ALBERT

Description: Qualitative soil moisture assessment in semi-arid Africa – the role of experience and training on inter-rater reliability Hydrology and Earth System Sciences, 19, 3505-3516, 2015 Author(s): M. Rinderer, H. C. Komakech, D. Müller, G. L. B. Wiesenberg, and J. Seibert Soil and water management is particularly relevant in semi-arid regions to enhance agricultural productivity. During periods of water scarcity, soil moisture differences are important indicators of the soil water deficit and are traditionally used for allocating water resources among farmers of a village community. Here we present a simple, inexpensive soil wetness classification scheme based on qualitative indicators which one can see or touch on the soil surface. It incorporates the local farmers' knowledge on the best soil moisture conditions for seeding and brick making in the semi-arid environment of the study site near Arusha, Tanzania. The scheme was tested twice in 2014 with farmers, students and experts (April: 40 persons, June: 25 persons) for inter-rater reliability, bias of individuals and functional relation between qualitative and quantitative soil moisture values. During the test in April farmers assigned the same wetness class in 46 % of all cases, while students and experts agreed on about 60 % of all cases. Students who had been trained in how to apply the method gained higher inter-rater reliability than their colleagues with only a basic introduction. When repeating the test in June, participants were given improved instructions, organized in small subgroups, which resulted in a higher inter-rater reliability among farmers. In 66 % of all classifications, farmers assigned the same wetness class and the spread of class assignments was smaller. This study demonstrates that a wetness classification scheme based on qualitative indicators is a robust tool and can be applied successfully regardless of experience in crop growing and education level when an in-depth introduction and training is provided. The use of a simple and clear layout of the assessment form is important for reliable wetness class assignments.

Description: Impacts of beaver dams on hydrologic and temperature regimes in a mountain stream Hydrology and Earth System Sciences, 19, 3541-3556, 2015 Author(s): M. Majerova, B. T. Neilson, N. M. Schmadel, J. M. Wheaton, and C. J. Snow Beaver dams affect hydrologic processes, channel complexity, and stream temperature in part by inundating riparian areas, influencing groundwater–surface water interactions, and changing fluvial processes within stream systems. We explored the impacts of beaver dams on hydrologic and temperature regimes at different spatial and temporal scales within a mountain stream in northern Utah over a 3-year period spanning pre- and post-beaver colonization. Using continuous stream discharge, stream temperature, synoptic tracer experiments, and groundwater elevation measurements, we documented pre-beaver conditions in the first year of the study. In the second year, we captured the initial effects of three beaver dams, while the third year included the effects of ten dams. After beaver colonization, reach-scale (~ 750 m in length) discharge observations showed a shift from slightly losing to gaining. However, at the smaller sub-reach scale (ranging from 56 to 185 m in length), the discharge gains and losses increased in variability due to more complex flow pathways with beaver dams forcing overland flow, increasing surface and subsurface storage, and increasing groundwater elevations. At the reach scale, temperatures were found to increase by 0.38 °C (3.8 %), which in part is explained by a 230 % increase in mean reach residence time. At the smallest, beaver dam scale (including upstream ponded area, beaver dam structure, and immediate downstream section), there were notable increases in the thermal heterogeneity where warmer and cooler niches were created. Through the quantification of hydrologic and thermal changes at different spatial and temporal scales, we document increased variability during post-beaver colonization and highlight the need to understand the impacts of beaver dams on stream ecosystems and their potential role in stream restoration.

Description: Relating seasonal dynamics of enhanced vegetation index to the recycling of water in two endorheic river basins in north-west China Hydrology and Earth System Sciences, 19, 3387-3403, 2015 Author(s): M. A. Matin and C. P.-A. Bourque This study associates the dynamics of enhanced vegetation index in lowland desert oases to the recycling of water in two endorheic (hydrologically closed) river basins in Gansu Province, north-west China, along a gradient of elevation zones and land cover types. Each river basin was subdivided into four elevation zones representative of (i) oasis plains and foothills, and (ii) low-, (iii) mid-, and (iv) high-mountain elevations. Comparison of monthly vegetation phenology with precipitation and snowmelt dynamics within the same basins over a 10-year period (2000–2009) suggested that the onset of the precipitation season (cumulative % precipitation 〉 7–8 %) in the mountains, typically in late April to early May, was triggered by the greening of vegetation and increased production of water vapour at the base of the mountains. Seasonal evolution of in-mountain precipitation correlated fairly well with the temporal variation in oasis-vegetation coverage and phenology characterised by monthly enhanced vegetation index, yielding coefficients of determination of 0.65 and 0.85 for the two basins. Convergent cross-mapping of related time series indicated bi-directional causality (feedback) between the two variables. Comparisons between same-zone monthly precipitation amounts and enhanced vegetation index provided weaker correlations. Start of the growing season in the oases was shown to coincide with favourable spring warming and discharge of meltwater from low- to mid-elevations of the Qilian Mountains (zones 1 and 2) in mid-to-late March. In terms of plant requirement for water, mid-seasonal development of oasis vegetation was seen to be controlled to a greater extent by the production of rain in the mountains. Comparison of water volumes associated with in-basin production of rainfall and snowmelt with that associated with evaporation seemed to suggest that about 90 % of the available liquid water (i.e. mostly in the form of direct rainfall and snowmelt in the mountains) was recycled locally.

Description: Investigating suspended sediment dynamics in contrasting agricultural catchments using ex situ turbidity-based suspended sediment monitoring Hydrology and Earth System Sciences, 19, 3349-3363, 2015 Author(s): S. C. Sherriff, J. S. Rowan, A. R. Melland, P. Jordan, O. Fenton, and D. Ó hUallacháin Soil erosion and suspended sediment (SS) pose risks to chemical and ecological water quality. Agricultural activities may accelerate erosional fluxes from bare, poached or compacted soils, and enhance connectivity through modified channels and artificial drainage networks. Storm-event fluxes dominate SS transport in agricultural catchments; therefore, high temporal-resolution monitoring approaches are required, but can be expensive and technically challenging. Here, the performance of in situ turbidity sensors, conventionally installed submerged at the river bankside, is compared with installations where river water is delivered to sensors ex situ, i.e. within instrument kiosks on the riverbank, at two experimental catchments (Grassland B and Arable B). The in situ and ex situ installations gave comparable results when calibrated against storm-period, depth-integrated SS data, with total loads at Grassland B estimated at 12 800 and 15 400 t, and 22 600 and 24 900 t at Arable B, respectively. The absence of spurious turbidity readings relating to bankside debris around the in situ sensor and its greater security make the ex situ sensor more robust. The ex situ approach was then used to characterise SS dynamics and fluxes in five intensively managed agricultural catchments in Ireland which feature a range of landscape characteristics and land use pressures. Average annual suspended sediment concentration (SSC) was below the Freshwater Fish Directive (78/659/EEC) guideline of 25 mg L −1 , and the continuous hourly record demonstrated that exceedance occurred less than 12 % of the observation year. Soil drainage class and proportion of arable land were key controls determining flux rates, but all catchments reported a high degree of inter-annual variability associated with variable precipitation patterns compared to the long-term average. Poorly drained soils had greater sensitivity to runoff and soil erosion, particularly in catchments with periods of bare soils. Well drained soils were less sensitive to erosion even on arable land; however, under extreme rainfall conditions, all bare soils remain a high sediment loss risk. Analysis of storm-period and seasonal dynamics (over the long term) using high-resolution monitoring would be beneficial to further explore the impact of landscape, climate and land use characteristics on SS export.

Description: Landscape heterogeneity drives contrasting concentration–discharge relationships in shale headwater catchments Hydrology and Earth System Sciences, 19, 3333-3347, 2015 Author(s): E. M. Herndon, A. L. Dere, P. L. Sullivan, D. Norris, B. Reynolds, and S. L. Brantley Solute concentrations in stream water vary with discharge in patterns that record complex feedbacks between hydrologic and biogeochemical processes. In a comparison of three shale-underlain headwater catchments located in Pennsylvania, USA (the forested Shale Hills Critical Zone Observatory), and Wales, UK (the peatland-dominated Upper Hafren and forest-dominated Upper Hore catchments in the Plynlimon forest), dissimilar concentration–discharge ( C – Q ) behaviors are best explained by contrasting landscape distributions of soil solution chemistry – especially dissolved organic carbon (DOC) – that have been established by patterns of vegetation and soil organic matter (SOM). Specifically, elements that are concentrated in organic-rich soils due to biotic cycling (Mn, Ca, K) or that form strong complexes with DOC (Fe, Al) are spatially heterogeneous in pore waters because organic matter is heterogeneously distributed across the catchments. These solutes exhibit non-chemostatic behavior in the streams, and solute concentrations either decrease (Shale Hills) or increase (Plynlimon) with increasing discharge. In contrast, solutes that are concentrated in soil minerals and form only weak complexes with DOC (Na, Mg, Si) are spatially homogeneous in pore waters across each catchment. These solutes are chemostatic in that their stream concentrations vary little with stream discharge, likely because these solutes are released quickly from exchange sites in the soils during rainfall events. Furthermore, concentration–discharge relationships of non-chemostatic solutes changed following tree harvest in the Upper Hore catchment in Plynlimon, while no changes were observed for chemostatic solutes, underscoring the role of vegetation in regulating the concentrations of certain elements in the stream. These results indicate that differences in the hydrologic connectivity of organic-rich soils to the stream drive differences in concentration behavior between catchments. As such, in catchments where SOM is dominantly in lowlands (e.g., Shale Hills), we infer that non-chemostatic elements associated with organic matter are released to the stream early during rainfall events, whereas in catchments where SOM is dominantly in uplands (e.g., Plynlimon), these non-chemostatic elements are released later during rainfall events. The distribution of SOM across the landscape is thus a key component for predictive models of solute transport in headwater catchments.

Description: A pan-African medium-range ensemble flood forecast system Hydrology and Earth System Sciences, 19, 3365-3385, 2015 Author(s): V. Thiemig, B. Bisselink, F. Pappenberger, and J. Thielen The African Flood Forecasting System (AFFS) is a probabilistic flood forecast system for medium- to large-scale African river basins, with lead times of up to 15 days. The key components are the hydrological model LISFLOOD, the African GIS database, the meteorological ensemble predictions by the ECMWF (European Centre for Medium-Ranged Weather Forecasts) and critical hydrological thresholds. In this paper, the predictive capability is investigated in a hindcast mode, by reproducing hydrological predictions for the year 2003 when important floods were observed. Results were verified by ground measurements of 36 sub-catchments as well as by reports of various flood archives. Results showed that AFFS detected around 70 % of the reported flood events correctly. In particular, the system showed good performance in predicting riverine flood events of long duration (〉 1 week) and large affected areas (〉 10 000 km 2 ) well in advance, whereas AFFS showed limitations for small-scale and short duration flood events. The case study for the flood event in March 2003 in the Sabi Basin (Zimbabwe) illustrated the good performance of AFFS in forecasting timing and severity of the floods, gave an example of the clear and concise output products, and showed that the system is capable of producing flood warnings even in ungauged river basins. Hence, from a technical perspective, AFFS shows a large potential as an operational pan-African flood forecasting system, although issues related to the practical implication will still need to be investigated.

Description: A comprehensive filtering scheme for high-resolution estimation of the water balance components from high-precision lysimeters Hydrology and Earth System Sciences, 19, 3405-3418, 2015 Author(s): M. Hannes, U. Wollschläger, F. Schrader, W. Durner, S. Gebler, T. Pütz, J. Fank, G. von Unold, and H.-J. Vogel Large weighing lysimeters are currently the most precise method to directly measure all components of the terrestrial water balance in parallel via the built-in weighing system. As lysimeters are exposed to several external forces such as management practices or wind influencing the weighing data, the calculated fluxes of precipitation and evapotranspiration can be altered considerably without having applied appropriate corrections to the raw data. Therefore, adequate filtering schemes for obtaining most accurate estimates of the water balance components are required. In this study, we use data from the TERENO (TERrestrial ENvironmental Observatories) SoilCan research site in Bad Lauchstädt to develop a comprehensive filtering procedure for high-precision lysimeter data, which is designed to deal with various kinds of possible errors starting from the elimination of large disturbances in the raw data resulting e.g., from management practices all the way to the reduction of noise caused e.g., by moderate wind. Furthermore, we analyze the influence of averaging times and thresholds required by some of the filtering steps on the calculated water balance and investigate the ability of two adaptive filtering methods (the adaptive window and adaptive threshold filter (AWAT filter; Peters et al., 2014), and a new synchro filter applicable to the data from a set of several lysimeters) to further reduce the filtering error. Finally, we take advantage of the data sets of all 18 lysimeters running in parallel at the Bad Lauchstädt site to evaluate the performance and accuracy of the proposed filtering scheme. For the tested time interval of 2 months, we show that the estimation of the water balance with high temporal resolution and good accuracy is possible. The filtering code can be downloaded from the journal website as Supplement to this publication.

