ALBERT

Description: Two hydrological models with different structures and spatial capabilities are selected to simulate the runoff and actual evapotranspiration (AET) in Yingluoxia watershed, the upper reaches of Heihe River basin in northwest of China, to validate their performances in simulating hydrological processes. They are calibrated against the observed runoff at the watershed outlet (Yingluoxia station) for the period from 1990 to 1996 and validated for the period from 1997 to 2000. Results show that in terms of the simulated hydrograph against observations and the two selected objective functions, the conceptual, lumped Water And Snow balance MODeling system (WASMOD) with simple model structure could give the same, even better results than the semi-distributed Soil and Water Assessment Tool (SWAT) with complex structure. Compared with other model applications to the watershed, simulation for monthly runoff made in this study seems better. With regard to AET, results calculated from both models are comparable as well. Both WASMOD and SWAT are proved to be suitable and satisfactory tools in simulating hydrological processes in the study area, although both of them have strengths and limitations in applications. WASMOD model may be one of the promising alternatives in hydrological modelling. © 2010 John Wiley & Sons, Ltd.

Description: Digital elevation models (DEMs) at different resolutions (180, 360, and 720 m) are used to examine the impact of different levels of landscape representation on the hydrological response of a 690-km2 catchment in southern Quebec. Frequency distributions of local slope, plan curvature, and drainage area are calculated for each grid size resolution. This landscape analysis reveals that DEM grid size significantly affects computed topographic attributes, which in turn explains some of the differences in the hydrological simulations. The simulations that are then carried out, using a coupled, process-based model of surface and subsurface flow, examine the effects of grid size on both the integrated response of the catchment (discharge at the main outlet and at two internal points) and the distributed response (water table depth, surface saturation, and soil water storage). The results indicate that discharge volumes increase as the DEM is coarsened, and that coarser DEMs are also wetter overall in terms of water table depth and soil water storage. The reasons for these trends include an increase in the total drainage area of the catchment for larger DEM cell sizes, due to aggregation effects at the boundary cells of the catchment, and to a decrease in local slope and plan curvature variations, which in turn limits the capacity of the watershed to transmit water downslope and laterally. The results obtained also show that grid resolution effects are less pronounced during dry periods when soil moisture dynamics are mostly controlled by vertical fluxes of evaporation and percolation. © 2010 John Wiley & Sons, Ltd.

Description: Tropical montane cloud forests (TMCF) typically experience conditions of frequent to persistent fog. On the basis of the altitudinal limits between which TMCF generally occur (800-3500 m.a.s.l. depending on mountain size and distance to coast) their current areal extent is estimated at ∼215 000 km2 or 6·6% of all montane tropical forests. Alternatively, on the basis of remotely sensed frequencies of cloud occurrence, fog-affected forest may occupy as much as 2·21 Mkm2. Four hydrologically distinct montane forest types may be distinguished, viz. lower montane rain forest below the cloud belt (LMRF), tall lower montane cloud forest (LMCF), upper montane cloud forest (UMCF) of intermediate stature and a group that combines stunted sub-alpine cloud forest (SACF) and 'elfin' cloud forest (ECF). Average throughfall to precipitation ratios increase from 0·72 ± 0·07 in LMRF (n = 15) to 0·81 ± 0·11 in LMCF (n = 23), to 1·0 ± 0·27 (n = 18) and 1·04 ± 0·25 (n = 8) in UMCF and SACF-ECF, respectively. Average stemflow fractions increase from LMRF to UMCF and ECF, whereas leaf area index (LAI) and annual evapotranspiration (ET) decrease along the same sequence. Although the data sets for UMCF (n = 3) and ECF (n = 2) are very limited, the ET from UMCF (783 ± 112 mm) and ECF (547 ± 25 mm) is distinctly lower than that from LMCF (1188 ± 239 mm, n = 9) and LMRF (1280 ± 72 mm; n = 7). Field-measured annual 'cloud-water' interception (CWI) totals determined with the wet-canopy water budget method (WCWB) vary widely between locations and range between 22 and 1990 mm (n = 15). Field measured values also tend to be much larger than modelled amounts of fog interception, particularly at exposed sites. This is thought to reflect a combination of potential model limitations, a mismatch between the scale at which the model was applied (1 × 1 km) and the scale of the measurements (small plots), as well as the inclusion of near-horizontal wind-driven precipitation in the WCWB-based estimate of CWI. Regional maps of modelled amounts of fog interception across the tropics are presented, showing major spatial variability. Modelled contributions by CWI make up less than 5% of total precipitation in wet areas to more than 75% in low-rainfall areas. Catchment water yields typically increase from LMRF to UMCF and SACF-ECF reflecting concurrent increases in incident precipitation and decreases in evaporative losses. The conversion of LMCF (or LMRF) to pasture likely results in substantial increases in water yield. Changes in water yield after UMCF conversion are probably modest due to trade-offs between concurrent changes in ET and CWI. General circulation model (GCM)-projected rates of climatic drying under SRES greenhouse gas scenarios to the year 2050 are considered to have a profound effect on TMCF hydrological functioning and ecology, although different GCMs produce different and sometimes opposing results. Whilst there have been substantial increases in our understanding of the hydrological processes operating in TMCF, additional research is needed to improve the quantification of occult precipitation inputs (CWI and wind-driven precipitation), and to better understand the hydrological impacts of climate- and land-use change. Copyright © 2010 John Wiley & Sons, Ltd.

Description: Two analyses, one based on multiple regression and the other using the Holt-Winters algorithm, for investigating non-stationarity in environmental time series are presented. They are applied to monthly rainfall and average maximum temperature time series of lengths between 38 and 108 years, from six stations in the Murray Darling Basin and four cities in eastern Australia. The first analysis focuses on the residuals after fitting regression models which allow for seasonal variation, the Pacific Decadal Oscillation (PDO) and the Southern Oscillation Index (SOI). The models provided evidence that rainfall is reduced during periods of negative SOI, and that the interaction between PDO and SOI pronounces this effect during periods of negative PDO. Following this, there was no evidence of any trend in either the PDO or SOI time series. The residuals from this regression were analysed with a cumulative sum (CUSUM) technique, and the statistical significance was assessed using a Monte Carlo method. The residuals were also analysed for volatility, autocorrelation, long-range dependence and spatial correlation. For all ten rainfall and temperature time series, CUSUM plots of the residuals provided evidence of non-stationarity for both temperature and rainfall, after removing seasonal effects and the effects of PDO and SOI. Rainfall was generally lower in the first half of the twentieth century and higher during the second half. However, it decreased again over the last 10 years. This pattern was highlighted with 5-year moving average plots. The residuals for temperature showed a complementary pattern with increases in temperature corresponding to decreased rainfall. The second analysis decomposed the rainfall and temperature time series into random variation about an underlying level, trend and additive seasonal effects and changes in the level; trend and seasonal effects were tracked using a Holt-Winters algorithm. The results of this analysis were qualitatively similar to those of the regression analysis. © 2010 John Wiley & Sons, Ltd.

Description: For large-scale sites, difficulties for applying coupled one-dimensional (1D)/2D models for simulating floodplain inundation may be encountered related to data scarcity, complexity for establishing channel-floodplain connections, computational cost, long duration of floods and the need to represent precipitation and evapotranspiration processes. This paper presents a hydrologic simulation system, named SIRIPLAN, developed to accomplish this aim. This system is composed by a 1D hydrodynamic model coupled to a 2D raster-based model, and by two modules to compute the vertical water balance over floodplain and the water exchanges between channel and floodplain. Results are presented for the Upper Paraguay River Basin (UPRB), including the Pantanal, one of the world's largest wetlands. A total of 3965 km of river channels and 140 000 km2 of floodplains are simulated for a period of 11 years. Comparison of observed and calculated hydrographs at 15 gauging stations showed that the model was capable to simulate distinct, complex flow regimes along main channels, including channel-floodplain interactions. The proposed system was also able to reproduce the Pantanal seasonal flood pulse, with estimated inundated areas ranging from 35 000 km2 (dry period) to more than 120 000 km2 (wet period). Floodplain inundation maps obtained with SIRIPLAN were consistent with previous knowledge of Pantanal dynamics, but comparison with inundation extent provided by a previous satellite-based study indicates that permanently flooded areas may have been underestimated. The results obtained are promising, and further work will focus on improving vertical processes representation over floodplains and analysing model sensitivity to floodplain parameters, time step and precipitation estimates uncertainty. © 2010 John Wiley & Sons, Ltd.

Description: The paper presents the development of a lumped conceptual rainfall-runoff model [Transformation of rainfall to runoff, Variability across timescales and Model parsimonization (TVM)] and a series of tests on various levels of model structure at different time resolutions. It is applied to the Bradford catchment in the United Kingdom. The TVM model is developed with a flexible structure through various relationships in each module that can be modified depending on the study catchments. Adopting the downward approach, parsimonious models are developed to examine at what level of complexity the model is able to capture runoff variability. The approach aims to compromise between parsimonious and complex alternatives in model development. This study shows that model structure requires data at different aggregation levels of timescales depending on its complexity. It reveals that the absence of the infiltration excess strongly affected all models. The analysis shows that the time resolution of hourly downwards must be used for the study catchment. The investigation of model complexity indicates that the combination of the most complicated model structure and timescale of quarter-hourly is adequate to capture the catchment runoff characteristics. The downward approach in the TVM model helps to gain a deeper understanding of water balance and runoff process in the study catchment. The approach could be applicable to other catchments to obtain parsimonious models. © 2010 John Wiley & Sons, Ltd.

Description: Darcian flow law in aquifers assumes that the aquifer hydraulic conductivity is constant and the groundwater movement is due only to the piezometric level changes through hydraulic gradient. In practice, after the well development the aquifer just around the well has comparatively larger hydraulic conductivity and gradient. Patchy aquifer solutions in the literature consider sudden hydraulic conductivity changes with distance for the steady state flow. The change of transmissivity is demonstrated by the application of slope-matching procedure to actual field data. It is the main purpose of this paper to derive simple analytical expressions for aquifer parameter evaluations with steadily decreasing hydraulic conductivity around the well. Spatial nonlinear hydraulic conductivity changes around a large-diameter well within the depression cone of a confined aquifer are considered as exponentially decreasing functions of the radial distance. © 2010 John Wiley & Sons, Ltd.

Description: This study used hourly data of rainfall, water captured by a sheltered fog gauge and wind speed as collected at a montane forest site in northern Thailand during nearly 3 years to test the efficiency of the rain-protected passive fog gauge as a predictor of fog occurrence. To separate possible contributions by wind-driven rain (WDR) from fog, the maximum rate of water input to the fog gauge during rainless periods (Fogmax) was derived as a function of wind speed. During periods with rain and fog, the fog gauge often produced values above the Fogmax line, suggesting contributions by WDR. The specific conditions of rainfall intensity and wind speed under which this happened were identified and the corresponding data were excluded from the fog data-set for subsequent reanalysis. Based on the recalculated data-set, inter-annual and seasonal variations as well as the diurnal pattern of fog occurrence at the studied forest are described. Fog-induced canopy drip during rainless periods was only 19·3 mm over the 3 years, being less than 0·5% of total throughfall and ∼33% of the corresponding catch by the fog gauge (58 mm). However, the fog gauge captured nearly 18 times more water (1033 mm) during all times when WDR could reasonably be excluded. Copyright © 2010 John Wiley & Sons, Ltd.

Description: A characterization of hyporheic exchange for dry and wet season baseflow, as well as partially dewatered discharge, was done in Prieta Creek, a first-order cascade in northern Honduras. The cascade had discharges from 1 to 15 l s-1, had average slopes of 12%, pool spacing of 3 m, and shallow substrate of sand and gravel. Tracer tests were conducted in a 15-m sub-reach, a length considered to be adequate for the experiment based on the DaI test, a ratio of exchange and transport processes. In the three tests, between 9 and 18% of tracer was not recovered, possibly due to entrainment in flowpaths passing beneath the downstream monitoring location. Tracer data were analysed by the one-dimensional transport with inflow and storage (OTIS) transient storage model (TSM) to derive standard exchange parameters, and by the solute transport in rivers (STIR) model to examine hyporheic residence time distributions (RTDs). The best fit of the observed tracer breakthrough curves was obtained by using the STIR model with a combination of two exponential RTDs to represent hyporheic retention. With increasing discharge, the OTIS model predicted increasing storage exchange fluxes and exchange coefficients and decreasing storage zone areas and transient storage times, which are trends supported by riparian and streambed piezometric head data. Riparian water levels rose during the transition from the dry to wet season, which could constrict the hyporheic storage zone. Thirteen of the 19 streambed piezometers recorded seasonal changes in hydraulic gradients and flux direction, with fewer yet stronger upwelling zones during higher discharges. The MODFLOW model missed the observed seasonal changes, possibly due to subtle changes in the seasonal change in water surface profiles. We conclude that partially dewatered dry season exchange, compared to wet season exchange, was initiated and terminated with smaller pressure gradients and, in different streambed locations, was smaller in volume, had longer residence times, and may connect with deeper and longer flow paths. © 2010 John Wiley & Sons, Ltd.

