forcing and other boundary conditions. Hargreaves et al. (2011) analysed the reliability of the Paleoclimate Modelling Intercomparison Project, PMIP2 model ensemble with respect to the MARGO sea surface temperature data synthesis (MARGO Project Members, 2009) for the Last Glacial Maximum (LGM, 21 ka BP). Here we extend that work to include a new comprehensive collection of land surface data (Bartlein et al., 2011), and introduce a novel analysis of the predictive skill of the models. We include output from the PMIP3 experiments, from the two models for which suitable data are currently available. We also perform the same analyses for the PMIP2 mid-Holocene (6 ka BP) ensembles and available proxy data sets. Our results are predominantly positive for the LGM, suggesting that as well as the global mean change, the models can reproduce the observed pattern of change on the broadest scales, such as the overall land–sea contrast and polar amplification, although the more detailed sub-continental scale patterns of change remains elusive. In contrast, our results for the mid-Holocene are substantially negative, with the models failing to reproduce the observed changes with any degree of skill. One cause of this problem could be that the globally- and annually-averaged forcing anomaly is very weak at the mid-Holocene, and so the results are dominated by the more localised regional patterns in the parts of globe for which data are available. The root cause of the model-data mismatch at these scales is unclear. If the proxy calibration is itself reliable, then representativity error in the data-model comparison, and missing climate feedbacks in the models are other possible sources of error.

Description: Socio-hydrology: conceptualising human-flood interactions Hydrology and Earth System Sciences Discussions, 10, 4515-4536, 2013 Author(s): G. Di Baldassarre, A. Viglione, G. Carr, L. Kuil, J. L. Salinas, and G. Blöschl Over history, humankind has tended to settle near streams because of the role of rivers as transportation corridors and the fertility of riparian areas. However, human settlements in floodplains have been threatened by the risk of flooding. Possible responses have been to resettle away and/or modify the river system by building flood control structures. This has led to a complex web of interactions and feedback mechanisms between hydrological and social processes in settled floodplains. This paper is an attempt to conceptualise these interplays for hypothetical human-flood systems. We develop a simple, dynamic model to represent the interactions and feedback loops between hydrological and social processes. The model is then used to explore the dynamics of the human-flood system and the effect of changing individual characteristics, including external forcing such as technological development. The results show that the conceptual model is able to reproduce reciprocal effects between floods and people as well as the emergence of typical patterns. For instance, when levees are built or raised to protect floodplain areas, their presence not only reduces the frequency of flooding, but also exacerbates high water levels. Then, because of this exacerbation, higher flood protection levels are required by the society. As a result, more and more flooding events are avoided, but rare and catastrophic events take place.

Description: Integration of remote sensing, RUSLE and GIS to model potential soil loss and sediment yield (SY) Hydrology and Earth System Sciences Discussions, 10, 4567-4596, 2013 Author(s): H. Kamaludin, T. Lihan, Z. Ali Rahman, M. A. Mustapha, W. M. R. Idris, and S. A. Rahim Land use activities within a basin serve as one of the contributing factors which cause deterioration of river water quality through its potential effect on erosion. Sediment yield in the form of suspended solid in the river water body which is transported to the coastal area occurs as a sign of lowering of the water quality. Hence, the aim of this study was to determine potential soil loss using the Revised Universal Soil Loss Equation (RUSLE) model and the sediment yield, in the Geographical Information Systems (GIS) environment within selected sub-catchments of Pahang River Basin. RUSLE was used to estimate potential soil losses and sediment yield by utilizing information on rainfall erosivity ( R ) using interpolation of rainfall data, soil erodibility ( K ) using field measurement and soil map, vegetation cover ( C ) using satellite images, topography (LS) using DEM and conservation practices ( P ) using satellite images. The results indicated that the rate of potential soil loss in these sub-catchments ranged from very low to extremely high. The area covered by very low to low potential soil loss was about 99%, whereas moderate to extremely high soil loss potential covered only about 1% of the study area. Sediment yield represented only 1% of the potential soil loss. The sediment yield (SY) value in Pahang River turned out to be higher closer to the river mouth because of the topographic character, climate, vegetation type and density, and land use within the drainage basin.

Description: Probability distributions for explaining hydrological losses in South Australian catchments Hydrology and Earth System Sciences Discussions, 10, 4597-4626, 2013 Author(s): S. H. P. W. Gamage, G. A. Hewa, and S. Beecham The wide variability of hydrological losses in catchments is due to multiple variables that affect the rainfall-runoff process. Accurate estimation of hydrological losses is required for making vital decisions in design applications that are based on design rainfall models and rainfall-runoff models. Using representative single values of losses, despite their wide variability, is common practice, especially in Australian studies. This practice leads to issues such as over or under estimation of design floods. Probability distributions can be used as a better representation of losses. In particular, using joint probability approaches (JPA), probability distributions can be incorporated into hydrological loss parameters in design models. However, lack of understanding of loss distributions limits the benefit of using JPA. The aim of this paper is to identify a probability distribution function that can successfully describe hydrological losses in South Australian (SA) catchments. This paper describes suitable parametric and non-parametric distributions that can successfully describe observed loss data. The goodness-of-fit of the fitted distributions and quantification of the errors associated with quantile estimation are also discussed a two-parameter Gamma distribution was identified as one that successfully described initial loss (IL) data of the selected catchments. Also, a non-parametric standardised distribution of losses that describes both IL and continuing loss (CL) data were identified. The results obtained for the non-parametric methods were compared with similar studies carried out in other parts of Australia and a remarkable degree of consistency was observed. The results will be helpful in improving design flood applications.

Description: Technical Note: Using wavelet analyses on water depth time series to detect glacial influence in high-mountain hydrosystems Hydrology and Earth System Sciences Discussions, 10, 4369-4395, 2013 Author(s): S. Cauvy-Fraunié, T. Condom, A. Rabatel, M. Villacis, D. Jacobsen, and O. Dangles Worldwide, the rapid shrinking of glaciers in response to ongoing climate change is currently modifying the glacial meltwater contribution to hydrosystems in glacierized catchments. Assessing the contribution of glacier run-off to stream discharge is therefore of critical importance to evaluate potential impact of glacier retreat on water quality and aquatic biota. This task has challenged both glacier hydrologists and ecologists over the last 20 yr due to both structural and functional complexity of the glacier-stream system interface. Here we propose a new methodological approach based on wavelet analyses on water depth time series to determine the glacial influence in glacierized catchments. We performed water depth measurement using water pressure loggers over ten months in 15 stream sites in two glacier-fed catchments in the Ecuadorian Andes (〉 4000 m). We determined the global wavelet spectrum of each time series and defined the Wavelet Glacier Signal (WGS) as the ratio between the global wavelet power spectrum value at a 24 h-scale and its corresponding significance value. To test the relevance of the WGS we compared it with the percentage of the glacier cover in the catchments, a metric of glacier influence often used in the literature. We then tested whether one month data could be sufficient to reliably determine the glacial influence. As expected we found that the WGS of glacier-fed streams decreased downstream with the increasing of non-glacial tributaries. We also found that the WGS and the percentage of the glacier cover in the catchment were significantly positively correlated and that one month data was sufficient to identify and compare the glacial influence between two sites, provided that the water level time series were acquired over the same period. Furthermore, we found that our method permits to detect glacial signal in supposedly non-glacial sites, thereby evidencing glacial meltwater infiltrations. While we specifically focused on the tropical Andes in this paper, our approach to determine glacier influence would be applicable to temperate and arctic glacierized catchments. The WGS therefore appears as a powerful and cost effective tool to better understand the hydrological links between glaciers and hydrosystems and assess the consequences of rapid glacier melting.

Description: Spatio-temporal heterogeneity of riparian soil morphology in a restored floodplain Hydrology and Earth System Sciences Discussions, 10, 4337-4367, 2013 Author(s): B. Fournier, C. Guenat, G. Bullinger-Weber, and E. A. D. Mitchell Floodplains have been intensively altered in industrialized countries, but are now increasingly being restored and it is therefore important to assess the effect of these restoration projects on the aquatic and terrestrial components of ecosystems. Soils are a functionally crucial component of terrestrial ecosystems but are generally overlooked in floodplain restoration assessment. We studied the spatio-temporal heterogeneity of soil morphology in a restored (riverbed widening) river reach along River Thur (Switzerland) using three criteria (soil diversity, dynamism and typicality) and their associated indicators. We hypothesized that these criteria would correctly discriminate the post-restoration changes in soil morphology within the study site, and that these changes correspond to patterns of vascular plant diversity. Soil diversity and dynamism increased five years after the restoration, but typical soils of braided rivers were still missing. Soil typicality and dynamism correlated to vegetation changes. These results suggest a limited success of the project in agreement with evaluations carried out at the same site using other, more resource demanding methods (e.g. soil fauna, fish, ecosystem functioning). Soil morphology provides structural and functional information on floodplain ecosystems and allows predicting broad changes in plant diversity. The spatio-temporal heterogeneity of soil morphology represents a cost-efficient ecological indicator that could easily be integrated into rapid assessment protocols of floodplain and river restoration projects.

Description: Space-time kriging extension of precipitation variability at 12 km spacing from tree-ring chronologies and its implications for drought analysis Hydrology and Earth System Sciences Discussions, 10, 4301-4335, 2013 Author(s): F. Biondi Understanding and preparing for future hydroclimatic variability greatly benefits from long (i.e., multi-century) records at seasonal to annual time steps that have been gridded at km-scale spatial intervals over a geographic region. Kriging is a geostatistical technique commonly used for optimal interpolation of environmental data, and space-time geostatistical models can improve kriging estimates when long temporal sequences of observations exist at relatively few points on the landscape. Here I present how a network of 22 tree-ring chronologies from single-leaf pinyon ( Pinus monophylla ) in the central Great Basin of North America was used to extend hydroclimatic records both temporally and spatially. First, the Line of Organic Correlation (LOC) method was used to reconstruct October–May total precipitation anomalies at each tree-ring site, as these ecotonal environments at the lower forest border are typically moisture limited. Individual site reconstructions were then combined using a hierarchical model of spatio-temporal kriging that produced annual anomaly maps on a 12 × 12 km grid during the period in common among all chronologies (1650–1976). Hydro-climatic episodes were numerically identified and modeled using their duration, magnitude, and peak. Spatial patterns were more variable during wet years than during dry years, and the evolution of drought episodes over space and time could be visualized and quantified. The most remarkable episode in the entire reconstruction was the early 1900s pluvial, followed by the late 1800s drought. The 1930s "Dust Bowl" drought was among the top ten hydroclimatic episodes in the past few centuries. These results directly address the needs of water and natural resource managers with respect to planning for "worst case" scenarios of drought duration and magnitude at the watershed level. For instance, it is possible to analyze which geographical areas are more likely to be impacted by severe and sustained droughts at annual or multiannual timescales and at spatial resolutions commonly used by regional climate models.

Description: Stable isotopic evidence of El Niño-like atmospheric circulation in the Pliocene western United States Climate of the Past, 9, 903-912, 2013 Author(s): M. J. Winnick, J. M. Welker, and C. P. Chamberlain Understanding how the hydrologic cycle has responded to warmer global temperatures in the past is especially important today as concentrations of CO 2 in the atmosphere continue to increase due to human activities. The Pliocene offers an ideal window into a climate system that has equilibrated with current atmospheric p CO 2 . During the Pliocene the western United States was wetter than modern, an observation at odds with our current understanding of future warming scenarios, which involve the expansion and poleward migration of the subtropical dry zone. Here we compare Pliocene oxygen isotope profiles of pedogenic carbonates across the western US to modern isotopic anomalies in precipitation between phases of the El Niño–Southern Oscillation (ENSO). We find that when accounting for seasonality of carbonate formation, isotopic changes through the late Pliocene match modern precipitation isotopic anomalies in El Niño years. Furthermore, isotopic shifts through the late Pliocene mirror changes through the early Pleistocene, which likely represents the southward migration of the westerly storm track caused by growth of the Laurentide ice sheet. We propose that the westerly storm track migrated northward through the late Pliocene with the development of the modern cold tongue in the east equatorial Pacific, then returned southward with widespread glaciation in the Northern Hemisphere – a scenario supported by terrestrial climate proxies across the US. Together these data support the proposed existence of background El Niño-like conditions in western North America during the warm Pliocene. If the earth behaves similarly with future warming, this observation has important implications with regard to the amount and distribution of precipitation in western North America.