Description: The Global Network of Isotopes in Rivers (GNIR): integration of water isotopes in watershed observation and riverine research Hydrology and Earth System Sciences, 19, 3419-3431, 2015 Author(s): J. Halder, S. Terzer, L. I. Wassenaar, L. J. Araguás-Araguás, and P. K. Aggarwal We introduce a new online global database of riverine water stable isotopes (Global Network of Isotopes in Rivers, GNIR) and evaluate its longer-term data holdings. Overall, 218 GNIR river stations were clustered into three different groups based on the seasonal variation in their isotopic composition, which was closely coupled to precipitation and snowmelt water runoff regimes. Sinusoidal fit functions revealed phases within each grouping and deviations from the sinusoidal functions revealed important river alterations or hydrological processes in these watersheds. The seasonal isotopic amplitude of δ 18 O in rivers averaged 2.5 ‰, and did not increase as a function of latitude, like it does for global precipitation. Low seasonal isotopic amplitudes in rivers suggest the prevalence of mixing and storage such as occurs via lakes, reservoirs, and groundwater. The application of a catchment-constrained regionalized cluster-based water isotope prediction model (CC-RCWIP) allowed for direct comparison between the expected isotopic compositions for the upstream catchment precipitation with the measured isotopic composition of river discharge at observation stations. The catchment-constrained model revealed a strong global isotopic correlation between average rainfall and river discharge ( R 2 = 0.88) and the study demonstrated that the seasonal isotopic composition and variation of river water can be predicted. Deviations in data from model-predicted values suggest there are important natural or anthropogenic catchment processes like evaporation, damming, and water storage in the upstream catchment.

Description: Diagnosing the seasonal land–atmosphere correspondence over northern Australia: dependence on soil moisture state and correspondence strength definition Hydrology and Earth System Sciences, 19, 3433-3447, 2015 Author(s): M. Decker, A. Pitman, and J. Evans The similarity of the temporal variations of land and atmospheric states during the onset (September) through to the peak (February) of the wet season over northern Australia is statistically diagnosed using ensembles of offline land surface model simulations that produce a range of different background soil moisture states. We derive the temporal correspondence between variations in the soil moisture and the planetary boundary layer via a statistical measure of rank correlation. The simulated evaporative fraction and the boundary layer are shown to be strongly correlated during both SON (September–October–November) and DJF (December–January–February) despite the differing background soil moisture states between the two seasons and among the ensemble members. The sign and magnitude of the boundary layer–surface layer soil moisture association during the onset of the wet season (SON) differs from the correlation between the evaporative fraction and boundary layer from the same season, and from the correlation between the surface soil moisture and boundary layer association during DJF. The patterns and magnitude of the surface flux–boundary layer correspondence are not captured when the relationship is diagnosed using the surface layer soil moisture alone. The conflicting results arise because the surface layer soil moisture lacks strong correlation with the atmosphere during the monsoon onset because the evapotranspiration is dominated by transpiration. Our results indicate that accurately diagnosing the correspondence and therefore coupling strength in seasonally dry regions, such as northern Australia, requires root zone soil moisture to be included.

Description: Seasonal predictions of agro-meteorological drought indicators for the Limpopo basin Hydrology and Earth System Sciences, 19, 2577-2586, 2015 Author(s): F. Wetterhall, H. C. Winsemius, E. Dutra, M. Werner, and E. Pappenberger The rainfall in southern Africa has a large inter-annual variability, which can cause rain-fed agriculture to fail. The staple crop maize is especially sensitive to dry spells during the early growing season. An early prediction of the probability of dry spells and below normal precipitation can potentially mitigate damages through water management. This paper investigates how well ECMWF's seasonal forecasts predict dry spells over the Limpopo basin during the rainy season December–February (DJF) with lead times from 0 to 4 months. The seasonal forecasts were evaluated against ERA-Interim reanalysis data, which in turn were corrected with GPCP (EGPCP) to match monthly precipitation totals. The seasonal forecasts were also bias-corrected with the EGPCP using quantile mapping as well as post-processed using a precipitation threshold to define a dry day. The results indicate that the forecasts show skill in predicting dry spells in comparison with a climatological ensemble based on previous years. Quantile mapping in combination with a precipitation threshold improved the skill of the forecast. The skill in prediction of dry spells was largest over the most drought-sensitive region. Seasonal forecasts have the potential to be used in a probabilistic forecast system for drought-sensitive crops, though these should be used with caution given the large uncertainties.

Description: Surface seiches in Flathead Lake Hydrology and Earth System Sciences, 19, 2605-2615, 2015 Author(s): G. Kirillin, M. S. Lorang, T. C. Lippmann, C. C. Gotschalk, and S. Schimmelpfennig Standing surface waves or seiches are inherent hydrodynamic features of enclosed water bodies. Their two-dimensional structure is important for estimating flood risk, coastal erosion, and bottom sediment transport, and for understanding shoreline habitats and lake ecology in general. In this work, we present analysis of two-dimensional seiche characteristics in Flathead Lake, Montana, USA, a large intermountain lake known to have high seiche amplitudes. To examine spatial characteristics of different seiche modes, we used the original procedure of determining the seiche frequencies from the primitive equation model output with subsequent derivation of the spatial seiche structure at fixed frequencies akin to the tidal harmonic analysis. The proposed procedure revealed specific seiche oscillation features in Flathead Lake, including maximum surface level amplitudes of the first fundamental mode in straights around the largest island; several higher modes appearing locally in the vicinity of the river inflow; the "Helmholtz" open harbor mode, with the period approximately twice that of the longest seiche mode, generated by a large shallow bay connected to the main lake basin; and several rotating seiche modes potentially affecting the lake-wide circulation. We discuss lake management problems related to the spatial seiche distribution, such as shoreline erosion, floods, and transport of sediments and invasive species in Flathead Lake.

Description: Estimating flow and transport parameters in the unsaturated zone with pore water stable isotopes Hydrology and Earth System Sciences, 19, 2617-2635, 2015 Author(s): M. Sprenger, T. H. M. Volkmann, T. Blume, and M. Weiler Determining the soil hydraulic properties is a prerequisite to physically model transient water flow and solute transport in the vadose zone. Estimating these properties by inverse modelling techniques has become more common within the last 2 decades. While these inverse approaches usually fit simulations to hydrometric data, we expanded the methodology by using independent information about the stable isotope composition of the soil pore water depth profile as a single or additional optimization target. To demonstrate the potential and limits of this approach, we compared the results of three inverse modelling strategies where the fitting targets were (a) pore water isotope concentrations, (b) a combination of pore water isotope concentrations and soil moisture time series, and (c) a two-step approach using first soil moisture data to determine water flow parameters and then the pore water stable isotope concentrations to estimate the solute transport parameters. The analyses were conducted at three study sites with different soil properties and vegetation. The transient unsaturated water flow was simulated by solving the Richards equation numerically with the finite-element code of HYDRUS-1D. The transport of deuterium was simulated with the advection-dispersion equation, and a modified version of HYDRUS was used, allowing deuterium loss during evaporation. The Mualem–van Genuchten and the longitudinal dispersivity parameters were determined for two major soil horizons at each site. The results show that approach (a), using only the pore water isotope content, cannot substitute hydrometric information to derive parameter sets that reflect the observed soil moisture dynamics but gives comparable results when the parameter space is constrained by pedotransfer functions. Approaches (b) and (c), using both the isotope profiles and the soil moisture time series, resulted in good simulation results with regard to the Kling–Gupta efficiency and good parameter identifiability. However, approach (b) has the advantage that it considers the isotope data not only for the solute transport parameters but also for water flow and root water uptake, and thus increases parameter realism. Approaches (b) and (c) both outcompeted simulations run with parameters derived from pedotransfer functions, which did not result in an acceptable representation of the soil moisture dynamics and pore water stable isotope composition. Overall, parameters based on this new approach that includes isotope data lead to similar model performances regarding the water balance and soil moisture dynamics and better parameter identifiability than the conventional inverse model approaches limited to hydrometric fitting targets. If only data from isotope profiles in combination with textural information is available, the results are still satisfactory. This method has the additional advantage that it will not only allow us to estimate water balance and response times but also site-specific time variant transit times or solute breakthrough within the soil profile.

Description: Corrigendum to "Seasonal predictions of agro-meteorological drought indicators for the Limpopo basin" published in Hydrol. Earth Syst. Sci., 19, 2577–2586, 2015 Hydrology and Earth System Sciences, 19, 2637-2637, 2015 Author(s): F. Wetterhall, H. C. Winsemius, E. Dutra, M. Werner, and F. Pappenberger

Description: The representation of location by a regional climate model in complex terrain Hydrology and Earth System Sciences, 19, 3449-3456, 2015 Author(s): D. Maraun and M. Widmann To assess potential impacts of climate change for a specific location, one typically employs climate model simulations at the grid box corresponding to the same geographical location. For most of Europe, this choice is well justified. But, based on regional climate simulations, we show that simulated climate might be systematically displaced compared to observations. In particular in the rain shadow of mountain ranges, a local grid box is therefore often not representative of observed climate: the simulated windward weather does not flow far enough across the mountains; local grid boxes experience the wrong air masses and atmospheric circulation. In some cases, also the local climate change signal is deteriorated. Classical bias correction methods fail to correct these location errors. Often, however, a distant simulated time series is representative of the considered observed precipitation, such that a non-local bias correction is possible. These findings also clarify limitations of bias correcting global model errors, and of bias correction against station data.

Description: How to predict hydrological effects of local land use change: how the vegetation parameterisation for short rotation coppices influences model results Hydrology and Earth System Sciences, 19, 3457-3474, 2015 Author(s): F. Richter, C. Döring, M. Jansen, O. Panferov, U. Spank, and C. Bernhofer Among the different bioenergy sources, short rotation coppices (SRC) with poplar and willow trees are one of the promising options in Europe. SRC provide not only woody biomass but also additional ecosystem services. However, a known shortcoming is the potentially lower groundwater recharge caused by the potentially higher evapotranspiration demand compared to annual crops. The complex feedbacks between vegetation cover and water cycle can be only correctly assessed by application of well-parameterised and calibrated numerical models. In the present study, the hydrological model system WaSim (Wasserhaushalts-Simulations-Model) is implemented for assessment of the water balance. The focus is the analysis of simulation uncertainties caused by the use of guidelines or transferred parameter sets from scientific literature compared to "actual" parameterisations derived from local measurements of leaf area index (LAI), stomatal resistance (Rsc) and date of leaf unfolding (LU). The analysis showed that uncertainties in parameterisation of vegetation lead to implausible model results. LAI, Rsc and LU are the most sensitive plant physiological parameters concerning the effects of enhanced SRC cultivation on water budget or groundwater recharge. Particularly sensitive is the beginning of the growing season, i.e. LU. When this estimation is wrong, the accuracy of LAI and Rsc description plays a minor role. Our analyses illustrate that the use of locally measured vegetation parameters, like maximal LAI, and meteorological variables, like air temperature, to estimate LU give better results than literature data or data from remote network stations. However, the direct implementation of locally measured data is not always advisable or possible. Regarding Rsc, the adjustment of local measurements gives the best model evaluation. For local and accurate studies, measurements of model sensitive parameters like LAI, Rsc and LU are valuable information. The derivation of these model parameters based on local measurements shows the best model fit. Additionally, the adjusted seasonal course of LAI and Rsc is less sensitive to different estimates for LU. Different parameterisations, as they are all eligible either from local measurements or scientific literature, can result in modelled ground water recharge to be present or completely absent in certain years under poplar SRC.

Description: Quantitative historical hydrology in Europe Hydrology and Earth System Sciences, 19, 3517-3539, 2015 Author(s): G. Benito, R. Brázdil, J. Herget, and M. J. Machado In recent decades, the quantification of flood hydrological characteristics (peak discharge, hydrograph shape, and runoff volume) from documentary evidence has gained scientific recognition as a method to lengthen flood records of rare and extreme events. This paper describes the methodological evolution of quantitative historical hydrology under the influence of developments in hydraulics and statistics. In the 19th century, discharge calculations based on flood marks were the only source of hydrological data for engineering design, but were later left aside in favour of systematic gauge records and conventional hydrological procedures. In the last two decades, there has been growing scientific and public interest in understanding long-term patterns of rare floods, in maintaining the flood heritage and memory of extremes, and developing methods for deterministic and statistical application to different scientific and engineering problems. A compilation of 46 case studies across Europe with reconstructed discharges demonstrates that (1) in most cases present flood magnitudes are not unusual within the context of the last millennium, although recent floods may exceed past floods in some temperate European rivers (e.g. the Vltava and Po rivers); (2) the frequency of extreme floods has decreased since the 1950s, although some rivers (e.g. the Gardon and Ouse rivers) show a reactivation of rare events over the last two decades. There is a great potential for gaining understanding of individual extreme events based on a combined multiproxy approach (palaeoflood and documentary records) providing high-resolution time flood series and their environmental and climatic changes; and for developing non-systematic and non-stationary statistical models based on relations of past floods with external and internal covariates under natural low-frequency climate variability.