Description: Understanding of the 'typical' amounts of fog intercepted by different types of cloud forests is hampered by a lack of comparative information on local fog climatology. Usually some kind of 'fog gauge' is used to characterize fog occurrence and amounts. Moreover, wind-driven fog and precipitation are difficult to measure separately and reported measurements of 'fog' often represent a combination of the two. In this paper, the term 'occult precipitation' (HP) is used to represent fog in combination with the horizontal component of wind-driven precipitation (WDR). Collection efficiencies of three widely used types of passive fog gauges, viz. a wire harp (WH) screen, a modified cylindrical gauge (MJU, Juvik-type) and a tunnel gauge (TTG, Daube-type), were derived by comparing the volumes of water collected by the respective gauges with horizontal cloud water fluxes (CWFs) derived from wind speed (u) and the fog liquid water content (LWC) as measured by a cloud particle spectrometer during conditions of fog at a windward cloud forest site in northern Costa Rica. Under conditions of fog-only, the collection efficiencies of the three gauges were linearly related to the horizontal CWF as measured by the gauges themselves. Therefore, additional information on wind speed, droplet size and fog LWC was not needed. During conditions of HP, relative collection efficiencies were derived by comparing the volumes collected by the respective gauge types. The modified Juvik gauge had an efficiency close to 100%, independently of the wind speed and direction, whereas the efficiency of the WH depended critically on the wind speed. The tunnel gauge had an efficiency comparable to that of the Juvik gauge, with some additional catch occurring under conditions of low precipitation angles due to the reclined frontal surface of the gauge. Copyright © 2010 John Wiley & Sons, Ltd.

Description: Understanding the hydrology of tropical montane cloud forests (TMCF) has become essential as deforestation of mountain areas proceeds at an increased rate worldwide. Passive and active cloud-water collectors, throughfall and stemflow collectors, visibility or droplet size measurements, and micrometeorological sensors are typically used to measure the fog water inputs to ecosystems. In addition, stable isotopes may be used as a natural tracer for fog and rain. Previous studies have shown that the isotopic signature of fog tends to be more enriched in the heavier isotopes 2H and 18O than that of rain, due to differences in condensation temperature and history. Differences between fog and rain isotopes are largest when rain is from synoptic-scale storms, and fog or orographic cloud water is generated locally. Smaller isotopic differences have been observed between rain and fog on mountains with orographic clouds, but only a few studies have been conducted. Quantifying fog deposition using isotope methods is more difficult in forests receiving mixed precipitation, because of limitations in the ability of sampling equipment to separate fog from rain, and because fog and rain may, under some conditions, have similar isotopic composition. This article describes the various types of fog most relevant to montane cloud forests and the importance of fog water deposition in the hydrologic budget. A brief overview of isotope hydrology provides the background needed to understand isotope applications in cloud forests. A summary of previous work explains isotopic differences between rain and fog in different environments, and how monitoring the isotopic signature of surface water, soil water and tree xylem water can yield estimates of the contribution of fog water to streamflow, groundwater recharge and transpiration. Next, instrumentation to measure fog and rain, and methods to determine isotopic concentrations in plant and soil water are discussed. The article concludes with the identification of some of the more pressing research questions in this field and offers various suggestions for future research. © 2010 This article is a US Government work and is in the public domain in the USA.

Description: Over small-scale topography in windy areas, precipitation tends to be redistributed by wind through the modification of precipitation inclination. The latter is often derived from wind speed and conventional rain gauge records by application of relations-derived mainly for convective rainfall conditions-between (1) precipitation intensity and drop diameter, and (2) drop diameter and terminal fall velocity. However, it remains to be seen whether such relationships give valid results for the typically low precipitation intensities prevailing in tropical montane cloud forests. On the basis of the assumption that the total amount of near-surface atmospheric liquid water, defined hereafter as the 'potential precipitation', is most likely to be identical over small distances, this paper introduces a device to measure amounts of potential precipitation. The gauge captures both the vertical and horizontal component of precipitation, and this allows derivation of precipitation inclination using simple trigonometry. Results on precipitation inclinations obtained with the 'potential precipitation gauge' on a wet and windy site in northern Costa Rica suggest the droplets to be smaller than those predicted by the commonly used relationships referred to above. The current gauge is also shown to be more effective in catching inclined precipitation than two different types of spherical gauges. In addition, 'effective' fall velocities were determined for each precipitation event using derivated precipitation inclination and wind speed. The assumption of spatially similar potential precipitation amounts and effective fall velocities throughout a small catchment allows the catchment-wide determination of precipitation inclination and therefore of hydrologically effective precipitation from a single-point measurement of potential precipitation and wind speed in combination with modelled spatial wind speed pattern. This approach is believed to yield appreciably better estimates of spatial precipitation inputs compared to reliance on conventional rain gauges and derivation of terminal fall velocities from precipitation intensity records. Copyright © 2010 John Wiley & Sons, Ltd.

Description: The contribution of intercepted cloud water to precipitation at windward and leeward cloud forest sites on the slopes of Haleakalā, Maui was assessed using two approaches. Canopy water balance estimates based on meteorological monitoring were compared with interpretations of fog screen measurements collected over a 2-year period at each location. The annual incident rainfall was 973 mm at the leeward site (Auwahi) and 2550 mm at the windward site (Waikamoi). At the leeward, dry forest site, throughfall was less than rainfall (87%), and, at the windward, wet forest site, throughfall exceeded rainfall (122%). Cloud water interception estimated from canopy water balance was 166 mm year-1 at Auwahi and 1212 mm year-1 at Waikamoi. Annual fog screen measurements of cloud water flux, corrected for wind-blown rainfall, were 132 and 3017 mm for the dry and wet sites respectively. Event totals of cloud water flux based on fog screen measurements were poorly correlated with event cloud water interception totals derived from the canopy water balance. Hence, the use of fixed planar fog screens to estimate cloud water interception is not recommended. At the wet windward site, cloud water interception made up 32% of the total precipitation, adding to the already substantial amount of rainfall. At the leeward dry site, cloud water interception was 15% of the total precipitation. Vegetation at the dry site, where trees are more exposed and isolated, was more efficient at intercepting the available cloud water than at the rainy site, but events were less frequent, shorter in duration and lower in intensity. A large proportion of intercepted cloud water, 74% and 83%, respectively for the two sites, was estimated to become throughfall, thus adding significantly to soil water at both sites. Published in 2010 by John Wiley & Sons, Ltd. This article is a US Government work and is in the public domain in the USA.

Description: We used hydrochemistry and environmental isotope data (δ18O, δD, tritium, and 14C) to investigate the characteristics of river water, groundwater, and groundwater recharge in China's Heihe River basin. The river water and groundwater could be characterized as Ca2+-Mg2+-HCO3--SO42- and Na+-Mg2+-SO42--Cl- types, respectively. Hydrogeochemical modelling using PHREEQC software revealed that the main hydrogeochemical processes are dissolution (except for gypsum and anhydrite) along groundwater flow paths from the upper to middle Heihe reaches. Towards the lower reaches, dolomite and calcite tend to precipitate. The isotopic data for most of the river water and groundwater lie on the global meteoric water line (GMWL) or between the GMWL and the meteoric water line in northwestern China, indicating weak evaporation. No direct relationship existed between recharge and discharge of groundwater in the middle and lower reaches based on the isotope ratios, d-excess, and 14C values. On the basis of tritium in precipitation and by adopting an exponential piston-flow model, we evaluated the mean residence time of shallow groundwater with high tritium activities, which was around 50 years (a). Furthermore, based on the several popular models, it is calculated that the deep groundwaters in piedmont alluvial fan zone of the middle reaches and in southern part of the lower reaches are modern water, whereas the deep groundwaters in the edge of the middle reaches and around Juyan Lake in the lower reaches of Heihe river basin are old water. © 2010 John Wiley & Sons, Ltd.

Description: Limited area numerical weather predication (NWP) models such as MM5 have become a popular method for generating rainfall estimates for hydrological analysis, particularly for catchments where rainfall data are sparse. Although several studies have been undertaken to investigate the appropriateness of MM5 parameterization schemes for hydrological applications, the size of the nested domains and the distance between them have been overlooked as a source of uncertainty in model precipitation estimates for hydrological purposes. This study examines the uncertainty of model rainfall estimates derived from MM5 by varying the domain size and the distance between the domains. The results from this study show that domain size and buffer zone have a significant impact on model rainfall estimates, which should not be overlooked by hydrologists. © 2010 John Wiley & Sons, Ltd.

Description: Groundwater is the most important and valuable natural resources especially in coastal urban environment where surface water is insufficient to satisfy the water requirement. Puri city is located on the east coast of India where groundwater is the only source available to meet city water supply. As the city is situated on the sandy aquifer, quality of groundwater is deteriorating because of anthropogenic activities, lack of sewerage system, etc. The objective of the study was to assess the groundwater fluctuation during post-monsoon and summer with respect to hydrogeological conditions, topography, and groundwater consumption pattern of the city. For this assessment and analysis, Geographic Information System (GIS) was used to visualize topography of the area through digital elevation model (DEM) and distribution of groundwater contours spatially and temporally. The probable areas prone to contamination were identified based on aquifer property and depths to water table below ground. © 2010 John Wiley & Sons, Ltd.

Description: Climate warming and human disturbance in north-western Canada have been accompanied by degradation of permafrost, which introduces considerable uncertainty to the future availability of northern freshwater resources. This study demonstrates the rate and spatial pattern of permafrost loss in a region that typifies the southern boundary of permafrost. Remote-sensing analysis of a 1.0 km2 area indicates that permafrost occupied 0.70 km2 in 1947 and decreased with time to 0.43 km2 by 2008. Ground-based measurements demonstrate the importance of horizontal heat flows in thawing discontinuous permafrost, and show that such thaw produces dramatic land-cover changes that can alter basin runoff production in this region. A major challenge to northern water resources management in the twenty-first century therefore lies in predicting stream flows dynamically in the context of widely occurring permafrost thaw. The need for appropriate water resource planning, mitigation, and adaptation strategies is explained. © 2010 John Wiley & Sons, Ltd.

Description: Two major criteria in choosing climate data for use in hydrological modelling are the period of record of the data set and the proximity of the collection platform(s) to the basin under study. Conventional data sets are derived from weather stations; however, in many cases there are no weather stations sufficiently close to a basin to be representative of climate conditions in that basin. In addition, it is often the case either that the period of record for the weather station(s) does not cover the period of the proposed simulation or that there are gaps in the data. Therefore, the objectives of this study are to investigate alternative climate data sources for use in hydrological modelling and to develop a protocol for creating hydrological data sets that are spatially and temporally harmonized. The methods we used for constructing daily, spatially distributed, climatic data sets of precipitation, maximum and minimum temperature, wind speed, solar radiation, potential evapotranspiration, and relative humidity are described. The model used in this study was the Soil and Water Assessment Tool implemented on the Mimbres River Basin located in southwestern New Mexico, USA, for the period 2003-2006. Our hydrological simulations showed that two events in January and February 2005 were missed, while an event in August 2006 was well simulated. We have also investigated the usefulness of several other precipitation data sets and compared the simulation results. © 2010 John Wiley & Sons, Ltd.

Description: An integrated field and modelling study was carried out on the 35-ha La Reina catchment, Chile, to test the hypothesis that the effect of forest cover on flood peaks becomes less important as the size of the hydrological event increases. Meteorological and discharge data were measured at the catchment before and after the pine plantation that covered 80% of the catchment area was logged. Analysis of the measured response of the catchment provides support for the hypothesis but is not conclusive. Therefore, modelling of the catchment using 1000 years of generated rainfall data representative of the current conditions was carried out for the forested and logged states. The simulations show that the absolute difference in discharge between the two cases remains approximately constant as the discharge increases: thus as a percentage of discharge it decreases. This relative convergence appears to become significant at return periods of greater than approximately 10 years. Tests with different hypothetical soil depths for the forested and logged catchments show an absolute convergence in discharge between the two cases for shallow soils and no convergence for deep soils. Sediment transport simulations show that forest cover provides a clear benefit in protecting the soil from erosion. © 2010 John Wiley & Sons, Ltd.

Description: Severe hydrological droughts in the Amazon have generally been associated with strong El Niño events. More than 100 years of stage record at Manaus harbour confirms that minimum water levels generally coincide with intense warming in the tropical Pacific sea waters. During 2005, however, the Amazon experienced a severe drought which was not associated with an El Niño event. Unless what usually occurs during strong El Niño events, when negative rainfall anomalies usually affect central and eastern Amazon drainage basin; rainfall deficiencies in the drought of 2005 were spatially constrained to the west and southwest of the basin. In spite of this, discharge stations at the main-stem recorded minimum water levels as low as those observed during the basin-wide 1996-1997 El Niño-related drought. The analysis of river discharges along the main-stem and major tributaries during the drought of 2004-2005 revealed that the recession on major tributaries began almost simultaneously. This was not the case in the 1996-1997 drought, when above-normal contribution of some tributaries for a short period during high water was crucial to partially counterbalance high discharge deficits of the other tributaries. Since time-lagged contributions of major tributaries are fundamental to damp the extremes in the main-stem, an almost coincident recession in almost all tributaries caused a rapid decrease in water discharges during the 2005 event. © 2010 John Wiley & Sons, Ltd.

