bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrologic and land-use change influence landscape diversity in the Ebro River (NE Spain)
Authors: Cabezas A. , Comin F. A. , Begueria S. , Trabucchi M.
Published: April 2010

Abstract. The landscape dynamics (1927–2003) of one reach at the Middle Ebro River (NE Spain) was examined using aerial pictures and GIS techniques. Moreover, changes in the natural flow regime and anthropic activities within the river-floodplain system were investigated. Our results indicate that hydrological and landscape patterns have been dramatically changed during the last century as a consequence of human alteration of the fluvial dynamics within the studied reach, as well as the overall basin. The magnitude and variability of river discharge events have decreased, especially since 1981, and flood protection structures have disrupted the river floodplain connectivity. As a result, the succesional pathways of riparian ecotopes have been heavily modified because natural rejuvenation no longer takes place, resulting in decreased landscape diversity. It is apparent from these data that floodplain restoration must be incorporated as a significant factor into river management plans if a more natural functioning wants to be retrieved. The ecotope structure and dynamics of the 1927–1957 should be adopted as the guiding image, whereas hydrologic and landscape (dykes, raised surfaces) patters should be considered. Under the current socio-economic context, the more realistic option seems to create a dynamic river corridor reallocating dykes and lowering floodplain heights. The extent of this river corridor should adapt to the restored flow regime, although periodic economic investments could be an option if the desired self-sustained dynamism is not reached.
The European Flood Alert System EFAS – Part 2: Statistical skill assessment of probabilistic and deterministic operational forecasts
Authors: Bartholmes J. C. , Thielen J. , Ramos M. H. , Gentilini S.
Published: April 2010

Abstract. Since 2005 the European Flood Alert System (EFAS) has been producing probabilistic hydrological forecasts in pre-operational mode at the Joint Research Centre (JRC) of the European Commission. EFAS aims at increasing preparedness for floods in trans-national European river basins by providing medium-range deterministic and probabilistic flood forecasting information from 3 to 10 days in advance, to national hydro-meteorological services. This paper is Part 2 of a study presenting the development and skill assessment of EFAS. In Part 1, the scientific approach adopted in the development of the system has been presented, as well as its basic principles and forecast products. In the present article, two years of existing operational EFAS forecasts are statistically assessed and the skill of EFAS forecasts is analysed with several skill scores. The analysis is based on the comparison of threshold exceedances between proxy-observed and forecasted discharges. Skill is assessed both with and without taking into account the persistence of the forecasted signal during consecutive forecasts. Skill assessment approaches are mostly adopted from meteorology and the analysis also compares probabilistic and deterministic aspects of EFAS. Furthermore, the utility of different skill scores is discussed and their strengths and shortcomings illustrated. The analysis shows the benefit of incorporating past forecasts in the probability analysis, for medium-range forecasts, which effectively increases the skill of the forecasts.
HESS Opinions "The art of hydrology"*
Authors: Savenije H. H. G.
Published: April 2010

Abstract. Hydrological modelling is the same as developing and encoding a hydrological theory. A hydrological model is not a tool but a theory. The whole discussion about the inadequacy of hydrological models we have witnessed of late, is related to the wrong concept of what a model is. Good models don't exist. Instead, hydrological research should focus on improving models and enhancing understanding. The process of modelling should be top-down, learning from the data. There is always a need for calibration, which implies that we need tailor-made and site-specific models. Only flexible models are fit for this modelling process, as opposed to most of the "established" models, "one-size-fits-all" models or "models of everywhere". The process of modelling requires imagination, inspiration, creativity, ingenuity, experience and skill. These are qualities that belong to the field of art. Hydrology is an art as much as it is science and engineering.
Landscape elements and river chemistry as affected by river regulation – a 3-D perspective
Authors: Smedberg E. , Humborg C. , Jakobsson M. , Mörth C.-M.
Published: April 2010

Abstract. We tested the hypothesis whether individual land classes within a river catchment contribute equally to river loading with dissolved constituents or whether some land classes act as "hot spots" to river loading and if so, are these land classes especially affected by hydrological alterations. The amount of land covered by forests and wetlands and the average soil depth of a river catchment explain 58–93% of the variability in total organic carbon (TOC) and dissolved silicate (DSi) concentrations for 22 river catchments in Northern Sweden. Whereas only 3% of the headwater areas of the Luleälven have been inundated by the creation of reservoirs, some 10% of the soils and aggregated forest and wetland areas have been lost due to damming and further hydrological alteration such as bypassing entire sub-catchments by headrace tunnels. However, looking at individual forest classes, our estimates indicate that some 37% of the deciduous forests have been inundated by the four major reservoirs built in the Luleälven headwaters. These deciduous forest and wetlands formerly growing on top of alluvial deposits along the river corridors forming the riparian zone play a vital role in loading river water with dissolved constituents, especially DSi. A digital elevation model draped with land classes and soil depths which highlights that topography of various land classes acting as hot spots is critical in determining water residence time in soils and biogeochemical fluxes. Thus, headwater areas of the Luleälven appear to be most sensitive to hydrological alterations due to the thin soil cover (on average 2.7–4.5 m) and only patchy appearance of forest and wetlands that were significantly perturbed. Moreover, since these headwater areas are characterized often by high specific discharge, this relatively minor change in the landscape when compared to the entire river catchment may indeed explain the significant lower fluxes at the river mouth.
Mapping model behaviour using Self-Organizing Maps
Authors: Herbst M. , Gupta H. V. , Casper M. C.
Published: April 2010