Description: Characterization of precipitation product errors across the United States using multiplicative triple collocation Hydrology and Earth System Sciences, 19, 3489-3503, 2015 Author(s): S. H. Alemohammad, K. A. McColl, A. G. Konings, D. Entekhabi, and A. Stoffelen Validation of precipitation estimates from various products is a challenging problem, since the true precipitation is unknown. However, with the increased availability of precipitation estimates from a wide range of instruments (satellite, ground-based radar, and gauge), it is now possible to apply the triple collocation (TC) technique to characterize the uncertainties in each of the products. Classical TC takes advantage of three collocated data products of the same variable and estimates the mean squared error of each, without requiring knowledge of the truth. In this study, triplets among NEXRAD-IV, TRMM 3B42RT, GPCP 1DD, and GPI products are used to quantify the associated spatial error characteristics across a central part of the continental US. Data are aggregated to biweekly accumulations from January 2002 through April 2014 across a 2° × 2° spatial grid. This is the first study of its kind to explore precipitation estimation errors using TC across the US. A multiplicative (logarithmic) error model is incorporated in the original TC formulation to relate the precipitation estimates to the unknown truth. For precipitation application, this is more realistic than the additive error model used in the original TC derivations, which is generally appropriate for existing applications such as in the case of wind vector components and soil moisture comparisons. This study provides error estimates of the precipitation products that can be incorporated into hydrological and meteorological models, especially those used in data assimilation. Physical interpretations of the error fields (related to topography, climate, etc.) are explored. The methodology presented in this study could be used to quantify the uncertainties associated with precipitation estimates from each of the constellations of GPM satellites. Such quantification is prerequisite to optimally merging these estimates.

Description: Improving multi-objective reservoir operation optimization with sensitivity-informed dimension reduction Hydrology and Earth System Sciences, 19, 3557-3570, 2015 Author(s): J. Chu, C. Zhang, G. Fu, Y. Li, and H. Zhou This study investigates the effectiveness of a sensitivity-informed method for multi-objective operation of reservoir systems, which uses global sensitivity analysis as a screening tool to reduce computational demands. Sobol's method is used to screen insensitive decision variables and guide the formulation of the optimization problems with a significantly reduced number of decision variables. This sensitivity-informed method dramatically reduces the computational demands required for attaining high-quality approximations of optimal trade-off relationships between conflicting design objectives. The search results obtained from the reduced complexity multi-objective reservoir operation problems are then used to pre-condition the full search of the original optimization problem. In two case studies, the Dahuofang reservoir and the inter-basin multi-reservoir system in Liaoning province, China, sensitivity analysis results show that reservoir performance is strongly controlled by a small proportion of decision variables. Sensitivity-informed dimension reduction and pre-conditioning are evaluated in their ability to improve the efficiency and effectiveness of multi-objective evolutionary optimization. Overall, this study illustrates the efficiency and effectiveness of the sensitivity-informed method and the use of global sensitivity analysis to inform dimension reduction of optimization problems when solving complex multi-objective reservoir operation problems.

Description: Measurement and interpolation uncertainties in rainfall maps from cellular communication networks Hydrology and Earth System Sciences, 19, 3571-3584, 2015 Author(s): M. F. Rios Gaona, A. Overeem, H. Leijnse, and R. Uijlenhoet Accurate measurements of rainfall are important in many hydrological and meteorological applications, for instance, flash-flood early-warning systems, hydraulic structures design, irrigation, weather forecasting, and climate modelling. Whenever possible, link networks measure and store the received power of the electromagnetic signal at regular intervals. The decrease in power can be converted to rainfall intensity, and is largely due to the attenuation by raindrops along the link paths. Such an alternative technique fulfils the continuous effort to obtain measurements of rainfall in time and space at higher resolutions, especially in places where traditional rain gauge networks are scarce or poorly maintained. Rainfall maps from microwave link networks have recently been introduced at country-wide scales. Despite their potential in rainfall estimation at high spatiotemporal resolutions, the uncertainties present in rainfall maps from link networks are not yet fully comprehended. The aim of this work is to identify and quantify the sources of uncertainty present in interpolated rainfall maps from link rainfall depths. In order to disentangle these sources of uncertainty, we classified them into two categories: (1) those associated with the individual microwave link measurements, i.e. the errors involved in link rainfall retrievals, such as wet antenna attenuation, sampling interval of measurements, wet/dry period classification, dry weather baseline attenuation, quantization of the received power, drop size distribution (DSD), and multi-path propagation; and (2) those associated with mapping, i.e. the combined effect of the interpolation methodology and the spatial density of link measurements. We computed ~ 3500 rainfall maps from real and simulated link rainfall depths for 12 days for the land surface of the Netherlands. Simulated link rainfall depths refer to path-averaged rainfall depths obtained from radar data. The ~ 3500 real and simulated rainfall maps were compared against quality-controlled gauge-adjusted radar rainfall fields (assumed to be the ground truth). Thus, we were able to not only identify and quantify the sources of uncertainty in such rainfall maps, but also test the actual and optimal performance of one commercial microwave network from one of the cellular providers in the Netherlands. Errors in microwave link measurements were found to be the source that contributes most to the overall uncertainty.

Description: GlobWat – a global water balance model to assess water use in irrigated agriculture Hydrology and Earth System Sciences, 19, 3829-3844, 2015 Author(s): J. Hoogeveen, J.-M. Faurès, L. Peiser, J. Burke, and N. van de Giesen GlobWat is a freely distributed, global soil water balance model that is used by the Food and Agriculture Organization (FAO) to assess water use in irrigated agriculture, the main factor behind scarcity of freshwater in an increasing number of regions. The model is based on spatially distributed high-resolution data sets that are consistent at global level and calibrated against values for internal renewable water resources, as published in AQUASTAT, the FAO's global information system on water and agriculture. Validation of the model is done against mean annual river basin outflows. The water balance is calculated in two steps: first a "vertical" water balance is calculated that includes evaporation from in situ rainfall ("green" water) and incremental evaporation from irrigated crops. In a second stage, a "horizontal" water balance is calculated to determine discharges from river (sub-)basins, taking into account incremental evaporation from irrigation, open water and wetlands ("blue" water). The paper describes the methodology, input and output data, calibration and validation of the model. The model results are finally compared with other global water balance models to assess levels of accuracy and validity.

Description: Influence of solar forcing, climate variability and modes of low-frequency atmospheric variability on summer floods in Switzerland Hydrology and Earth System Sciences, 19, 3807-3827, 2015 Author(s): J. C. Peña, L. Schulte, A. Badoux, M. Barriendos, and A. Barrera-Escoda The higher frequency of severe flood events in Switzerland in recent decades has given fresh impetus to the study of flood patterns and their possible forcing mechanisms, particularly in mountain environments. This paper presents a new index of summer flood damage that considers severe and catastrophic summer floods in Switzerland between 1800 and 2009, and explores the influence of external forcings on flood frequencies. In addition, links between floods and low-frequency atmospheric variability patterns are examined. The flood damage index provides evidence that the 1817–1851, 1881–1927, 1977–1990 and 2005–present flood clusters occur mostly in phase with palaeoclimate proxies. The cross-spectral analysis documents that the periodicities detected in the coherency and phase spectra of 11 (Schwabe cycle) and 104 years (Gleissberg cycle) are related to a high frequency of flooding and solar activity minima, whereas the 22-year cyclicity detected (Hale cycle) is associated with solar activity maxima and a decrease in flood frequency. The analysis of low-frequency atmospheric variability modes shows that Switzerland lies close to the border of the principal summer mode. The Swiss river catchments situated on the centre and southern flank of the Alps are affected by atmospherically unstable areas defined by the positive phase of the pattern, while those basins located in the northern slope of the Alps are predominantly associated with the negative phase of the pattern. Furthermore, a change in the low-frequency atmospheric variability pattern related to the major floods occurred over the period from 1800 to 2009; the summer principal mode persists in the negative phase during the last cool pulses of the Little Ice Age (1817–1851 and 1881–1927 flood clusters), whereas the positive phases of the mode prevail during the warmer climate of the last 4 decades (flood clusters from 1977 to present).

Description: Use of satellite and modeled soil moisture data for predicting event soil loss at plot scale Hydrology and Earth System Sciences, 19, 3845-3856, 2015 Author(s): F. Todisco, L. Brocca, L. F. Termite, and W. Wagner The potential of coupling soil moisture and a Universal Soil Loss Equation-based (USLE-based) model for event soil loss estimation at plot scale is carefully investigated at the Masse area, in central Italy. The derived model, named Soil Moisture for Erosion (SM4E), is applied by considering the unavailability of in situ soil moisture measurements, by using the data predicted by a soil water balance model (SWBM) and derived from satellite sensors, i.e., the Advanced SCATterometer (ASCAT). The soil loss estimation accuracy is validated using in situ measurements in which event observations at plot scale are available for the period 2008–2013. The results showed that including soil moisture observations in the event rainfall–runoff erosivity factor of the USLE enhances the capability of the model to account for variations in event soil losses, the soil moisture being an effective alternative to the estimated runoff, in the prediction of the event soil loss at Masse. The agreement between observed and estimated soil losses (through SM4E) is fairly satisfactory with a determination coefficient (log-scale) equal to ~ 0.35 and a root mean square error (RMSE) of ~ 2.8 Mg ha −1 . These results are particularly significant for the operational estimation of soil losses. Indeed, currently, soil moisture is a relatively simple measurement at the field scale and remote sensing data are also widely available on a global scale. Through satellite data, there is the potential of applying the SM4E model for large-scale monitoring and quantification of the soil erosion process.

Description: Computation of vertically averaged velocities in irregular sections of straight channels Hydrology and Earth System Sciences, 19, 3857-3873, 2015 Author(s): E. Spada, T. Tucciarelli, M. Sinagra, V. Sammartano, and G. Corato Two new methods for vertically averaged velocity computation are presented, validated and compared with other available formulas. The first method derives from the well-known Huthoff algorithm, which is first shown to be dependent on the way the river cross section is discretized into several subsections. The second method assumes the vertically averaged longitudinal velocity to be a function only of the friction factor and of the so-called "local hydraulic radius", computed as the ratio between the integral of the elementary areas around a given vertical and the integral of the elementary solid boundaries around the same vertical. Both integrals are weighted with a linear shape function equal to zero at a distance from the integration variable which is proportional to the water depth according to an empirical coefficient β. Both formulas are validated against (1) laboratory experimental data, (2) discharge hydrographs measured in a real site, where the friction factor is estimated from an unsteady-state analysis of water levels recorded in two different river cross sections, and (3) the 3-D solution obtained using the commercial ANSYS CFX code, computing the steady-state uniform flow in a cross section of the Alzette River.

Description: Performance evaluation of groundwater model hydrostratigraphy from airborne electromagnetic data and lithological borehole logs Hydrology and Earth System Sciences, 19, 3875-3890, 2015 Author(s): P. A. Marker, N. Foged, X. He, A. V. Christiansen, J. C. Refsgaard, E. Auken, and P. Bauer-Gottwein Large-scale hydrological models are important decision support tools in water resources management. The largest source of uncertainty in such models is the hydrostratigraphic model. Geometry and configuration of hydrogeological units are often poorly determined from hydrogeological data alone. Due to sparse sampling in space, lithological borehole logs may overlook structures that are important for groundwater flow at larger scales. Good spatial coverage along with high spatial resolution makes airborne electromagnetic (AEM) data valuable for the structural input to large-scale groundwater models. We present a novel method to automatically integrate large AEM data sets and lithological information into large-scale hydrological models. Clay-fraction maps are produced by translating geophysical resistivity into clay-fraction values using lithological borehole information. Voxel models of electrical resistivity and clay fraction are classified into hydrostratigraphic zones using k -means clustering. Hydraulic conductivity values of the zones are estimated by hydrological calibration using hydraulic head and stream discharge observations. The method is applied to a Danish case study. Benchmarking hydrological performance by comparison of performance statistics from comparable hydrological models, the cluster model performed competitively. Calibrations of 11 hydrostratigraphic cluster models with 1–11 hydraulic conductivity zones showed improved hydrological performance with an increasing number of clusters. Beyond the 5-cluster model hydrological performance did not improve. Due to reproducibility and possibility of method standardization and automation, we believe that hydrostratigraphic model generation with the proposed method has important prospects for groundwater models used in water resources management.

Description: Groundwater flow processes and mixing in active volcanic systems: the case of Guadalajara (Mexico) Hydrology and Earth System Sciences, 19, 3937-3950, 2015 Author(s): A. Hernández-Antonio, J. Mahlknecht, C. Tamez-Meléndez, J. Ramos-Leal, A. Ramírez-Orozco, R. Parra, N. Ornelas-Soto, and C. J. Eastoe Groundwater chemistry and isotopic data from 40 production wells in the Atemajac and Toluquilla valleys, located in and around the Guadalajara metropolitan area, were determined to develop a conceptual model of groundwater flow processes and mixing. Stable water isotopes (δ 2 H, δ 18 O) were used to trace hydrological processes and tritium ( 3 H) to evaluate the relative contribution of modern water in samples. Multivariate analysis including cluster analysis and principal component analysis were used to elucidate distribution patterns of constituents and factors controlling groundwater chemistry. Based on this analysis, groundwater was classified into four groups: cold groundwater, hydrothermal groundwater, polluted groundwater and mixed groundwater. Cold groundwater is characterized by low temperature, salinity, and Cl and Na concentrations and is predominantly of Na-HCO 3 -type. It originates as recharge at "La Primavera" caldera and is found predominantly in wells in the upper Atemajac Valley. Hydrothermal groundwater is characterized by high salinity, temperature, Cl, Na and HCO 3 , and the presence of minor elements such as Li, Mn and F. It is a mixed-HCO 3 type found in wells from Toluquilla Valley and represents regional flow circulation through basaltic and andesitic rocks. Polluted groundwater is characterized by elevated nitrate and sulfate concentrations and is usually derived from urban water cycling and subordinately from agricultural return flow. Mixed groundwaters between cold and hydrothermal components are predominantly found in the lower Atemajac Valley. Twenty-seven groundwater samples contain at least a small fraction of modern water. The application of a multivariate mixing model allowed the mixing proportions of hydrothermal fluids, polluted waters and cold groundwater in sampled water to be evaluated. This study will help local water authorities to identify and dimension groundwater contamination, and act accordingly. It may be broadly applicable to other active volcanic systems on Earth.