Description: Most of the water from the Nile originates in Ethiopia but there is no agreement on how land degradation or climate change affects the future flow in downstream countries. The objective of this paper is to improve the understanding of future conditions by analysing historical trends. During the period 1964-2003, the average monthly basin-wide precipitation and monthly discharge data were collected and analysed statistically for two stations in the upper 30% of the Blue Nile Basin and monthly and 10-day discharge data of one station at the Sudan-Ethiopia border. A rainfall-runoff model examined the causes for observed trends. The results show that, while there was no significant trend in the seasonal and annual basin-wide average rainfall, significant increases in discharge during the long rainy season (June to September) were observed at all three stations. In the upper Blue Nile, the short rainy season flow (March to May) increased, while the dry season flow (October to February) stayed the same. At the Sudan border, the dry season flow decreased significantly with no change in the short rainy season flow. The difference in response was likely due to the construction of weir in the 1990s at the Lake Tana outlet that affected the upper Blue Nile discharge significantly but affected less than 10% of the discharge at the Sudan border. The rainfall-runoff model reproduced the observed trends, assuming that an additional 10% of the hillsides were eroded in the 40-year time span and generated overland flow instead of interflow and base flow. Models concerning future trends in the Nile cannot assume that the landscape runoff processes will remain static. © 2010 John Wiley & Sons, Ltd..

Description: This article presents the development of distributed thermodynamic model for energy and mass balance computation between soil surface and shallow atmospheric layers and its inclusion into the hydrological model FEST-EWB (Flash-flood Event-based Spatially distributed rainfall-runoff Transformation-Energy Water Balance). This model is also thought for a synergic use of hydrological model with remote sensing data. In particular, the energy budget is solved looking for the representative thermodynamic equilibrium temperature (RET) defined as the land surface temperature (LST) that closes the energy balance equation for any pixel of basin surface. So using this approach, through the system between the mass and energy equations, soil moisture (SM) is linked to the latent heat flux (LE) and then to LST. The RET thermodynamic approach solves most of the problems of the actual evapotranspiration (ET) and SM computation. In fact, it permits to avoid computing the effective ET as an empirical fraction of the potential one. This approach, based on the RET, has been tested at field scale (10 ha) with energy fluxes and LST measured with an eddy covariance station in Landriano (Italy). © 2010 John Wiley & Sons, Ltd.

Description: There is still wide uncertainty about past flash-flood processes in mountain regions owing to the lack of systematic databases on former events. This paper presents a methodology to reconstruct peak discharge of flash floods and illustrates a case in an ungauged catchment in the Spanish Central System. The use of dendrogeomorphic evidence (i.e. scars on trees) together with the combined use of a two-dimensional (2D) numerical hydraulic model and a terrestrial laser scan (TLS) has allowed estimation of peak discharge of a recent flash flood. The size and height distribution of scars observed in the field have been used to define three hypothetical scenarios (Smin or minimum scenario; Smed or medium scenario; and Smax or maximum scenario), thus illustrating the uncertainty involved in peak-discharge estimation of flash floods in ungauged torrents. All scars analysed with dendrogeomorphic techniques stem from a large flash flood which took place on 17 December 1997. On the basis of the scenarios, peak discharge is estimated to 79 ± 14 m3 s-1. The average deviation obtained between flood stage and expected scar height was - 0·09 ± 0·53 m. From the data, it becomes obvious that the geomorphic position of trees is the main factor controlling deviation rate. In this sense, scars with minimum deviation were located on trees growing in exposed locations, especially on unruffled bedrock where the model predicts higher specific kinetic energy. The approach used in this study demonstrates the potential of tree-ring analysis in palaeohydrology and for flood-risk assessment in catchments with vulnerable goods and infrastructure. Copyright © 2010 John Wiley & Sons, Ltd.

Description: Vegetation indices derived from remote sensing data still remain to be used for analysing the relationship between climatic factors and vegetation seasonal phenology in middle latitudes with subtropical conditions forests such as the Canarian laurel forest. The Garajonay National Park, located in the La Gomera Island, protects one of the best preserved examples of the Macaronesian laurel forest, due to the cloud banks produced by trade winds, with rainfall and temperature field data showing a clear Mediterranean climatic pattern. We have analysed seasonal vegetation indices trend for different types of forest inside the Garajonay National Park using normalized difference vegetation index (NDVI) and enhanced vegetation index (EVI) products derived from moderate resolution imaging spectrometer (MODIS) Aqua data for two hydrological years (October 2003 to September 2005) in relationship with the existing field climatic data: rainfall, net fog water and temperature. Maximum annual EVI maps show the highest vegetation indices in the laurel forest of La Gomera that occur during the dry season, mainly in late spring to early summer, with EVI temporal profiles showing that valley-bottom laurel forest areas have the most clear seasonal trend. Difference maps of EVI values between months with the lowest and highest rainfall of each hydrological year clearly confirm the highest photosynthetic activity in the laurel forest during the dry season. In addition, these forests show a significative temporal correlation between EVI values and the temperature in the forest (p 〈 0·001). Our results prove the absence of summer drought stress in the laurel forest implying that the fog drip income is high enough to maintain enough soil moisture to allow the forest fully transpire when temperatures are higher. As the laurel forest of La Gomera occurs in the main recharge area of the island's aquifer system, our analysis of EVI data suggests that fog drip constitutes a key hydrological factor. © 2010 John Wiley & Sons, Ltd.

Description: The Manning equation is one of the most widely used formulae for calculating the velocity of shallow overland flow in hydrological and erosion models. Precise estimation of the Manning's friction coefficient (n) is critical to determining overland flow and soil erosion processes. Few studies have been conducted to quantify the effects of sediment load on Manning's n on steep slopes. This study was conducted to investigate the potential effects of sediment load on Manning's n in a flume with a fixed bed, under wide ranges of hydraulics and sediment loads. Slope gradient varied from 8.7 to 34.2%, unit flow rate from 0.66 to 5.26 × 10-3 m2 s-1, and sediment load from 0 to 6.95 kg m-1 s-1. The Reynolds number ranged from 350 to 5899. Results showed that Manning's n varied in both sediment-free and sediment-laden flows ranging from 0.012 to 0.055. The apparent Manning's coefficients of sediment-laden flow were much greater than those of sediment-free flow. The mean Manning coefficient of sediment-laden flow was 51.27% greater than the mean value of sediment-free flow. For sediment-laden flow, Manning's n could be estimated with a power function of unit flow discharge and sediment content. Further studies are needed to quantify the potential effects of sediment load on the Manning's n on erodible beds and in fields. © 2010 John Wiley & Sons, Ltd.

Description: Hydrological scientists develop perceptual models of the catchments they study, using field measurements and observations to build an understanding of the dominant processes controlling the hydrological response. However, conceptual and numerical models used to simulate catchment behaviour often fail to take advantage of this knowledge. It is common instead to use a pre-defined model structure which can only be fitted to the catchment via parameter calibration. In this article, we suggest an alternative approach where different sources of field data are used to build a synthesis of dominant hydrological processes and hence provide recommendations for representing those processes in a time-stepping simulation model. Using analysis of precipitation, flow and soil moisture data, recommendations are made for a comprehensive set of modelling decisions, including Evapotranspiration (ET) parameterization, vertical drainage threshold and behaviour, depth and water holding capacity of the active soil zone, unsaturated and saturated zone model architecture and deep groundwater flow behaviour. The second article in this two-part series implements those recommendations and tests the capability of different model sub-components to represent the observed hydrological processes. Copyright © 2010 John Wiley & Sons, Ltd.

Description: Most natural disasters are caused by water-/climate-related hazards, such as floods, droughts, typhoons, and landslides. In the last few years, great attention has been paid to climate change, and especially the impact of climate change on water resources and the natural disasters that have been an important issue in many countries. As climate change increases the frequency and intensity of extreme rainfall, the number of water-related disasters is expected to rise. In this regard, this study intends to analyse the changes in extreme weather events and the associated flow regime in both the past and the future. Given trend analysis, spatially coherent and statistically significant changes in the extreme events of temperature and rainfall were identified. A weather generator based on the non-stationary Markov chain model was applied to produce a daily climate change scenario for the Han River basin for a period of 2001-2090. The weather generator mainly utilizes the climate change SRES A2 scenario driven by input from the regional climate model. Following this, the SLURP model, which is a semi-distributed hydrological model, was applied to produce a long-term daily runoff ensemble series. Finally, the indicator of hydrologic alteration was applied to carry out a quantitative analysis and assessment of the impact of climate change on runoff, the river flow regime, and the aquatic ecosystem. It was found that the runoff is expected to decrease in May and July, while no significant changes occur in June. In comparison with historical evidence, the runoff is expected to increase from August to April. A remarkable increase, which is about 40%, in runoff was identified in September. The amount of the minimum discharge over various durations tended to increase when compared to the present hydrological condition. A detailed comparison for discharge and its associated characteristics was discussed. © 2010 John Wiley & Sons, Ltd.

Description: Given the structural shortcomings of conceptual rainfall-runoff models and the common use of time-invariant model parameters, these parameters can be expected to represent broader aspects of the rainfall-runoff relationship than merely the static catchment characteristics that they are commonly supposed to quantify. In this article, we relax the common assumption of time-invariance of parameters, and instead seek signature information about the dynamics of model behaviour and performance. We do this by using a temporal clustering approach to identify periods of hydrological similarity, allowing the model parameters to vary over the clusters found in this manner, and calibrating these parameters simultaneously. The diagnostic information inferred from these calibration results, based on the patterns in the parameter sets of the various clusters, is used to enhance the model structure. This approach shows how diagnostic model evaluation can be used to combine information from the data and the functioning of the hydrological model in a useful manner. © 2010 John Wiley & Sons, Ltd.

Description: Forest harvesting activities, if not carefully carried out, can disturb the forest soils and can cause significant suspended solid concentration increases in receiving water. This study examined how harvesting, following forestry guidelines, influenced suspended solid concentrations and loads in the receiving water of a blanket peat salmonid catchment. The study site comprised of two forest coupes of 34-year-old conifers drained by a first-order stream. The upper coupe was not felled and acted as a baseline 'control' catchment; the downstream coupe was completely harvested in summer 2005 and served as the 'experimental' catchment. Good management practices such as the proper use of brash mats and harvesting only in dry weather were implemented to minimize soil surface disturbance and streambank erosion. Stream flow and suspended solid measurements at an upstream station (US) and a downstream station (DS) in the study stream commenced over a year before felling took place. The suspended solid concentrations, yields and release patterns at US and DS were compared before and after harvesting. These showed that post-guideline harvesting of upland blanket peat forest did not significantly increase the suspended solid concentrations in the receiving water and the aquatic zone need not be adversely affected by soil releases from sites without a buffer strip. © 2010 John Wiley & Sons, Ltd.

Description: Characterization of streambed hydraulic conductivity from the channel surface to a great depth below the channel surface can provide needed information for the determination of stream-aquifer hydrologic connectedness, and it is also important to river restoration. However, knowledge on the streambed hydraulic conductivity for sediments 1 m below the channel surface is scarce. This study describes a method that was used to determine the distribution patterns of streambed hydraulic conductivity for sediments from channel surface to a depth of 15 m below. The method includes Geoprobe's direct-push techniques and Permeameter tests. Direct-push techniques were used to generate the electrical conductivity (EC) logs and to collect sequences of continuous sediment cores from river channels, as well as from the alluvial aquifer connected to the river. Permeameter tests on these sediment cores give the profiles of vertical hydraulic conductivity (Kv) of the channel sediments and the aquifer materials. This method was applied to produce Kv profiles for a streambed and an alluvial aquifer in the Platte River Valley of Nebraska, USA. Comparison and statistical analysis of the Kv profiles from the river channel and from the proximate alluvial aquifer indicates a special pattern of Kv in the channel sediments. This depth-dependent pattern of Kv distribution for the channel sediments is considered to be produced by hyporheic processes. This Kv-distribution pattern implied that the effect of hyporheic processes on streambed hydraulic conductivity can reach the sediments about 9 m below the channel surface. © 2010 John Wiley & Sons, Ltd.

Description: Evaluation of flow and transport processes in a watershed-scale requires that the watershed be divided into homogenous spatial units referred to as hydrologically similar units (HSUs). Although a few discretization schemes are already in use, a universally acceptable method of obtaining HSUs is yet to emerge. In this study, we developed a fuzzy inference system (FIS) to classify the saturated hydraulic conductivity (Ks) and two water-retention parameters α and n into fuzzy logic-based soil hydrologic classes (FSHCs). Analysis of these classes showed that soil properties within an FSHC have less variability and those between two FSHCs have large variability. This result suggested that soils belonging to a specific FSHC may be more similar than those across different FSHCs and may be grouped together to represent an HSU. Soils within a specific hydrologic class were aggregated to delineate HSUs within the watershed. For the Dengei Pahad micro-watershed (DPW), this approach showed five distinct regions representing a discretized zone having similar soil hydraulic properties. Application of this approach on a larger international database of soil hydraulic properties revealed that the developed hydrologic classes are quite comparable across different databases. The delineated HSUs based on these FSHCs were also better than the soil series map of the watershed in maintaining the soil heterogeneity of the watershed. Moreover, this new discretization scheme using the SWAT modelling environment showed better performance than the soil series-based discretization approach. © 2010 John Wiley & Sons, Ltd.