Description: Mass-movement and flood-induced deposits in Lake Ledro, southern Alps, Italy: implications for Holocene palaeohydrology and natural hazards Climate of the Past, 9, 825-840, 2013 Author(s): A. Simonneau, E. Chapron, B. Vannière, S. B. Wirth, A. Gilli, C. Di Giovanni, F. S. Anselmetti, M. Desmet, and M. Magny High-resolution seismic profiles and sediment cores from Lake Ledro combined with soil and riverbed samples from the lake's catchment area are used to assess the recurrence of natural hazards (earthquakes and flood events) in the southern Italian Alps during the Holocene. Two well-developed deltas and a flat central basin are identified on seismic profiles in Lake Ledro. Lake sediments have been finely laminated in the basin since 9000 cal. yr BP and frequently interrupted by two types of sedimentary events (SEs): light-coloured massive layers and dark-coloured graded beds. Optical analysis (quantitative organic petrography) of the organic matter present in soil, riverbed and lacustrine samples together with lake sediment bulk density and grain-size analysis illustrate that light-coloured layers consist of a mixture of lacustrine sediments and mainly contain algal particles similar to the ones observed in background sediments. Light-coloured layers thicker than 1.5 cm in the main basin of Lake Ledro are synchronous to numerous coeval mass-wasting deposits remoulding the slopes of the basin. They are interpreted as subaquatic mass-movements triggered by historical and pre-historical regional earthquakes dated to AD 2005, AD 1891, AD 1045 and 1260, 2545, 2595, 3350, 3815, 4740, 7190, 9185 and 11 495 cal. yr BP. Dark-coloured SEs develop high-amplitude reflections in front of the deltas and in the deep central basin. These beds are mainly made of terrestrial organic matter (soils and lignocellulosic debris) and are interpreted as resulting from intense hyperpycnal flood event. Mapping and quantifying the amount of soil material accumulated in the Holocene hyperpycnal flood deposits of the sequence allow estimating that the equivalent soil thickness eroded over the catchment area reached up to 5 mm during the largest Holocene flood events. Such significant soil erosion is interpreted as resulting from the combination of heavy rainfall and snowmelt. The recurrence of flash flood events during the Holocene was, however, not high enough to affect pedogenesis processes and highlight several wet regional periods during the Holocene. The Holocene period is divided into four phases of environmental evolution. Over the first half of the Holocene, a progressive stabilization of the soils present through the catchment of Lake Ledro was associated with a progressive reforestation of the area and only interrupted during the wet 8.2 event when the soil destabilization was particularly important. Lower soil erosion was recorded during the mid-Holocene climatic optimum (8000–4200 cal. yr BP) and associated with higher algal production. Between 4200 and 3100 cal. yr BP, both wetter climate and human activities within the drainage basin drastically increased soil erosion rates. Finally, from 3100 cal. yr BP to the present-day, data suggest increasing and changing human land use.

Description: Optimising predictor domains for spatially coherent precipitation downscaling Hydrology and Earth System Sciences Discussions, 10, 4015-4061, 2013 Author(s): S. Radanovics, J.-P. Vidal, E. Sauquet, A. Ben Daoud, and G. Bontron Statistical downscaling is widely used to overcome the scale gap between predictors from Numerical Weather Prediction (NWP) models or General Circulation Models (GCMs) and predictands like local precipitation, required for example for medium-term operational forecasts or climate change impact studies. The predictors are considered over a given spatial domain which is rarely optimised with respect to the target predictand location. In this study the geopotential predictor domains used by an analogue downscaling method are optimised for 608 target zones covering France. An extended version of the growing rectangular domain algorithm provides an ensemble of five near-optimum domains for each target zone. All five near-optimum domains are consistently equally skillful based on the Continuous Rank Probability Score. Relevance maps calculated for selected target zones first reveal high skill geopotential regions with specific shapes for locations in south-eastern France compared to the rest of the country. In all cases, the optimised domains tend to include the most relevant area on the relevance maps. The domain centers of the optimised domains are mainly distributed following the geographical location of the target location, but there are apparent differences between the windward and the lee side of mountain ridges. Moreover, domains for target zones located in south-eastern France are centered more east and south than the ones for target locations on the same longitude. The size of the optimised domains tends to be larger in the southeastern part of the country, while domains with a very small meridional extent can be found in a east-west band around 47° N. Sensitivity tests on the archive length for the analogue method show a general robustness except for zones with high interannual variability like in the Cévennes area. Moreover, results appear to be rather unsensitive to the starting point of the optimisation algorithm except for zones located in the transition area north of the zones having optimized domains with a small meridional extent. This study paves the way for defining regions with homogeneous geopotential predictor domains for precipitation downscaling over France.

Description: Opportunities and challenges for the use of scintillometer-based catchment-averaged evapotranspiration estimates as model forcing Hydrology and Earth System Sciences Discussions, 10, 3973-4013, 2013 Author(s): B. Samain and V. R. N. Pauwels To date, lumped rainfall-runoff models rely on rough estimates of catchment-averaged potential evapotranspiration (ET p ) rates as meteorological forcing. A model parameter converts this ET p input into actual evapotranspiration (ET act ) estimates. This paper examines the potential use of scintillometer-based ET act rates for rainfall-runoff modeling. It has been found that the reservoir-structure of the rainfall-runoff model functions as a low-pass filter for the ET p input. If the long-term volume of the ET p used in the model simulations is consistent with the data set used for calibration, a good match of the seasonal pattern, using temporally constant ET p data, is sufficient to obtain adequate discharge simulations. However, these results are then obtained with strongly erroneous evapotranspiration estimates. A better match of the diurnal cycle does not lead to better model results. Replacing the ET p inputs by scintillometer-based ET act estimates does not lead to better model predictions. Small underestimations of ET act under stable conditions, which occur at night and during the Winter, and which accumulate to significant amounts, are the cause of this problem. Consistent with other studies, the scintillometer-based ET act estimates can be considered reliable and realistic under unstable conditions. These values can thus be used as forcing for rainfall-runoff models.

Description: Using data assimilation to investigate the causes of Southern Hemisphere high latitude cooling from 10 to 8 ka BP Climate of the Past, 9, 887-901, 2013 Author(s): P. Mathiot, H. Goosse, X. Crosta, B. Stenni, M. Braida, H. Renssen, C. J. Van Meerbeeck, V. Masson-Delmotte, A. Mairesse, and S. Dubinkina From 10 to 8 ka BP (thousand years before present), paleoclimate records show an atmospheric and oceanic cooling in the high latitudes of the Southern Hemisphere. During this interval, temperatures estimated from proxy data decrease by 0.8 °C over Antarctica and 1.2 °C over the Southern Ocean. In order to study the causes of this cooling, simulations covering the early Holocene have been performed with the climate model of intermediate complexity LOVECLIM constrained to follow the signal recorded in climate proxies using a data assimilation method based on a particle filtering approach. The selected proxies represent oceanic and atmospheric surface temperature in the Southern Hemisphere derived from terrestrial, marine and glaciological records. Two mechanisms previously suggested to explain the 10–8 ka BP cooling pattern are investigated using the data assimilation approach in our model. The first hypothesis is a change in atmospheric circulation, and the second one is a cooling of the sea surface temperature in the Southern Ocean, driven in our experimental setup by the impact of an increased West Antarctic melting rate on ocean circulation. For the atmosphere hypothesis, the climate state obtained by data assimilation produces a modification of the meridional atmospheric circulation leading to a 0.5 °C Antarctic cooling from 10 to 8 ka BP compared to the simulation without data assimilation, without congruent cooling of the atmospheric and sea surface temperature in the Southern Ocean. For the ocean hypothesis, the increased West Antarctic freshwater flux constrainted by data assimilation (+100 mSv from 10 to 8 ka BP) leads to an oceanic cooling of 0.7 °C and a strengthening of Southern Hemisphere westerlies (+6%). Thus, according to our experiments, the observed cooling in Antarctic and the Southern Ocean proxy records can only be reconciled with the reconstructions by the combination of a modified atmospheric circulation and an enhanced freshwater flux.

Description: Temporal stability of soil moisture patterns measured by proximal ground-penetrating radar Hydrology and Earth System Sciences Discussions, 10, 4063-4097, 2013 Author(s): J. Minet, N. E. C. Verhoest, S. Lambot, and M. Vanclooster We analyzed the temporal stability of soil moisture patterns acquired using a proximal ground-penetrating radar (GPR) in a 2.5 ha agricultural field at five different dates over three weeks. The GPR system was mounted on a mobile platform, allowing for real-time mapping of soil moisture with a high spatial resolution (2–5 m). The spatio-temporal soil moisture patterns were in accordance with the meteorological data and with soil moisture measurements from soil core sampling. Time-stable areas showing the field-average moisture could be revealed by two methods: (1) by the computation of temporal stability indicators based on relative differences of soil moisture to the field-average and (2) by the spatial intersection of the areas showing the field-average. Locations where the mean relative difference was below 0.02 m 3 m −3 extended up to 10% of the field area whereas the intersection of areas showing the field-average within a tolerance of 0.02 m 3 m −3 covered 5% of the field area. Compared to most of the previous studies about temporal stability of soil moisture, time-stable areas and their spatial patterns could be revealed instead of single point locations, owing to the advanced GPR method for real-time mapping. It is believed that determining spatially coherent time-stable areas is more informative rather than determining time-stable points. Other acquisitions over larger time periods would be necessary to assert the robustness of the time-stable areas.

Description: Model sensitivity to North Atlantic freshwater forcing at 8.2 ka Climate of the Past, 9, 955-968, 2013 Author(s): C. Morrill, A. N. LeGrande, H. Renssen, P. Bakker, and B. L. Otto-Bliesner We compared four simulations of the 8.2 ka event to assess climate model sensitivity and skill in responding to North Atlantic freshwater perturbations. All of the simulations used the same freshwater forcing, 2.5 Sv for one year, applied to either the Hudson Bay (northeastern Canada) or Labrador Sea (between Canada's Labrador coast and Greenland). This freshwater pulse induced a decadal-mean slowdown of 10–25% in the Atlantic Meridional Overturning Circulation (AMOC) of the models and caused a large-scale pattern of climate anomalies that matched proxy evidence for cooling in the Northern Hemisphere and a southward shift of the Intertropical Convergence Zone. The multi-model ensemble generated temperature anomalies that were just half as large as those from quantitative proxy reconstructions, however. Also, the duration of AMOC and climate anomalies in three of the simulations was only several decades, significantly shorter than the duration of ~150 yr in the paleoclimate record. Possible reasons for these discrepancies include incorrect representation of the early Holocene climate and ocean state in the North Atlantic and uncertainties in the freshwater forcing estimates.

Description: Impacts of tropical cyclones on hydrochemistry of a subtropical forest Hydrology and Earth System Sciences Discussions, 10, 4537-4566, 2013 Author(s): C. T. Chang, S. P. Hamburg, J. L. Hwong, N. H. Lin, M. L. Hsueh, M. C. Chen, and T. C. Lin Tropical cyclones (typhoons/hurricanes) have major impacts on the biogeochemistry of forest ecosystems, but the stochastic nature and the long intervals between storms means that there are limited data on their effects. We characterized the impacts of 14 typhoons over six years on hydrochemistry of a subtropical forest plantation in Taiwan, a region experiencing frequent typhoons. Typhoons contributed 1/3 of annual rainfall on average, but ranged from 4% to 55%. The stochastic nature of annual typhoon related precipitation poses a challenge with respect to managing the impacts of these extreme events. This challenge is exacerbated by the fact that typhoon-related rainfall is not significantly correlated with wind velocity, the current focus of weather forecasts. Thus little advance warning is provided for the hydrological impacts of these storms. The typhoons we studied contributed approximately one third of the annual input and output of most nutrients (except nitrogen) during an average 9.5d yr −1 period, resulting in nutrient input/output rates an order of magnitude greater than during non-typhoon period. Nitrate output balanced input during the non-typhoon period, but during the typhoon period an average of 10 kg ha −1 yr −1 nitrate was lost. Streamwater chemistry exhibited similarly high variability during typhoon and non-typhoon periods and returned to pre-typhoon levels one to three weeks following each typhoon. The streamwater chemistry appears to be very resilient in response to typhoons, resulting in minimal loss of nutrients.