Description: Performance and robustness of probabilistic river forecasts computed with quantile regression based on multiple independent variables Hydrology and Earth System Sciences, 19, 3969-3990, 2015 Author(s): F. Hoss and P. S. Fischbeck This study applies quantile regression (QR) to predict exceedance probabilities of various water levels, including flood stages, with combinations of deterministic forecasts, past forecast errors and rates of water level rise as independent variables. A computationally cheap technique to estimate forecast uncertainty is valuable, because many national flood forecasting services, such as the National Weather Service (NWS), only publish deterministic single-valued forecasts. The study uses data from the 82 river gauges, for which the NWS' North Central River Forecast Center issues forecasts daily. Archived forecasts for lead times of up to 6 days from 2001 to 2013 were analyzed. Besides the forecast itself, this study uses the rate of rise of the river stage in the last 24 and 48 h and the forecast error 24 and 48 h ago as predictors in QR configurations. When compared to just using the forecast as an independent variable, adding the latter four predictors significantly improved the forecasts, as measured by the Brier skill score and the continuous ranked probability score. Mainly, the resolution increases, as the forecast-only QR configuration already delivered high reliability. Combining the forecast with the other four predictors results in a much less favorable performance. Lastly, the forecast performance does not strongly depend on the size of the training data set but on the year, the river gauge, lead time and event threshold that are being forecast. We find that each event threshold requires a separate configuration or at least calibration.

Description: Technical Note: The use of an interrupted-flow centrifugation method to characterise preferential flow in low permeability media Hydrology and Earth System Sciences, 19, 3991-4000, 2015 Author(s): R. A. Crane, M. O. Cuthbert, and W. Timms We present an interrupted-flow centrifugation technique to characterise preferential flow in low permeability media. The method entails a minimum of three phases: centrifuge-induced flow, no flow and centrifuge-induced flow, which may be repeated several times in order to most effectively characterise multi-rate mass transfer behaviour. In addition, the method enables accurate simulation of relevant in situ total stress conditions during flow by selecting an appropriate centrifugal force. We demonstrate the utility of the technique for characterising the hydraulic properties of smectite-clay-dominated core samples. All core samples exhibited a non-Fickian tracer breakthrough (early tracer arrival), combined with a decrease in tracer concentration immediately after each period of interrupted flow. This is indicative of dual (or multi-)porosity behaviour, with solute migration predominately via advection during induced flow, and via molecular diffusion (between the preferential flow network(s) and the low hydraulic conductivity domain) during interrupted flow. Tracer breakthrough curves were simulated using a bespoke dual porosity model with excellent agreement between the data and model output (Nash–Sutcliffe model efficiency coefficient was 〉 0.97 for all samples). In combination, interrupted-flow centrifuge experiments and dual porosity transport modelling are shown to be a powerful method to characterise preferential flow in low permeability media.

Description: From runoff to rainfall: inverse rainfall–runoff modelling in a high temporal resolution Hydrology and Earth System Sciences, 19, 4619-4639, 2015 Author(s): M. Herrnegger, H. P. Nachtnebel, and K. Schulz Rainfall exhibits a large spatio-temporal variability, especially in complex alpine terrain. Additionally, the density of the monitoring network in mountainous regions is low and measurements are subjected to major errors, which lead to significant uncertainties in areal rainfall estimates. In contrast, the most reliable hydrological information available refers to runoff, which in the presented work is used as input for an inverted HBV-type rainfall–runoff model that is embedded in a root finding algorithm. For every time step a rainfall value is determined, which results in a simulated runoff value closely matching the observed runoff. The inverse model is applied and tested to the Schliefau and Krems catchments, situated in the northern Austrian Alpine foothills. The correlations between inferred rainfall and station observations in the proximity of the catchments are of similar magnitude compared to the correlations between station observations and independent INCA (Integrated Nowcasting through Comprehensive Analysis) rainfall analyses provided by the Austrian Central Institute for Meteorology and Geodynamics (ZAMG). The cumulative precipitation sums also show similar dynamics. The application of the inverse model is a promising approach to obtain additional information on mean areal rainfall. This additional information is not solely limited to the simulated hourly data but also includes the aggregated daily rainfall rates, which show a significantly higher correlation to the observed values. Potential applications of the inverse model include gaining additional information on catchment rainfall for interpolation purposes, flood forecasting or the estimation of snowmelt contribution. The application is limited to (smaller) catchments, which can be represented with a lumped model setup, and to the estimation of liquid rainfall.

Description: The SPARSE model for the prediction of water stress and evapotranspiration components from thermal infra-red data and its evaluation over irrigated and rainfed wheat Hydrology and Earth System Sciences, 19, 4653-4672, 2015 Author(s): G. Boulet, B. Mougenot, J.-P. Lhomme, P. Fanise, Z. Lili-Chabaane, A. Olioso, M. Bahir, V. Rivalland, L. Jarlan, O. Merlin, B. Coudert, S. Er-Raki, and J.-P. Lagouarde Evapotranspiration is an important component of the water cycle, especially in semi-arid lands. A way to quantify the spatial distribution of evapotranspiration and water stress from remote-sensing data is to exploit the available surface temperature as a signature of the surface energy balance. Remotely sensed energy balance models enable one to estimate stress levels and, in turn, the water status of continental surfaces. Dual-source models are particularly useful since they allow derivation of a rough estimate of the water stress of the vegetation instead of that of a soil–vegetation composite. They either assume that the soil and the vegetation interact almost independently with the atmosphere (patch approach corresponding to a parallel resistance scheme) or are tightly coupled (layer approach corresponding to a series resistance scheme). The water status of both sources is solved simultaneously from a single surface temperature observation based on a realistic underlying assumption which states that, in most cases, the vegetation is unstressed, and that if the vegetation is stressed, evaporation is negligible. In the latter case, if the vegetation stress is not properly accounted for, the resulting evaporation will decrease to unrealistic levels (negative fluxes) in order to maintain the same total surface temperature. This work assesses the retrieval performances of total and component evapotranspiration as well as surface and plant water stress levels by (1) proposing a new dual-source model named Soil Plant Atmosphere and Remote Sensing Evapotranspiration (SPARSE) in two versions (parallel and series resistance networks) based on the TSEB (Two-Source Energy Balance model, Norman et al., 1995) model rationale as well as state-of-the-art formulations of turbulent and radiative exchange, (2) challenging the limits of the underlying hypothesis for those two versions through a synthetic retrieval test and (3) testing the water stress retrievals (vegetation water stress and moisture-limited soil evaporation) against in situ data over contrasted test sites (irrigated and rainfed wheat). We demonstrated with those two data sets that the SPARSE series model is more robust to component stress retrieval for this cover type, that its performance increases by using bounding relationships based on potential conditions (root mean square error lowered by up to 11 W m −2 from values of the order of 50–80 W m −2 ), and that soil evaporation retrieval is generally consistent with an independent estimate from observed soil moisture evolution.

Description: Climate change and its impacts on river discharge in two climate regions in China Hydrology and Earth System Sciences, 19, 4609-4618, 2015 Author(s): H. Xu and Y. Luo Understanding the heterogeneity of climate change and its impacts on annual and seasonal discharge and the difference between median flow and extreme flow in different climate regions is of utmost importance to successful water management. To quantify the spatial and temporal heterogeneity of climate change impacts on hydrological processes, this study simulated river discharge in the River Huangfuchuan in semi-arid northern China and in the River Xiangxi in humid southern China. The study assessed the uncertainty in projected discharge for three time periods (2020s, 2050s and 2080s) using seven equally weighted GCMs (global climate models) for the SRES (Special Reports on Emissions Scenarios) A1B scenario. Climate projections that were applied to semi-distributed hydrological models (Soil Water Assessment Tools, SWAT) in both catchments showed trends toward warmer and wetter conditions, particularly for the River Huangfuchuan. Results based on seven GCMs' projections indicated changes from −1.1 to 8.6 °C and 0.3 to 7.0 °C in seasonal temperature and changes from −29 to 139 % and −32 to 85 % in seasonal precipitation in the rivers Huangfuchuan and Xiangxi, respectively. The largest increases in temperature and precipitation in both catchments were projected in the spring and winter seasons. The main projected hydrologic impact was a more pronounced increase in annual discharge in the River Huangfuchuan than in the River Xiangxi. Most of the GCMs projected increased discharge in all seasons, especially in spring, although the magnitude of these increases varied between GCMs. The peak flows were projected to appear earlier than usual in the River Huangfuchuan and later than usual in the River Xiangxi, while the GCMs were fairly consistent in projecting increased extreme flows in both catchments with varying magnitude compared to median flows. For the River Huangfuchuan in the 2080s, median flow changed from −2 to 304 %, compared to a −1 to 145 % change in high flow (Q05 exceedance threshold). For the River Xiangxi, low flow (Q95 exceedance threshold) changed from −1 to 77 % and high flow changed from −1 to 62 %, while median flow changed from −4 to 23 %. The uncertainty analysis provided an improved understanding of future hydrologic behavior in the watershed. Furthermore, this study indicated that the uncertainty constrained by GCMs was critical and should always be considered in analysis of climate change impacts and adaptation.

Description: Moving sociohydrology forward: a synthesis across studies Hydrology and Earth System Sciences, 19, 3667-3679, 2015 Author(s): T. J. Troy, M. Konar, V. Srinivasan, and S. Thompson Sociohydrology is the study of coupled human–water systems, building on the premise that water and human systems co-evolve: the state of the water system feeds back onto the human system, and vice versa, a situation denoted as "two-way coupling". A recent special issue in HESS/ESD, "Predictions under change: water, earth, and biota in the Anthropocene", includes a number of sociohydrologic publications that allow for a survey of the current state of understanding of sociohydrology and the dynamics and feedbacks that couple water and human systems together, of the research methodologies being employed to date, and of the normative and ethical issues raised by the study of sociohydrologic systems. Although sociohydrology is concerned with coupled human–water systems, the feedback may be filtered by a connection through natural or social systems, for example, the health of a fishery or through the global food trade, and therefore it may not always be possible to treat the human–water system in isolation. As part of a larger complex system, sociohydrology can draw on tools developed in the social–ecological and complex systems literature to further our sociohydrologic knowledge, and this is identified as a ripe area of future research.

Description: Transferring global uncertainty estimates from gauged to ungauged catchments Hydrology and Earth System Sciences, 19, 2535-2546, 2015 Author(s): F. Bourgin, V. Andréassian, C. Perrin, and L. Oudin Predicting streamflow hydrographs in ungauged catchments is challenging, and accompanying the estimates with realistic uncertainty bounds is an even more complex task. In this paper, we present a method to transfer global uncertainty estimates from gauged to ungauged catchments and we test it over a set of 907 catchments located in France, using two rainfall–runoff models. We evaluate the quality of the uncertainty estimates based on three expected qualities: reliability, sharpness, and overall skill. The robustness of the method to the availability of information on gauged catchments was also evaluated using a hydrometrical desert approach. Our results show that the method presents advantageous perspectives, providing reliable and sharp uncertainty bounds at ungauged locations in a majority of cases.

Description: Extending periodic eddy covariance latent heat fluxes through tree sap-flow measurements to estimate long-term total evaporation in a peat swamp forest Hydrology and Earth System Sciences, 19, 2513-2534, 2015 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 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. Actual total evaporation (ET a ) was measured during three window periods (between 7 and 9 days each) using an eddy covariance (EC) system on a telescopic mast above the forest canopy. Sap flows of an understory tree and an emergent tree were 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 ET a from the Nkazana PSF and sap-flow measurements. These overlapped during two of the window periods ( R 2 = 0.92 and 0.90), providing hourly estimates of ET a from the Nkazana PSF for a year, totalling 1125 mm (while rainfall was 650 mm). In building the empirical model, it was found that to include the understory tree sap flow provided no benefit to the model performance. In addition, the relationship between the emergent tree sap flow with ET a between the two field campaigns was consistent and could be represented by a single empirical model ( R 2 = 0.90; RMSE = 0.08 mm h −1 ). During the window periods of EC measurement, no single meteorological variable was found to describe the Nkazana PSF ET a satisfactorily. However, in terms of evaporation models, the hourly FAO Penman–Monteith reference evaporation (ET o ) best described ET a 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 potential evaporation (ET p ) model ( R 2 = 0.54, 0.74 and 0.62 during the respective field campaigns). From the extended record of ET a (derived in this study from sap flow) and ET o , a monthly crop factor ( K c ) was derived for the Nkazana PSF, providing a method of estimating long-term swamp forest water-use from meteorological data. The monthly K c 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 sap flow 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 a over remote heterogeneous forests. In addition, the contrast in annual ET a and rainfall emphasised the reliance of the Nkazana PSF on groundwater.