Abstract. Hydrological model evaluation and identification essentially depends on the extraction of information from model time series and its processing. However, the type of information extracted by statistical measures has only very limited meaning because it does not relate to the hydrological context of the data. To overcome this inadequacy we exploit the diagnostic evaluation concept of Signature Indices, in which model performance is measured using theoretically relevant characteristics of system behaviour. In our study, a Self-Organizing Map (SOM) is used to process the Signatures extracted from Monte-Carlo simulations generated by a distributed conceptual watershed model. The SOM creates a hydrologically interpretable mapping of overall model behaviour, which immediately reveals deficits and trade-offs in the ability of the model to represent the different functional behaviours of the watershed. Further, it facilitates interpretation of the hydrological functions of the model parameters and provides preliminary information regarding their sensitivities. Most notably, we use this mapping to identify the set of model realizations (among the Monte-Carlo data) that most closely approximate the observed discharge time series in terms of the hydrologically relevant characteristics, and to confine the parameter space accordingly. Our results suggest that Signature Index based SOMs could potentially serve as tools for decision makers inasmuch as model realizations with specific Signature properties can be selected according to the purpose of the model application. Moreover, given that the approach helps to represent and analyze multi-dimensional distributions, it could be used to form the basis of an optimization framework that uses SOMs to characterize the model performance response surface. As such it provides a powerful and useful way to conduct model identification and model uncertainty analyses.
Modeling the monthly mean soil-water balance with a statistical-dynamical ecohydrology model as coupled to a two-component canopy model
Authors: Kochendorfer J. P. , Ramírez J. A.
Published: April 2010

Abstract. The statistical-dynamical annual water balance model of Eagleson (1978) is a pioneering work in the analysis of climate, soil and vegetation interactions. This paper describes several enhancements and modifications to the model that improve its physical realism at the expense of its mathematical elegance and analytical tractability. In particular, the analytical solutions for the root zone fluxes are re-derived using separate potential rates of transpiration and bare-soil evaporation. Those potential rates, along with the rate of evaporation from canopy interception, are calculated using the two-component Shuttleworth-Wallace (1985) canopy model. In addition, the soil column is divided into two layers, with the upper layer representing the dynamic root zone. The resulting ability to account for changes in root-zone water storage allows for implementation at the monthly timescale. This new version of the Eagleson model is coined the Statistical-Dynamical Ecohydrology Model (SDEM). The ability of the SDEM to capture the seasonal dynamics of the local-scale soil-water balance is demonstrated for two grassland sites in the US Great Plains. Sensitivity of the results to variations in peak green Leaf Area Index (LAI) suggests that the mean peak green LAI is determined by some minimum in root zone soil moisture during the growing season. That minimum appears to be close to the soil matric potential at which the dominant grass species begins to experience water stress and well above the wilting point, thereby suggesting an ecological optimality hypothesis in which the need to avoid water-stress-induced leaf abscission is balanced by the maximization of carbon assimilation (and associated transpiration). Finally, analysis of the sensitivity of model-determined peak green LAI to soil texture shows that the coupled model is able to reproduce the so-called "inverse texture effect", which consists of the observation that natural vegetation in dry climates tends to be most productive in sandier soils despite their lower water holding capacity. Although the determination of LAI based on near-complete utilization of soil moisture is not a new approach in ecohydrology, this paper demonstrates its use for the first time with a new monthly statistical-dynamical model of the water balance. Accordingly, the SDEM provides a new framework for studying the controls of soil texture and climate on vegetation density and evapotranspiration.
Use of regional climate model simulations as input for hydrological models for the Hindukush–Karakorum–Himalaya region
Authors: Akhtar M. , Ahmad N. , Booij M. J.
Published: April 2010