Description: A mid-Holocene climate reconstruction for eastern South America Climate of the Past, 9, 2117-2133, 2013 Author(s): L. F. Prado, I. Wainer, C. M. Chiessi, M.-P. Ledru, and B. Turcq The mid-Holocene (6000 calibrated years before present) is a key period in palaeoclimatology because incoming summer insolation was lower than during the late Holocene in the Southern Hemisphere, whereas the opposite happened in the Northern Hemisphere. However, the effects of the decreased austral summer insolation over South American climate have been poorly discussed by palaeodata syntheses. In addition, only a few of the regional studies have characterised the mid-Holocene climate in South America through a multiproxy approach. Here, we present a multiproxy compilation of mid-Holocene palaeoclimate data for eastern South America. We compiled 120 palaeoclimatological datasets, which were published in 84 different papers. The palaeodata analysed here suggest a water deficit scenario in the majority of eastern South America during the mid-Holocene if compared to the late Holocene, with the exception of northeastern Brazil. Low mid-Holocene austral summer insolation caused a reduced land–sea temperature contrast and hence a weakened South American monsoon system circulation. This scenario is represented by a decrease in precipitation over the South Atlantic Convergence Zone area, saltier conditions along the South American continental margin, and lower lake levels.

Description: Downscaling a global climate model to simulate climate change over the US and the implication on regional and urban air quality Geoscientific Model Development, 6, 1429-1445, 2013 Author(s): M. Trail, A. P. Tsimpidi, P. Liu, K. Tsigaridis, Y. Hu, A. Nenes, and A. G. Russell Climate change can exacerbate future regional air pollution events by making conditions more favorable to form high levels of ozone. In this study, we use spectral nudging with the Weather Research and Forecasting (WRF) model to downscale NASA earth system GISS modelE2 results during the years 2006 to 2010 and 2048 to 2052 over the contiguous United States in order to compare the resulting meteorological fields from the air quality perspective during the four seasons of five-year historic and future climatological periods. GISS results are used as initial and boundary conditions by the WRF regional climate model (RCM) to produce hourly meteorological fields. The downscaling technique and choice of physics parameterizations used are evaluated by comparing them with in situ observations. This study investigates changes of similar regional climate conditions down to a 12 km by 12 km resolution, as well as the effect of evolving climate conditions on the air quality at major US cities. The high-resolution simulations produce somewhat different results than the coarse-resolution simulations in some regions. Also, through the analysis of the meteorological variables that most strongly influence air quality, we find consistent changes in regional climate that would enhance ozone levels in four regions of the US during fall (western US, Texas, northeastern, and southeastern US), one region during summer (Texas), and one region where changes potentially would lead to better air quality during spring (Northeast). Changes in regional climate that would enhance ozone levels are increased temperatures and stagnation along with decreased precipitation and ventilation. We also find that daily peak temperatures tend to increase in most major cities in the US, which would increase the risk of health problems associated with heat stress. Future work will address a more comprehensive assessment of emissions and chemistry involved in the formation and removal of air pollutants.

Description: The SOCOL version 3.0 chemistry–climate model: description, evaluation, and implications from an advanced transport algorithm Geoscientific Model Development, 6, 1407-1427, 2013 Author(s): A. Stenke, M. Schraner, E. Rozanov, T. Egorova, B. Luo, and T. Peter We present the third generation of the coupled chemistry–climate model (CCM) SOCOL (modeling tools for studies of SOlar Climate Ozone Links). The most notable modifications compared to the previous model version are (1) the dynamical core has been updated with the fifth generation of the middle-atmosphere general circulation model MA-ECHAM (European Centre/HAMburg climate model), and (2) the advection of the chemical species is now calculated by a mass-conserving and shape-preserving flux-form transport scheme instead of the previously used hybrid advection scheme. The whole chemistry code has been rewritten according to the ECHAM5 infrastructure and transferred to Fortran95. In contrast to its predecessors, SOCOLvs3 is now fully parallelized. The performance of the new SOCOL version is evaluated on the basis of transient model simulations (1975–2004) with different horizontal (T31 and T42) resolutions, following the approach of the CCMVal-1 model validation activity. The advanced advection scheme significantly reduces the artificial loss and accumulation of tracer mass in regions with strong gradients that was observed in previous model versions. Compared to its predecessors, SOCOLvs3 generally shows more realistic distributions of chemical trace species, especially of total inorganic chlorine, in terms of the mean state, but also of the annual and interannual variability. Advancements with respect to model dynamics are for example a better representation of the stratospheric mean state in spring, especially in the Southern Hemisphere, and a slowdown of the upward propagation in the tropical lower stratosphere. Despite a large number of improvements model deficiencies still remain. Examples include a too-fast vertical ascent and/or horizontal mixing in the tropical stratosphere, the cold temperature bias in the lowermost polar stratosphere, and the overestimation of polar total ozone loss during Antarctic springtime.

Description: Stable water isotopes in the coupled atmosphere–land surface model ECHAM5-JSBACH Geoscientific Model Development, 6, 1463-1480, 2013 Author(s): B. Haese, M. Werner, and G. Lohmann In this study we present first results of a new model development, ECHAM5-JSBACH-wiso, where we have incorporated the stable water isotopes H 2 18 O and HDO as tracers in the hydrological cycle of the coupled atmosphere–land surface model ECHAM5-JSBACH. The ECHAM5-JSBACH-wiso model was run under present-day climate conditions at two different resolutions (T31L19, T63L31). A comparison between ECHAM5-JSBACH-wiso and ECHAM5-wiso shows that the coupling has a strong impact on the simulated temperature and soil wetness. Caused by these changes of temperature and the hydrological cycle, the δ 18 O in precipitation also shows variations from −4‰ up to 4‰. One of the strongest anomalies is shown over northeast Asia where, due to an increase of temperature, the δ 18 O in precipitation increases as well. In order to analyze the sensitivity of the fractionation processes over land, we compare a set of simulations with various implementations of these processes over the land surface. The simulations allow us to distinguish between no fractionation, fractionation included in the evaporation flux (from bare soil) and also fractionation included in both evaporation and transpiration (from water transport through plants) fluxes. While the isotopic composition of the soil water may change for δ 18 O by up to +8&permil:, the simulated δ 18 O in precipitation shows only slight differences on the order of ±1‰. The simulated isotopic composition of precipitation fits well with the available observations from the GNIP (Global Network of Isotopes in Precipitation) database.

Description: Glacial fluctuations of the Indian monsoon and their relationship with North Atlantic climate: new data and modelling experiments Climate of the Past, 9, 2135-2151, 2013 Author(s): C. Marzin, N. Kallel, M. Kageyama, J.-C. Duplessy, and P. Braconnot Several paleoclimate records such as from Chinese loess, speleothems or upwelling indicators in marine sediments present large variations of the Asian monsoon system during the last glaciation. Here, we present a new record from the northern Andaman Sea (core MD77-176) which shows the variations of the hydrological cycle of the Bay of Bengal. The high-resolution record of surface water δ 18 O dominantly reflects salinity changes and displays large millennial-scale oscillations over the period 40 000 to 11 000 yr BP. Their timing and sequence suggests that events of high (resp. low) salinity in the Bay of Bengal, i.e. weak (resp. strong) Indian monsoon, correspond to cold (resp. warm) events in the North Atlantic and Arctic, as documented by the Greenland ice core record. We use the IPSL_CM4 Atmosphere-Ocean coupled General Circulation Model to study the processes that could explain the teleconnection between the Indian monsoon and the North Atlantic climate. We first analyse a numerical experiment in which such a rapid event in the North Atlantic is obtained under glacial conditions by increasing the freshwater flux in the North Atlantic, which results in a reduction of the intensity of the Atlantic meridional overturning circulation. This freshwater hosing results in a weakening of the Indian monsoon rainfall and circulation. The changes in the continental runoff and local hydrological cycle are responsible for an increase in salinity in the Bay of Bengal. This therefore compares favourably with the new sea water δ 18 O record presented here and the hypothesis of synchronous cold North Atlantic and weak Indian monsoon events. Additional sensitivity experiments are produced with the LMDZ atmospheric model to analyse the teleconnection mechanisms between the North Atlantic and the Indian monsoon. The changes over the tropical Atlantic are shown to be essential in triggering perturbations of the subtropical jet over Africa and Eurasia, that in turn affect the intensity of the Indian monsoon. These relationships are also found to be valid in additional coupled model simulations in which the Atlantic meridional overturning circulation (AMOC) is forced to resume.

Description: δ 18 O water isotope in the i LOVECLIM model (version 1.0) – Part 2: Evaluation of model results against observed δ 18 O in water samples Geoscientific Model Development, 6, 1493-1504, 2013 Author(s): D. M. Roche and T. Caley The H 2 18 O stable isotope was previously introduced in the three coupled components of the earth system model i LOVECLIM: atmosphere, ocean and vegetation. The results of a long (5000 yr) pre-industrial equilibrium simulation are presented and evaluated against measurement of H 2 18 O abundance in present-day water for the atmospheric and oceanic components. For the atmosphere, it is found that the model reproduces the observed spatial distribution and relationships to climate variables with some merit, though limitations following our approach are highlighted. Indeed, we obtain the main gradients with a robust representation of the Rayleigh distillation but caveats appear in Antarctica and around the Mediterranean region due to model limitation. For the oceanic component, the agreement between the modelled and observed distribution of water δ 18 O is found to be very good. Mean ocean surface latitudinal gradients are faithfully reproduced as well as the mark of the main intermediate and deep water masses. This opens large prospects for the applications in palaeoclimatic context.

Description: Hurricane impacts on a pair of coastal forested watersheds: implications of selective hurricane damage to forest structure and streamflow dynamics Hydrology and Earth System Sciences Discussions, 10, 11519-11557, 2013 Author(s): A. D. Jayakaran, T. M. Williams, H. Ssegane, D. M. Amatya, B. Song, and C. C. Trettin Hurricanes are infrequent but influential disruptors of ecosystem processes in the southeastern Atlantic and Gulf coasts. Every southeastern forested wetland has the potential to be struck by a tropical cyclone. We examined the impact of Hurricane Hugo on two paired coastal watersheds in South Carolina in terms of stream flow and vegetation dynamics, both before and after the hurricane's passage in 1989. The study objectives were to quantify the magnitude and timing of changes including a reversal in relative streamflow-difference between two paired watersheds, and to examine the selective impacts of a hurricane on the vegetative composition of the forest. We related these impacts to their potential contribution to change watershed hydrology through altered evapotranspiration processes. Using over thirty years of monthly rainfall and streamflow data we showed that there was a significant transformation in the hydrologic character of the two watersheds – a transformation that occurred soon after the hurricane's passage. We linked the change in the rainfall-runoff relationship to a catastrophic shift in forest vegetation due to selective hurricane damage. While both watersheds were located in the path of the hurricane, extant forest structure varied between the two watersheds as a function of experimental forest management techniques on the treatment watershed. We showed that the primary damage was to older pines, and to some extent larger hardwood trees. We believe that lowered vegetative water use impacted both watersheds with increased outflows on both watersheds due to loss of trees following hurricane impact. However, one watershed was able to recover to pre hurricane levels of canopy transpiration at a quicker rate due to the greater abundance of pine seedlings and saplings in that watershed.

Description: Mid-Holocene ocean and vegetation feedbacks over East Asia Climate of the Past, 9, 2153-2171, 2013 Author(s): Z. Tian and D. Jiang Mid-Holocene ocean and vegetation feedbacks over East Asia are investigated by a set of numerical experiments performed with the version 4 of the Community Climate System Model (CCSM4). With reference to the pre-industrial period, most of the mid-Holocene annual and seasonal surface-air temperature and precipitation changes are found to result from a direct response of the atmosphere to insolation forcing, while dynamic ocean and vegetation modulate regional climate of East Asia to some extent. Because of its thermal inertia, the dynamic ocean induced an additional warming of 0.2 K for the annual mean, 0.5 K in winter (December–February), 0.0003 K in summer (June–August), and 1.0 K in autumn (September–November), but a cooling of 0.6 K in spring (March–May) averaged over China, and it counteracted (amplified) the direct effect of insolation forcing for the annual mean and in winter and autumn (spring) for that period. The dynamic vegetation had an area-average impact of no more than 0.4 K on the mid-Holocene annual and seasonal temperatures over China, with an average cooling of 0.2 K for the annual mean. On the other hand, ocean feedback induced a small increase of precipitation in winter (0.04 mm day −1 ) and autumn (0.05 mm day −1 ), but a reduction for the annual mean (0.14 mm day −1 ) and in spring (0.29 mm day −1 ) and summer (0.34 mm day −1 ) over China, while it also suppressed the East Asian summer monsoon rainfall. The effect of dynamic vegetation on the mid-Holocene annual and seasonal precipitation was comparatively small, ranging from −0.03 mm day −1 to 0.06 mm day −1 averaged over China. In comparison, the CCSM4 simulated annual and winter cooling over China agrees with simulations within the Paleoclimate Modeling Intercomparison Project (PMIP), but the results are contrary to the warming reconstructed from multiple proxy data for the mid-Holocene. Ocean feedback narrows this model–data mismatch, whereas vegetation feedback plays an opposite role but with a level of uncertainty.