Description: We assess the ability of multivariate statistical analyses applied to event hydrographs parameters, to characterize a catchment hydrological behaviour. Motivation for such an approach lies in the fact that streamflow records have yet to be exploited to their full potential towards hydrological interpretation and can be used to infer a catchment state of connectivity from a qualitative standpoint. We have therefore processed 96 event hydrographs from a small headwater temperate humid forested catchment using principal component analysis, variation partitioning and classification tree analysis. These techniques prove to be promising in discriminating contrasted types of hydrologic responses (e.g. low- vs high-magnitude events, slow vs quick timing events), identifying the main hydro-meteorological variables that control these responses and determining thresholds values of the hydro-meteorological variables leading to a switch between catchment response types. © 2010 John Wiley & Sons, Ltd.

Description: This study explores the hydrograph characteristics of quick and slow runoffs in watershed outlet hydrographs. The quick and slow runoffs were modelled using a conceptual model of three linear cascade reservoirs that have exponential decay response expressions. Mean rainfall for model inputs was estimated using the block Kriging method. The 107 storms during the 1966-2008 events were classified as large, medium and small events according to the observed streamflow. The optimal hydrograph parameters for 61 rainfall-runoff events were calibrated using the shuffled complex evolution optimal algorithm. The efficacy of the model was verified using the seven averaged parameters of three types of 46 events and was compared with three evaluation criteria resulting from the Nash model. The 61 calibrations were used to analyse and compare the characteristics of quick and slow flows in early and later periods (1966-2002 and 2003-2008). Finally, the following five conclusions were obtained: (1) The base time of a slow runoff hydrograph is the same as that of a total runoff hydrograph. (2) A quick runoff with a long period occurs when soil antecedent moisture is low and with a short period under a high value. (3) The time to peak of hydrograph components is directly proportional to peak time of a hyetograph; the time to peak of quick and slow flows is about 0·97 and 1·12 times the peak time of a hyetograph, respectively. (4) The peak of hydrograph components is relative to a total runoff hydrograph; the percentages for quick runoff are approximately 71% and 13% for slow flow. Finally, (5) the volume of a quick runoff component is 49% of a total runoff volume and 37% for a slow runoff volume. © 2010 John Wiley & Sons, Ltd.

Description: Seawater intrusion into fresh groundwater formations generally results inadvertently from human activities, such as over-abstraction from coastal aquifers. This article describes the data analysis to quantify drain-aquifer interactions in a low-lying pump-drained coastal aquifer, which is subject to saline intrusion due to widespread land drainage, and the resulting development and application of a numerical groundwater model to understand the spatial groundwater system behaviour (including groundwater salinity fluxes). Without measured flow data in this pump-drained catchment, a novel groundwater head-dependent approach to hydrograph separation is described. Time-variant and time-invariant MODFLOW analyses are utilised to examine the flow processes. A new approach to calculate drain coefficients, which represent the extensive network of drainage ditches in the regional model, using field information, is described; the sum of the drainage coefficients are close to the values independently estimated from the head-dependent hydrograph separation. Results show that (1) the groundwater flows into the drainage systems are well reproduced using the new drain coefficients, (2) particle tracking of fresh and saline water can explain observed spatial salinity distribution within drainage networks and (3) the modelled flow of seawater across the coast is approximately 25% greater than that discharged by the pumps, demonstrating the need for drainage management to be aware of the slow response of groundwater systems to past drainage system changes. The article demonstrates that numerical groundwater modelling can produce the improved understanding needed to inform management decisions in such complex environments. Copyright © 2010 John Wiley & Sons, Ltd.

Description: The spatial and temporal variations of precipitation in the desert region of China (DRC) from 1951 to 2005 were investigated using a rotated empirical orthogonal function (REOF), the precipitation concentration index (PCI) and the Mann-Kendall trend test method (M-K method). In addition, the association between variation patterns of precipitation and large-scale circulation were also explored using the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data. The results indicated that the spatial pattern of precipitation was primarily the local climate effect significant type, with the first three EOFs explaining a total of 55.3% of the variance, and the large-scale climate system effect type, which explained 9.8% of the variance. Prior to the 1970s, the East Asian summer monsoon was stronger, which resulted in abundant precipitation in the Inner Mongolia region. Conversely, the climate of the Xinjiang region was controlled by westerly circulation and had lower precipitation. However, this situation has been reversed since the 1980s. It is predicted that precipitation will decrease by 15-40 and 0-10 mm/year in the Inner Mongolia plateau and southern Xinjiang, respectively, whereas it will likely increase by 10-40 mm/year in northern Xinjiang. Additionally, 58-62% of the annual rainfall occurred during summer in the DRC, with precipitation increasing during spring and summer and decreasing in winter. The intra-annual precipitation is becoming uniform, but the inter-annual variability in precipitation has been increasing in the western portions of the DRC. The probability of precipitation during the study period increased by 30% and 22.2% in the extreme-arid zones and arid zones, respectively. Conversely, the probability of precipitation during the study period decreased by 18.5% and 37.5% in the semi-arid zones and semi-wet zones, respectively. It is predicted that the northwest portion of the DRC will become warmer and wetter, while the central portion will become warmer and drier and the northeast portion will be subjected to drought. © 2010 John Wiley & Sons, Ltd.

Description: Understanding how the soil moisture regime changes following hydrological restoration activities in wetlands is essential for managers interested in establishing targeted wetland vegetation species. Based on observations from two floodplain sites in southwestern Wisconsin, a variably saturated hydrological model was developed and used to illustrate the importance of changing evapotranspiration (ET) partitioning [through changes in leaf-area index (LAI)], the plant water stress function, and the thickness of a surficial silt-loam alluvial deposit on the soil moisture regime. Floodplain restoration activities at these sites consisted of removing a layer of post-settlement alluvium, which is a part of this deposit. Field observations following restoration of the pre-settlement floodplain surface at one of the sites show a drier soil moisture regime at 10 and 25 cm depths at the restored (RES) site than at the unrestored site even though the potentiometric surface in a shallow monitoring piezometer was closer to the surface at the RES site. Simulations show that four factors may have contributed to this observation of relatively drier soils at the RES site: (1) lower LAI increases soil evaporation, (2) anaerobiosis limits transpiration near saturation, (3) a confining unit inhibits upward flow of water, and (4) removal of a 0.5-m silt-loam layer decreases the reservoir of soil moisture available to plant roots. Our work suggests the importance of effectively characterizing parameters that affect ET partitioning (i.e. LAI), determining the appropriate plant water stress function, and considering the effect of floodplain deposits that act as confining units when simulating the hydrology of floodplain wetland ecosystems. © 2010 John Wiley & Sons, Ltd.

Description: The hillslope-riparian-stream system is a key functional unit of catchments, yet very difficult to measure and monitor due to its tremendous complexity and high spatio-temporal variability. Here, we present a simple and practical tool for imaging directly these hillslope-riparian-area connections. We used a FLIR b50 infrared camera to produce thermal images at the scale of 140 × 140 pixels over the spectral range 7·5-13 μm. Our IR imaging technique is sensitive to the upper 0·1 mm of the water column. Images were obtained from a constant position on the right bank of the Weierbach catchment in Luxembourg, at an incidence angle of approximately 45° over a 5-week period. The study site measured 5 × 3m. Our results show that ground-based IR imagery can discriminate between areas with snow cover, snow melt, soil seepage, and stream water. More importantly, it can detect when and where variably saturated areas are active and when connectivity exists between the hillslope-riparian-stream system. Our proof of concept suggests that this is a simple, inexpensive technology for sequential mapping and characterisation of surface saturated areas and a useful complement to conventional tracer techniques. © 2010 John Wiley & Sons, Ltd.

Description: In the Soil Conservation Service Curve Number (SCS-CN) method, the three levels of antecedent moisture condition (AMC) permit unreasonable sudden jumps in curve numbers, which result into corresponding jumps in the estimated runoff. A few recently developed SCS-CN-based models obviate this problem, yet they have several limitations. In this study, such a model incorporating a continuous function for antecedent moisture has been presented. It has several advantages over the other existing SCS-CN-based models. Its application to a large dataset from US watersheds showed to perform better than the existing SCS-CN method and the others based on it. © 2010 John Wiley & Sons, Ltd.

Description: Nonparametric estimation of the distribution function of the annual maxima (AM) flood series is considered. In practice, the good behaviour of the nonparametric estimators depends heavily on the smoothing parameter or bandwidth. Nowadays, there exist only two (optimal under a mathematical point of view) bandwidth parameter selection methods in nonparametric distribution function estimation: cross-validation and plug-in. In this work, the cross-validation procedure of Bowman et al. [Bowman A, Hall P, Prvan T. 1998. Bandwidth selection for the smoothing of distribution functions. Biometrika 85: 799-808] is analysed. A simulation study checks the finite sample performance of the corresponding estimators, and a comparison of this method with a parametric procedure (the fitting of a extreme value distribution) is done with flow data of Salt River (AZ, USA). Along this work, we point out some common mistakes made in some papers dealing with statistical problems in hydrology, such as the use of the empirical distribution function instead of the observed data, or the bandwidth parameter selection by means of some method designed for nonparametric density estimation. © 2010 John Wiley & Sons, Ltd..

Description: Quantifying snowmelt-derived fluxes at the watershed scale within hillslope environments is critical for investigating local meadow scale groundwater dynamics in high elevation riparian ecosystems. In this article, we investigate the impact of snowmelt-derived groundwater flux from the surrounding hillslopes on water table dynamics in Tuolumne Meadows, which is located in the Sierra Nevada Mountains of California, USA. Results show water levels within the meadow are controlled by a combination of fluxes at the hillslope boundaries, snowmelt within the meadow and changes in the stream stage. Observed water level fluctuations at the boundaries of the meadow show the hydrologic connection and subsequent disconnection between the hillslope and meadow aquifers. Timing of groundwater flux entering the meadow as a result of spring snowmelt can vary over 20 days based on the location, aspect, and local geology of the contributing area within the larger watershed. Identifying this temporal and spatial variability in flux entering the meadow is critical for simulating changes in water levels within the meadow. Model results can vary significantly based on the temporal and spatial scales at which watershed processes are linked to local processes within the meadow causing errors when boundary fluxes are lumped in time or space. Without a clear understanding of the surrounding hillslope hydrology, it is difficult to simulate groundwater dynamics within high elevation riparian ecosystems with the accuracy necessary for understanding ecosystem response. © 2010 John Wiley & Sons, Ltd.

Description: In this study, an approach is presented for handling hydraulic uncertainties in the prediction of floodplain. Different factors affect river flood characteristics. Furthermore, the high changeability of flooding conditions leads to high variability of the inundation.River morphology is one of the most effective factors in river flood characteristics. This factor is influenced by sedimentation and erosion in the river cross sections, which affects the discharge variation. The depth and the width of the river cross section lead to an increase or decrease in the river flow path. This results in changes in the extent of the floodplain based on the generated rainfall. The inundated region boundaries are determined by utilizing the mean first-order second-moment analysis. The proposed method is applied to the Kajoo River in the south-eastern part of Iran. Determination of floodplain uncertainty is a damage-reduction policy in this region. Also, it is useful to prepare the necessary activities for overcoming the flood hazards.Climate change is the second effective factor on the floodplain uncertainties. Climate change affects the magnitude, extent and depth of inundation and it may intensify the flood problem. Therefore, the future rainfall pattern of the study area under climate change is simulated to evaluate its impacts on the river flow characteristic. Subsequently, a hydraulic routing model is used to determine floodplain. Finally, the copula function is used to estimate the joint probability of the changes in the inundation area due to changes in river morphology and the rainfall changes due to impacts of climate change.Results show that the uncertainties of the extent of floodplain are affected by climate change and river morphology, leading to noticeable changes in the magnitude and frequency of floods. Evaluating these impacts and estimating corresponding river discharges will help in the study of river dynamics, and will also contribute towards devising effective mitigation and management strategies. © 2010 John Wiley & Sons, Ltd.