Abstract. The most important climatological inputs required for the calibration and validation of hydrological models are temperature and precipitation that can be derived from observational records or alternatively from regional climate models (RCMs). In this paper, meteorological station observations and results of the PRECIS (Providing REgional Climate for Impact Studies) RCM driven by the outputs of reanalysis ERA-40 data and HadAM3P general circulation model (GCM) results are used as input in the hydrological model. The objective is to investigate the effect of precipitation and temperature simulated with the PRECIS RCM nested in these two data sets on discharge simulated with the HBV model for three river basins in the Hindukush-Karakorum-Himalaya (HKH) region. Three HBV model experiments are designed: HBV-Met, HBV-ERA and HBV-Had where HBV is driven by meteorological station data and by the outputs from PRECIS nested with ERA-40 and HadAM3P data, respectively. Present day PRECIS simulations possess strong capacity to simulate spatial patterns of present day climate characteristics. However, there also exist some quantitative biases in the HKH region, where PRECIS RCM simulations underestimate temperature and overestimate precipitation with respect to CRU observations. The calibration and validation results of the HBV model experiments show that the performance of HBV-Met is better than the HBV models driven by the PRECIS outputs. However, using input data series from sources different from the data used in the model calibration shows that HBV models driven by the PRECIS outputs are more robust compared to HBV-Met. The Gilgit and Astore river basin, which discharges are depending on the preceding winter precipitation, have higher uncertainties compared to the Hunza river basin which discharge is driven by the energy inputs. The smaller uncertainties in the Hunza river basin may be because of the stable behavior of the input temperature series compared to the precipitation series. The resulting robustness and uncertainty ranges of the HBV models suggest that in data sparse regions such as the HKH region data from regional climate models may be used as input in hydrological models for climate scenarios studies.
Observing soil moisture temporal variability under fluctuating climatic conditions
Authors: Longobardi A.
Published: April 2010

Abstract. The paper focuses on the observation of interannual and intra-annual climate variability impact on soil moisture temporal patterns and variation, for an experimental site located in Southern Italy and characterized by a typical Mediterranean climate. Analysed data consist of three years soil water content time series measured during the period 2004–2007, under intermediate (2004/2005), wet (2005/2006) and dry (2006/2007) climatological conditions. Results show that, for the case study, interannual precipitation fluctuation highly impact the annual soil moisture cycle, modifying the number and length of characteristic periods revealed by the cycle patterns. Annual rainfall variation also affects the weight of the wet and dry soil moisture conditions, making the distinction between preferred states more and more evident for increasing precipitation variability. Intra-annual precipitation fluctuation instead mainly impact soil moisture dynamic during the dry period of the year, shifting the position of the modes and the weight of the wet mode and nearly leading the dry mode to disappear for larger mean seasonal rainfall. Reported analyses would be a support and a premise for further modeling implications.
Application of satellite microwave remote sensed brightness temperature in the regional soil moisture simulation
Authors: Shi X. K. , Wen J. , Wang L. , Zhang T. T. , Tian H. , Wang X. , Liu R. , Zhang J. H.
Published: April 2010

Abstract. As the satellite microwave remote sensed brightness temperature is sensitive to land surface soil moisture (SM) and SM is a basic output variable in model simulation, it is of great significance to use the brightness temperature data to improve SM numerical simulation. In this paper, the theory developed by Yan et al. (2004) about the relationship between satellite microwave remote sensing polarization index and SM was used to estimate the land surface SM from AMSR-E (Advanced Microwave Scanning Radiometer – Earth Observing System) brightness temperature data. With consideration of land surface soil texture, surface roughness, vegetation optical thickness, and the AMSR-E monthly SM products, the regional daily land surface SM was estimated over the eastern part of the Qinghai-Tibet Plateau. The results show that the estimated SM is lower than the ground measurements and the NCEP (American National Centers for Environmental Prediction) reanalysis data at the Maqu Station (33.85° N, 102.57° E) and the Tanglha Station (33.07° N, 91.94° E), but its regional distribution is reasonable and somewhat better than that from the daily AMSR-E SM product, and its temporal variation shows a quick response to the ground daily precipitations. Furthermore, in order to improve the simulating ability of the WRF (Weather Research and Forecasting) model to land surface SM, the estimated SM was assimilated into the Noah land surface model by the Newtonian relaxation (NR) method. The results indicate that, by fine tuning of the quality factor in NR method, the simulated SM values are improved most in desert area, followed by grassland, shrub and grass mixed zone. At temporal scale, Root Mean Square Error (RMSE) values between simulated and observed SM are decreased 0.03 and 0.07 m3/m3 by using the NR method in the Maqu Station and the Tanglha Station, respectively.
HESS Opinions "Urgent water challenges are not sufficiently researched"
Authors: van der Zaag P. , Gupta J. , Darvis L. P.
Published: April 2010

Abstract. In this opinion paper we submit that water experts conduct comparatively little research on the more urgent challenges facing the global community. Apparently there is a mismatch between the global demand for knowledge and the finance for and supply of knowledge. This mismatch is identified here as a problem that we water scientists must try to confront and resolve. We need to understand why this mismatch occurs and persists, in order to find ways to break out of the impasse. Although this paper addresses a critical challenge it does not aim to be exhaustive or definitive. We merely identify the persistence of intransigent water problems as a research object in itself.
SOM dynamics and erosion in an agricultural test field of the Clear Creek, IA watershed
Authors: Wilson C. G. , Papanicolaou A. N. T. , Abaci O.
Published: April 2010