Description: The Rock Geochemical Model (RokGeM) v0.9 Geoscientific Model Development, 6, 1543-1573, 2013 Author(s): G. Colbourn, A. Ridgwell, and T. M. Lenton A new model of terrestrial rock weathering – the Rock Geochemical Model (RokGeM) – was developed for incorporation into the GENIE Earth System modelling framework. In this paper we describe the model. We consider a range of previously devised parameterizations, ranging from simple dependencies on global mean temperature following Berner et al. (1983), to spatially explicit dependencies on run-off and temperature (GKWM, Bluth and Kump, 1994; GEM-CO2, Amiotte-Suchet et al., 2003) – fields provided by the energy-moisture balance atmosphere model component in GENIE. Using long-term carbon cycle perturbation experiments, we test the effects of a wide range of model parameters, including whether or not the atmosphere was "short-circuited" in the carbon cycle; the sensitivity and feedback strength of temperature and run-off on carbonate and silicate weathering; different river-routing schemes; 0-D (global average) vs. 2-D (spatially explicit) weathering schemes; and the lithology dependence of weathering. Included are details of how to run the model and visualize the results.

Description: Water-soluble organic carbon in snow and ice deposited at Alpine, Greenland, and Antarctic sites: a critical review of available data and their atmospheric relevance Climate of the Past, 9, 2195-2211, 2013 Author(s): M. Legrand, S. Preunkert, B. Jourdain, J. Guilhermet, X. Fa{ï}n, I. Alekhina, and J. R. Petit While it is now recognized that organic matter dominates the present-day atmospheric aerosol load over continents, its sources remain poorly known. The studies of organic species or organic fractions trapped in ice cores may help to overcome this lack of knowledge. Available data on the dissolved (or total) organic carbon (DOC or TOC) content of snow and ice often appear largely inconsistent, and, until now, no critical review has been conducted to understand the causes of these inconsistencies. To draw a more consistent picture of the organic carbon amount present in solid precipitation that accumulates on cold glaciers, we here review available data and, when needed, complete the data set with analyses of selected samples. The different data sets are then discussed by considering the age (modern versus pre-industrial, Holocene versus Last glacial Maximum) and type (surface snow, firn, or ice) of investigated samples, the deployed method, and the applied contamination control. Finally, the OC (DOC or TOC) levels of Antarctic, Greenland, and Alpine ice cores are compared and discussed with respect to natural (biomass burning, vegetation emissions) and anthropogenic sources (fossil fuel combustion) contributing to atmospheric OC aerosol.

Description: An approach to computing direction relations between separated object groups Geoscientific Model Development, 6, 1591-1599, 2013 Author(s): H. Yan, Z. Wang, and J. Li Direction relations between object groups play an important role in qualitative spatial reasoning, spatial computation and spatial recognition. However, none of existing models can be used to compute direction relations between object groups. To fill this gap, an approach to computing direction relations between separated object groups is proposed in this paper, which is theoretically based on gestalt principles and the idea of multi-directions. The approach firstly triangulates the two object groups, and then it constructs the Voronoi diagram between the two groups using the triangular network. After this, the normal of each Voronoi edge is calculated, and the quantitative expression of the direction relations is constructed. Finally, the quantitative direction relations are transformed into qualitative ones. The psychological experiments show that the proposed approach can obtain direction relations both between two single objects and between two object groups, and the results are correct from the point of view of spatial cognition.

Description: Recent evolution of China's virtual water trade: analysis of selected crops and considerations for policy Hydrology and Earth System Sciences Discussions, 10, 11613-11641, 2013 Author(s): J. Shi, J. Liu, and L. Pinter China has dramatically increased its virtual water import unconsciously for recent years. Many studies have focused on the quantity of traded virtual water but very few go into analysing geographic distribution and the properties of China's virtual water trade network. This paper provides a calculation and analysis of the crop-related virtual water trade network of China based on 27 major primary crops between 1986 and 2009. The results show that China is a net importer of virtual water from water-abundant areas of North and South America, and a net virtual water exporter to water-stressed areas of Asia, Africa, and Europe. Virtual water import is far larger than virtual water export and in both import and export a small number of trade partners control the supply chain. Grain crops are the major contributors to virtual water trade, and among grain crops soybeans, mostly imported from the US, Brazil and Argentina are the most significant. As crop yield and crop water productivity in North and South America are generally higher than those in Asia and Africa, the effect of China's crop-related virtual water trade positively contributes to optimizing crop water use efficiency at the global scale. In order to mitigate water scarcity and secure the food supply, virtual water should be actively incorporated into national water management strategies. From the national perspective, China should reduce the export and increase the import of water-intensive crops. But the sources of virtual water import need to be further diversified to reduce supply chain risks and increase resilience.

Description: A method to represent ozone response to large changes in precursor emissions using high-order sensitivity analysis in photochemical models Geoscientific Model Development, 6, 1601-1608, 2013 Author(s): G. Yarwood, C. Emery, J. Jung, U. Nopmongcol, and T. Sakulyanontvittaya Photochemical grid models (PGMs) are used to simulate tropospheric ozone and quantify its response to emission changes. PGMs are often applied for annual simulations to provide both maximum concentrations for assessing compliance with air quality standards and frequency distributions for assessing human exposure. Efficient methods for computing ozone at different emission levels can improve the quality of ozone air quality management efforts. This study demonstrates the feasibility of using the decoupled direct method (DDM) to calculate first- and second-order sensitivity of ozone to anthropogenic NO x and VOC emissions in annual PGM simulations at continental scale. Algebraic models are developed that use Taylor series to produce complete annual frequency distributions of hourly ozone at any location and any anthropogenic emission level between zero and 100%, adjusted independently for NO x and VOC. We recommend computing the sensitivity coefficients at the midpoint of the emissions range over which they are intended to be applied, in this case with 50% anthropogenic emissions. The algebraic model predictions can be improved by combining sensitivity coefficients computed at 10 and 50% anthropogenic emissions. Compared to brute force simulations, algebraic model predictions tend to be more accurate in summer than winter, at rural than urban locations, and with 100% than zero anthropogenic emissions. Equations developed to combine sensitivity coefficients computed with 10 and 50% anthropogenic emissions are able to reproduce brute force simulation results with zero and 100% anthropogenic emissions with a mean bias of less than 2 ppb and mean error of less than 3 ppb averaged over 22 US cities.

Description: Major dust events in Europe during marine isotope stage 5 (130–74 ka): a climatic interpretation of the "markers" Climate of the Past, 9, 2213-2230, 2013 Author(s): D.-D. Rousseau, M. Ghil, G. Kukla, A. Sima, P. Antoine, M. Fuchs, C. Hatté, F. Lagroix, M. Debret, and O. Moine At present, major dust storms are occurring at mid-latitudes in the Middle East and Asia, as well as at low latitudes in Northern Africa and in Australia. Western Europe, though, does not experience such dramatic climate events, except for some African dust reaching it from the Sahara. This modern situation is of particular interest, in the context of future climate projections, since the present interglacial is usually interpreted, in this context, as an analog of the warm Eemian interval. European terrestrial records show, however, major dust events during the penultimate interglacial and early glacial. These events are easily observed in loess records by their whitish-color deposits, which lie above and below dark chernozem paleosols in Central European records of Marine Isotope Stage (MIS) 5 age. We describe here the base of the Dolni Vestonice (DV) loess sequence, Czech Republic, as the reference of such records. The dust is deposited during intervals that are characterized by poor vegetation – manifested by high δ 13 C values and low magnetic susceptibility – while the fine sand and clay in the deposits shows grain sizes that are clearly different from the overlying pleniglacial loess deposits. Some of these dust events have been previously described as "Markers" or Marker Silts (MS) by one of us (G. Kukla), and are dated at about 111–109 ka and 93–92 ka, with a third and last one slightly visible at about 75–73 ka. Other events correspond to the loess material of Kukla's cycles, and are described as eolian silts (ES); they are observed in the same DV sequence and are dated at about 106–105 ka, 88–86 ka, and 78.5–77 ka. These dates are determined by considering the OSL ages with their errors measured on the studied sequence, and the comparison with Greenland ice-core and European speleothem chronologies. The fine eolian deposits mentioned above, MS as well as ES, correspond to short events that lasted about 2 ka; they are synchronous with re-advances of the polar front over the North Atlantic, as observed in marine sediment cores. These deposits also correlate with important changes observed in European vegetation. Some ES and MS events appear to be coeval with significant dust peaks recorded in the Greenland ice cores, while others are not. This decoupling between the European eolian and Greenland dust depositions is of considerable interest, as it differs from the fully glacial situation, in which the Eurasian loess sedimentation mimics the Greenland dust record. Previous field observations supported an interpretation of MS events as caused by continental dust storms. We show here, by a comparison with speleothems of the same age found in the northern Alps, that different atmospheric-circulation modes seem to be responsible for the two categories of dust events, MS vs. ES.

Description: A Lagrangian advection scheme with shape matrix (LASM) for solving advection problems Geoscientific Model Development, 7, 2951-2968, 2014 Author(s): L. Dong, B. Wang, and L. Liu A new Lagrangian advection scheme with shape matrix (LASM) is proposed to take advantage of the extreme low numerical diffusion of the Lagrangian methods. The tracer is discretized into finite parcels, which move along the downstream trajectories. Different from other Lagrangian schemes, the parcel shape is simulated explicitly by a linear transformation matrix. By doing so, the aliasing error in the Lagrangian schemes is largely reduced without introducing substantial interparcel mixing in the pure advection stage, because the flow information will be respected when remapping tracer density onto the fixed model grids. An adaptive interparcel mixing algorithm is constructed to ensure the validity of the linear approximation of the parcel shape, where the mixing is only triggered when it is necessary and resembles the physical mixing. The total tracer mass on the parcels is conserved exactly. The new scheme is validated by using several test cases.

Description: Extending periodic eddy covariance latent heat fluxes through tree sapflow measurements to estimate long-term total evaporation in a peat swamp forest Hydrology and Earth System Sciences Discussions, 11, 13607-13661, 2014 Author(s): A. D. Clulow, C. S. Everson, M. G. Mengistu, J. S. Price, A. Nickless, and G. P. W. Jewitt A combination of measurement and modelling was used to find a pragmatic solution to estimate the annual total evaporation (ET) from the rare and indigenous Nkazana Peat Swamp Forest (PSF) on the east coast of Southern Africa to improve the water balance estimates within the area. Total evaporation was measured during three window periods (between seven and nine days each) using an eddy covariance (EC) system on a telescopic mast above the forest canopy. Sapflow of an understory and an emergent tree was measured using a low maintenance heat pulse velocity system for an entire hydrological year (October 2009 to September 2010). An empirical model was derived, describing the relationship between the observed ET of the Nkazana PSF measured during two of the window periods ( R 2 = 0.92 and 0.90) which, overlapped with sapflow measurements, thereby providing hourly estimates of predicted ET of the Nkazana PSF for a year, totalling 1125 mm (while rainfall was 650 mm). In building the empirical model, it was found that including the understory tree sapflow provided no benefit to the model performance. In addition, the observed emergent tree sapflow relationship with observed ET between the two field campaigns was consistent and could be represented by a single empirical model ( R 2 = 0.90; RMSE = 0.08 mm). During the window periods of EC measurement, no single meteorological variable was found to describe the Nkazana PSF ET satisfactorily. However, in terms of evaporation models, the hourly FAO56 Penman–Monteith equation best described the observed ET from EC during the August 2009 ( R 2 = 0.75), November 2009 ( R 2 = 0.85) and March 2010 ( R 2 = 0.76) field campaigns, compared to the Priestley–Taylor model ( R 2 = 0.54, 0.74 and 0.62 during the respective field campaigns). From the empirical model of ET and the FAO56 Penman–Monteith equation, a monthly crop factor ( K c ) was derived for the Nkazana PSF providing a method of estimating long-term swamp forest ET from meteorological data. The monthly crop factor indicated two distinct periods. From February to May, it was between 1.2 and 1.4 compared with June to January, when the crop factor was 0.8 to 1.0. The derived monthly K c values were verified as accurate (to one significant digit) using historical data measured at the same site, also using EC, from a~previous study. The measurements provided insights into the microclimate within a subtropical peat swamp forest and the contrasting sapflow of emergent and understory trees. They showed that expensive, high maintenance equipment can be used during manageable window periods in conjunction with low maintenance systems, dedicated to individual trees, to derive a model to estimate long-term ET over remote heterogeneous forests. In addition, the contrast in ET and rainfall emphasises the reliance of the Nkazana PSF on groundwater.