Description: Himalayan basins have considerable snow- and glacier-covered areas, which are an important source of water, particularly during summer season. In the Himalayan region, in general, the glacier melt season is considered to be from May to October. Changes in hydrological characteristics of the runoff over the melt season can be understood by studying the variation in time to peak and time lag between melt generation and its emergence as runoff. In the present study, the runoff-delaying characteristics of Gangotri Glacier, one of the largest glaciers in the Indian Himalayas, have been studied. For this purpose, hourly discharge and temperature data were collected near the snout of the glacier (4000 m) for three ablation seasons (2004-2006). The diurnal variations in discharge and temperature provided useful information on water storage and runoff characteristics of the glacier. In the early stages of the ablation period, poor drainage network and stronger storage characteristics of the glaciers due to the presence of seasonal snow cover resulted in a much delayed response of melt water, providing a higher time lag and time to peak as compared to the peak melt season. A comparison of runoff-delaying parameters with the discharge ratio clearly indicated that changes in time lag and time to peak are inversely correlated with variations in discharge. Impact of such meltwater storage and delaying characteristics of glaciers on hydropower projects being planned/developed on glacier-fed streams in India has been discussed. © 2010 John Wiley & Sons, Ltd.

Description: The erosion of a composite river bank critically depends on the erodibility of its fine soils, as the fine soil has higher resistance against erosion. Therefore, for the estimation of the bank erosion in the case of a composite river bank, it is important to determine the critical shear stress and erodibility coefficients of the bank soil and their spatial distribution. In the present study, erodibility parameters of the river bank of Brahmaputra in India have been estimated through 58 in situ submerged jet tests. The significance of spatial and layer-wise distribution of the erodibility parameters was tested through analysis of variance (ANOVA). Results indicate that the spatial variation of erodibility parameters is highly significant, but layer-wise variations of the erodibility parameters are not significant. Therefore, the erodibility of the riverbank depends on the particular location, whereas layer-wise average erodibility parameters can be lumped for the estimation of the bank erosion for the specific site. Using the measured erodibility parameters, yearly river bank erosions at the study locations were computed and found to fall within the reported range of the bank erosion in the Brahmaputra River. © 2010 John Wiley & Sons, Ltd.

Description: In this paper two models are presented for calculating the hourly evapotranspiration λE (W m-2) using the Penman-Monteith equation. These models were tested on four irrigated crops (grass, soya bean, sweet sorghum and vineyard), with heights between 0.1 and 2.2 m at the adult growth stage. In the first model (Katerji N, Perrier A. 1983. Modélisation de l'évapotranspiration réelle ETR d'une parcelle de luzerne rôle d'un coefficient cultural. Agronomie 3(6): 513-521, KP model), the canopy resistance rc is parameterized by a semi-empirical approach. In the second model (Todorovic M. 1999. Single-layer evapotranspiration model with variable canopy resistance. Journal of Irrigation and Drainage Engineering-ASCE 125: 235-245, TD model), the resistance rc is parameterized by a mechanistic model. These two approaches are critically analysed with respect to the underlying hypotheses and the limitations of their practical application. In the case of the KP model, the mean slope between measured and calculated values of λE was 1.01 ± 0.6 and the relative correlation coefficients r2 ranged between 0.8 and 0.93. The observed differences in slopes, between 0.96 and 1.07, were not associated with the crop height. This model seemed to be applicable to all the crops examined. In the case of the TD model, the observed slope between measured and calculated values of λE for the grass canopy was 0.79. For the other crops, it varied between 1.24 and 1.34. In all the situations examined, the values of r2 ranged between 0.73 and 0.92. The TD model underestimated λE in the case of grass and overestimated it in the cases of the other three crops. The under- or overestimation of λE in the TD model were due: (i) to some inaccuracies in the theory of this model, (ii) to not taking into account the effect of aerodynamic resistance ra in the canopy resistance modelling. Therefore, the values of rc were under- or overestimated in consequence of mismatching the crop height. The high value of air vapour pressure deficit also contributed to the overestimation of λE, mainly for the tallest crop. The results clarify aspects of the scientific controversy in the literature about the mechanistic and semi-empirical approaches for estimating λE. From the practical point of view the results also present ways for identifying the most appropriate approach for the experimental situations encountered. © 2010 John Wiley & Sons, Ltd.

Description: The Soil Conservation Service Curve Number (SCS-CN) method is widely used in determination of direct surface run-off in long-term (continuous) hydrologic simulation models. Of late, Michel et al. (2005) reviewed the soil moisture accounting (SMA) procedure that lies behind the original SCS-CN method and pointed out severe structural inconsistencies in the treatment of antecedent condition and, in turn, proposed a sounder methodology. However, this method still needs refinement in the definition of initial moisture level (V0) to make it usable in field. Thus, in the present study, the Michel et al. (2005) model is modified to avoid the unrealistic sudden jump in V0 by incorporating conceptual SMA procedure and variation of daily CN based on antecedent moisture amount instead of antecedent moisture condition. When applied to 17 watersheds from different agro-climatic regions of India, the proposed model simulates daily stream flows better than those due to Michel et al. model. The proposed model performed better in high run-off producing (wet) watersheds than in low run-off producing (dry) watersheds, and the base flow was more and less significant in high and low run-off producing watersheds, respectively, whereas the evapotranspiration showed a reverse trend. Copyright © 2010 John Wiley & Sons, Ltd.

Description: The impacts of historical land cover changes witnessed between 1973 and 2000 on the hydrologic response of the Nyando River Basin were investigated. The land cover changes were obtained through consistent classifications of selected Landsat satellite images. Their effects on runoff peak discharges and volumes were subsequently assessed using selected hydrologic models for runoff generation and routing available within the HEC-HMS. Physically based parameters of the models were estimated from the land cover change maps together with a digital elevation model and soil datasets of the basin. Observed storm events for the simulation were selected and their interpolated spatial distributions obtained using the univariate ordinary Kriging procedure. The simulated flows from the 14 sub-catchments were routed downstream afterwards to obtain the accrued effects in the entire river basin. Model results obtained generally revealed significant and varying increases in the runoff peak discharges and volumes within the basin. In the upstream sub-catchments with higher rates of deforestation, increases between 30 and 47% were observed in the peak discharge. In the entire basin, however, the flood peak discharges and volumes increased by at least 16 and 10% respectively during the entire study period. The study successfully outlined the hydrological consequences of the eminent land cover changes and hence the need for sustainable land use and catchment management strategies. © 2010 John Wiley & Sons, Ltd.

Description: The conceptual hydrogeological model of the low to medium temperature Daying and Qicun geothermal fields has been proposed, based on hydrochemical characteristics and isotopic compositions. The two geothermal fields are located in the Xinzhou basin of Shanxi, China and exhibit similarities in their broad-scale flow patterns. Geothermal water is derived from the regional groundwater flow system of the basin and is characterized by Cl·SO4-Na type. Thermal water is hydrochemically distinct from cold groundwater having higher total dissolved solids (TDS) (〉0.8 g/l) and Sr contents, but relatively low Ca, Mg and HCO3 contents. Most shallow groundwater belongs to local flow systems which are subject to evaporation and mixing with irrigation returns. The groundwater residence times estimated by tritium and 14C activities indicate that deep non-thermal groundwater (130-160 m) in the Daying region range from modern (post-1950s) in the piedmont area to more than 9.4ka BP (Before Present) in the downriver area and imply that this water belong to an intermediate flow system. Thermal water in the two geothermal fields contains no detectable active 14C, indicating long residence times (〉50 ka), consistent with this water being part of a large regional flow system. The mean recharge elevation estimated by using the obtained relationship Altitude (m) = -23.8 × δ2H(‰) - 121.3, is 1980 and 1880 m for the Daying and Qicun geothermal fields, respectively. The annual infiltration rates in the Daying and Qicun geothermal fields can be estimated to be 9029 × 103 and 4107 × 103 m3/a, respectively. The variable 86Sr/87Sr values in the thermal and non-thermal groundwater in the two fields reflect different lithologies encountered along the flow path(s) and possibly different extents of water-rock interaction. Based on the analysis of groundwater flow systems in the two geothermal fields, hydrogeochemical inverse modelling was performed to indicate the possible water-rock interaction processes that occur under different scenarios. © 2010 John Wiley & Sons, Ltd.

Description: Groundwater responses in temperate mountainous terrain are assessed using groundwater, hydrometric and climatic data from southern British Columbia, Canada. Well and stream hydrographs are analysed using a series of diagnostic tools including time series plots, hysteresis plots, and cross-correlation plots. Characterizing the seasonal timing of the response requires consideration of the hydroclimatology of the region: rainfall-dominated (pluvial), snowmelt-dominated (nival) or hybrid (mixture of rain and snow). The magnitude and timing of the recharge and discharge response of the groundwater system was shown to depend on the storage and permeability characteristics of the aquifer and whether the system is stream-driven or recharge-driven. These two dominant stream-aquifer system types were defined based on classifying different aquifer types found in the southwest portion of the province. The classification scheme and diagnostic tools have the potential to provide a framework for evaluating the responses of wells in other mountainous regions. Using this framework, the potential consequences of future climate change may then be better understood based on the interactions between the hydrogeological and hydroclimatic settings of these aquifers. © 2010 Her Majesty the Queen in right of Canada.

Description: Five alternative regionalization approaches in two broad categories, named function-free and functional approaches, have been proposed to predict periodic behaviours in the basic parameters of monthly stream flows throughout homogeneous regions defined. Function-free and functional approaches rely on the standardized (or normalized) forms of raw and fitted values of the monthly periodic parameters considered. Homogeneous regions are identified based on these standardized/normalized parameters by means of the hierarchical clustering analysis. The proposed models are tested for two major river basins in south Turkey. It is concluded that the proposed regional models are very effective to estimate periodic behaviour of monthly flows. The functional approaches are quite plausible, and the function-free approach needs much more parameters. Both types of regionalization approaches can be reliably used to get regional monthly flow estimates for the flow sections where monthly records are not available or too short. © 2010 John Wiley & Sons, Ltd.

Description: Two-dimensional ice-sphere arrays were produced in a cold room and studied as a geometrically simplified model of dry snow aggregates. The structural evolution of the ice-sphere arrays under either a quasi-isothermal condition or a temperature gradient was examined temporally. Two observational techniques were combined for the structural characterization. Optical microscopy was used to perform periodic observations, whereas scanning electron microscopy was used to both acquire high-resolution images and confirm the hexagonal crystal structure. Different thermal conditions led to the development of different morphologies of necks between two ice spheres by affecting the water vapour transfer in the pore spaces and the sublimation-condensation of water molecules. The microstructure of necks could also play a significant role in the structure development at later times by inducing or enhancing the local temperature gradient. This feature was discussed on the basis of steady-state heat transfer modelling of a two-sphere structure. Copyright © 2010 John Wiley & Sons, Ltd.

Description: An increase of the spatial and temporal resolution of snowpack measurements in Alpine or Arctic regions will improve the predictability of flood and avalanche hazards and increase the spatial validity of snowpack simulation models. In the winter season 2009, we installed a ground-penetrating radar (GPR) system beneath the snowpack to measure snowpack conditions above the antennas. In comparison with modulated frequency systems, GPR systems consist of a much simpler technology, are commercially available and therefore are cheaper. The radar observed the temporal alternation of the snow height over more than 2.5 months. The presented data showed that with moved antennas, it is possible to record the snow height with an uncertainty of less than 8% in comparison with the probed snow depth. Three persistent melt crusts, which formed at the snow surface and were buried by further new snow events, were used as reflecting tracers to follow the snow cover evolution and to determine the strain rates of underlaying layers between adjacent measurements. The height in two-way travel time of each layer changed over time, which is a cumulative effect of settlement and variation of wave speed in response to densification and liquid water content. The infiltration of liquid water with depth during melt processes was clearly observed during one event. All recorded reflections appeared in concordance with the physical principles (e.g. in phase structure), and one can assume that distinct density steps above a certain threshold result in reflections in the radargram. The accuracy of the used impulse radar system in determining the snow water equivalent is in good agreement with previous studies, which used continuous wave radar systems. The results of this pilot study encourage further investigations with radar measurements using the described test arrangement on a daily basis for continuous destruction-free monitoring of the snow cover. © 2010 John Wiley & Sons, Ltd.

Description: Depending on season, rainfall characteristics and tree species, interception amounts to 15-50% of total precipitation in a forest under temperate climates. Many studies have investigated the importance of interception of different tree species in all kinds of different climates. Often authors merely determine interception storage capacity of that specific species and the considered event, and only sometimes a distinction is made between foliated and non-foliated trees. However, interception is highly variable in time and space. First, since potential evaporation is higher in summer, but secondly because the storage capacity has a seasonal pattern. Besides weather characteristics, such as wind and rain intensity, snow causes large variations in the maximum storage capacity. In an experimental beech plot in Luxembourg, we found storage capacity of canopy interception to show a clear seasonal pattern varying from 0·1 mm in winter to 1·2 mm in summer. The capacity of the forest floor appears to be rather constant over time at 1.8 mm. Both have a standard deviation as high as ±100%. However, the process is not sensitive to this variability resulting only in 11% variation of evaporation estimates. Hence, the number of raindays and the potential evaporation are stronger driving factors on interception. Furthermore, the spatial correlation of the throughfall and infiltration has been investigated with semi-variograms and time stability plots. Within 6-7 m distance, throughfall and infiltration are correlated and the general persistence is rather weak. © 2010 John Wiley & Sons, Ltd.