Abstract. To date, few studies have examined in detail the role of spatial variabilities of erosion on Soil Organic Matter (SOM). More specifically, the role of deposition is still poorly understood. The nature of the research is novel because it combines dynamic model simulations using the Water Erosion Prediction Project (WEPP) and CENTURY SOM dynamics model to evaluate soil and SOM loss in an agricultural test field of the Clear Creek, IA watershed. In addition, numerical simulations were coupled with limited field investigations calibrating and verifying WEPP and CENTURY. The main task of this study was to evaluate changes in SOM dynamics in a field using CENTURY and accounting for the interdependence of historical and current management practices, erosion (i.e., soil loss and deposition), and decomposition. Simulations were conducted under three different erosion scenarios determined using WEPP to demonstrate the importance of including deposition in studies of SOM dynamics: (1) assuming no erosion, (2) using an average erosion rate for the whole field, and (3) dividing the field into an erosional upland and depositional floodplain. The total SOM concentrations produced by the segmented field simulation agreed best with the measured field values. Simulated SOM concentrations values for the upland were 13% lower and values for the floodplain were 16% higher than measured field values. The results of this investigation compare well with the simulation results of other studies in terms of the effects of deposition on SOM distributions and that more detailed erosion values lead to better performance of the model. Deposition decreased SOM loss from the field by accounting for sequestration of carbon.
Explicitation of an important scale dependence in TOPMODEL using a dimensionless topographic index
Authors: Ducharne A.
Published: April 2010

Abstract. This paper stems from the fact that the topographic index used in TOPMODEL is not dimensionless. In each pixel i in a catchment, it is defined as xi=ln (ai /Si), where ai is the specific contributing area per unit contour length and Si is the topographic slope. In the SI unit system, ai /Si is in meters, and the unit of xi is problematic. Even if all the equations in TOPMODEL are homogeneous, it is confusing to use the logarithm of a non-dimensionless quantity as an index, and we propose a simple solution to this issue in the nowadays widespread cases where the topographic index is computed from a regular raster digital elevation model (DEM). The pixel length C being constant, we can define a dimensionless topographic index yi=xi−ln C. Reformulating TOPMODEL's equations to use yi instead of xi helps giving the units of all the terms in TOPMODEL's equations. Another advantage is to raise awareness about the scale dependence of these equations via the explicit use of the DEM cell size C outside from the topographic index, in what what can be defined as the transmissivity at saturation per unit contour length T0/C. We eventually demonstrate, based on various examples from the literature, that both T0/C and the spatial mean y of the proposed dimensionless topographic index are very stable with respect to DEM resolution. This markedly reduces the recalibration necessity when changing DEM resolution, thus offering an efficient rescaling framework.
How crucial is it to account for the Antecedent Moisture Conditions in flood forecasting? Comparison of event-based and continuous approaches on 178 catchments
Authors: Berthet L. , Andréassian V. , Perrin C. , Javelle P.
Published: April 2010

Abstract. This paper compares event-based and continuous hydrological modelling approaches for real-time forecasting of river flows. Both approaches are compared using a lumped hydrologic model (whose structure includes a soil moisture accounting (SMA) store and a routing store) on a data set of 178 French catchments. The main focus of this study was to investigate the actual impact of soil moisture initial conditions on the performance of flood forecasting models and the possible compensations with updating techniques. The rainfall runoff model assimilation technique we used does not impact the SMA component of the model but only its routing part. Tests were made by running the SMA store continuously or on event basis, everything else being equal. The results show that the continuous approach remains the reference to ensure good forecasting performances. We show, however, that the possibility to assimilate the last observed flow considerably reduces the differences in performance. Last, we present a robust alternative to initialize the SMA store where continuous approaches are impossible because of data availability problems.
Evaluation of a probabilistic hydrometeorological forecast system
Authors: Jaun S. , Ahrens B.
Published: April 2010

Abstract. Medium range hydrological forecasts in mesoscale catchments are only possible with the use of hydrological models driven by meteorological forecasts, which in particular contribute quantitative precipitation forecasts (QPF). QPFs are accompanied by large uncertainties, especially for longer lead times, which are propagated within the hydrometeorological model system. To deal with this limitation of predictability, a probabilistic forecasting system is tested, which is based on a hydrological-meteorological ensemble prediction system. The meteorological component of the system is the operational limited-area ensemble prediction system COSMO-LEPS that downscales the global ECMWF ensemble to a horizontal resolution of 10 km, while the hydrological component is based on the semi-distributed hydrological model PREVAH with a spatial resolution of 500 m. Earlier studies have mostly addressed the potential benefits of hydrometeorological ensemble systems in short case studies. Here we present an analysis of hydrological ensemble hindcasts for two years (2005 and 2006). It is shown that the ensemble covers the uncertainty during different weather situations with an appropriate spread-skill relationship. The ensemble also shows advantages over a corresponding deterministic forecast, even under consideration of an artificial spread.
Deriving inherent optical properties and associated uncertainties for the Dutch inland waters during the Eagle Campaign
Authors: Salama M. S. , Su Z. , Mannaerts C. M. , Verhoef W.
Published: April 2010