Description: Dye tracing for investigating flow and transport properties of hydrocarbon-polluted Rabots glaciär, Kebnekaise, Sweden Hydrology and Earth System Sciences Discussions, 11, 13711-13744, 2014 Author(s): C. C. Clason, C. Coch, J. Jarsjö, K. Brugger, P. Jansson, and G. Rosqvist Over 11 000 L of hydrocarbon pollution was deposited on the surface of Rabots glaciär on the Kebnekaise Massif, northern Sweden, following the crash of a Royal Norwegian Air Force aircraft in March 2012. An environmental monitoring programme was subsequently commissioned, including water, snow and ice sampling. The scientific programme further included a series of dye tracing experiments during the 2013 melt season, conducted to investigate flow pathways for pollutants through the glacier hydrological system, and to gain new insight to the internal hydrological system of Rabots glaciär. Results of dye tracing reveal a degree of homogeneity in the topology of the drainage system throughout July and August, with an increase in efficiency as the season progresses, as reflected by decreasing temporary storage and dispersivity. Early onset of melting likely led to formation of an efficient, discrete drainage system early in the melt season, subject to decreasing sinuosity and braiding as the season progressed. Analysis of turbidity-discharge hysteresis further supports the formation of discrete, efficient drainage, with clockwise diurnal hysteresis suggesting easy mobilisation of readily-available sediments in channels. Dye injection immediately downstream of the pollution source zone revealed prolonged storage of dye followed by fast, efficient release. Twinned with a low dye recovery, and supported by sporadic detection of hydrocarbons in the proglacial river, we suggest that meltwater, and thus pollutants in solution, may be released periodically from this zone of the glacier hydrological system. The here identified dynamics of dye storage, dispersion and breakthrough indicate that the ultimate fate and permanence of pollutants in the glacier system is likely to be governed by storage of pollutants in the firn layer and ice mass, or within the internal hydrological system, where it may refreeze. This shows that future studies on the fate of hydrocarbons in pristine, glaciated mountain environments should address the extent to which pollutants in solution act like water molecules or whether they are more susceptible to, for example, refreezing into the surrounding ice, becoming stuck in micro-fractures and pore spaces, or sorption onto subglacial sediments.

Description: Laminated sediments in the Bering Sea reveal atmospheric teleconnections to Greenland climate on millennial to decadal timescales during the last deglaciation Climate of the Past, 10, 2215-2236, 2014 Author(s): H. Kuehn, L. Lembke-Jene, R. Gersonde, O. Esper, F. Lamy, H. Arz, G. Kuhn, and R. Tiedemann During the last glacial termination, the upper North Pacific Ocean underwent dramatic and rapid changes in oxygenation that lead to the transient intensification of oxygen minimum zones (OMZs), recorded by the widespread occurrence of laminated sediments on circum-Pacific continental margins. We present a new laminated sediment record from the mid-depth (1100 m) northern Bering Sea margin that provides insight into these deglacial OMZ maxima with exceptional, decadal-scale detail. Combined ultrahigh-resolution micro-X-ray-fluorescence (micro-XRF) data and sediment facies analysis of laminae reveal an alternation between predominantly terrigenous and diatom-dominated opal sedimentation. The diatomaceous laminae are interpreted to represent spring/summer productivity events related to the retreating sea ice margin. We identified five laminated sections in the deglacial part of our site. Lamina counts were carried out on these sections and correlated with the Bølling–Allerød and Preboreal phases in the North Greenland Ice Core (NGRIP) oxygen isotope record, indicating an annual deposition of individual lamina couplets (varves). The observed rapid decadal intensifications of anoxia, in particular within the Bølling–Allerød, are tightly coupled to short-term warm events through increases in regional export production. This dependence of laminae formation on warmer temperatures is underlined by a correlation with published Bering Sea sea surface temperature records and δ 18 O data of planktic foraminifera from the Gulf of Alaska. The rapidity of the observed changes strongly implies a close atmospheric teleconnection between North Pacific and North Atlantic regions. We suggest that concomitant increases in export production and subsequent remineralization of organic matter in the Bering Sea, in combination with oxygen-poor waters entering the Being Sea, drove down oxygen concentrations to values below 0.1 mL L −1 and caused laminae preservation. Calculated benthic–planktic ventilation ages show no significant variations throughout the last deglaciation, indicating that changes in formation rates or differing sources of North Pacific mid-depth waters are not prime candidates for strengthening the OMZ at our site. The age models established by our correlation procedure allow for the determination of calendar age control points for the Bølling–Allerød and the Preboreal that are independent of the initial radiocarbon-based chronology. Resulting surface reservoir ages range within 730–990 yr during the Bølling–Allerød, 800–1100 yr in the Younger Dryas, and 765–775 yr for the Preboreal.

Description: Implication of methodological uncertainties for mid-Holocene sea surface temperature reconstructions Climate of the Past, 10, 2237-2252, 2014 Author(s): I. Hessler, S. P. Harrison, M. Kucera, C. Waelbroeck, M.-T. Chen, C. Anderson, A. de Vernal, B. Fréchette, A. Cloke-Hayes, G. Leduc, and L. Londeix We present and examine a multi-sensor global compilation of mid-Holocene (MH) sea surface temperatures (SST), based on Mg/Ca and alkenone palaeothermometry and reconstructions obtained using planktonic foraminifera and organic-walled dinoflagellate cyst census counts. We assess the uncertainties originating from using different methodologies and evaluate the potential of MH SST reconstructions as a benchmark for climate-model simulations. The comparison between different analytical approaches (time frame, baseline climate) shows the choice of time window for the MH has a negligible effect on the reconstructed SST pattern, but the choice of baseline climate affects both the magnitude and spatial pattern of the reconstructed SSTs. Comparison of the SST reconstructions made using different sensors shows significant discrepancies at a regional scale, with uncertainties often exceeding the reconstructed SST anomaly. Apparent patterns in SST may largely be a reflection of the use of different sensors in different regions. Overall, the uncertainties associated with the SST reconstructions are generally larger than the MH anomalies. Thus, the SST data currently available cannot serve as a target for benchmarking model simulations. Further evaluations of potential subsurface and/or seasonal artifacts that may contribute to obscure the MH SST reconstructions are urgently needed to provide reliable benchmarks for model evaluations.

Description: Sensitivity of the Mediterranean sea level to atmospheric pressure and free surface elevation numerical formulation in NEMO Geoscientific Model Development, 7, 3001-3015, 2014 Author(s): P. Oddo, A. Bonaduce, N. Pinardi, and A. Guarnieri The sensitivity of the dynamics of the Mediterranean Sea to atmospheric pressure and free surface elevation formulation using NEMO (Nucleus for European Modelling of the Ocean) was evaluated. Four different experiments were carried out in the Mediterranean Sea using filtered or explicit free surface numerical schemes and accounting for the effect of atmospheric pressure in addition to wind and buoyancy fluxes. Model results were evaluated by coherency and power spectrum analysis with tide gauge data. We found that atmospheric pressure plays an important role for periods shorter than 100 days. The free surface formulation is important to obtain the correct ocean response for periods shorter than 30 days. At frequencies higher than 15 days −1 the Mediterranean basin's response to atmospheric pressure was not coherent and the performance of the model strongly depended on the specific area considered. A large-amplitude seasonal oscillation observed in the experiments using a filtered free surface was not evident in the corresponding explicit free surface formulation case, which was due to a phase shift between mass fluxes in the Gibraltar Strait and at the surface. The configuration with time splitting and atmospheric pressure always performed best; the differences were enhanced at very high frequencies.

Description: Sampling frequency trade-offs in the assessment of mean transit times of tropical montane catchment waters under semi-steady-state conditions Hydrology and Earth System Sciences Discussions, 11, 12443-12488, 2014 Author(s): E. Timbe, D. Windhorst, R. Celleri, L. Timbe, P. Crespo, H.-G. Frede, J. Feyen, and L. Breuer Stream and soil waters were collected on a weekly basis in a tropical montane cloud forest catchment for two years and analyzed for stable water isotopes in order to infer transit time distribution functions and to define the mean transit times. Depending on the water type (stream or soil water), lumped distribution functions such as Exponential-Piston flow, Linear-Piston flow and Gamma models using temporal isotopic variations of precipitation event samples as input, were fitted. Samples were aggregated to daily, weekly, biweekly, monthly and bimonthly time scales in order to check the sensitivity of temporal sampling on model predictions. The study reveals that the effect of decreasing sampling frequency depends on the water type. For soil waters with transit times in the order of weeks to months, there was a clear trend of over prediction. In contrast, the trend of prediction for stream waters, with a dampened isotopic signal and mean transit times in the order of 2 to 4 years, was less clear and depending on the type of model used. The trade-off to coarse data resolutions could potentially lead to misleading conclusions on how water actually moves through the catchment, while at the same time predictions can reach better fitting efficiencies, lesser uncertainties, errors and biases. For both water types an optimal sampling frequency seems to be one or at most two weeks. The results of our analyses provide information for the planning (in particular in terms of cost-benefit and time requirements) of future fieldwork in similar Andean or other catchments.

Description: Gaseous chemistry and aerosol mechanism developments for version 3.5.1 of the online regional model, WRF-Chem Geoscientific Model Development, 7, 2557-2579, 2014 Author(s): S. Archer-Nicholls, D. Lowe, S. Utembe, J. Allan, R. A. Zaveri, J. D. Fast, Ø. Hodnebrog, H. Denier van der Gon, and G. McFiggans We have made a number of developments to the Weather, Research and Forecasting model coupled with Chemistry (WRF-Chem), with the aim of improving model prediction of trace atmospheric gas-phase chemical and aerosol composition, and of interactions between air quality and weather. A reduced form of the Common Reactive Intermediates gas-phase chemical mechanism (CRIv2-R5) has been added, using the Kinetic Pre-Processor (KPP) interface, to enable more explicit simulation of VOC degradation. N 2 O 5 heterogeneous chemistry has been added to the existing sectional MOSAIC aerosol module, and coupled to both the CRIv2-R5 and existing CBM-Z gas-phase schemes. Modifications have also been made to the sea-spray aerosol emission representation, allowing the inclusion of primary organic material in sea-spray aerosol. We have worked on the European domain, with a particular focus on making the model suitable for the study of nighttime chemistry and oxidation by the nitrate radical in the UK atmosphere. Driven by appropriate emissions, wind fields and chemical boundary conditions, implementation of the different developments are illustrated, using a modified version of WRF-Chem 3.4.1, in order to demonstrate the impact that these changes have in the Northwest European domain. These developments are publicly available in WRF-Chem from version 3.5.1 onwards.

Description: Oxygen stable isotopes during the Last Glacial Maximum climate: perspectives from data–model ( i LOVECLIM) comparison Climate of the Past, 10, 1939-1955, 2014 Author(s): T. Caley, D. M. Roche, C. Waelbroeck, and E. Michel We use the fully coupled atmosphere–ocean three-dimensional model of intermediate complexity i LOVECLIM to simulate the climate and oxygen stable isotopic signal during the Last Glacial Maximum (LGM, 21 000 years). By using a model that is able to explicitly simulate the sensor (δ 18 O), results can be directly compared with data from climatic archives in the different realms. Our results indicate that i LOVECLIM reproduces well the main feature of the LGM climate in the atmospheric and oceanic components. The annual mean δ 18 O in precipitation shows more depleted values in the northern and southern high latitudes during the LGM. The model reproduces very well the spatial gradient observed in ice core records over the Greenland ice sheet. We observe a general pattern toward more enriched values for continental calcite δ 18 O in the model at the LGM, in agreement with speleothem data. This can be explained by both a general atmospheric cooling in the tropical and subtropical regions and a reduction in precipitation as confirmed by reconstruction derived from pollens and plant macrofossils. Data–model comparison for sea surface temperature indicates that i LOVECLIM is capable to satisfyingly simulate the change in oceanic surface conditions between the LGM and present. Our data–model comparison for calcite δ 18 O allows investigating the large discrepancies with respect to glacial temperatures recorded by different microfossil proxies in the North Atlantic region. The results argue for a strong mean annual cooling in the area south of Iceland and Greenland between the LGM and present (〉 6 °C), supporting the foraminifera transfer function reconstruction but in disagreement with alkenones and dinocyst reconstructions. The data–model comparison also reveals that large positive calcite δ 18 O anomaly in the Southern Ocean may be explained by an important cooling, although the driver of this pattern is unclear. We deduce a large positive δ 18 Osw anomaly for the north Indian Ocean that contrasts with a large negative δ 18 Osw anomaly in the China Sea between the LGM and the present. This pattern may be linked to changes in the hydrological cycle over these regions. Our simulation of the deep ocean suggests that changes in δ 18 Osw between the LGM and the present are not spatially homogeneous. This is supported by reconstructions derived from pore fluids in deep-sea sediments. The model underestimates the deep ocean cooling thus biasing the comparison with benthic calcite δ 18 O data. Nonetheless, our data–model comparison supports a heterogeneous cooling of a few degrees (2–4 °C) in the LGM Ocean.

