http://www.hydrol-earth-syst-sci.net/ Hydrology and Earth System Sciences Latest Articlesenhttp://www.hydrol-earth-syst-sci.net/14/1715/2010/<b>The benefits of gravimeter observations for modelling water storage changes at the field scale</b><br /><br />Hydrology and Earth System Sciences, 14, 1715-1730, 2010<br /><br />Author(s): B. Creutzfeldt, A. Güntner, S. Vorogushyn, and B. Merz<br /><br />Water storage is the fundamental state variable of hydrological systems. However, comprehensive data on total water storage changes (WSC) are practically inaccessible by hydrological measurement techniques at the field or catchment scale, and hydrological models are highly uncertain in representing the storage term due to the lack of adequate validation or calibration data. In this study, we assess the benefit of temporal gravimeter measurements for modelling WSC at the field scale. A simple conceptual hydrological model is calibrated and evaluated against records of a superconducting gravimeter (SG), soil moisture, and groundwater time series. The model is validated against independently estimated WSC based on lysimeter measurements. Using gravimeter data as a calibration constraint improves the model results substantially in terms of predictive capability and variation of the behavioural model runs. Thanks to their capacity to integrate over different storage components and a larger area, gravimeters provide information on total WSC that can be used to constrain the overall status of the hydrological system in a model. The general problem of specifying the internal model structure or individual parameter sets can, however, not be solved with gravimeters alone.Wed, 01 Sep 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1697/2010/<b>A geophysical analysis of hydro-geomorphic controls within a headwater wetland in a granitic landscape, through ERI and IP</b><br /><br />Hydrology and Earth System Sciences, 14, 1697-1713, 2010<br /><br />Author(s): E. S. Riddell, S. A. Lorentz, and D. C. Kotze<br /><br />Wetlands are undergoing considerable degradation in South Africa. As interventions are often technical and costly, there is a requirement to develop conceptual process models for these wetland systems so that rehabilitation attempts will be successful. This paper presents an approach using the geophysical methods of Electrical Resistivity Imaging (ERI) and Induced Polarization (IP) to delineate sub-surface hydro-geomorphic controls that maintain equilibrium disconnectivity of wetland-catchment processes, which through gully erosion are increasing the catchments connectivity through loss of water and sediment. The findings presented here give insight into the geomorphic processes that maintain the wetland in an un-degraded state, this allows for the development of a conceptual model outlining the wetland forming processes. The analysis suggests that sub-surface clay-plugs, within an otherwise sandy substrate are created by illuviation of clays from the surrounding hillslopes particularly at zones of valley confinement.Tue, 31 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1681/2010/<b>Possibilistic uncertainty analysis of a conceptual model of snowmelt runoff</b><br /><br />Hydrology and Earth System Sciences, 14, 1681-1695, 2010<br /><br />Author(s): A. P. Jacquin<br /><br />This study presents the analysis of predictive uncertainty of a conceptual type snowmelt runoff model. The method applied uses possibilistic rather than probabilistic calculus for the evaluation of predictive uncertainty. Possibility theory is an information theory meant to model uncertainties caused by imprecise or incomplete knowledge about a real system rather than by randomness. A snow dominated catchment in the Chilean Andes is used as case study. Predictive uncertainty arising from parameter uncertainties of the watershed model is assessed. Model performance is evaluated according to several criteria, in order to define the possibility distribution of the parameter vector. The plausibility of the simulated glacier mass balance and snow cover are used for further constraining the model representations. Possibility distributions of the discharge estimates and prediction uncertainty bounds are subsequently derived. The results of the study indicate that the use of additional information allows a reduction of predictive uncertainty. In particular, the assessment of the simulated glacier mass balance and snow cover helps to reduce the width of the uncertainty bounds without a significant increment in the number of unbounded observations.Mon, 30 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1669/2010/<b>Sustainability of water resources management in the Indus Basin under changing climatic and socio economic conditions</b><br /><br />Hydrology and Earth System Sciences, 14, 1669-1680, 2010<br /><br />Author(s): D. R. Archer, N. Forsythe, H. J. Fowler, and S. M. Shah<br /><br />Pakistan is highly dependent on water resources originating in the mountain sources of the upper Indus for irrigated agriculture which is the mainstay of its economy. Hence any change in available resources through climate change or socio-economic factors could have a serious impact on food security and the environment. In terms of both ratio of withdrawals to runoff and per-capita water availability, Pakistan's water resources are already highly stressed and will become increasingly so with projected population changes. Potential changes to supply through declining reservoir storage, the impact of waterlogging and salinity or over-abstraction of groundwater, or reallocations for environmental remediation of the Indus Delta or to meet domestic demands, will reduce water availability for irrigation. <br><br> The impact of climate change on resources in the Upper Indus is considered in terms of three hydrological regimes – a nival regime dependent on melting of winter snow, a glacial regime, and a rainfall regime dependent on concurrent rainfall. On the basis of historic trends in climate, most notably the decline in summer temperatures, there is no strong evidence in favour of marked reductions in water resources from any of the three regimes. Evidence for changes in trans-Himalayan glacier mass balance is mixed. Sustainability of water resources appears more threatened by socio-economic