Description: Effects of Multiple Doppler Radar data assimilation on the numerical simulation of a Flash Flood Event during the HyMeX campaign Ida Maiello, Sabrina Gentile, Rossella Ferretti, Luca Baldini, Nicoletta Roberto, Errico Picciotti, Pier Paolo Alberoni, and Frank S. Marzano Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-320,2016 Manuscript under review for HESS (discussion: open, 0 comments) An analysis to evaluate the impact of assimilating multiple radar data with a three dimensional variational (3D-Var) system on a heavy precipitation event is presented. The main goal is to establish a general methodology to quantitatively assess the performance of flash-flood numerical weather prediction at mesoscale. In this respect, during the first Special Observation Period (SOP1) of HyMeX (Hydrological cycle in the Mediterranean Experiment) campaign several Intensive Observing Periods (IOPs) were launched and nine occurred in Italy. Among them IOP4 is chosen for this study because of its low predictability. This event hit central Italy on 14 September 2012 producing heavy precipitation and causing several damages. Data taken from three C-band radars running operationally during the event are assimilated to improve high resolution initial conditions. In order to evaluate the impact of the assimilation procedure at different horizontal resolution and to assess the impact of assimilating multiple radars data, several experiments using Weather Research and Forecasting (WRF) model are performed. Finally, the statistical indexes as accuracy, equitable threat score, false alarm ratio and frequency bias are used to objectively compare the experiments, using rain gauges data as benchmark.

Description: On the propagation of diel signals in river networks using analytic solutions of flow equations Morgan Fonley, Ricardo Mantilla, Scott J. Small, and Rodica Curtu Hydrol. Earth Syst. Sci., 20, 2899-2912, doi:10.5194/hess-20-2899-2016, 2016 We design and implement a theoretical experiment to show that, under low-flow conditions, observed streamflow discrepancies between early and late summer can be attributed to different flow velocities in the river network. By developing an analytic solution to represent flow along a given river network, we emphasize the dependence of streamflow amplitude and time delay on the geomorphology of the network. We also simulate using a realistic river network to highlight the effects of scale.

Description: Looking beyond general metrics for model comparison – lessons from an international model intercomparison study Tanja de Boer-Euser, Laurène Bouaziz, Jan De Niel, Claudia Brauer, Benjamin Dewals, Gilles Drogue, Fabrizio Fenicia, Benjamin Grelier, Jiri Nossent, Fernando Pereira, Hubert Savenije, Guillaume Thirel, and Patrick Willems Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-339,2016 Manuscript under review for HESS (discussion: open, 0 comments) In this study the rainfall–runoff models of eight international research groups were compared for a set of subcatchments of the Meuse basin to investigate the influence of certain model components on the modelled discharge. Although the models showed similar performances based on general metrics, clear differences could be observed for specific events. The differences during drier conditions could indeed be linked back to differences in model structures.

Description: River water quality changes in New Zealand over 26 years (1989–2014): Response to land use and land disturbance Jason P. Julian, Kirsten M. de Beurs, Braden Owsley, Robert J. Davies-Colley, and Anne-Gaelle E. Ausseil Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-323,2016 Manuscript under review for HESS (discussion: open, 0 comments) New Zealand (NZ) is a natural laboratory for investigating water quality responses to land use change because its landscape is managed intensively. We interpreted water quality state and trends (1989–2014) of 77 river sites across NZ. We show that the greatest long-term impacts on river water quality in NZ have been densely stocked pastures (due to high nutrient inputs), followed by plantation forestry (due to sediment/nutrient runoff during harvesting).

Description: A post-wildfire response in cave dripwater chemistry Gurinder Nagra, Pauline C. Treble, Martin S. Andersen, Ian J. Fairchild, Katie Coleborn, and Andy Baker Hydrol. Earth Syst. Sci., 20, 2745-2758, doi:10.5194/hess-20-2745-2016, 2016 Our current understanding of wildfires on Earth is filled with knowledge gaps. One reason for this is our poor record of fire in natural archives. We open the possibility for speleothems to be "a missing piece to the fire-puzzle". We find by effecting surface evaporation and transpiration rates, wildfires can have a multi-year impact on speleothem, forming dripwater hydrology and chemistry. We open a new avenue for speleothems as potential palaeo-fire archives.

Description: Improving together: better science writing through peer learning Mathew A. Stiller-Reeve, Céline Heuzé, William T. Ball, Rachel H. White, Gabriele Messori, Karin van der Wiel, Iselin Medhaug, Annemarie H. Eckes, Amee O'Callaghan, Mike J. Newland, Sian R. Williams, Matthew Kasoar, Hella Elisa Wittmeier, and Valerie Kumer Hydrol. Earth Syst. Sci., 20, 2965-2973, doi:10.5194/hess-20-2965-2016, 2016 Scientific writing must improve and the key to long-term improvement of scientific writing lies with the early-career scientist (ECS). We introduce the ClimateSnack project, which aims to motivate ECSs to start writing groups around the world to improve their skills together. Writing groups offer many benefits but can be a challenge to keep going. Several ClimateSnack writing groups formed, and this paper examines why some of the groups flourished and others dissolved.

Description: Validation of Terrestrial Water Storage Variations as Simulated by Different Global Numerical Models with GRACE Satellite Observations Liangjing Zhang, Henryk Dobslaw, Tobias Stacke, Andreas Güntner, Robert Dill, and Maik Thomas Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-330,2016 Manuscript under review for HESS (discussion: open, 0 comments) Global numerical models perform differently as has been found in some model intercomparison studies, which mainly focused on components as evapotranspiration, soil moisture or runoff. We have applied terrestrial water storage that is estimated from state-of-art post-processing method to validate four global numerical models and try to identify the advantages and deficiencies of a certain model. GRACE based TWS demonstrates its additional benefits to improve models in future.

Description: Model Study on Potential Contributions of the Proposed Huangpu Gate to Flood Control in Taihu Lake Basin Hanghui Zhang, Shuguang Liu, Jianchun Ye, and Pat Yeh Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-310,2016 Manuscript under review for HESS (discussion: open, 0 comments) The Taihu Lake basin is located in the hinterland of the Yangtze River Delta. Constructing a gate at the mouth of the Huangpu River is considered one of the effective solutions to the basin's flooding problems. The pattern of river flow changes from bi-directional to unidirectional flow when the estuary gate is operated. It is concluded that the Huangpu River with a proposed gate is more effective than a natural channel, and its beneficiaries include the lake and the related surrounding areas.

Description: Hydrological modeling in glacierized catchments of Central Asia: status and challenges Yaning Chen, Weihong Li, Gonghuan Fang, and Zhi Li Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-325,2016 Manuscript under review for HESS (discussion: open, 0 comments) This paper reviews the status of hydrological modeling in the mountainous region of Central Asia, discussing the limitations of the available models and shedding light on future directions. We conclude that the main sources of uncertainty in hydrological modeling are the input uncertainty and lack of understanding of the hydrological regimes. Future focuses should be on the use of multi-source of input data combined with multi-objective calibration and validation.

Description: Consequences and mitigation of saltwater intrusion induced by short-circuiting during aquifer storage and recovery (ASR) in a coastal subsurface Koen Gerardus Zuurbier and Pieter Jan Stuyfzand Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-343,2016 Manuscript under review for HESS (discussion: open, 0 comments) The subsurface is increasingly perforated for exploitation of water and energy. This has increased the risk of leakage between originally separated aquifers. It is shown how this leakage can have a very negative impact on the recovery of freshwater during aquifer storage and recovery (ASR) in brackish-saline aquifers. Deep interception of intruding brackish-saline water can mitigate the negative effects and buoyancy of freshwater to some extent, but not completely.

Description: The European 2015 drought from a hydrological perspective Gregor Laaha, Tobias Gauster, Lena M. Tallaksen, Jean-Philippe Vidal, Kerstin Stahl, Christel Prudhomme, Benedikt Heudorfer, Radek Vlnas, Monica Ionita, Henny A. J. Van Lanen, Mary-Jeanne Adler, Laurie Caillouet, Claire Delus, Miriam Fendekova, Sebastien Gailliez, Jamie Hannaford, Daniel Kingston, Anne F. Van Loon, Luis Mediero, Marzena Osuch, Renata Romanowicz, Eric Sauquet, James H. Stagge, and Wai K. Wong Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-366,2016 Manuscript under review for HESS (discussion: open, 0 comments) In 2015 large parts of Europe were affected by a drought. In terms of low flow magnitude, a region around the Czech Republic was most affected with annual low flows that exhibited return intervals of 100 years and more. In terms of deficit volumes, the geographical centre of the event was in the area of Southern Germany where the drought lasted particularly long. For an assessment of drought impacts on water resources hydrological data is required in addition to the hydro-meteorological indices.

Description: Hydrological threats for riparian wetlands of international importance – a global quantitative and qualitative analysis Christof Schneider, Martina Flörke, Lucia De Stefano, and Jacob D. Petersen-Perlman Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-350,2016 Manuscript under review for HESS (discussion: open, 0 comments) Riparian wetlands are disappearing worldwide due to altered river hydrology. The WaterGAP3 model is used to compare modified to natural flow regimes at 93 Ramsar sites. Results show that water resource management seriously impairs inundation patterns at 29 % of the sites. New dam initiatives are likely to affect especially wetlands located in South America, Africa, Asia and the Balkan Peninsula. Hotspots for climate change impacts could be Eastern Europe and South America.

Description: Leaf-scale experiments reveal important omission in the Penman-Monteith equation Stanislaus J. Schymanski and Dani Or Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-363,2016 Manuscript under review for HESS (discussion: open, 0 comments) Most of the rain falling on land is returned to the atmosphere by plant leaves, which release water vapour (transpire) through tiny pores. To better understand this process, we used artificial leaves in a special wind tunnel and discovered major problems with an established approach (PM equation), widely used to quantify transpiration and its sensitivity to climate change. We present an improved set of equations, consistent with experiments and displaying more realistic climate sensitivity.

Description: Assessment of land use impact on hydraulic threshold conditions for gully head cut initiation Aliakbar Nazari Samani, Qiuwen Chen, Shahram Khalighi, Robert James Wasson, and Mohammad Reza Rahdari Hydrol. Earth Syst. Sci., 20, 3005-3012, doi:10.5194/hess-20-3005-2016, 2016 We hypothesized that land use had important effects on hydraulic threshold conditions for gully head cut initiation. We investigated the effects using an experimental plot. The results indicated that the use of a threshold value of τ cr  = 35  dyne cm −2 and ω u  = 0.4 Cm S −1 in physically based soil erosion models is susceptible to high uncertainty when assessing gully erosion.

Description: Mekong River flow and hydrological extremes under climate change Long Phi Hoang, Hannu Lauri, Matti Kummu, Jorma Koponen, Michelle T. H. van Vliet, Iwan Supit, Rik Leemans, Pavel Kabat, and Fulco Ludwig Hydrol. Earth Syst. Sci., 20, 3027-3041, doi:10.5194/hess-20-3027-2016, 2016 We modelled hydrological changes under climate change in the Mekong River, focusing on extreme events. The scenario ensemble shows an intensification of the hydrological cycle under climate change. Annual river flow increases between 5 and 16 % depending on locations. Extreme high flows increase substantially in both magnitude and frequency, posing threats to flood safety in the basin. Extreme low-flow events are projected to reduce as a result of increased river flow during the dry season.

Description: On the non-stationarity of hydrological response in anthropogenically unaffected catchments: An Australian perspective Hoori Ajami, Ashish sharma, Lawrence E. Band, Jason P. Evans, Narendra K. Tuteja, G. E. Amirthanathan, and Mohammed A. Bari Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-353,2016 Manuscript under review for HESS (discussion: open, 0 comments) We present the first data-based framework for explaining why catchments behave in a non-stationary manner, even when they are unaffected by deforestation or urbanization. The role of vegetation dynamics on stream flow are indicated by similar or greater sensitivity of annual runoff ratio to annual fractional vegetation cover. We formulated a novel ecohydrologic catchment classification framework that incorporates the role of vegetation dynamics on catchment scale water partitioning.

Description: Sustainability of water uses in managed hydrosystems: human- and climate-induced changes for the mid-21st century Julie Fabre, Denis Ruelland, Alain Dezetter, and Benjamin Grouillet Hydrol. Earth Syst. Sci., 20, 3129-3147, doi:10.5194/hess-20-3129-2016, 2016 We assess the sustainability of planned water uses in complex mesoscale river basins by modeling water demand and availability under climatic and anthropogenic changes. We present an analysis through indicators that relate to water management goals. The impacts of climate projections on both water availability and demand question the water allocations and environmental constraints currently planned for the coming decades. This work brings an essential long-term perspective to water sharing plans.

Description: Modeling liquid water transport in snow under rain-on-snow conditions – considering preferential flow Sebastian Würzer, Nander Wever, Roman Juras, Michael Lehning, and Tobias Jonas Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-351,2016 Manuscript under review for HESS (discussion: open, 0 comments) We discuss a dual-domain water transport model in a physics based snowpack model to account for preferential flow (PF) in addition to matrix flow. Yet so far no operationally used snow model was explicitly accounting for PF. The new approach is compared to existing water transport models and validated against in-situ data from sprinkling and natural rain-on-snow (ROS) events. Our work demonstrates the benefit of considering PF in modeling hourly snowpack runoff, especially during ROS conditions.