Description: In organic soils, hydraulic conductivity is related to the degree of decomposition and soil compression, which reduce the effective pore diameter and consequently restrict water flow. This study investigates how the size distribution and geometry of air-filled pores control the unsaturated hydraulic conductivity of peat soils using high-resolution (45 μm) three-dimensional (3D) X-ray computed tomography (CT) and digital image processing of four peat sub-samples from varying depths under a constant soil water pressure head. Pore structure and configuration in peat were found to be irregular, with volume and cross-sectional area showing fractal behaviour that suggests pores having smaller values of the fractal dimension in deeper, more decomposed peat, have higher tortuosity and lower connectivity, which influences hydraulic conductivity. The image analysis showed that the large reduction of unsaturated hydraulic conductivity with depth is essentially controlled by airfilled pore hydraulic radius, tortuosity, air-filled pore density and the fractal dimension due to degree of decomposition and compression of the organic matter. The comparisons between unsaturated hydraulic conductivity computed from the air-filled pore size and geometric distribution showed satisfactory agreement with direct measurements using the permeameter method. This understanding is important in characterizing peat properties and its heterogeneity for monitoring the progress of complex flow processes at the field scale in peatlands. © 2010 John Wiley & Sons, Ltd.

Description: This study is focused on the analysis of the relationship between sap-flow-derived transpiration measured in a Scots pine stand in the Vallcebre research catchments (NE Iberian Peninsula) and meteorological and rainfall data. The first part of the study is focused on the analysis of temperature and rainfall anomalies. Then, the Scots pine transpiration response to inter-annual rainfall variability, soil water stress and water table depth variations during the period 1997-2000 is analysed. This period includes the extremely dry year of 1998, which allows us to infer the response of Scots pine transpiration to severe droughts. Scots pine transpiration during the summer presented a high inter-annual variability, largely related to rainfall amounts. Daily transpiration during dry summers was 40% of the transpiration of a summer day with average rainfall. Moreover, during dry summers, transpiration rates were not fully recovered even after significant rainfall events. The analysis of the dependence of Scots pine transpiration on available water indicated the strong limitation on transpiration induced by water content in the whole soil profile as well as by water table position. Under these drought conditions, a reduction of runoff and deep water stores was observed at the catchment scale, suggesting that the predicted increase in the frequency of severe summer droughts may threaten the current role of Mediterranean mountain catchments as suppliers of water resources for lowland areas. © 2010 John Wiley & Sons, Ltd.

Description: Spatially distributed groundwater recharge was simulated for a segment of a semi-arid valley using three different treatments of meteorological input data and potential evapotranspiration (PET). For the same area, timeframe, land cover characteristics and soil properties, groundwater recharge was estimate using (i) single-station climate data with monthly PET calculated by the Thornthwaite method; (ii) single-station climate data with daily PET calculated by the Penman-Monteith method; and (iii) daily gridded climate data with spatially distributed PET calculated using the Penman-Monteith method. For each treatment, the magnitude and distribution of actual evapotranspiration (AET) for summer months compared well with those estimated for a 5-year crop study, suggesting that the near-surface hydrological processes were replicated and that subsequent groundwater recharge rates are realistic. However, for winter months, calculated AET was near zero when using the Thornthwaite PET method. Mean annual groundwater recharge varied from ~3.2 to 10.0 mm when PET was calculated by the Thornthwaite method, and from ~1.8 to 7.5 mm when PET was calculated by the Penman-Monteith method. Comparisons of bivariate plots of seasonal recharge rates estimated from single-station versus gridded surface climate reveal that there is greater variability between the different methods for spring months, which is the season of greatest recharge. Furthermore, these seasonal differences are shown to provide different results when compared to the depth to water table, which could lead to different results of evaporative extinction depth. These findings illustrate potential consequences of using different approaches for representing spatial meteorological input data, which could provide conflicting predictions when modelling the influence of climate change on groundwater recharge. © 2010 John Wiley & Sons, Ltd.

Description: A one-dimensional, two-layer solute transport model is developed to simulate chemical transport process in an initially unsaturated soil with ponding water on the soil surface before surface runoff starts. The developed mathematical model is tested against a laboratory experiment. The infiltration and diffusion processes are mathematically lumped together and described by incomplete mixing parameters. Based on mass conservation and water balance equations, the model is developed to describe solute transport in a two-zone layer, a ponding runoff zone and a soil mixing zone. The two-zone layer is treated as one system to avoid describing the complicated chemical transport processes near the soil surface in the mixing zone. The proposed model was analytically solved, and the solutions agreed well with the experimental data. The developed experimental method and mathematical model were used to study the effect of the soil initial moisture saturation on chemical concentration in surface runoff. The study results indicated that, when the soil was initially saturated, chemical concentration in surface runoff was significantly (two orders of magnitude) higher than that with initially unsaturated soil, while the initial chemical concentrations at the two cases were of the same magnitude. The soil mixing depth for the initially unsaturated soil was much larger than that for the initially saturated soil, and the incomplete runoff mixing parameter was larger for the initially unsaturated soil. The higher the infiltration rate of the soil, the greater the infiltration-related incomplete mixing parameter. According to the quantitative analysis, the soil mixing depth was found to be sensitive for both initially unsaturated and saturated soils, and the incomplete runoff mixing parameter was sensitive for initially saturated soil but not for the initially unsaturated soil; the incomplete infiltration mixing parameter behaved just the opposite. Some suggestions are made for reducing chemical loss from runoff. © 2010 John Wiley & Sons, Ltd.

Description: Variability and time-stability analysis for field-scale (800 m) Electronically Scanned Thinned Array Radiometer soil moisture within a satellite scale footprint (~50 km) were quantified using observations from the Southern Great Plains Hydrology Experiment 1997 and 1999 (SGP97 and SGP99). The pixels' time-stability properties were examined with respect to soil, vegetation and topographic parameters in order to determine which physical parameters can be used to identify good candidate observation locations for validating soil moisture from satellite observations and global-scale model output. The results show that the time-stability concept remains valid at the satellite scale. The root mean square error values were 1.47, 1.51, 1.93 and 2.32% for the 1st, 2nd, 50th and 100th most stable fields, respectively. The most stable locations had sand and clay percentages consistent with sandy loam soils and moderate to high normalized difference vegetation index values. Neither land cover nor topography properties could be used to identify potentially stable fields in the study region. © 2010 John Wiley & Sons, Ltd.

Description: The role of bedrock groundwater in rainfall-runoff processes is poorly understood. Hydrometric, tracer and subsurface water potential observations were conducted to study the role of bedrock groundwater and subsurface flow in the rainfall-runoff process in a small headwater catchment in Shiranui, Kumamoto prefecture, south-west Japan. The catchment bedrock consists of a strongly weathered, fractured andesite layer and a relatively fresh continuous layer. Major chemical constituents and stable isotopic ratios of δ18O and δD were analysed for spring water, rainwater, soil water and bedrock groundwater. Temporal and spatial variation in SiO2 showed that stream flow under the base flow condition was maintained by bedrock groundwater. Time series of three components of the rainstorm hydrograph (rainwater, soil water and bedrock groundwater) separated by end member mixing analysis showed that each component fluctuated during rainstorm, and their patterns and magnitudes differed between events. During a typical mid-magnitude storm event, a delayed secondary runoff peak with 1.0 l s-1 was caused by increase in the bedrock groundwater component, whereas during a large rainstorm event the bedrock groundwater component increased to ≈2.5 l s-1. This research shows that the contribution of bedrock groundwater and soil water depends strongly on the location of the groundwater table, i.e. whether or not it rises above the soil-bedrock interface. © 2010 John Wiley & Sons, Ltd.

Description: In this study, the Surface Energy Balance Algorithm for Land (SEBAL) method from the meteorological stations and remote sensing data was used to compute the evapotranspiration (ET) rate for the middle reach of Heihe River Basin in China, in order to analyse the distribution of ET over the whole area including and surrounding the river. Energy fluxes and daily ET maps were calculated for the study area, and a number of statistics computed for each type of land cover. The results show that the ET in the study area ranged from 0 to 4.94, with an average value of 1.68 mm, on 23 September 2007. The highest ET values appeared over all types of water bodies, including rivers, reservoirs, etc., and the lowest values appeared over residential areas and in the Gobi desert. The differing values of ET for different land-cover types were due mainly to the differences in evaporative fraction. The quantity of ET was about 1.06 × 107 m3 in the oasis over the course of the day, with 6.50 × 106 m3 of this amount generated by farmland, approximately 61%. Micro-lysimeters were placed in the study area in 2009, in order to calculate cumulative ET over an entire growing season, in the future. © 2010 John Wiley & Sons, Ltd.

Description: Growing human pressure and potential change in precipitation pattern induced by climate change require a more efficient and sustainable use of water resources. Hydrological models can provide a fundamental contribution to this purpose, especially as increasing availability of meteorological data and forecast allows for more accurate runoff predictions. In this article, two models are presented for describing the flow formation process in a sub-alpine catchment: a distributed parameter, physically based model, and a lumped parameter, empirical model. The scope is to compare the two modelling approaches and to assess the impact of hydrometeorological information, either observations or forecast, on water resources management. This is carried out by simulating the real-time management of the regulated lake that drains the catchment, using the inflow predictions provided by the two models. © 2010 John Wiley & Sons, Ltd.

Description: An accurate prediction of solute infiltration in a soil profile is important in the area of environmental science, groundwater and civil engineering. We examined the infiltration pattern and monitored the infiltration process using a combined method of dye tracer test and electrical resistivity tomography (ERT) in an undisturbed field soil (1 m × 1 m). A homogeneous matrix flow was observed in the surface soil (A horizon), but a preferential flow along macropores and residual rock structure was the dominant infiltration pattern in the subsurface soil. Saturated interflow along the slopping boundaries of A and C1 horizons and of an upper sandy layer and a lower thin clay layer in the C horizon was also observed. The result of ERT showed that matrix flow started first in A horizon and then the infiltration was followed by the preferential flows along the sloping interfaces and macropores. The ERT did not show as much detail as the dye-stained image for the preferential flow. However, the area with the higher staining density where preferential flow was dominant showed a relatively lower electrical resistivity. The result of this study indicates that ERT can be applied for the monitoring of solute transportation in the vadose zone. © 2010 John Wiley & Sons, Ltd.

Description: Brazilian semi-arid regions are characterized by water scarcity, vulnerability to desertification, and climate variability. The investigation of hydrological processes in this region is of major interest not only for water planning strategies but also to address the possible impact of future climate and land-use changes on water resources. A hydrological distributed catchment-scale model (DiCaSM) has been applied to simulate hydrological processes in a small representative catchment of the Brazilian northeast semi-arid region, and also to investigate the impact of climate and land-use changes, as well as changes associated with biofuel/energy crops production. The catchment is part of the Brazilian network for semi-arid hydrology, established by the Brazilian Federal Government. Estimating and modelling streamflow (STF) and recharge in semi-arid areas is a challenging task, mainly because of limitation in in situ measurements, and also due to the local nature of some processes. Direct recharge measurements are very difficult in semi-arid catchments and contain a high level of uncertainty. The latter is usually addressed by short- and long-time-scale calibration and validation at catchment scale, as well as by examining the model sensitivity to the physical parameters responsible for the recharge. The DiCaSM model was run from 2000 to 2008, and streamflow was successfully simulated, with a Nash-Sutcliffe (NS) efficiency coefficient of 0.73, and R2 of 0.79. On the basis of a range of climate change scenarios for the region, the DiCaSM model forecasted a reduction by 35%, 68%, and 77%, in groundwater recharge (GWR), and by 34%, 65%, and 72%, in streamflow, for the time spans 2010-2039, 2040-2069, and 2070-2099, respectively, could take place for a dry future climate scenario. These reductions would produce severe impact on water availability in the region. Introducing castor beans to the catchment would increase the GWR and streamflow, mainly if the caatinga areas would be converted into castor beans production. Changing an area of 1000 ha from caatinga to castor beans would increase the GWR by 46% and streamflow by 3%. If the same area of pasture is converted into castor beans, there would be an increase in GWR and streamflow by 24% and 5%, respectively. Such results are expected to contribute towards environmental policies for north-east Brazil (NEB), and to biofuel production perspectives in the region. © 2010 John Wiley & Sons, Ltd.

Description: The growing concern for health-related problems deriving from pollutants leaching is driving national and international administrations to support the development of tools for evaluating the effects of alternate management scenarios and identifying vulnerable areas. Cropping systems models are powerful tools for evaluating leachates under different environmental, social, and management conditions. As percolating water is the transport vehicle for pollutants transport in soil, a reliable evaluation of water balance models is a fundamental prerequisite for investigating pesticides and nitrate fate. As specific approaches for the evaluation of multi-layer evolution of state variables are missing, we propose a fuzzy-based, integrated indicator (ISWC: 0, best; 1, worst) for a comprehensive evaluation of soil water content (SWC) simulations. We aggregated error metrics with others quantifying the homogeneity of errors across different soil layers, the capability of models to reproduce complex dynamics function of both time and soil depth, and model complexity. We tested ISWC on a sample dataset where the models CropSyst and CERES-Wheat were used to simulate SWC for winter wheat systems. ISWC revealed that, in the explored conditions, the global assessment of the two models' performances allowed identification of CropSyst as the best (average ISWC = 0.441, with a value of 0.537 obtained by CERES-Wheat), although each model prevailed for some of the metrics. CropSyst presented the highest accuracy (average agreement module = 0.400), whereas CERES-Wheat's accuracy was slightly worse, although achieved with a simplified modelling approach (average Akaike Information Criterion = -230.44), thereby favouring largearea applicability. The non-univocal scores achieved by the models for the different metrics support the use of multi-metric evaluation approaches for quantifying the different aspects of water balance model performances. © 2010 John Wiley & Sons, Ltd.