Description: Quantitative high-resolution observations of soil water dynamics in a complicated architecture with time-lapse Ground-Penetrating Radar Hydrology and Earth System Sciences Discussions, 11, 12365-12404, 2014 Author(s): P. Klenk, S. Jaumann, and K. Roth High-resolution time-lapse Ground-Penetrating Radar (GPR) observations of advancing and retreating water tables can yield a wealth of information about near-surface water content dynamics. In this study, we present and analyze a series of imbibition, drainage and infiltration experiments which have been carried out at our artificial ASSESS test site and observed with surface based GPR. The test site features a complicated but known subsurface architecture constructed with three different kinds of sand. It allows studying soil water dynamics with GPR under a wide range of different conditions. Here, we assess in particular (i) the accurate determination of soil water dynamics averaged over the whole vertical extent by evaluating the bottom reflection and (ii) the feasibility of monitoring the dynamic shape of the capillary fringe reflection. The phenomenology of the GPR response of a dynamically changing capillary fringe is developed from a soil physical point of view. We then explain experimentally observed phenomena based on numerical simulations of both the water content dynamics and the expected GPR response.

Description: Simulating long-term past changes in the balance between water demand and availability and assessing their main drivers at the river basin management scale Hydrology and Earth System Sciences Discussions, 11, 12315-12364, 2014 Author(s): J. Fabre, D. Ruelland, A. Dezetter, and B. Grouillet The aim of this study was to assess the balance between water demand and availability and its spatial and temporal variability from 1971 to 2009 in the Herault (2500 km 2 , France) and the Ebro (85 000 km 2 , Spain) catchments. Natural streamflow was evaluated using a conceptual hydrological model. The regulation of river flow was accounted for through a widely applicable demand-driven reservoir management model applied to the largest dam in the Herault basin and to 11 major dams in the Ebro basin. Urban water demand was estimated from population and monthly unit water consumption data. Water demand for irrigation was computed from irrigated area, crop and soil data, and climatic forcing. Finally, a series of indicators comparing water supply and water demand at strategic resource and demand nodes were computed at a 10 day time step. Variations in water stress in each catchment over the past 40 years were successfully modeled, taking into account climatic and anthropogenic pressures and changes in water management strategies over time. Observed changes in discharge were explained by separating human and hydro-climatic pressures on water resources: respectively 20 and 3% of the decrease in the Ebro and the Herault discharges were linked to human-induced changes. Although key areas of the Herault basin were shown to be highly sensitive to hydro-climatic variability, the balance between water uses and availability in the Ebro basin appears to be more critical, owing to high agricultural pressure on water resources. The proposed modeling framework is currently being used to assess water stress under climatic and socio-economic prospective scenarios. Further research will investigate the effectiveness of adaptation policies aimed at maintaining the balance between water use and availability.

Description: Time-series analysis of the long-term hydrologic impacts of afforestation in the Águeda watershed of North-Central Portugal Hydrology and Earth System Sciences Discussions, 11, 12223-12256, 2014 Author(s): D. Hawtree, J. P. Nunes, J. J. Keizer, R. Jacinto, J. Santos, M. E. Rial-Rivas, A.-K. Boulet, F. Tavares-Wahren, and K.-H. Feger The north-central region of Portugal has undergone significant afforestation of the species Pinus pinaster and Eucalyptus globulus since the early 1900s; however, the long-term hydrologic impacts of this land cover change are not fully understood. To contribute to a better understanding of the potential hydrologic impacts of this land cover change, this study examines the temporal trends in 7 years of data from the Águeda watershed (part of the Vouga Basin) over the period of 1936 to 2010. Meteorological and hydrological records were analysed using a combined Thiel–Sen/Mann–Kendall trend testing approach, to assess the magnitude and significance of patterns in the observed data. These trend tests indicated that there had been no significant reduction in streamflow yield over either the entire test period, or during sub-record periods, despite the large-scale afforestation which had taken place. This lack of change is attributed to both the characteristics of the watershed and the nature of the land cover change. By contrast, a number of significant trends were found for baseflow index, which showed positive trends in the early data record (primarily during Pinus pinaster afforestation), followed by a reversal to negative trends later in the data record (primarily during Eucalyptus globulus afforestation). These changes are attributed to vegetation impacts on streamflow generating processes, both due to the species differences and to alterations in soil properties (i.e. promoting water repellency of the topsoil). These results highlight the importance of considering both vegetation types/dynamics and watershed characteristic when assessing hydrologic impacts, in particular with respect to soil properties.

Description: Reply to D. L. Peters' comment on "Streamflow input to Lake Athabasca, Canada" by Rasouli et al. (2013) Hydrology and Earth System Sciences Discussions, 11, 12257-12270, 2014 Author(s): K. Rasouli, M. A. Hernández-Henríquez, and S. J. Déry This paper provides a reply to a comment from Peters (2014) on our recent effort focused on evaluating changes in streamflow input to Lake Athabasca, Canada. Lake Athabasca experienced a 21.2% decline in streamflow input between 1960 and 2010 that has led to a marked decline in its water levels in recent decades. A reassessment of trends in naturalized Lake Athabasca water levels shows insignificant changes from our previous findings reported in Rasouli et al. (2013), and hence our previous conclusions remain unchanged. The reply closes with recommendations for future research to minimize uncertainties in historical assessments of trends in Lake Athabasca water levels and to better project its future water levels driven by climate change and anthropogenic activities in the Athabasca Lake Basin.

Description: Is sinuosity a function of slope and bankfull discharge? – A case study of the meandering rivers in the Pannonian Basin Hydrology and Earth System Sciences Discussions, 11, 12271-12290, 2014 Author(s): J. Petrovszki, G. Timár, and G. Molnár Pre-regulation channel sinuosities of the meandering rivers of the Pannonian Basin are analysed in order to define a mathematical model to estimate the influence of the bankfull discharge and the channel slope on them. As a primary database, data triplets of slope, discharge and sinuosity values were extracted from historical and modern datasets and pre-regulation historical topographic maps. Channel slope values were systematically modified to estimate figures valid before the river regulation works. The bankfull discharges were estimated from the average discharges using a robust yet complex method. The "classical" graphs of Leopold and Wolman (1957), Ackers and Charlton (1970b) and Schumm and Khan (1972) were compiled to a set up a theoretical surface, whose parameters are estimated by the real values of the above database, containing characteristics of the Pannonian Basin rivers. As a result it occurred that there is a two-dimensional function of the bankfull discharges, which provides a good estimation of the most probable sinuosity values of the rivers with the given slope and discharge characteristics. The average RMS error of this estimation is around 15% on this dataset and believed to be the effect of the non-analysed changes in the sediment discharge and size distribution.

Description: Technical Note: Field experiences using UV/VIS sensors for high-resolution monitoring of nitrate in groundwater Hydrology and Earth System Sciences Discussions, 11, 12291-12314, 2014 Author(s): M. Huebsch, F. Grimmeisen, M. Zemann, O. Fenton, K. G. Richards, P. Jordan, A. Sawarieh, P. Blum, and N. Goldscheider Two different in-situ spectrophotometers are compared that were used in the field to determine nitrate-nitrogen (NO 3 -N) concentrations at two distinct spring discharge sites. One sensor was a double wavelength spectrophotometer (DWS) and the other a multiple wavelength spectrophotometer (MWS). The objective of the study was to review the hardware options, determine ease of calibration, accuracy, influence of additional substances and to assess positive and negative aspects of the two sensors as well as troubleshooting and trade-offs. Both sensors are sufficient to monitor highly time-resolved NO 3 -N concentrations in emergent groundwater. However, the chosen path length of the sensors had a significant influence on the sensitivity and the range of detectable NO 3 -N. The accuracy of the calculated NO 3 -N concentrations of the sensors can be affected, if the content of additional substances such as turbidity, organic matter, nitrite or hydrogen carbonate significantly varies after the sensors have been calibrated to a particular water matrix. The MWS offers more possibilities for calibration and error detection, but requires more expertise compared with the DWS.

Description: Complex networks, streamflow, and hydrometric monitoring system design Hydrology and Earth System Sciences Discussions, 11, 13663-13710, 2014 Author(s): M. Halverson and S. Fleming Network theory is applied to an array of streamflow gauges located in the Coast Mountains of British Columbia and Yukon, Canada. The goal of the analysis is to assess whether insights from this branch of mathematical graph theory can be meaningfully applied to hydrometric data, and more specifically, whether it may help guide decisions concerning stream gauge placement so that the full complexity of the regional hydrology is efficiently captured. The streamflow data, when represented as a complex network, has a global clustering coefficient and average shortest path length consistent with small-world networks, which are a class of stable and efficient networks common in nature, but the results did not clearly suggest a scale-free network. Stability helps ensure that the network is robust to the loss of nodes; in the context of a streamflow network, stability is interpreted as insensitivity to station removal at random. Community structure is also evident in the streamflow network. A community detection algorithm identified 10 separate communities, each of which appears to be defined by the combination of its median seasonal flow regime (pluvial, nival, hybrid, or glacial, which in this region in turn mainly reflects basin elevation) and geographic proximity to other communities (reflecting shared or different daily meteorological forcing). Betweenness analyses additionally suggest a handful of key stations which serve as bridges between communities and might therefore be highly valued. We propose that an idealized sampling network should sample high-betweenness stations, as well as small-membership communities which are by definition rare or undersampled relative to other communities, while retaining some degree of redundancy to maintain network robustness.

Description: A strategy for GIS-based 3-D slope stability modelling over large areas Geoscientific Model Development, 7, 2969-2982, 2014 Author(s): M. Mergili, I. Marchesini, M. Alvioli, M. Metz, B. Schneider-Muntau, M. Rossi, and F. Guzzetti GIS-based deterministic models may be used for landslide susceptibility mapping over large areas. However, such efforts require specific strategies to (i) keep computing time at an acceptable level, and (ii) parameterize the geotechnical data. We test and optimize the performance of the GIS-based, 3-D slope stability model r.slope.stability in terms of computing time and model results. The model was developed as a C- and Python-based raster module of the open source software GRASS GIS and considers the 3-D geometry of the sliding surface. It calculates the factor of safety (FoS) and the probability of slope failure ( P f ) for a number of randomly selected potential slip surfaces, ellipsoidal or truncated in shape. Model input consists of a digital elevation model (DEM), ranges of geotechnical parameter values derived from laboratory tests, and a range of possible soil depths estimated in the field. Probability density functions are exploited to assign P f to each ellipsoid. The model calculates for each pixel multiple values of FoS and P f corresponding to different sliding surfaces. The minimum value of FoS and the maximum value of P f for each pixel give an estimate of the landslide susceptibility in the study area. Optionally, r.slope.stability is able to split the study area into a defined number of tiles, allowing parallel processing of the model on the given area. Focusing on shallow landslides, we show how multi-core processing makes it possible to reduce computing times by a factor larger than 20 in the study area. We further demonstrate how the number of random slip surfaces and the sampling of parameters influence the average value of P f and the capacity of r.slope.stability to predict the observed patterns of shallow landslides in the 89.5 km 2 Collazzone area in Umbria, central Italy.

Description: Monitoring and modelling of soil–plant interactions: the joint use of ERT, sap flow and Eddy Covariance data to characterize the volume of an orange tree root zone Hydrology and Earth System Sciences Discussions, 11, 13353-13384, 2014 Author(s): G. Cassiani, J. Boaga, D. Vanella, M. T. Perri, and S. Consoli Mass and energy exchanges between soil, plants and atmosphere control a number of key environmental processes involving hydrology, biota and climate. The understanding of these exchanges also play a critical role for practical purposes e.g. in precision agriculture. In this paper we present a methodology based on coupling innovative data collection and models in order to obtain quantitative estimates of the key parameters of such complex flow system. In particular we propose the use of hydro-geophysical monitoring via 4-D Electrical Resistivity Tomography (ERT) in conjunction with measurements of plant transpiration via sap flow and evapotranspiration from Eddy Covariance (EC). This abundance of data is fed to a spatially distributed soil model in order to characterize the distribution of active roots. We conducted experiments in an orange orchard in Eastern Sicily (Italy), characterized by the typical Mediterranean semi-arid climate. The subsoil dynamics, particularly influenced by irrigation and root uptake, were characterized mainly by the ERT setup, consisting of 48 buried electrodes on 4 instrumented micro boreholes (about 1.2 m deep) placed at the corners of a square (about 1.3 m in side) surrounding the orange tree, plus 24 mini-electrodes on the surface spaced 0.1 m on a square grid. During the monitoring, we collected repeated ERT and TDR soil moisture measurements, soil water samples, sap flow measurements from the orange tree and EC data. We conducted a laboratory calibration of the soil electrical properties as a function of moisture content and pore water electrical conductivity. Irrigation, precipitation, sap flow and ET data are available allowing knowledge of the system's long term forcing conditions on the system. This information was used to calibrate a 1-D Richards' equation model representing the dynamics of the volume monitored via 3-D ERT. Information on the soil hydraulic properties was collected from laboratory and field experiments. The successful results of the calibrated modeling exercise allow the quantification of the soil volume interested by root water uptake. This volume is much smaller (with a surface area less than 2 m 2 , and about 40 cm thickness) than expected and assumed in the design of classical drip irrigation schemes that prove to be losing at least half of the irrigated water that is not uptaken by the plants.