Description: Can integrative catchment management mitigate future water quality issues caused by climate change and socio-economic development? Mark Honti, Nele Schuwirth, Jörg Rieckermann, and Christian Stamm Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-297,2016 Manuscript under review for HESS (discussion: open, 0 comments) Catchments are complex systems where water quantity, quality and the provided ecological services are determined by interacting physical, chemical, biological, economic, and social factors. The awareness of these interactions led to the prevailing catchment management paradigm of Integrated Water Resources Management. The design and evaluation of solutions for integrated water resources management requires to predict changes of local or regional water quality, which requires integrated approach for modeling too. On one hand, integrated models have to be comprehensive enough to cover the aspects relevant for management decisions, allow for mapping of global change processes – as climate change, population growth, migration, and socio-economic development – to the regional and local contexts. On the other hand, models have to be sufficiently simple and fast enough to apply proper methods of uncertainty analysis, which can consider model structure deficits and propagate errors through the chain of submodels. Here, we present an integrated catchment model satisfying both objectives. The conceptual "iWaQa" model was developed to support the integrated management of small streams. It can predict both traditional water quality parameters like nutrients and a wide set of organic micropollutants originating from plant and material protection products. Due to the model's simplicity, it allows for a full, propagative analysis of predictive uncertainty, including certain structural and input errors. The usefulness of the model is demonstrated by predicting future water quality in a small catchment with mixed land use in the Swiss Plateau. The focus of our study is the change of water quality over the next decades driven by climate change, population growth or decline, socio-economic development and the implementation of management strategies for improving water quality. Our results indicate that input and model structure uncertainties are the most influential factors on certain water quality parameters and in these cases the uncertainty of modeling is already very high for the present conditions. Nevertheless, a proper quantification of today's uncertainty can make the management fairly robust for the foreseen range of possible evolution into the next decades. With a time-horizon of 2050, it seems that human land use and management decisions have a larger influence on water quality than climate change. However, the analysis of single climate model chains indicates that the importance of climate grows when a certain climate prediction is considered instead of the ensemble forecast.

Description: Improved large-scale hydrological modelling through the assimilation of streamflow and downscaled satellite soil moisture observations Patricia López López, Niko Wanders, Jaap Schellekens, Luigi J. Renzullo, Edwin H. Sutanudjaja, and Marc F. P. Bierkens Hydrol. Earth Syst. Sci., 20, 3059-3076, doi:10.5194/hess-20-3059-2016, 2016 We perform a joint assimilation experiment of high-resolution satellite soil moisture and discharge observations in the Murrumbidgee River basin with a large-scale hydrological model. Additionally, we study the impact of high- and low-resolution meteorological forcing on the model performance. We show that the assimilation of high-resolution satellite soil moisture and discharge observations has a significant impact on discharge simulations and can bring them closer to locally calibrated models.

Description: Application of tritium in precipitation and baseflow in Japan: a case study of groundwater transit times and storage in Hokkaido watersheds Maksym A. Gusyev, Uwe Morgenstern, Michael K. Stewart, Yusuke Yamazaki, Kazuhisa Kashiwaya, Terumasa Nishihara, Daisuke Kuribayashi, Hisaya Sawano, and Yoichi Iwami Hydrol. Earth Syst. Sci., 20, 3043-3058, doi:10.5194/hess-20-3043-2016, 2016 Tritium-estimated groundwater mean transit times (MTTs) and storage volumes provide useful information for water resources management especially during droughts. In Hokkaido, we find that (1) one tritium measurement at baseflow is already sufficient to estimate MTT for some catchments, (2) the hydrogeological settings control tritium transit times of subsurface groundwater storage at baseflow, and (3) in future, one tritium measurement will be sufficient to estimate MTT in most Japanese catchments.

Description: Redox controls on methane formation, migration and fate in shallow aquifers Pauline Humez, Bernhard Mayer, Michael Nightingale, Veith Becker, Andrew Kingston, Stephen Taylor, Guy Bayegnak, Romain Millot, and Wolfram Kloppmann Hydrol. Earth Syst. Sci., 20, 2759-2777, doi:10.5194/hess-20-2759-2016, 2016 Development of unconventional energy resources if often associated with public concerns regarding potential contamination of shallow groundwater due to methane leakage. We combined chemical and isotopic analyses of gas and water samples obtained from shallow aquifers in Alberta (Canada) to assess baseline methane sources and found that 〉 67 % of the samples contained biogenic methane formed in situ in the aquifers. There was no evidence of deep thermogenic methane migration into shallow aquifers.

Description: Spatial and Temporal Variability in Baseflow in the Mattole River Headwaters, California, USA Nathan Queener and Andrew P. Stubblefield Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-300,2016 Manuscript under review for HESS (discussion: open, 0 comments) Understanding controls on stream low flow is critical for managing aquatic resources. Baseflows in small river basins in northern California, USA were found to be quite divergent. The difference in water yield was much greater than the difference in precipitation. Steep, high elevation areas, dissected by many channels, had the highest baseflow. The positive correlation between basin steepness and flow is thought to result from greater basin storage capacity in thick weathered bedrock layers.

Description: Variations of global and continental water balance components as impacted by climate forcing uncertainty and human water use Hannes Müller Schmied, Linda Adam, Stephanie Eisner, Gabriel Fink, Martina Flörke, Hyungjun Kim, Taikan Oki, Felix Theodor Portmann, Robert Reinecke, Claudia Riedel, Qi Song, Jing Zhang, and Petra Döll Hydrol. Earth Syst. Sci., 20, 2877-2898, doi:10.5194/hess-20-2877-2016, 2016 The assessment of water balance components of the global land surface by means of hydrological models is affected by large uncertainties, in particular related to meteorological forcing. We analyze the effect of five state-of-the-art forcings on water balance components at different spatial and temporal scales modeled with WaterGAP. Furthermore, the dominant effect (precipitation/human alteration) for long-term changes in river discharge is assessed.

Description: Simultaneous calibration of hydrological models in geographical space András Bárdossy, Yingchun Huang, and Thorsten Wagener Hydrol. Earth Syst. Sci., 20, 2913-2928, doi:10.5194/hess-20-2913-2016, 2016 This paper explores the simultaneous calibration method to transfer model parameters from gauged to ungauged catchments. It is hypothesized that the model parameters can be separated into two categories: one reflecting the dynamic behavior and the other representing the long-term water balance. The results of three numerical experiments indicate that a good parameter transfer to ungauged catchments can be achieved through simultaneous calibration of models for a number of catchments.

Description: Morphological dynamics of an englacial channel Geir Vatne and Tristram D. L. Irvine-Fynn Hydrol. Earth Syst. Sci., 20, 2947-2964, doi:10.5194/hess-20-2947-2016, 2016 Ten years of direct observations of an englacial conduit in a cold based glacier in Svalbard document for the first time how a vertical meltwater waterfall (moulin) is formed from gradual incision of a meltwater channel. This evolution appears to be dominated by knickpoints that incise upstream at rates several times faster than the vertical incision in adjacent near horizontal channel sections.

Description: A practical approach to lake water density from electrical conductivity and temperature Santiago Moreira, Martin Schultze, Karsten Rahn, and Bertram Boehrer Hydrol. Earth Syst. Sci., 20, 2975-2986, doi:10.5194/hess-20-2975-2016, 2016 Density calculations in lakes are essential in the study of stability, stratification and numerical modelling. However, density equations which use fixed constant coefficients are still common in use, despite their limitations. We present a practical approach which can specifically include the effect of dissolved substances by fitting two coefficients. The method has been tested against density equations and density measurements in lakes.

Description: Improving estimates of water resources in a semi-arid region by assimilating GRACE data into the PCR-GLOBWB hydrological model N. Tangdamrongsub, S. C. Steele-Dunne, B. C. Gunter, P. G. Ditmar, E. H. Sutanudjaja, Y. Sun, T. Xia, and Z. Wang Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-354,2016 Manuscript under review for HESS (discussion: open, 0 comments) An accurate estimation of water resources dynamics is crucial for proper management of both agriculture and the local ecology, particularly in semi-arid regions. Imperfections in model physics, uncertainties in model land parameters and meteorological data, as well as the human impact on land changes often limit the accuracy of hydrological models in estimating water storages. To mitigate this problem, this study investigated the assimilation of Terrestrial Water Storage (TWS) estimates derived from the Gravity Recovery And Climate Experiment (GRACE) data using an Ensemble Kalman Filter (EnKF) approach. The region considered was the Hexi Corridor of Northern China. The hydrological model used for the analysis was PCR-GLOBWB, driven by satellite-based forcing data from April 2002 to December 2010. In this study, EnKF 3D scheme, which accounts for the GRACE spatially-correlated errors, was used. The correlated errors were propagated from the full error variance-covariance matrices provided as a part of the GRACE data product. The impact of the GRACE Data Assimilation (DA) scheme was evaluated in terms of the TWS, as well as individual hydrological storage estimates. The capability of GRACE DA to adjust the storage level was apparent not only for the entire TWS but also for the groundwater component, which had annual amplitude, phase, and long-term trend estimates closer to the GRACE observations. This study also assessed the benefits of taking into account correlations of errors in GRACE-based estimates. The assessment was carried out by comparing the EnKF results, with and without taking into account error correlations, with the in situ groundwater data from 5 well sites and the in situ streamflow data from two river gauges. On average, the experiments showed that GRACE DA improved the accuracy of groundwater storage estimates by as much as 25 %. The inclusion of error correlations provided an equal or greater improvement in the estimates. No significant benefits of GRACE DA were observed in terms of streamflow estimates, which reflect a limited spatial and temporal resolution of GRACE observations. Results from the 9-year long GRACE DA study were used to assess the status of water resources over the Hexi Corridor. Areally-averaged values revealed that TWS, soil moisture, and groundwater storages over the region decreased with an average rate of approximately 0.2, 0.1, and 0.1 cm/yr in terms of equivalent water heights, respectively. A substantial decline in TWS (approximately −0.4 cm/yr) was seen over the Shiyang River Basin in particular, and the reduction mostly occurred in the groundwater layer. An investigation of the relationship between water resources and agriculture suggested that groundwater consumption required to maintain the growing period in this specific basin was likely the cause of the groundwater depletion.

Description: Monitoring surface water quality using social media in the context of citizen science Hang Zheng, Hong Yang, Di Long, and Hua Jing Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-359,2016 Manuscript under review for HESS (discussion: open, 0 comments) Do you feel angry if the river in your living place is polluted by industries? Do you want to do something to save your environment? Just log in http://www.thuhjjc.com and use the Tsinghua Environment Monitoring Platform (TEMP) to photograph the water pollution actives and make your report. This study established a social media platform to monitor and report surface water quality. The effectiveness of the platform was demonstrated by the 265 water quality reports across 29 provinces in China.

Description: Identifying water deficit and vegetation response during the 2009/10 drought over North China: Implications for the South-to-North Water Diversion project Bowen Zhu, Xianhong Xie, and Kang Zhang Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-313,2016 Manuscript under review for HESS (discussion: open, 0 comments) This study attempts to identify water deficit using GRACE data and vegetation response during the 2009/10 drought over North China. There was a decling trend in total water storage for the past decade based on GRACE data, and the regional deficit of water storage was approximately 25 km 3 in 2009/10. This drought event has led to suppression of vegetation growth in North China. The SNWD project may ease the water storage deficit in North China for this level of drought intensity.

Description: The Budyko functions under non-steady state conditions: new approach and comparison with previous formulations Roger Moussa and Jean-Paul Lhomme Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-379,2016 Manuscript under review for HESS (discussion: open, 0 comments) This paper presents a new approach to transform any Budyko function under steady-state conditions into a function valid for non-steady state conditions. It involves an additional parameter which accounts for change in soil water storage. Compared to previous formulations it gives similar results as the analytical solution of Greve et al. (2016). However, the domain of variation of the new formulation differs from those of Chen et al. (2013) and Du et al. (2016).

Description: Effect of restoration vegetation on the stochasticity of soil erosion in a semi-arid environment Ji Zhou, Bojie Fu, Guangyao Gao, Yihe Lü, and Shuai Wang Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-386,2016 Manuscript under review for HESS (discussion: open, 0 comments) By monitoring soil erosion in the Loess Plateau, we constructed an integrated analysis system to quantify the stochasticity of environment, found that the morphological structures in vegetation types are the source of different stochasticities of soil erosion, and proved that Poisson model is fit for predicting erosion stochasticity at larger temporal scale. This study could be meaningful for the selection of restoration vegetation for conserving soil and water resources in the Loess Plateau.

Description: Assessing land–ocean connectivity via submarine groundwater discharge (SGD) in the Ria Formosa Lagoon (Portugal): combining radon measurements and stable isotope hydrology Carlos Rocha, Cristina Veiga-Pires, Jan Scholten, Kay Knoeller, Darren R. Gröcke, Liliana Carvalho, Jaime Anibal, and Jean Wilson Hydrol. Earth Syst. Sci., 20, 3077-3098, doi:10.5194/hess-20-3077-2016, 2016 We combine radon and stable isotopes in water to determine total submarine groundwater discharge (SGD) in the Ria Formosa and discriminate its component modes. We show that tidal action filters the entire water volume in the lagoon through local beaches 3.5 times a year, driving an estimated 350Ton nitrogen/year into the system. Conversely, fresh groundwater is discharged into the lagoon only occasionally, adding ~ 61 Ton nitrogen/year, but is capable of driving new production in the system.