Abstract. During the Eagle 2006 campaign intensive in-situ and air/space borne measurements were carried out over the Wolderwijd and Veluwemeer natural waters in the Netherlands. In this paper, we modify the GSM semi-analytical inversion model for these lakes to derive inherent optical properties (IOPs) and their spectral dependencies from air and space borne data. Uncertainties of the derived IOPs are estimated using a nonlinear regression technique. The modified model succeeded in deriving accurate estimates of IOPs with R2 higher than 0.9 and RMSE values equal to 0.12 and 0.05 for absorption and scattering coefficients, respectively. Finally, we show that the uncertainty of derived absorption coefficients is slightly independent of absorption's magnitude. While the uncertainty of all derived IOPs increases with water turbidity.
Does WEPP meet the specificity of soil erosion in steep mountain regions?
Authors: Konz N. , Bänninger D. , Nearing M. , Alewell C.
Published: April 2010

Abstract. We chose the WEPP model (Water Erosion Prediction Project) to describe soil erosion in the Urseren Valley (central Switzerland) as it seems to be one of the most promising models for steep mountain environments. Crucial model parameters were determined in the field (slope, plant species, fractional vegetation cover, initial saturation level), by laboratory analyses (grain size, organic matter) or by the WEPP manual (rill- and interrill erodibility, effective hydraulic conductivity, cation exchange capacity). The quantification of soil erosion was performed on hill slope scale for three different land use types: meadows, pastures with dwarf shrubs and pastures without dwarf shrubs. Erosion rates for the vegetation period were measured with sediment traps between June 2006 and November 2007. Long-term soil erosion rates were estimated by measuring Cs-137 redistribution, deposited after the Chernobyl accident. In addition to the erosion rates, soil moisture and surface flow was additionally measured during the vegetation period in the field and compared to model output. Short-term erosion rates are simulated well whereas long term erosion rates were underestimated by the model. Simulated soil moisture has a parallel development compared to measured data from April onwards but a converse dynamic in early spring (simulated increase and measured decrease in March and April). The discrepancy in soil water during springtime was explained by delayed simulated snow cover melting. The underestimation of simulated long term erosion rates is attributed to alpine processes other than overland flow and splash. Snow gliding processes might dominate erosion processes during winter time. We assume that these differences lead to the general simulated underestimation of erosion rates. Thus, forcing erosion processes which dominate erosion rates in mountainous regions have to be implemented to WEPP for a successful application in the future.
Comparison of six algorithms to determine the soil thermal diffusivity at a site in the Loess Plateau of China
Authors: Gao Z. , Wang L. , Horton R.
Published: April 2010

Abstract. Soil thermal diffusivity is a crucial physical parameter that affects soil temperature. Six prevalent algorithms to calculate soil thermal diffusivity are inter-compared by using soil temperature data collected at the depths of 0.05 m and 0.10 m at a bare site in the China Loess Plateau from DOY 201 through DOY 207 in 2005. Five of the six algorithms (i.e., Amplitude, Phase, Arctangent, Logarithm, and Harmonic or HM algorithms) are developed from the traditional one-dimensional heat conduction equation. The other algorithm is based on the one-dimensional heat conduction-convection equation which considers the vertical heterogeneity of thermal diffusivity in soil and couples thermal conduction and convection processes (hereinafter referred to as the Conduction-convection algorithm). To assess these six algorithms, we (1) calculate the soil thermal diffusivities by using each of the algorithms, (2) use the soil thermal diffusivities to predict soil temperature at the 0.10 m depth, and (3) compare the estimated soil temperature against direct measurements. Results show that (1) HM algorithm gives the most reliable estimates among the traditional five algorithms; and (2) generally, the Conduction-convection algorithm provides the second best estimates. Among all of the algorithms, the HM algorithm has the best description of the upper boundary temperature with time, but it only includes conduction heat transfer in the soil. Compared to the HM algorithm, the Conduction-convection algorithm has a less accurate description of the upper boundary temperature, but by accounting for the vertical gradient of soil diffusivity and the water flux density it includes more physics in the soil heat transfer process. The Conduction-convection algorithm has potential application within land surface models, but future effort should be made to combine the HM and Conduction-convection algorithms in order to make use of the advantages of each.
Effects of intersite dependence of nested catchment structures on probabilistic regional envelope curves
Authors: Guse B. , Castellarin A. , Thieken A. H. , Merz B.
Published: April 2010