Description: This article discusses preferential flow paths through soil and rock and how these contribute to the style and timing of landslides. The importance of geological compartmentalization because of the presence of aquicludes such as weathered dykes and faults is emphasized as is channel flow through fracture networks and through natural pipes in soil-like material. Although piping is a contributing factor to some landslides, as generally recognized, it can also be a sign of inherent distress in a developing landslide where water flow exploits cracks in the dilating rock mass. It is suggested that the association might be targeted in ground investigation. Inactive or low activity pipe systems can be identified by the anomalous presence of alluvial sediments at depth in the geological profile, whereas active pipe systems may simply comprise voids that could be misinterpreted as core loss during ground investigation. Examples of pipe systems encountered during ground investigations are given for various landslides and several case studies are illustrated in this article. Mitigation measures for preventing landslides triggered by rainfall are discussed together with the difficulties associated with preferential flow paths. Copyright © 2010 John Wiley & Sons, Ltd.

Description: There exists a growing need to improve our understanding of catchment processes on larger scales. This need is especially enhanced in rapidly developing countries such as China where the turnover of traditionally used land to urbanized and industrialized areas influences water resources. In this study, we chose a multi-tracer approach in a large, ungauged basin in Inner Mongolia to elucidate the processes that generate stream flow. We applied end member mixing analysis (EMMA) to identify and quantify the major runoff generating sources in a three end member system. Stream water and a set of eight possible end members were sampled throughout three consecutive vegetation periods. Samples were analysed with an inductively coupled plasma-mass spectrometry (ICP-MS) and an ion chromatograph (IC) for a suite of 33 solutes including 24 cations and 7 anions. We determined that seven tracers exhibited conservative behaviour, they were Li, Rb, Sr, Na, Mg, Cl and electrical conductivity (EC). Stable water isotopes (δD and δ18O) highlight differences between the end members. Our results indicate strong interannual variability of end member composition and contribution between the 3 years. We were able to identify shallow groundwater aquifers as important runoff generating sources in some years and deeper groundwater aquifers in other years which vary in rainfall and discharge. A shallow sand dune aquifer which covers a significant part of the area plays an important role in storing and contributing water to the river. Our results also suggest that the major runoff generating source in the dryer year has not been identified yet. Our results prompt us to focus future work on understanding interannual changes in end member contribution especially in semi-arid regions. © 2010 John Wiley & Sons, Ltd.

Description: Diffuse sediment pollution impairs water quality, exerts a key control on the transfer and fate of nutrients and contaminants and causes deleterious impacts on freshwater ecology. A variety of catchment sediment sources can contribute to such problems. Sediment control strategies and effective targeting of mitigation options therefore require robust quantitative information on the key sources of the sediment problem at catchment scale. Recent observations by Catchment Sensitive Farming Officers (CSFO's) in England have highlighted road verges damaged and eroded by passing vehicles, particularly large farm machinery, and livestock herd movement as visually important potential sources of local sediment problems. A study was therefore undertaken to assess the relative importance of damaged road verges as a suspended sediment source in three sub-catchments of the Hampshire Avon drainage basin, southern UK. Road verge sediment contributions were apportioned in conjunction with those from agricultural topsoils and channel banks/subsurface sources. Time-integrating isokinetic samplers were deployed to sample suspended sediment fluxes at the outlets of two control sub-catchments drained by the Rivers Chitterne and Till selected to characterize areas with a low road network density and limited visual evidence of verge damage, as well as the River Sem sub-catchment used to represent areas where road verge damage is more prevalent. The findings of a sediment source fingerprinting investigation based on a combination of intermittent sampling campaigns spanning the period 22/5/02-27/4/08 suggested that the respective overall mean relative sediment contributions from damaged road verges were 5 ± 3%, 4 ± 2% and 20 ± 2%. Relative inputs from damaged road verges for any specific sampling period in the River Sem sub-catchment were as high as 33 ± 2%. Reconstruction of historical sources in the same sub-catchment, based on the geochemical record stored in a floodplain depth profile, suggested that the significance of damaged road verges as a sediment source has increased over the past 15-20 years. The findings provide important information on damaged road verges as a primary source of suspended sediment and imply that catchment sediment control strategies and mitigation plans should consider such verges in addition to those agricultural and channel sources traditionally taken into account when attempting to reduce sediment pressures on aquatic resources. Copyright © 2010 John Wiley & Sons, Ltd.

Description: There is now a wide literature on the use of tracer age and transit time distributions to diagnose transport in environmental systems. Theories have been proposed using idealized tracer age modelling for ocean ventilation, atmospheric circulation, soil, stream and groundwater flow. Most approaches assume a steady flow regime and stationarity in the concentration (tracer) distribution function for age, although recent work shows that this is not a necessary assumption. In this paper, dynamic model for flow, concentration, and age in volume-averaged and a spatially distributed watershed system are derived in terms of the moments of the underlying distribution function for tracer age, time, and position. Several theoretical and practical issues are presented: (1) The low-order moments of the age distribution function are sufficient to construct a dynamical system for the mean age and concentration under steady or transient flow conditions. (2) Solutions to the coupled system of equations for flow, concentration and age show that 'age' of solutes stored within the watershed or leaving the watershed is a dynamic process which depends on flow variations as well as the solute or tracer dynamics. (3) Intermittency of wetting and drying cycles leads to an apparent increase in the tracer age in proportional to the duration of the 'dry' phase. (4) The question of how mobile/immobile flow may affect the age of solutes is examined by including a low permeable, passive store that relaxes the well-mixed assumption. (5). A spatially distributed advective and dispersive transport solution for age evolution over a simple 1-D hillslope is developed to demonstrate the age theory for a distributed source of water and tracer, and the solution is shown to have very similar input-output behaviour when compared to the volume-average model for comparable parameters. Copyright © 2010 John Wiley & Sons, Ltd.

Description: The rapid development of data mining provides a new method for water resource management, hydrology and hydroinformatics research. In the paper, based on data mining theory and technology, we analyse hydrological daily discharge time series of the Shaligunlanke Station in the Tarim River Basin in China from the year 1961 to 2000. Firstly, according to the four monthly statistics, namely mean monthly discharge, monthly maximum discharge, monthly amplitude and monthly standard deviation, K-mean clustering was used to segment the annual process of the daily discharge. The clustering result showed that the annual process of the daily discharge can be divided into five segments: snowmelt period I (April), snowmelt period II (May), rainfall period I (June-August), rainfall period II (September) and dry period (October-December and January-March). Secondly, dynamic time warping (DTW), which is a different distance metric method from the traditional Euclidian distance metric, was used to look for similarities in the discharge process. On the basis of the similarity matrix, the similar discharge processes can be mined in each period. Thirdly, agglomerative hierarchical clustering was used to cluster and discover the discharge patterns in terms of the autoregressive model. It was found that the discharge had a close relationship with the temperature and the precipitation, and the discharge processes were more similar under the same climatic condition. Our study shows that data mining is a feasible and efficient approach to discover the hidden information in the historical hydrological data and mining the implicative laws under the hydrological process. Copyright © 2010 John Wiley & Sons, Ltd.

Description: Revegetation is critical to restoring hydrological function on waste disposal sites in order to minimize runoff and drainage and safeguard the water quality of the catchment. In this study, we determined the components of soil-water balance between late 2006 and the end of 2008 for three vegetation types established over sites used for waste disposal: (i) a juvenile plantation of mixed Australian woody species; (ii) a block of mixed tree seedlings; (iii) and an ungrazed grass pasture. These were compared against a nearby natural woodland taken as an analogue of a pre-existing hydrological state. Evapotranspiration (ET) was the major component of the soil-water balance in all the four vegetation types. In the plantation and woodland, ET accounted for 60-93% of the annual rainfall compared to 44-88% in the grass and seedling blocks. While the balance of rainfall was largely lost to runoff in the plantation and the woodland, it was split almost equally between runoff and drainage in the other two vegetation covers. The plantation maintained parity in its ET with woodland due to groundcover that contributed at least 70% of the water use, while seasonal growth and periodic mowing reduced ET from the grass. Over the 2 years, the height of the deep (?19 m above sea level) water table under the plantation and grass declined by an average of 0?3 m, while it rose by a similar magnitude in the woodland. The height of the shallow water table (?8 m above sea level) showed no consistent change. We conclude that, with a good groundcover of mixed herbaceous species, a juvenile plantation can restore hydrological function and minimize deep recharge of a waste disposal site to the status of that under a pre-existing undisturbed woodland. Copyright © 2010 John Wiley & Sons, Ltd.

Description: The headwaters of the Ganga (the Alaknanda, Bhagirathi and the Ganga) were analysed for their dissolved major ions, Sr and 87 Sr/ 86 Sr on a biweekly to monthly basis over a period of one year to determine their temporal variations and the factors contributing to them. The concentrations of major ions and Sr show significant seasonal variation with lower values during monsoon period in all the three rivers. A similar trend is also observed for 87 Sr/ 86 Sr and Na * /Ca (Na * = Na r -Cl r ) suggesting relatively lower contribution of Sr and Na from silicates (which are more radiogenic in Sr) during monsoon. Budget calculations show that silicate derived dissolved Sr (Sr s ) in the river Ganga, Alaknanda and the Bhagirathi varied from 10 ± 4 to 27 ± 11, 7 ± 3 to 30 ± 12, 16 ± 6 to 57 ± 23% of measured Sr respectively with lower values during monsoon. The relative decrease in silicate erosion compared to carbonate during monsoon can result from several factors, these include higher dissolution kinetics of the carbonates, lower water-rock interaction time and availability of larger area for weathering. The annual discharge weighted Sr flux derived from the time series data is higher by ~20% from that based on peak flow Sr, and lower by ~40% compared to that derived from lean flow Sr concentration. The area-normalized annual flux of dissolved Sr from the Ganga at Rishikesh is about five times its flux at Rajshahi (Bangladesh) and a few other major global rivers, such as the Amazon, indicating higher erosion rate over the Himalaya. Copyright © 2010 John Wiley & Sons, Ltd.

Description: Characterizing zones of a watershed based on the water table is used to understand and predict internal watershed processes. In watersheds dominated by lateral preferential flow, the water table response typically shows a distinct hydraulically limited pattern. This response is characterized by a capping of the rising water table when the lateral preferential flow features are activated and subsurface flow still increases. We expected that this response would be related to the contributing area since nearby hillslope excavations showed that the development of preferential flow network was positively correlated with the contributing area. The watershed was stratified into three predetermined zones and installed 25 piezometers to measure the water table dynamics. The objectives were (1) to characterize the water table-runoff relationship, (2) to prove preferential flow by observable characteristics and (3) to test the feasibility of identifying areas within a watershed that are dominated by lateral preferential flow. Watershed zones were not well defined and there was no strong relationship between the hydraulically limited response and observable watershed characteristics. Although zones might still be useful for grouping the hillslope processes, the piezometric response may not be an appropriate indicator for mapping the watershed into areas with runoff dominated by lateral preferential flow. Copyright © 2010 John Wiley & Sons, Ltd.

Description: Catchment travel time distributions reflect how precipitation from different storms is stored and mixed as it is transported to the stream. Catchment travel time distributions can be described by the mean travel time and the shape of the distribution around the mean. Whereas mean travel times have been quantified in a range of catchment studies, only rarely has the shape of the distribution been estimated. The shape of the distribution affects both the short-term and long-term catchment response to a pulse input of a soluble contaminant. Travel time distributions are usually estimated from conservative tracer concentrations in precipitation and streamflow, which are analyzed using time-domain convolution or spectral methods. Of these two approaches, spectral methods are better suited to determining the shape of the distribution. Previous spectral analyses of both rainfall and streamflow tracer time series from several catchments in Wales showed that rainfall chemistry spectra resemble white noise, whereas the stream tracer spectra in these same catchments exhibit fractal 1/f scaling over three orders of magnitude. Here we test the generality of the observed fractal scaling of streamflow chemistry, using spectral analysis of long-term tracer time series from 22 catchments in North America and Europe. We demonstrate that 1/f fractal scaling of stream chemistry is a common feature of these catchments. These observations imply that catchments typically exhibit an approximate power-law distribution of travel times, and thus retain a long memory of past inputs. The observed fractal scaling places strong constraints on possible models of catchment behavior, because it is inconsistent with the exponential travel time distributions that are predicted by simple mixing models. Copyright © 2010 John Wiley & Sons, Ltd.