Description: Variation of soil hydraulic properties with alpine grassland degradation in the Eastern Tibetan Plateau Tao Pan, Shuai Hou, Shaohong Wu, Yanhua Liu, Xintong Zou, Anna Herzberger, and Jianguo Liu Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-333,2016 Manuscript under review for HESS (discussion: open, 0 comments) The study show that soil hydraulic properties, especially those of the top soil, varied greatly with alpine swamp meadow degradation. Soil porosity is the dominant influencing factor of soil hydraulic properties. The results suggest that alpine swamp meadow degradation would inevitably lead to negative hydrological effects. Hydrological modelling in Tibetan Plateau and similar regions are recommended to understand the effects of degradation on soil hydraulic properties.

Description: Contrasting transit times of water from peatlands and eucalypt forests in the Australian Alps determined by tritium: implications for vulnerability and the source of water in upland catchments I. Cartwright and U. Morgenstern Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-361,2016 Manuscript under review for HESS (discussion: open, 0 comments) This research determines timescales over which water is stored in peatlands and adjacent eucalyptus forest catchments in upland river systems in southeast Australia using tritium. The mean transit times in the peatland catchments were in many cases less than one year which contrasts with the longer transit times (years to decades) in the eucalyptus catchments. The results indicate that the peat is susceptible to drying which renders it vulnerable to degradation and bushfire.

Description: Acclimatizing Fast Orthogonal Search (FOS) Model for River Stream-flow Forecasting Abdalla Osman, Mohammed Falah Allawi, Haitham Abdulmohsin Afan, Aboelmagd Noureldin, and Ahmed El-shafie Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-347,2016 Manuscript under review for HESS (discussion: open, 0 comments) The current research is significant not only for researchers but also for decision-makers for water resources system management more specifically for dam and reservoir operations. Fast Orthogonal Search (FOS) model might result in a system that could be used in several river basins. Supported by efficient FOS-based pattern recognition model, accurate information about future river stream flow could be utilized by the decision-maker to formulate better water resources system management.

Description: Willingness-to-pay for a probabilistic flood forecast: a risk-based decision-making game Louise Arnal, Maria-Helena Ramos, Erin Coughlan de Perez, Hannah Louise Cloke, Elisabeth Stephens, Fredrik Wetterhall, Schalk Jan van Andel, and Florian Pappenberger Hydrol. Earth Syst. Sci., 20, 3109-3128, doi:10.5194/hess-20-3109-2016, 2016 Forecasts are produced as probabilities of occurrence of specific events, which is both an added value and a challenge for users. This paper presents a game on flood protection, "How much are you prepared to pay for a forecast?", which investigated how users perceive the value of forecasts and are willing to pay for them when making decisions. It shows that users are mainly influenced by the perceived quality of the forecasts, their need for the information and their degree of risk tolerance.

Description: Real-time monitoring of nitrate transport in the deep vadose zone under a crop field – implications for groundwater protection Tuvia Turkeltaub, Daniel Kurtzman, and Ofer Dahan Hydrol. Earth Syst. Sci., 20, 3099-3108, doi:10.5194/hess-20-3099-2016, 2016 Efficient groundwater protection from pollution originating in agriculture requires effective monitoring means capable of tacking pollution processes in the vadose zone, long before groundwater pollution turns into an unavoidable fact. In this study, a vadose zone monitoring system that was installed under a crop field fertilized by dairy slurry enabled real-time tracking of nitrate plum migration down the vadose zone from the land surface to the water table at 18m depth.

Description: Fresh groundwater resources in a large sand replenishment Sebastian Huizer, Gualbert H. P. Oude Essink, and Marc F. P. Bierkens Hydrol. Earth Syst. Sci., 20, 3149-3166, doi:10.5194/hess-20-3149-2016, 2016 The anticipation of sea-level rise has led to an innovative project called the Sand Engine, where a large volume of sand was placed on the Dutch coast. The intention is that the sand is redistributed by wind, current and tide, reinforcing coastal defence structures. Model simulations show that this large sand replenishment can result in a substantial growth of fresh groundwater resources. Thus, sand replenishments could combine coastal protection with an increase of fresh groundwater resources.

Description: CFSv2-based sub-seasonal precipitation and temperature forecast skill over the contiguous United States Di Tian, Eric F. Wood, and Xing Yuan Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-376,2016 Manuscript under review for HESS (discussion: open, 0 comments) Forecasts from global seasonal climate forecast models can be potentially exploited for sub-seasonal forecasts of precipitation and 2-m temperature. The probabilistic sub-seasonal forecast skill of ten precipitation and temperature indices is investigated using the 28-years’ hindcasts of the Climate Forecast System version 2 (CFSv2) over the contiguous United States (CONUS). The forecast skill is highly dependent on the forecast indices, regions, seasons, leads, and methods. Indices characterizing mean precipitation and temperature as well as measuring frequency or duration of precipitation and temperature extremes for 7-, 14-, and 30-day forecasts were skillful depending on seasons, regions, and forecast leads. Forecasts for 7- and 14-day temperature indices showed skill even at weeks 3 and 4, and generally more skillful than precipitation indices. Overall, temperature indices showed higher skill than precipitation indices over the entire CONUS region. While the forecast skill related to mean precipitation indices were low in summer over the CONUS, the number of rainy days, number of consecutive rainy days, and the number of consecutive dry days showed considerable high skill for the west coast region. The 30-day forecasts of precipitation and temperature indices calculated from the downscaled monthly CFSv2 forecasts are less skillful than those calculated from the daily CFSv2 forecasts, suggesting the potential usefulness of the CFSv2 daily forecasts for hydrological applications relative to the temporally disaggregated CFSv2 monthly forecasts. While the presence of active Madden-Julian Oscillation (MJO) events improves CFSv2 weekly mean precipitation forecast skill over major areas of CONUS, MJO or El Niño Southern Oscillation did not have same strong effects on weekly mean temperature forecasts.

Description: Gauge-Adjusted Rainfall Estimates from Commercial Microwave Links Martin Fencl, Michal Dohnal, Jörg Rieckermann, and Vojtěch Bareš Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-397,2016 Manuscript under review for HESS (discussion: open, 0 comments) Commercial microwave links (CMLs) can provide rainfall observations with high space-time resolution. Unfortunately, CML rainfall estimates are usually biased because we lack detailed information on the processes which attenuate the transmitted microwaves. We suggest removing the bias by dynamically adjusting CMLs to cumulative data from rain gauges (RGs), which can be remote from the CMLs. Our approach practically eliminates the bias, which we demonstrate on unique data from several CMLs a RGs.

Description: The socioecohydrology of rainwater harvesting in India: understanding water storage and release dynamics across spatial scales Kimberly J. Van Meter, Michael Steiff, Daniel L. McLaughlin, and Nandita B. Basu Hydrol. Earth Syst. Sci., 20, 2629-2647, doi:10.5194/hess-20-2629-2016, 2016 Although village-scale rainwater harvesting (RWH) structures have been used for millennia in India, many of these structures have fallen into disrepair due to increased dependence on groundwater. This dependence has contributed to declines in groundwater resources, and in turn to efforts to revive older RWH systems. In the present study, we use field data to quantify water fluxes in a cascade of irrigation tanks to better our understanding of the impact of RWH systems on the water balance in con

Description: Comparison of uncertainty in multi-parameter and multi-model ensemble hydrologic analysis of climate change Younggu Her, Seung-Hwan Yoo, Chounghyun Seong, Jaehak Jeong, Jaepil Cho, and Syewoon Hwang Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-160,2016 Manuscript under review for HESS (discussion: open, 0 comments) This study demonstrated that the significance of GCM and hydrological parameter selection varied depending on the hydrologic components (e.g. direct runoff, soil moisture, and baseflow) of interest and the thresholds used to identify the behavioral parameter sets in a hydrologic analysis of climate change. A newly proposed analysis strategy enabled to investigate the contributions of each GCM to the overall uncertainty in a multi-GCM ensemble for hydrologic analysis.

Description: Towards a tracer-based conceptualization of meltwater dynamics and streamflow response in a glacierized catchment Daniele Penna, Michael Engel, Giacomo Bertoldi, and Francesco Comiti Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-334,2016 Manuscript under review for HESS (discussion: open, 0 comments) In this research we used environmental tracers in the Saldur River catchment, Italian Alps to obtain new insight into the hydrology of glacierized catchments. We analysed the spatio-temporal variability of the tracer signature within the catchment, distinguished the contribution of groundwater, glacier melt and snowmelt to stream discharge, identified the sources of uncertainty in the estimation of streamflow components and presented a paradigm of hydrological function of glacierized catchments.

Description: Estimation of flood warning runoff thresholds in ungauged basins with asymmetric error functions Elena Toth Hydrol. Earth Syst. Sci., 20, 2383-2394, doi:10.5194/hess-20-2383-2016, 2016 Runoff thresholds for activating flood warnings might be estimated with regionally derived relationships between catchment descriptors and assigned flood quantiles. Since the consequences of overestimated thresholds (leading to missing alarms) are generally more severe than those of an underestimation (leading to false alarms), the work proposes to parameterise the regression model with an asymmetric error function, instead of using a traditional, symmetric square errors sum.

Description: Comment on "Using groundwater age and hydrochemistry to understand sources and dynamics of nutrient contamination through the catchment into Lake Rotorua, New Zealand" by Morgenstern et al. (2015) Jonathan M. Abell, David P. Hamilton, and Christopher G. McBride Hydrol. Earth Syst. Sci., 20, 2395-2401, doi:10.5194/hess-20-2395-2016, 2016 We comment on "Using groundwater age and hydrochemistry to understand sources and dynamics of nutrient contamination through the catchment into Lake Rotorua, New Zealand" by Morgenstern et al. (2015). They propose that "the only effective way to limit algae blooms and improve lake water quality in such environments is by limiting the nitrate load". We outline four reasons why it is important to instead limit both phosphorus and nitrogen loads to this iconic lake, consistent with current policy.

Description: EnKF with closed-eye period – towards a consistent aggregation of information in soil hydrology Hannes H. Bauser, Stefan Jaumann, Daniel Berg, and Kurt Roth Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-296,2016 Manuscript under review for HESS (discussion: open, 0 comments) The representation of soil water movement comes with uncertainties in all model components. We assess the key uncertainties for the case of a one-dimensional soil profile with measured water contents. We employ a data assimilation method to represent and reduce the key uncertainties. For intermittent phases where model assumptions are violated, we introduce a "closed-eye period" to bridge the gap. We also demonstrate the need to include heterogeneity.

Description: The cumulative effects of forest disturbance and climate variability on baseflow in a large watershed in British Columbia, Canada Qiang Li, Xiaohua Wei, Mingfang Zhang, Wenfei Liu, Krysta Giles-Hansen, Yi Wang, and Liangliang Duan Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-291,2016 Manuscript under review for HESS (discussion: open, 0 comments) Assessing how forest disturbance and climate change affect baseflow or groundwater discharge is critical for understanding water resource supply and protecting aquatic functions. Previous studies have mainly evaluated the effects of forest disturbance on streamflow, with rare attention on baseflow, particularly in large watersheds. However, studying this topic is challenging as it requires explicit inclusion of climate into assessment due to their interactions at any large watersheds. In this study, we used Upper Similkameen River watershed (USR) (1810 km 2 ), located in the southern interior of British Columbia, Canada to examine how forest disturbance and climate variability affect baseflow. The conductivity mass balance method was first used for baseflow separation, and the modified double mass curves were then employed to quantitatively separate the relative contributions of forest disturbance and climate variability to annual baseflow. Our results showed that average annual baseflow and baseflow index (baseflow/streamflow) were about 85.2 ± 21.5 mm year -1 and 0.22 ± 0.05 for the study period of 1954–2013, respectively. The forest disturbance increased the annual baseflow of 18.4 mm, while climate variability decreased 19.4 mm. In addition, forest disturbance also shifted the baseflow regime with increasing of the spring baseflow and decreasing of the summer baseflow. We conclude that forest disturbance significantly altered the baseflow magnitudes and patterns, and its role in annual baseflow was equal to that caused by climate variability in the study watershed despite their opposite changing directions. The implications of our results are discussed in the context of future forest disturbance (or land cover changes) and climate changes.

Description: Geostatistical upscaling of rain gauge data to support uncertainty analysis of lumped urban hydrological models Manoranjan Muthusamy, Alma Schellart, Simon Tait, and Gerard B. M. Heuvelink Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-279,2016 Manuscript under review for HESS (discussion: open, 0 comments) In this study we develop a method to estimate the spatially averaged rainfall intensity together with associated level of uncertainty using geostatistical upscaling. Rainfall data collected from a cluster of eight paired rain gauges in a small urban catchment are used in this study. Results show that the prediction uncertainty comes mainly from two sources: spatial variability of rainfall and measurement error. Results from this study can be used for uncertainty analyses of hydrologic modelling.

Description: Improvement of hydrological model calibration by selecting multiple parameter ranges Qiaofeng Wu, Shuguang Liu, Yi Cai, Xinjian Li, and Yangming Jiang Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-275,2016 Manuscript under review for HESS (discussion: open, 0 comments) We proposed a method to calibrate the hydrological model by selecting parameter range. The results show the probability distribution can be used to determine the optimal range of single parameter. Analysis of parameter sensitivity and correlation is helpful to obtain the optimal combination of multi-parameter ranges which contributes to a higher and more concentrated value of the objective function. The findings can provide references for enhancing the precision of hydrological process modeling.