Abstract. Regional flood quantile estimates are affected by intersite correlation between flood sequences observed at different discharge gauges. This study analyses the intersite dependence of nested catchment structures and investigates the possibility of improving the accuracy of regional flood quantiles, by modelling cross-correlations for pairs of nested and unnested catchments separately. Probabilistic Regional Envelope Curves are utilised to derive regional flood quantiles for 89 catchments belonging to Saxony, in the Southeast of Germany. The study area has a nested structure and a definitely stronger intersite correlation for nested pairs of catchments than for unnested ones. Probabilistic Regional Envelope Curves are constructed on the basis of flood flows observed within pooling groups of sites (regions). Their recurrence intervals are based on the number of effective sample-years of data (i.e., equivalent number of uncorrelated data). The evaluation of the effective sample-years of data required the modelling of intersite dependence, which we performed globally, using a cross-correlation formula identified for the whole study area, and by using two different cross-correlation formulas, one for nested pairs and another for unnested pairs. These two modelling approaches returned significantly different effective sample-years of data estimates, and therefore also recurrence intervals, in the majority of the cases. The differences result from various assumptions of the size and homogeneity degree of the pooling group. The reduction of the recurrence interval, when using two different cross-correlation functions, is larger for higher recurrence intervals and for a higher fraction of nested catchment within the pooling group. A separation into nested and unnested pairs of catchments gives a more realistic representation of the characteristic river network structure and improves the accuracy of the estimation of regional information content. Hence, applying two different cross-correlation functions is recommended.
Simulation and validation of subsurface lateral flow paths in an agricultural landscape
Authors: Zhu Q. , Lin H. S.
Published: April 2010

Abstract. The importance of soil water flow paths to the transport of nutrients and contaminants has long been recognized. However, effective means of detecting subsurface flow paths in a large landscape is still lacking. The flow direction and accumulation algorithm in GIS hydrologic modeling is a cost effective way to simulate potential flow paths over a large area. This study tested this algorithm for simulating lateral flow paths at three interfaces in soil profiles in a 19.5-ha agricultural landscape in central Pennsylvania, USA. These interfaces were (1) the surface plowed layers (Ap1 and Ap2 horizons) interface, (2) the interface with subsoil clay layer where clay content increased to over 40%, and (3) soil-bedrock interface. The simulated flow paths were validated through soil hydrologic monitoring, geophysical surveys, and observable soil morphological features. The results confirmed that subsurface lateral flow occurred at the interfaces with the clay layer and the underlying bedrock. At these two interfaces, the soils on the simulated flow paths were closer to saturation and showed more temporally unstable moisture dynamics than those off the simulated flow paths. Apparent electrical conductivity in the soil on the simulated flow paths was elevated and temporally unstable as compared to those outside the simulated paths. The soil cores collected from the simulated flow paths showed significantly higher Mn contents at these interfaces than those away from the simulated paths. These results suggest that (1) the algorithm is useful in simulating possible subsurface lateral flow paths if used appropriately with sufficiently detailed digital elevation model; (2) repeated electromagnetic surveys can reflect the temporal change of soil water storage and thus is an indicator of soil water movement over the landscape; and (3) observable Mn content in soil profiles can be used as a simple indicator of water flow paths in soils and over the landscape.
Impacts of climate change scenarios on runoff regimes in the southern Alps
Authors: Barontini S. , Grossi G. , Kouwen N. , Maran S. , Scaroni P. , Ranzi R.
Published: April 2010

Abstract. The potential impact of climate change scenarios on the runoff regime in the Italian Alpine area was investigated. A preliminary analysis of the output of three Global Circulation Models (PCM, HADCM, ECHAM) was needed to select IPCC-based scenarios for the 2000–2099 period. Two basins, 1840 and 236 km2 in size, respectively, and with different glaciated areas and storage capacity of reservoirs were selected as case studies. The PCM model, the one capable to better reproduce the observed rainfall regime in the investigated area, with the IPCC SRES A2 scenario was adopted for the meteorological forcing. On average for the two basins, an increase of annual precipitation of about 3% is expected for the 2050 scenario and should not significantly vary at the end of this century compared to present conditions. At the same time temperature should increase of 1.1°C in 2050 and 2.4°C for 2090. Because of the coarse resolution of the climate models' output, the statistics of the simulated rainy days and daily precipitation were adapted to the scale of the two selected basins using a modified version of the multiplicative cascade β-model, proposed in the literature to explain the statistics of intermittent fully developed turbulence. As regards to land cover, glaciated areas are decreased, in the future scenarios, according to the Kuhn's concept of equilibrium line adaptation to climate fluctuations. The tree-line altitude is increased, according to the observed trend since the end of the Little Ice Age: thus boundary conditions for evapotranspiration changed. The resulting meteorological variables and hydrological parameters were used to run the WATFLOOD hydrological model in order to assess the changes of runoff regimes in the two watersheds. A decrease of about 7% of annual runoff volume for the 2050 scenario and of 13% for the 2090 scenario was estimated, on average, at the outlet of the Oglio river basin, the largest one. In the smaller Lys basin, where the glaciated area is 8% of the total area, the annual runoff is foreseen to decrease by about 3% (for the 2050 scenario) and 14% at the end of this century. Also the runoff regime changes are significant, with an increase of spring melt and a decrease of summer and autumn runoff. No clear evidence is found for changes in the precipitation extremes and in the fraction of rainy days.
Understanding wetland sub-surface hydrology using geologic and isotopic signatures
Authors: Sikdar P. K. , Sahu P.
Published: April 2010