Description: Deciphering the spatio-temporal complexity of climate change of the last deglaciation: a model analysis Climate of the Past, 7, 591-602, 2011 Author(s): D. M. Roche, H. Renssen, D. Paillard, and G. Levavasseur Understanding the sequence of events occuring during the last major glacial to interglacial transition (21 ka BP to 9 ka BP) is a challenging task that has the potential to unveil the mechanisms behind large scale climate changes. Though many studies have focused on the understanding of the complex sequence of rapid climatic change that accompanied or interrupted the deglaciation, few have analysed it in a more theoretical framework with simple forcings. In the following, we address when and where the first significant temperature anomalies appeared when using slow varying forcing of the last deglaciation. We used here coupled transient simulations of the last deglaciation, including ocean, atmosphere and vegetation components to analyse the spatial timing of the deglaciation. To keep the analysis in a simple framework, we did not include freshwater forcings that potentially cause rapid climate shifts during that time period. We aimed to disentangle the direct and subsequent response of the climate system to slow forcing and moreover, the location where those changes are more clearly expressed. In a data – modelling comparison perspective, this could help understand the physically plausible phasing between known forcings and recorded climatic changes. Our analysis of climate variability could also help to distinguish deglacial warming signals from internal climate variability. We thus are able to better pinpoint the onset of local deglaciation, as defined by the first significant local warming and further show that there is a large regional variability associated with it, even with the set of slow forcings used here. In our model, the first significant hemispheric warming occurred simultaneously in the North and in the South and is a direct response to the obliquity forcing.

Description: Domestic wells have high probability of pumping septic tank leachate Hydrology and Earth System Sciences Discussions, 8, 5701-5732, 2011 Author(s): J. E. Horn and T. Harter Onsite wastewater treatment systems such as septic systems are common in rural and semi-rural areas around the world; in the US, about 25–30 % of households are served by a septic system and a private drinking water well. Site-specific conditions and local groundwater flow are often ignored when installing septic systems and wells. Particularly in areas with small lots, thus a high septic system density, these typically shallow wells are prone to contamination by septic system leachate. Typically, mass balance approaches are used to determine a maximum septic system density that would prevent contamination of the aquifer. In this study, we estimate the probability of a well pumping partially septic system leachate. A detailed groundwater and transport model is used to calculate the capture zone of a typical drinking water well. A spatial probability analysis is performed to assess the probability that a capture zone overlaps with a septic system drainfield depending on aquifer properties, lot and drainfield size. We show that a high septic system density poses a high probability of pumping septic system leachate. The hydraulic conductivity of the aquifer has a strong influence on the intersection probability. We conclude that mass balances calculations applied on a regional scale underestimate the contamination risk of individual drinking water wells by septic systems. This is particularly relevant for contaminants released at high concentrations, for substances which experience limited attenuation, and those being harmful even in low concentrations.

Description: Use of ENVISAT ASAR Global Monitoring Mode to complement optical data in the mapping of rapid broad-scale flooding in Pakistan Hydrology and Earth System Sciences Discussions, 8, 5769-5809, 2011 Author(s): D. O'Grady, M. Leblanc, and D. Gillieson Envisat ASAR Global Monitoring Mode (GM) data are used to produce maps of the extent of the flooding in Pakistan which are made available to the rapid response effort within 24 h of acquisition. The high temporal frequency and independence of the data from cloud-free skies makes GM data a viable tool for mapping flood waters during those periods where optical satellite data is unavailable, which may be crucial to rapid response disaster planning, where thousands of lives are affected. Image differencing techniques are used, with pre-flood baseline image backscatter values being deducted from target values to eliminate regions with a permanent flood-like radar response due to volume scattering and attenuation, and to highlight the low response caused by specular reflection by open flood water. The effect of local incidence angle on the received signal is mitigated by ensuring that the deducted image is acquired from the same orbit track as the target image. Poor separability of the water class with land in areas beyond the river channels is tackled using a region-growing algorithm which seeks threshold-conformance from seed pixels at the center of the river channels. The resultant mapped extents are tested against MODIS SWIR data where available, with encouraging results.

Description: Soil weathering rates in 21 catchments of the Canadian Shield Hydrology and Earth System Sciences Discussions, 8, 5743-5768, 2011 Author(s): D. Houle, P. Lamoureux, N. Bélanger, M. Bouchard, C. Gagnon, S. Couture, and A. Bouffard Soil mineral weathering represents an essential source of nutrient base cation (Ca, Mg and K) for forest growth in addition to provide a buffering power against precipitation acidity for soils and surface waters. Weathering rates of base cations were obtained for 21 catchments located within the temperate and the boreal forest of the Canadian Shield with the geochemical model PROFILE. Weathering rates ranged from 0.58 to 4.46 kmol c ha −1 yr −1 and their spatial variation within the studied area was mostly in agreement with spatial variations in soil mineralogy. Weathering rates of Ca and Mg were significantly correlated ( r = 0.80 and 0.64) with their respective lake concentrations. Weathering rates of K and Na did not correlate with lake concentrations of K and Na. The modeled weathering rates for each catchment were also compared with estimations of net catchment exportations. The result show that modeled weathering rates of Ca were not significantly different than the net catchment exportations while modeled weathering rates of Mg were higher by 51 %. Larger differences were observed for K and Na weathering rates that were significantly different than net catchment exportations being 6.9 and 2.2 times higher than net exportations, respectively. The results for K were expected given its high reactivity with biotic compartments and suggest that most of the K produced by weathering reactions was retained within soil catchments and/or above ground biomass. This explanation does not apply to Na, however, which is a conservative element in forest ecosystems because of the insignificant needs of Na for soil microorganisms and above ground vegetations. It raises concern about the liability of the PROFILE model to provide reliable values of Na weathering rates. Overall, we concluded that the PROFILE model is powerful enough to reproduce spatial geographical gradients in weathering rates for relatively large areas as well as adequately predict absolute weathering rates values for the sum of base cations, Ca and Mg.

Description: The role of catchment classification in rainfall-runoff modeling Hydrology and Earth System Sciences Discussions, 8, 6113-6153, 2011 Author(s): Y. He, A. Bárdossy, and E. Zehe A sound catchment classification scheme is a fundamental step towards improved catchment hydrology science and prediction in ungauged basins. Two categories of catchment classification methods are presented in the paper. The first one is based directly on physiographic properties and climatic conditions over a catchment and regarded as a Linnaean type or natural classification scheme. The second one is based on numerical clustering and regionalization methods and considered as a statistical or arbitrary classification scheme. This paper reviews each category including what has been done since recognition of the intrinsic value of catchment classification, what is being done in the current research, as well as what is to be done in the future.

Description: The last deglaciation: timing the bipolar seesaw Climate of the Past, 7, 671-683, 2011 Author(s): J. B. Pedro, T. D. van Ommen, S. O. Rasmussen, V. I. Morgan, J. Chappellaz, A. D. Moy, V. Masson-Delmotte, and M. Delmotte Precise information on the relative timing of north-south climate variations is a key to resolving questions concerning the mechanisms that force and couple climate changes between the hemispheres. We present a new composite record made from five well-resolved Antarctic ice core records that robustly represents the timing of regional Antarctic climate change during the last deglaciation. Using fast variations in global methane gas concentrations as time markers, the Antarctic composite is directly compared to Greenland ice core records, allowing a detailed mapping of the inter-hemispheric sequence of climate changes. Consistent with prior studies the synchronized records show that warming (and cooling) trends in Antarctica closely match cold (and warm) periods in Greenland on millennial timescales. For the first time, we also identify a sub-millennial component to the inter-hemispheric coupling. Within the Antarctic Cold Reversal the strongest Antarctic cooling occurs during the pronounced northern warmth of the Bølling. Warming then resumes in Antarctica, potentially as early as the Intra-Allerød Cold Period, but with dating uncertainty that could place it as late as the onset of the Younger Dryas stadial. There is little-to-no time lag between climate transitions in Greenland and opposing changes in Antarctica. Our results lend support to fast acting inter-hemispheric coupling mechanisms, including recently proposed bipolar atmospheric teleconnections and/or rapid bipolar ocean teleconnections.

Description: Infiltration-soil moisture redistribution under natural conditions: experimental evidence as a guideline for realizing simulation models Hydrology and Earth System Sciences Discussions, 8, 6199-6225, 2011 Author(s): R. Morbidelli, C. Corradini, C. Saltalippi, A. Flammini, and E. Rossi The evolution in time, t , of the experimental soil moisture vertical profile under natural conditions is investigated in order to address the corresponding simulation modelling. The measurements were conducted in a plot with a bare silty loam soil. The soil water content, θ, was continuously monitored at different depths, z , using a Time Domain Reflectometry (TDR) system. For each profile four buriable three-rod waveguides were inserted horizontally at different depths (5, 15, 25 and 35 cm). In addition, we used sensors of air temperature and relative humidity, wind speed, solar radiation, evaporation and rain as supports for the application of selected simulation models, as well as for the detection of elements leading to their improvement. The results indicate that, under natural conditions, very different trends of the θ( z , t ) function can be observed in the given fine-textured soil, where the formation of a sealing layer over the parent soil requires an adjustment of the simulation modelling commonly used for hydrological applications. In particular, because of the considerable variations in the shape of the moisture content vertical profile as a function of time, a generalization of the existing models should incorporate a representation of the variability in time of the saturated hydraulic conductivity of the uppermost soil. This conclusion is supported by the fact that the observed shape of θ( z ) can be appropriately reproduced by adopting this approach, however the observed rainfall rate and the occurrence of freeze-thaw cycles with high soil moisture contents have to be explicitly incorporated.

Description: Reply to Henriksson et al.'s comment on "Using multiple observationally-based constraints to estimate climate sensitivity" by Annan and Hargreaves (2010) Climate of the Past, 7, 587-589, 2011 Author(s): J. D. Annan and J. C. Hargreaves Henriksson et al. (2010), hereafter HALTL10, criticize Annan and Hargreaves (2006a) (AH06) primarily on the grounds that we assumed that different sources of data were conditionally independent given the climate sensitivity. While we consider this approximation to have been a reasonable one under the circumstances (and provided arguments to justify this approach), we also acknowledged its importance in our original paper and performed several sensitivity analyses. The alternative calculations presented by HALTL10 appear to strengthen rather than contradict our conclusion. HALTL10 additionally criticize Annan and Hargreaves (2009) (AH09) for proposing a Cauchy type prior (as an alternative to the use of a uniform prior, which was widespread up to that time) "without sufficient support", and further claim that anticipated economic damages were used as a means of selecting the prior. We are surprised by these claims, especially considering that the proposed prior was justified at some length both on the basis of both the "Charney report" (National Research Council, 1979) and basic physical arguments, and also in light of our elementary demonstration of the pathological failings of the most commonly-used alternative. Thus, these claims are factually incorrect.