Description: Water budget modelling of the Upper Blue Nile basin using the JGrass-NewAge model system and satellite data Wuletawu Abera, Giuseppe Formetta, Luca Brocca, and Riccardo Rigon Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-290,2016 Manuscript under review for HESS (discussion: open, 0 comments) This study documented state-of-art in estimating water resource spatially by combining remote sensing, in situ data and hydrological model. It shows that the model is useful for estimating various water balance components (discharge, evapotranspiration, and storage) spatially given a few in situ observation available. The study is applied in the Upper Blue Nile basin where hydrological information is very scarce and these results can be used as baseline data for any activities in the region.

Description: Hydraulic and transport parameter assessment using column infiltration experiments A. Younes, T. A. Mara, M. Fahs, O. Grunenberger, and Ph. Ackerer Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-295,2016 Manuscript under review for HESS (discussion: open, 0 comments) In the present work, we study the quality of the statistical calibration of hydraulic and transport soil properties using an infiltration experiment in which, over a given period, tracer-contaminated water is injected into a laboratory column filled with a homogeneous soil. The numerical model is based on the Richards' equation for solving water flow and the advection-dispersion equation for solving solute transport. Several state variables (e.g., water content, solute concentration, pressure head) are measured during the experiment. Statistical calibration of the computer model is then carried out for different data sets and injection scenarios with the DREAM (ZS) Markov Chain Monte Carlo sampler. The results show that the injection period has a significant effect on the quality of the estimation, in particular, the posterior uncertainty range. The hydraulic and transport parameters of the investigated soil can be estimated from the infiltration experiment using the concentration and cumulative outflow, which are measured non-intrusively. A significant improvement of the identifiability of the parameters is observed when the pressure data from measurements taken inside the column are also considered in the inversion.

Description: Estimating extreme river discharges in Europe through a Bayesian Network Dominik Paprotny and Oswaldo Morales Nápoles Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-250,2016 Manuscript under review for HESS (discussion: open, 0 comments) Large-scale hydrological modelling of flood hazard requires adequate extreme discharge data. Models based on physics are applied alongside those utilizing only statistical analysis. The former requires enormous computation power, while the latter are most limited in accuracy and spatial coverage. In this paper we introduce an alternate, statistical approach based on Bayesian Networks (BN), a graphical model for dependent random variables. We use a non-parametric BN to describe the joint distribution of extreme discharges in European rivers and variables describing the geographical characteristics of their catchments. Data on annual maxima of daily discharges from more than 1800 river gauge stations were collected, together with information on terrain, land use and climate of catchments that drain to those locations. The (conditional) correlations between the variables are modelled through copulas, with the dependency structure defined in the network. The results show that using this method, mean annual maxima and return periods of discharges could be estimated with an accuracy similar to existing studies using physical models for Europe, and better than a comparable global statistical method. Performance of the model varies slightly between regions of Europe, but is consistent between different time periods, and is not affected by a split-sample validation. The BN was applied to a large domain covering all sizes of rivers in the continent, both for present and future climate, showing large variation in influence of climate change on river discharges, as well as large differences between emission scenarios. The method could be used to provide quick estimates of extreme discharges at any location for the purpose of obtaining input information for hydraulic modelling.

Description: Characteristics of rainfall events in RCM simulations for the Czech Republic Vojtěch Svoboda, Martin Hanel, Petr Máca, and Jan Kyselý Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-283,2016 Manuscript under review for HESS (discussion: open, 0 comments) The study presents validation of precipitation events as simulated by an ensemble of regional climate models for the Czech Republic. While the number of events per season, seasonal total precipitation due to heavy events and the distribution of rainfall depths is simulated relatively well, event maximum precipitation and event intensity are strongly underestimated. This underestimation cannot be explained by scale mismatch between point observations and area average (climate model simulations).

Description: Rapid attribution of the May/June 2016 flood-inducing precipitation in France and Germany to climate change Geert Jan van Oldenborgh, Sjoukje Philip, Emma Aalbers, Robert Vautard, Friederike Otto, Karsten Haustein, Florence Habets, Roop Singh, and Heidi Cullen Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-308,2016 Manuscript under review for HESS (discussion: open, 0 comments) Extreme rain caused flooding in France and Germany at the end of May 2016. After such an event the question is always posed to what extent it can be attributed to anthropogenic climate change. Using observations and five model ensembles we give a first answer. For the 3-day precipitation extremes over the Seine and Loire basins that caused the flooding all methods agree that the probability has increased by a factor of about two. For 1-day precipitation extremes in Germany the methods disagree.

Description: Can local climate variability be explained by weather patterns? A multi-station evaluation for the Rhine basin Aline Murawski, Gerd Bürger, Sergiy Vorogushyn, and Bruno Merz Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-286,2016 Manuscript under review for HESS (discussion: open, 0 comments) For understanding past flood changes in the Rhine catchment and the role of anthropogenic climate change for extreme flows, an attribution study relying on a proper GCM (General Circulation Model) downscaling is needed. A downscaling based on conditioning a stochastic weather generator on weather patterns is a promising approach. Here the link between patterns and local climate is tested, and the skill of GCMs to reproduce these patterns is evaluated.

Description: Evaluating the streamflow simulation capability of PERSIANN-CDR daily rainfall products in two river basins on the Tibetan Plateau Xiaomang Liu, Tiantian Yang, Koulin Hsu, Changming Liu, and Soroosh Sorooshian Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-282,2016 Manuscript under review for HESS (discussion: open, 0 comments) A long-term, global, high-resolution, satellite-based precipitation estimation database (PERSIANN-CDR) was recently released. We evaluate the streamflow simulation capability of PERSIANN-CDR over two major river basins on the Tibetan Plateau. Results show that PERSIANN-CDR is a good alternative for sparse gauge-network and has the potentials for future hydrological and climate studies. The streamflow uncertainties are due to the hydrological model parameters and the length of calibration data.

Description: Rainfall erosivity in catchments contaminated with fallout from the Fukushima Daiichi nuclear power plant accident J. Patrick Laceby, Caroline Chartin, Olivier Evrard, Yuichi Onda, Laurent Garcia-Sanchez, and Olivier Cerdan Hydrol. Earth Syst. Sci., 20, 2467-2482, doi:10.5194/hess-20-2467-2016, 2016 Characterizing rainfall erosivity in the Fukushima fallout-impacted region is important for predicting radiocesium behavior. The majority of rainfall (60 %) and rainfall erosivity (86 %) occurs between June and October. Tropical cyclones contribute 22 % of the precipitation though 44 % of the rainfall erosivity. Understanding the rainfall regime and the influence of tropical cyclones is important managing radiocesium transfers in contaminated catchments in the Fukushima prefecture.

Description: Application of CryoSat-2 altimetry data for river analysis and modelling Raphael Schneider, Peter Nygaard Godiksen, Heidi Villadsen, Henrik Madsen, and Peter Bauer-Gottwein Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-243,2016 Manuscript under review for HESS (discussion: open, 0 comments) We use water level observations from CryoSat-2 in combination with a river model of the Brahmaputra River, extracting satellite data over a dynamic river mask derived from Landsat imagery. The novelty of this work is the use of the CryoSat-2 satellite water level observations, collected using a complex spatio-temporal sampling scheme, to calibrate a hydrodynamic river model. The resulting model accurately reproduces water levels, without precise knowledge of river bathymetry.

Description: Quantifying uncertainty on sediment loads using bootstrap confidence intervals Johanna I. F. Slaets, Hans-Peter Piepho, Petra Schmitter, Thomas Hilger, and Georg Cadisch Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-264,2016 Manuscript under review for HESS (discussion: open, 0 comments) Determining measures of uncertainty on loads is not trivial, as a load is a product of concentration and discharge per time point, summed up over time. A bootstrap based approach was developed which enables the calculation of confidence intervals on constituent loads. Ignoring the uncertainty on the discharge will typically underestimate the width of 95 % confidence intervals with around 10 %. Furthermore, confidence intervals are asymmetric with the largest uncertainty on the upper limit.

Description: Estimation of surface energy fluxes in the Arctic tundra using the remote sensing thermal-based Two-Source Energy Balance model Jordi Cristóbal, Anupma Prakash, Martha C. Anderson, William P. Kustas, Eugénie S. Euskirchen, and Douglas L. Kane Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-257,2016 Manuscript under review for HESS (discussion: open, 0 comments) Quantifying trends in surface energy fluxes is crucial to forecast ecological responses in Arctic regions. An extensive evaluation using a thermal-based remote sensing model and ground measurements was performed in Alaska's Arctic tundra for 5 years. Results showed an accurate temporal trend of surface energy fluxes in concert with vegetation dynamics. This work builds toward a regional implementation over Arctic ecosystems to assess response of surface energy fluxes to climate change.

Description: Modelling evapotranspiration during precipitation deficits: identifying critical processes in a land surface model Anna M. Ukkola, Andy J. Pitman, Mark Decker, Martin G. De Kauwe, Gab Abramowitz, Jatin Kala, and Ying-Ping Wang Hydrol. Earth Syst. Sci., 20, 2403-2419, doi:10.5194/hess-20-2403-2016, 2016 Surface fluxes from land surface models (LSMs) have traditionally been evaluated against monthly, seasonal or annual mean states. The limited ability of LSMs to reproduce observed evaporative fluxes under water-stressed conditions has been previously noted, but very few studies have systematically evaluated these models during rainfall deficits. We evaluated latent heat fluxes simulated by the Community Atmosphere Biosphere Land Exchange (CABLE) LSM across 20 flux tower sites at sub-annual to inter-annual timescales, in particular focusing on model performance during seasonal-scale rainfall deficits. The importance of key model processes in capturing the latent heat flux was explored by employing alternative representations of hydrology, leaf area index, soil properties and stomatal conductance. We found that the representation of hydrological processes was critical for capturing observed declines in latent heat during rainfall deficits. By contrast, the effects of soil properties, LAI and stomatal conductance were highly site-specific. Whilst the standard model performs reasonably well at annual scales as measured by common metrics, it grossly underestimates latent heat during rainfall deficits. A new version of CABLE, with a more physically consistent representation of hydrology, captures the variation in the latent heat flux during seasonal-scale rainfall deficits better than earlier versions, but remaining biases point to future research needs. Our results highlight the importance of evaluating LSMs under water-stressed conditions and across multiple plant functional types and climate regimes.

Description: An experimental seasonal hydrological forecasting system over the Yellow River basin – Part 2: The added value from climate forecast models Xing Yuan Hydrol. Earth Syst. Sci., 20, 2453-2466, doi:10.5194/hess-20-2453-2016, 2016 This paper evaluates the added value from climate forecast models over the Yellow River basin. Without considering the errors in hydrological models, the climate-model-based seasonal hydrological forecasts show higher skill than the climatological forecasts, especially during the rainy season. The improvement decreases especially at short leads when the post-processed forecasts are verified against observed streamflow, and the added value mainly exists in the transition from wet to dry seasons.

Description: An experimental seasonal hydrological forecasting system over the Yellow River basin – Part 1: Understanding the role of initial hydrological conditions Xing Yuan, Feng Ma, Linying Wang, Ziyan Zheng, Zhuguo Ma, Aizhong Ye, and Shaoming Peng Hydrol. Earth Syst. Sci., 20, 2437-2451, doi:10.5194/hess-20-2437-2016, 2016 An experimental seasonal hydrological forecasting system is established over the Yellow River basin to provide adaptive support in a changing environment. The system consists of downscaled NMME climate prediction, hydrological models calibrated against naturalized streamflow along the mainstream, and a post-processor to account for the human interventions implicitly. As the first paper of a two-part series, this paper investigates the hydrological predictability by using reverse ESP simulations.

Description: Technical Note: Monitoring of unsteady open channel flows using continuous slope-area method Kyutae Lee, Ali R. Firoozfar, and Marian Muste Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-289,2016 Manuscript under review for HESS (discussion: open, 0 comments) Accurate estimation of stream/river flows is important for the public safety during floods as well as for the efficient use of limited water resources for hydropower generation and irrigation. In this paper, we have investigated a feasibility of the continuous slope area (CSA) method which utilizes the measurements of instantaneous water surface elevation changes, and the results showed promising capabilities of the suggested method for the accurate estimation of flows in natural streams/rivers.

Description: Modelling stream flow with a discrete rainfall–runoff model and 37 GHz PDBT microwave observations: the Xiangjiang River basin case study Haolu Shang, Massimo Menenti, and Li Jia Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-129,2016 Manuscript under review for HESS (discussion: open, 0 comments) The key point of the discrete rainfall–runoff model is to consider the temporal differences in the redisctribution of precipitation in a catchment through the weights and the duration of antecedent precipiation. The wetness conditions at the upper and lower boundaries of soil layer are the key parameters to describe regional moisture condition. The interannual variations in model weights indicates the different catchment response between dry and wet years.

Description: Analysis of the drought recovery of Andosols on southern Ecuadorian Andean páramos Vicente Iñiguez, Oscar Morales, Felipe Cisneros, Willy Bauwens, and Guido Wyseure Hydrol. Earth Syst. Sci., 20, 2421-2435, doi:10.5194/hess-20-2421-2016, 2016 The drought recovery of the soils in Neotropical Andean grasslands above 3500 m a.s.l. known as "páramo" was studied in this paper. The main aim was to estimate the recovery speed of the páramo soils after drought periods. A typical catchment on the páramo at 3500 m a.s.l. was compared to a lower grassland one at 2600 m a.s.l. The study revealed that, at the plot scale, the soil moisture drought recovery was higher in the páramo. At the catchment scale, however, was not as pronounced.