Abstract. This paper attempts to utilize hydrogeoloy and isotope composition of groundwater to understand the present hydrological processes prevalent in a freshwater wetland, source of wetland groundwater, surface water/groundwater interaction and mixing of groundwater of various depth zones in the aquifer. This study considers East Calcutta Wetlands (ECW) – a freshwater peri-urban inland wetland ecosystem located at the lower part of the deltaic alluvial plain of South Bengal Basin and east of Kolkata city. This wetland is well known over the world for its resource recovery systems, developed by local people through ages, using wastewater from the city. Geological investigations reveal that the sub-surface geology is completely blanketed by the Quaternary sediments comprising a succession of silty clay, sand of various grades and sand mixed with occasional gravels and thin intercalations of silty clay. Aquifer within the depths of 80 m to 120 m has the maximum potential to supply water. Groundwater mainly flows from east to west and is being over-extracted to the tune of 65×103 m3/day. δ18O and δD values of shallow and deep groundwater are similar indicating resemblance in hydrostratigraphy and climate of the recharge areas. Groundwater originates mainly from monsoonal rain with some evaporation prior to or during infiltration and partly from bottom of ponds, canals and infiltration of groundwater withdrawn for irrigation. Relatively high tritium content of the shallow groundwater indicates local recharge, while the deeper groundwater with very low tritium is recharged mainly from distant areas. At places the deeper aquifer has relatively high tritium, indicating mixing of groundwater of shallow and deep aquifers. Metals such as copper, lead, arsenic, cadmium, aluminum, nickel and chromium are also present in groundwater of various depths. Therefore, aquifers of wetland and surrounding urban areas which are heavily dependent on groundwater are vulnerable to pollution and hence surface water-groundwater interaction should be minimized by regulating tubewell operation time, introducing treated surface water supply system and artificially recharging the aquifer.
Recycling of moisture in Europe: contribution of evaporation to variability in very wet and dry years
Authors: Bisselink B. , Dolman A. J.
Published: April 2010

Abstract. Evaporation is a key parameter in the regional atmospheric water cycle. Precipitation recycling is defined as the contribution of local evaporation in a region to the precipitation in the same region. In this work, we apply a dynamic precipitation recycling mode, which includes the moisture storage term, to calculate the warm season variability of the precipitation recycling over central Europe at a daily scale for 2003 (dry) and 2006 (wet). For the central part of Europe advection is the most important contributor to precipitation. In dry spells in both years 2003 and 2006, when moisture of advective origin diminishes, the local evaporation becomes an important contributor to precipitation (negative feedback). In two periods (June 2003 and July 2006) where there is enough moisture storage in the soil to continue the evaporation the recycling is enhanced. In August 2003 the evaporation is affecting the recycling due the lack of water availability caused by the dryness of the preceding spring and summer season. According to a multi variance analyses the evaporation in 2003 is the most important factor to explain the variance in the recycling ratio. In 2006, the precipitable water and the moisture fluxes are more dominant and the evaporation becomes less important, except for the dry period in July. Not only evaporation is important for recycling, but also a mechanism to trigger precipitation. In case studies we follow the path of an air column of days with one of the highest recycling. At the 2 days with enough moisture availability (28 May 2003 and 5 July 2006) we see long path length due to weak winds. Following the paths, the air is transported over land for a very long distance before it precipitates and has a lot of time to traverse the region and capture moisture of evaporative origin. However, we hypothesize that the precipitation falling at those days originates (partly) from oceanic sources, but the triggering of precipitation may itself be a result of enhanced instability induced by soils, which still have enough moisture storage. In this way, the evaporation is an important driver in the recycling ratio variability. For the case study of 10 August 2003, the atmosphere is too dry to generate precipitation with exception of the mountainous regions due orographical lifting. However, the impact of land-use change in future climate will have the most impact on the evaporation in dry spells dominated by persistent blocking systems.
Hydropedological assessment of a vertisol climosequence on the Gulf Coast Prairie Land Resource Area of Texas
Authors: Nordt L. C. , Driese S. G.
Published: April 2010