Description: Methane variations on orbital timescales: a transient modeling experiment Climate of the Past, 7, 635-648, 2011 Author(s): T. Y. M. Konijnendijk, S. L. Weber, E. Tuenter, and M. van Weele Methane (CH 4 ) variations on orbital timescales are often associated with variations in wetland coverage, most notably in the summer monsoon areas of the Northern Hemisphere. Here we test this assumption by simulating orbitally forced variations in global wetland emissions, using a simple wetland distribution and CH 4 emissions model that has been run on the output of a climate model (CLIMBER-2) containing atmosphere, ocean and vegetation components. The transient climate modeling simulation extends over the last 650 000 yr and includes variations in land-ice distribution and greenhouse gases. Tropical temperature and global vegetation are found to be the dominant controls for global CH 4 emissions and therefore atmospheric concentrations. The relative importance of wetland coverage, vegetation coverage, and emission temperatures depends on the specific climatic zone (boreal, tropics and Indian/Asian monsoon area) and timescale (precession, obliquity and glacial-interglacial timescales). Despite the low spatial resolution of the climate model and crude parameterizations for methane production and release, simulated variations in CH 4 emissions agree well with those in measured concentrations, both in their time series and spectra. The simulated lags between emissions and orbital forcing also show close agreement with those found in measured data, both on the precession and obliquity timescale. We find causal links between atmospheric CH 4 concentrations and tropical temperatures and global vegetation, but only covariance between monsoon precipitation and CH 4 concentrations. The primary importance of the first two factors explains the lags found in the CH 4 record from ice cores. Simulation of the dynamical vegetation response to climate variation on orbital timescales would be needed to reduce the uncertainty in these preliminary attributions.

Description: Semi-Lagrangian methods in air pollution models Geoscientific Model Development, 4, 511-541, 2011 Author(s): A. B. Hansen, J. Brandt, J. H. Christensen, and E. Kaas Various semi-Lagrangian methods are tested with respect to advection in air pollution modeling. The aim is to find a method fulfilling as many of the desirable properties by Rasch andWilliamson (1990) and Machenhauer et al. (2008) as possible. The focus in this study is on accuracy and local mass conservation. The methods tested are, first, classical semi-Lagrangian cubic interpolation, see e.g. Durran (1999), second, semi-Lagrangian cubic cascade interpolation, by Nair et al. (2002), third, semi-Lagrangian cubic interpolation with the modified interpolation weights, Locally Mass Conserving Semi-Lagrangian (LMCSL), by Kaas (2008), and last, semi-Lagrangian cubic interpolation with a locally mass conserving monotonic filter by Kaas and Nielsen (2010). Semi-Lagrangian (SL) interpolation is a classical method for atmospheric modeling, cascade interpolation is more efficient computationally, modified interpolation weights assure mass conservation and the locally mass conserving monotonic filter imposes monotonicity. All schemes are tested with advection alone or with advection and chemistry together under both typical rural and urban conditions using different temporal and spatial resolution. The methods are compared with a current state-of-the-art scheme, Accurate Space Derivatives (ASD), see Frohn et al. (2002), presently used at the National Environmental Research Institute (NERI) in Denmark. To enable a consistent comparison only non-divergent flow configurations are tested. The test cases are based either on the traditional slotted cylinder or the rotating cone, where the schemes' ability to model both steep gradients and slopes are challenged. The tests showed that the locally mass conserving monotonic filter improved the results significantly for some of the test cases, however, not for all. It was found that the semi-Lagrangian schemes, in almost every case, were not able to outperform the current ASD scheme used in DEHM with respect to accuracy.

Description: Sand box experiments to evaluate the influence of subsurface temperature probe design on temperature based water flux calculation Hydrology and Earth System Sciences Discussions, 8, 6155-6197, 2011 Author(s): M. Munz, S. E. Oswald, and C. Schmidt Quantification of subsurface water fluxes based on the one dimensional solution to the heat transport equation depends on the accuracy of measured subsurface temperatures. The influence of temperature probe setup on the accuracy of vertical water flux calculation was systematically evaluated in this experimental study. Four temperature probe setups were installed into a sand box experiment to measure temporal highly resolved vertical temperature profiles under controlled water fluxes in the range of ±1.3 m d −1 . Pass band filtered time series provided amplitude and phase of the diurnal temperature signal varying with depth depending on water flux. Amplitude ratios of setups directly installed into the saturated sediment significantly varied with sand box hydraulic gradients. Amplitude ratios provided an accurate basis for the analytical calculation of water flow velocities, which matched measured flow velocities. Calculated flow velocities were sensitive to thermal properties of saturated sediment and to probe distance, but insensitive to thermal dispersivity equal to solute dispersivity. Amplitude ratios of temperature probe setups indirectly installed into piezometer pipes were influenced by thermal exchange processes within the pipes and significantly varied with water flux direction only. Temperature time lags of small probe distances of all setups were found to be insensitive to vertical water flux.

Description: The use of LIDAR as a data source for digital elevation models – a study of the relationship between the accuracy of digital elevation models and topographical attributes in northern peatlands Hydrology and Earth System Sciences Discussions, 8, 5497-5522, 2011 Author(s): A. Hasan, P. Pilesjö, and A. Persson It is important to study the factors affecting estimates of wetness since wetness is crucial in climate change studies. The availability of digital elevation models (DEMs) generated with high resolution data is increasing, and their use is expanding. LIDAR earth elevation data have been used to create several DEMs with different resolutions, using various interpolation parameters, in order to compare the models with collected surface data. The aim is to study the accuracy of DEMs in relation to topographical attributes such as slope and drainage area, which are normally used to estimate the wetness in terms of topographic wetness indices. Evaluation points were chosen from the high-resolution LIDAR dataset at a maximum distance of 10 mm from the cell center for each DEM resolution studied, 0.5, 1, 5, 10, 30 and 90 m. The interpolation method used was inverse distance weighting method with four search radii: 1, 2, 5 and 10 m. The DEM was evaluated using a quantile-quantile test and the normalized median absolute deviation. The accuracy of the estimated elevation for different slopes was tested using the DEM with 0.5 m resolution. Drainage areas were investigated at three resolutions, with coinciding evaluation points. The ability of the model to generate the drainage area at each resolution was obtained by pairwise comparison of three data subsets. The results show that the accuracy of the elevations obtained with the DEM model are the same for different resolutions, but vary with search radius. The accuracy of the values (NMAD of errors) varies from 29.7 mm to 88.9 mm, being higher for flatter areas. It was also found that the accuracy of the drainage area is highly dependent on DEM resolution. Coarse resolution yielded larger estimates of the drainage area but lower slope values. This may lead to overestimation of wetness values when using a coarse resolution DEM.

Description: Multivariate design via Copulas Hydrology and Earth System Sciences Discussions, 8, 5523-5558, 2011 Author(s): G. Salvadori, C. De Michele, and F. Durante Calculating return periods and design quantiles in a multivariate framework is a difficult problem: essentially, this is due to the lack of a natural total order in multi-dimensional Euclidean spaces. This paper tries to make the issue clear. First, we outline a possible way to introduce a coherent notion of multivariate total order, and discuss its consequences on the calculation of multivariate return period: in particular, the latter is based on Copulas and the Kendall's measure, which provides a consistent notion of multivariate quantile. Secondly, we introduce several approaches for the identification of critical design events: these latter quantities are of utmost importance in practical applications, but their calculation is yet limited, due to the lack of a suitable theoretical setting where to embed the problem. Throughout the paper, a case study involving the behavior of a dam is used to illustrate the new concepts outlined in this work.

Description: GEOCLIM reloaded (v 1.0): a new coupled earth system model for past climate change Geoscientific Model Development, 4, 451-481, 2011 Author(s): S. Arndt, P. Regnier, Y. Goddéris, and Y. Donnadieu We present a new version of the coupled Earth system model GEOCLIM. The new release, GEOCLIM reloaded (v 1.0), links the existing atmosphere and weathering modules to a novel, temporally and spatially resolved model of the global ocean circulation, which provides a physical framework for a mechanistic description of the marine biogeochemical dynamics of carbon, nitrogen, phosphorus and oxygen. The ocean model is also coupled to a fully formulated, vertically resolved diagenetic model. GEOCLIM reloaded is thus a unique tool to investigate the short- and long-term feedbacks between climatic conditions, continental inputs, ocean biogeochemical dynamics and diagenesis. A complete and detailed description of the resulting Earth system model and its new features is first provided. The performance of GEOCLIM reloaded is then evaluated by comparing steady-state simulation under present-day conditions with a comprehensive set of oceanic data and existing global estimates of bio-element cycling in the pelagic and benthic compartments.

Description: Influence of initial heterogeneities and recharge limitations on the evolution of aperture distributions in carbonate aquifers Hydrology and Earth System Sciences Discussions, 8, 5631-5666, 2011 Author(s): B. Hubinger and S. Birk Karst aquifers evolve where the dissolution of soluble rocks causes the enlargement of discrete pathways along fractures or bedding planes, thus creating highly conductive solution conduits. To identify general interrelations between hydrogeological conditions and the properties of the evolving conduit systems the aperture-size frequency distributions resulting from generic models of conduit evolution are analysed. For this purpose, a process-based numerical model coupling flow and rock dissolution is employed. Initial protoconduits are represented by tubes with log-normally distributed aperture sizes with a mean of 0.5 mm. Apertures are spatially uncorrelated and widen up to the metre range due to dissolution by chemically aggressive waters. Several examples of conduit development are examined focussing on influences of the initial heterogeneity and the available amount of recharge. If the available recharge is sufficiently high the evolving conduits compete for flow and those with large apertures and high hydraulic gradients attract more and more water. As a consequence, the positive feedback between increasing flow and dissolution causes the breakthrough of a conduit pathway connecting the recharge and discharge sides of the modelling domain. Under these competitive flow conditions dynamically stable bimodal aperture distributions are found to evolve, i.e. a certain percentage of tubes continues to be enlarged while the remaining tubes stay small-sized. The percentage of strongly widened tubes is found to be independent of the breakthrough time and decreases with increasing heterogeneity of the initial apertures and decreasing amount of available water. If the competition for flow is suppressed because the availability of water is strongly limited breakthrough of a conduit pathway is inhibited and the conduit pathways widen very slowly. The resulting aperture distributions are found to be unimodal covering some orders of magnitudes in size. Under these suppressed flow conditions the entire range of apertures continues to be enlarged. Hence, the number of tubes reaching aperture sizes in the order of centimetres or decimetres continues to increase with time and in the long term may exceed the number of large-sized tubes evolving under competitive flow conditions. This suggests that conduit development under suppressed flow conditions may significantly enhance the permeability of the formation e.g. in deep-seated carbonate settings.

Description: Skewness as measure of the invariance of instantaneous renormalized drop diameter distributions – Part 1: Convective vs. stratiform precipitation Hydrology and Earth System Sciences Discussions, 8, 5605-5629, 2011 Author(s): M. Ignaccolo and C. De Michele We investigate the variability of the instantaneous distribution shape of the renormalized drop diameter making use of the third order central moment: the skewness . Disdrometer data, collected at Darwin Australia, are considered either as whole or as divided in convective and stratiform precipitation intervals. We show that in all cases the distribution of the skewness is strongly peaked around 0.64. This allows to identify a most common distribution of renormalized drop diameters and two main variations, one with larger and one with smaller skewness. The distributions' shapes are independent from the stratiform vs. convective classification.

Description: The sensitivity of land emissivity estimates from AMSR-E at C and X bands to surface properties Hydrology and Earth System Sciences Discussions, 8, 5667-5699, 2011 Author(s): H. Norouzi, M. Temimi, W. B. Rossow, C. Pearl, M. Azarderakhsh, and R. Khanbilvardi Microwave observations at low frequencies exhibit more sensitivity to surface and subsurface properties with little interference from the atmosphere. The objective of this study is to develop a global land emissivity product using passive microwave observations from the Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) and to investigate its sensitivity to land surface properties. The developed product complements existing land emissivity products from SSM/I and AMSU by adding land emissivity estimates at two lower frequencies, 6.9 and 10.65 GHz (C- and X-band, respectively). Observations at these low frequencies penetrate deeper into the soil layer. Ancillary data used in the analysis, such as surface skin temperature and cloud mask, are obtained from International Satellite Cloud Climatology Project (ISCCP). Atmospheric properties are obtained from the TIROS Operational Vertical Sounder (TOVS) observations to determine the small upwelling and downwelling atmospheric emissions as well as the atmospheric transmission. A sensitivity test confirms the small effect of the atmosphere but shows that skin temperature accuracy can significantly affect emissivity estimates. Retrieved emissivities at C- and X-bands and their polarization differences exhibit similar patterns of variation with changes in land cover type, soil moisture, and vegetation density as seen at SSM/I-like frequencies (Ka and Ku bands). The emissivity maps from AMSR-E at these higher frequencies agree reasonably well with the existing SSM/I-based product. The inherent but small discrepancy introduced by the difference between SSM/I and AMSR-E frequencies and incidence angles has been examined and found to be small. Large differences between emissivity estimates from ascending and descending overpasses were found at the lower frequencies due to the inconsistency between the thermal IR skin temperatures and passive microwave brightness temperatures which can come from below the surface. This issue must be addressed in future studies to improve the accuracy of the emissivity estimates at lower frequencies.