Description: The integrated hydrological modelling system, IHMS, has been described in detail in Part 1 of this paper. The system comprises three models: Distributed Catchment Scale Model (DiCaSM), MODFLOW (v96 and v2000) and SWI. The DiCaSM simulates different components of the unsaturated zone water balance, including groundwater recharge. The recharge output from DiCaSM is used as input to the saturated zone model MODFLOW, which subsequently calculates groundwater flows and head distributions. The main objectives of this paper are: (1) to show the way more accurate predictions of groundwater levels in two Cyprus catchments can be obtained using improved estimates of groundwater recharge from the catchment water balance, and (2) to demonstrate the interface utility that simulates communication between unsaturated and saturated zone models and allows the transmission of data between the two models at the required spatial and temporal scales. The linked models can be used to predict the impact of future climate change on surface and groundwater resources and to estimate the future water supply shortfall in the island up to 2050. The DiCaSM unsaturated zone model was successfully calibrated and validated against stream flows with reasonable values for goodness of fit as shown by the Nash-Sutcliffe criterion. Groundwater recharge obtained from the successful tests was applied at various spatial and temporal scales to the Kouris and Akrotiri catchments in Cyprus. These recharge values produced good estimates of groundwater levels in both catchments. Once calibrated, the model was run using a number of possible future climate change scenarios. The results showed that by 2050, groundwater and surface water supplies would decrease by 35% and 24% for Kouris and 20% and 17% for Akrotiri, respectively. The gap between water supply and demand showed a linear increase with time. The results suggest that IHMS can be used as an effective tool for water authorities and decision makers to help balance demand and supply on the island. © 2010 John Wiley & Sons, Ltd.

Description: Concern has been expressed that Miscanthus x giganteus, a dedicated biomass crop, may have a high water use, with implications for its economic yield and impacts on water resources. There is particular uncertainty about one component of the water use, the interception loss. Measurements of the interception loss were made in a plot of the crop at a site in south-east England, during 1997/1998 and 1998/1999. The measured interception losses were 25 and 24% of gross rainfall, respectively. Winter interception losses are relatively high, which is attributed to the slow rate of leaf loss. A Monte Carlo procedure was used to optimize three of the parameters of the Gash interception model on the 1997/1998 data. The simulated values had an uncertainty of 1·1 mm per storm in 1997/1998 and 2·9 mm per storm in 1998/1999. The model was also used to investigate the potential effect of the evaporation rate being overestimated due to the measurements being made in an experimental plot. This showed that the interception losses might be reduced to 21 and 18% in field scale plantations. A consideration of the relative interception rate demonstrated that the crop behaved more like a forest, in terms of the interception losses, during the winter months. © Crown Copyright 2010. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

Description: Rapid flow in connected preferential flow paths is crucial for fast transport of water and solutes through soils, especially at tile-drained field sites. In the present study, we propose a spatially explicit approach to represent worm burrows as connected structures of realistic geometry, high conductivity and low retention capacity in a two-dimensional physically based model. We show that this approach allows successful prediction of a tile-drain discharge and preferential flow patterns in soil observed during the irrigation of a tile-drained hillslope in the Weiherbach catchment. However, we found a considerable equifinality in the spatial setup of the model when key parameters such as the area density of worm burrows, the maximum volumetric water flows inside these macropores and the conductivity of the tile drain were varied within the ranges of either our measurements or measurements reported in the literature. In total, we found that 67 out of 432 model runs were acceptable [Nash-Sutcliffe (NS) ≥75]. Among these, the 13 best yielded a NS coefficient of more than 0.9, which means that more than 90% of the flow variability is explained by the model. Also, the flow volumes were in good accordance and timing errors were less than or equal to 20 min. It is suggested that this uncertainty/equifinality could be reduced when more precise data on initial states of the subsurface and on the width of the control volume draining into a single drainage tube could be made available. However, such data are currently most difficult to assess even at very well investigated sites such as those studied here. We thus suggest that non-uniqueness of the spatial setup of process-based model seems to be an important factor causing predictive uncertainty at many sites where preferential flow dominates system response. Copyright © 2010 John Wiley & Sons, Ltd.

Description: Hydrological model parameter estimation is an important aspect in hydrologic modelling. Usually, parameters are estimated through an objective function minimization, quantifying the mismatch between the model results and the observations. The objective function choice has a large impact on the sensitivity analysis and calibration outcomes. In this study, it is assessed whether spectral objective functions can compete with an objective function in the time domain for optimization of the Soil and Water Assessment Tool (SWAT). Three empirical spectral objective functions were applied, based on matching (i) Fourier amplitude spectra, (ii) periodograms and (iii) Fourier series of simulated and observed discharge time series. It is shown that most sensitive parameters and their optimal values are distinct for different objective functions. The best results were found through calibration with an objective function based on the square difference between the simulated and observed discharge Fourier series coefficients. The potential strengths and weaknesses of using a spectral objective function as compared to utilising a time domain objective function are discussed. Copyright © 2010 John Wiley & Sons, Ltd.

Description: The chemical and isotopic composition of monthly composite rain samples collected at 13 meteoric stations in Syria during two hydrological cycles from 1991 to 1993 have been measured. The chemical analysis of the samples revealed at a number of stations pollution due to industry and sand storms. The temporal and spatial variation of the isotopic composition has been found to be comparable with one of the neighbouring countries such as Jordan and others. The average weighted oxygen-18 and deuterium values are -7·5 and -39·11‰, respectively, and the deuterium excess is 21‰. The individual isotope values can be divided into two groups. One group is represented by winter precipitation and fits closely the Mediterranean Meteorological Water Line (MMWL). Thus, for winter precipitation, condensation of Mediterranean water vapour appears to be the dominating isotope fractionation process. The other group represents spring precipitation and is spread along an evaporation line below the MMWL, thus indicating the influence of sub-cloud evaporation. The d-excess has been found to be lower in the north of Syria (19.9‰ at Tartous, 18.1‰ at Jarablous) than in the south of the country (23.4‰ at Sweida, 24.1‰ at Izra) where Mediterranean air mass dominates. The d-excess of precipitation in neighbouring countries is also close to the average value of the eastern Mediterranean basin of 22‰, e.g. for Jordan the value is 23‰, which signifies that Mediterranean water vapour is, for all these countries, the dominant source of precipitation. The tritium content of precipitation was found to increase with distance from the coast (5.3 TU at coastal station Tartous, 8.8 TU at continental station Palmyra). Low tritium content and high d-excess at coastal stations clearly indicate a Mediterranean air moisture source. Copyright © 2010 John Wiley & Sons, Ltd.

Description: Organized spatial distribution of plants (plant zonation) in salt marshes has been linked to the soil aeration condition in the rhizosphere through simplistic tidal inundation parameters. Here, a soil saturation index (ratio of saturation period to tidal period at a soil depth) is introduced to describe the soil aeration condition. This new index captures the effects of not only the tidal inundation period and frequency but also the flow dynamics of groundwater in the marsh soil. One-dimensional numerical models based on saturated flow with the Boussinesq approximations and a two-dimensional variably saturated flow model were developed to explore the behaviour of this new soil aeration variable under the influence of spring-neap tides. Simulations revealed two characteristic zones of soil aeration across the salt marsh: a relatively well aerated near-creek zone and a poorly aerated interior zone. In the near-creek zone, soils undergo periodic wetting and drying as the groundwater table fluctuates throughout the spring-neap cycle. In the interior, the soil remains largely water saturated except for neap tide periods when limited drainage occurs. Although such a change of soil aeration condition has been observed in previous numerical simulations, the soil saturation index provides a clear delineation of the zones that are separated by an 'inflexion point' on the averaged index curve. The results show how the saturation index represents the effects of soil properties, tidal parameters and marsh platform elevation on marsh soil aeration. Simulations of these combined effects have not been possible with traditional tidal inundation parameters. The saturation index can be easily derived using relatively simple models based on five non-dimensional variables. Copyright © 2010 John Wiley & Sons, Ltd.

Description: This article aims to identify the large-scale climate variables that yield significant statistical relationships with precipitation and discharge for a British river basin (Dyfi). Ranked correlation analysis was performed between gridded ERA-40 atmospheric data and Dyfi precipitation and discharge for individual months. Precipitation and discharge demonstrate significant negative correlation with mean sea level pressure (MSLP). Strongest MSLP correlation areas move from north of Britain in winter to central Britain in summer; this shift is associated with a displacement of geopotential (Z) and zonal wind (U). Movement of significant correlation regions (not captured by the North Atlantic Oscillation Index) highlights the dynamic nature of precipitation and river flow generating weather systems throughout the year. Existence of strong significant correlation shows potential for exploiting large-scale climate variables in forecasting precipitation and river flow in Britain. Copyright © 2010 John Wiley & Sons, Ltd.

Description: Understanding the impacts of land-use changes on hydrology at the watershed scale can facilitate development of sustainable water resource strategies. This paper investigates the hydrological effects of land-use change in Zanjanrood basin, Iran. The water balance was simulated using the Soil and Water Assessment Tool (AVSWAT2000). Model calibration and uncertainty analysis were performed with sequential uncertainty fitting (SUFI-2). Simulation results from January 1998 to December 2002 were used for parameter calibration, and then the model was validated for the period of January 2003 to December 2004. The predicted monthly streamflow matched the observed values: during calibration the correlation coefficient was 0·86 and the Nash-Sutcliffe coefficient 0·79, compared with 0·80 and 0·79, respectively, during validation. The model was used to simulate the main components of the hydrological cycle, in order to study the effects of land-use changes in 1967, 1994 and 2007. The study reveals that during 1967 a 34·5% decrease of grassland with concurrent increases of shrubland (13·9%), rain-fed agriculture (12·1%), bare ground (5·5%) irrigated agriculture (2·2%), and urban area (0·7%) led to a 33% increase in the amount of surface runoff and a 22% decrease in the groundwater recharge. Furthermore, the area of sub-basins that was influenced by high runoff (14-28 mm) increased. The results indicate that the hydrological response to overgrazing and the replacing of rangelands (grassland and shrubland) with rain-fed agriculture and bare ground (badlands) is nonlinear and exhibits a threshold effect. The runoff rises dramatically when more than 60% of the rangeland is removed. For groundwater this threshold lies at an 80% decrease in rangeland. Copyright © 2009 John Wiley & Sons, Ltd.

Description: Snowmelt is the most significant source of runoff generation and recharge in many of the mountainous watersheds worldwide and this is especially true in the southwestern United States. Yet, the isotopic and geochemical composition of the soil-meltwater endmember remains poorly constrained. Using the isotopic compositions of snow and snowmelt runoff samples taken from the landscape surface as proxies for soil-meltwater endmembers is problematic since they are typically not representative of the actual composition of soil meltwater. Furthermore, the applicability of current methodologies to collect the isotopic composition of meltwater is limited because of the remote and often seasonally inaccessible nature of the terrain where snowpacks develop. Therefore, a robust methodology requiring little maintenance or monitoring is desirable. A lab experiment was conducted to determine the suitability of using a modified passive capillary sampler (M-PCAPS) design to collect snowmelt infiltration for isotopic analysis. Passive capillary samplers are constructed from fiberglass wicks that can be installed in the soil to sample vadose-zone waters under a wide range of matric potentials and require little maintenance. Results from this lab experiment indicate that the wicking process associated with M-PCAPS does not fractionate water but certain precautions are necessary to prevent exchange between the wick and the atmosphere. In this experiment, M-PCAPS effectively tracked the changing isotopic composition of a soil reservoir undergoing evaporation. Therefore, M-PCAPS provide a robust methodology to sample the isotopic composition of snowmelt infiltration in remote watersheds and similar applications. Copyright © 2009 John Wiley & Sons, Ltd.

Description: An understanding of temporal evolution of snow on sea ice at different spatial scales is essential for improvement of snow parameterization in sea ice models. One of the problems we face, however, is that long-term climate data are routinely available for land and not for sea ice. In this paper, we examine the temporal evolution of snow over smooth land-fast first-year sea ice using observational and modelled data. Changes in probability density functions indicate that depositional and drifting events control the evolution of snow distribution. Geostatistical analysis suggests that snowdrifts increased over the study period, and the orientation was related to the meteorological conditions. At the microscale, the temporal evolution of the snowdrifts was a product of infilling in the valleys between drifts. Results using two shore-based climate reporting stations (Paulatuk and Tuktoyuktuk, NWT) suggest that on-ice air temperature and relative humidity can be estimated using air temperature recorded at either station. Wind speed, direction and precipitation on ice cannot be accurately estimated using meteorological data from either station. The temporal evolution of snow distribution over smooth land-fast sea ice was modelled using SnowModel and four different forcing regimes. The results from these model runs indicate a lack of agreement between observed distribution and model outputs. The reasons for these results are lack of meteorological measurements prior to the end of January, lack of spatially adequate surface topography and discrepancies between meteorological variables on land and ice. Copyright © 2009 John Wiley & Sons, Ltd.