Abstract. Vertisols contain slickensides and wedge-shaped aggregates formed by shrink-swell processes during wet-dry cycles in seasonal climates. The dynamic distribution of macro- and microvoids as a by-product of this unique process, accompanied by microtopographic lows and highs, mitigate our ability to make accurate and precise interpretations of aquic and hydric conditions in these problematic soils. We studied Vertisols across a subhumid to humid climosequence to assess the formation of redoximorphic features on planar landscape positions in response to varying levels of rainfall. Approximately 1000 mm of MAP is required to form soft iron masses that then increase in abundance, and to shallower depths, with increasing rainfall. More than 1200 mm of MAP is needed to form iron pore linings, regardless of microlow or microhigh topographic position. Soft iron masses with diffuse boundaries become more abundant with higher rainfall in microlows, whereas masses with nondiffuse boundaries are more common in microhighs. Iron depletions do not correlate with rainfall in terms of abundance or depth of occurrence. Most soft iron masses form in oxygenated ped interiors as water tends to first saturate and reduce voids where iron depletions form. The quantity of crayfish burrows is strongly correlated with rainfall and first appears coincidentally with soft iron masses in microlows near 1000 mm of MAP. Dithionite-citrate extractable and ammonium-oxalate extractable iron oxides increase systematically with rainfall indicating frequent episodes of iron reduction and precipitation into pedogenic forms. It appears that Vertisols forming in these landscapes with MAP greater than 1200 mm should classify as Aquerts because of the presence of aquic conditions. These same soils may also meet the definition of hydric as one criterion for the identification of Federally protected wetlands. However, there is a considerable disjunct between protracted periods of saturation and limited periods of reduction in these soils. Non-Darcian bypass flow appears to be the principle mechanism governing the flux of water through these cracking soils where water first accumulates and then persists in microlow bowls.
Interrelationships between MODIS/Terra remotely sensed snow cover and the hydrometeorology of the Quesnel River Basin, British Columbia, Canada
Authors: Tong J. , Déry S. J. , Jackson P. L.
Published: April 2010

Abstract. A spatial filter (SF) method is adopted to reduce the cloud coverage from the Moderate Resolution Imaging Spectroradiometer (MODIS) 8-day snow products (MOD10A2) between 2000–2007 in the Quesnel River Basin (QRB) of British Columbia, Canada. A threshold of k=2 cm of snow depth measurements at four in-situ observation stations in the QRB are used to evaluate the accuracy of MODIS snow products MOD10A1, MOD10A2, and SF. Based on the MOD10A2 and the SF, the relationships between snow ablation, snow cover extent (SCE), snow cover fraction (SCF), streamflow and climate variability are assessed. Based on our results we are able to draw several interesting conclusions. Firstly, the SF method reduces the average cloud coverage in the QRB from 15% for MOD10A2 to 9%. Secondly, the SF increases the overall accuracy (OA) based on the threshold k=2 cm by about 2% compared to MOD10A2 and by about 10% compared to MOD10A1 at higher elevations. The OA for the four in-situ stations decreases with elevation with 93.1%, 87.9%, 84.0%, and 76.5% at 777 m, 1265 m, 1460 m, and 1670 m, respectively. Thirdly, an aggregated 1°C rise in average air temperature during spring leads to a 10-day advance in reaching 50% SCF (SCF50%) in the QRB. The correlation coefficient between normalized SCE of the SF and normalized streamflow is −0.84 (p<0.001) for snow ablation seasons. There is a 32-day time lag for snow ablation to impact the streamflow the strongest at the basin outlet. The linear correlation coefficient between SCF50% and 50% normalized accumulated runoff (R50%) attains 0.82 (p<0.01). This clearly demonstrates the strong links that exist between the SCF depletion and the hydrology of this sub-boreal, mountainous watershed.
Evaluation of alternative formulae for calculation of surface temperature in snowmelt models using frequency analysis of temperature observations
Authors: Luce C. H. , Tarboton D. G.
Published: April 2010

Abstract. The snow surface temperature is an important quantity in the snow energy balance, since it modulates the exchange of energy between the surface and the atmosphere as well as the conduction of energy into the snowpack. It is therefore important to correctly model snow surface temperatures in energy balance snowmelt models. This paper focuses on the relationship between snow surface temperature and conductive energy fluxed that drive the energy balance of a snowpack. Time series of snow temperature at the surface and through the snowpack were measured to examine energy conduction in a snowpack. Based on these measurements we calculated the snowpack energy content and conductive energy flux at the snow surface. We then used these estimates of conductive energy flux to evaluate formulae for the calculation of the conductive flux at the snow surface based on surface temperature time series. We use a method based on Fourier frequency analysis to estimate snow thermal properties. Among the formulae evaluated, we found that a modified force-restore formula, based on the superimposition of the force-restore equation capturing diurnal fluctuations on a gradually changing temperature gradient, had the best agreement with observations of heat conduction. This formula is suggested for the parameterization of snow surface temperature in a full snowpack energy balance model.