changes than by climatic trends. Nevertheless, analysis and the understanding of the linkage of climate, glaciology and runoff is still far from complete; recent past climate experience may not provide a reliable guide to the future.Fri, 27 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1655/2010/<b>Spatial variability in floodplain sedimentation: the use of generalized linear mixed-effects models</b><br /><br />Hydrology and Earth System Sciences, 14, 1655-1668, 2010<br /><br />Author(s): A. Cabezas, M. Angulo-Martínez, M. Gonzalez-Sanchís, J. J. Jimenez, and F. A. Comín<br /><br />Sediment, Total Organic Carbon (TOC) and total nitrogen (TN) accumulation during one overbank flood (1.15 y return interval) were examined at one reach of the Middle Ebro River (NE Spain) for elucidating spatial patterns. To achieve this goal, four areas with different geomorphological features and located within the study reach were examined by using artificial grass mats. Within each area, 1 m² study plots consisting of three pseudo-replicates were placed in a semi-regular grid oriented perpendicular to the main channel. TOC, TN and Particle-Size composition of deposited sediments were examined and accumulation rates estimated. Generalized linear mixed-effects models were used to analyze sedimentation patterns in order to handle clustered sampling units, specific-site effects and spatial self-correlation between observations. Our results confirm the importance of channel-floodplain morphology and site micro-topography in explaining sediment, TOC and TN deposition patterns, although the importance of other factors as vegetation pattern should be included in further studies to explain small-scale variability. Generalized linear mixed-effect models provide a good framework to deal with the high spatial heterogeneity of this phenomenon at different spatial scales, and should be further investigated in order to explore its validity when examining the importance of factors such as flood magnitude or suspended sediment concentration.Wed, 25 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1639/2010/<b>A past discharge assimilation system for ensemble streamflow forecasts over France – Part 2: Impact on the ensemble streamflow forecasts</b><br /><br />Hydrology and Earth System Sciences, 14, 1639-1653, 2010<br /><br />Author(s): G. Thirel, E. Martin, J.-F. Mahfouf, S. Massart, S. Ricci, F. Regimbeau, and F. Habets<br /><br />The use of ensemble streamflow forecasts is developing in the international flood forecasting services. Ensemble streamflow forecast systems can provide more accurate forecasts and useful information about the uncertainty of the forecasts, thus improving the assessment of risks. Nevertheless, these systems, like all hydrological forecasts, suffer from errors on initialization or on meteorological data, which lead to hydrological prediction errors. This article, which is the second part of a 2-part article, concerns the impacts of initial states, improved by a streamflow assimilation system, on an ensemble streamflow prediction system over France. An assimilation system was implemented to improve the streamflow analysis of the SAFRAN-ISBA-MODCOU (SIM) hydro-meteorological suite, which initializes the ensemble streamflow forecasts at Météo-France. This assimilation system, using the Best Linear Unbiased Estimator (BLUE) and modifying the initial soil moisture states, showed an improvement of the streamflow analysis with low soil moisture increments. The final states of this suite were used to initialize the ensemble streamflow forecasts of Météo-France, which are based on the SIM model and use the European Centre for Medium-range Weather Forecasts (ECMWF) 10-day Ensemble Prediction System (EPS). Two different configurations of the assimilation system were used in this study: the first with the classical SIM model and the second using improved soil physics in ISBA. The effects of the assimilation system on the ensemble streamflow forecasts were assessed for these two configurations, and a comparison was made with the original (i.e. without data assimilation and without the improved physics) ensemble streamflow forecasts. It is shown that the assimilation system improved most of the statistical scores usually computed for the validation of ensemble predictions (RMSE, Brier Skill Score and its decomposition, Ranked Probability Skill Score, False Alarm Rate, etc.), especially for the first few days of the time range. The assimilation was slightly more efficient for small basins than for large ones.Tue, 24 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1623/2010/<b>A past discharges assimilation system for ensemble streamflow forecasts over France – Part 1: Description and validation of the assimilation system</b><br /><br />Hydrology and Earth System Sciences, 14, 1623-1637, 2010<br /><br />Author(s): G. Thirel, E. Martin, J.-F. Mahfouf, S. Massart, S. Ricci, and F. Habets<br /><br />Two Ensemble Streamflow Prediction Systems (ESPSs) have been set up at Météo-France. They are based on the French SIM distributed hydrometeorological model. A deterministic analysis run of SIM is used to initialize the two ESPSs. In order to obtain a better initial state, a past discharges assimilation system has been implemented into this analysis SIM run, using the Best Linear Unbiased Estimator (BLUE). Its role is to improve the model soil moisture by using streamflow observations in order to better simulate streamflow. The skills of the assimilation system were assessed for a 569-day period on six different configurations, including two different physics schemes of the model (the use of an exponential profile of hydraulic conductivity or not) and, for each one, three different ways of considering the model soil moisture in the BLUE state variables. Respect of the linearity hypothesis of the BLUE was verified by assessing of the impact of iterations of the BLUE. The configuration including the use of the exponential profile of hydraulic conductivity and the combination of the moisture of the two soil layers in the state variable showed a significant improvement of streamflow simulations. It led to a significantly better simulation than the reference one, and the lowest soil moisture corrections. These results were confirmed by the study of the impacts of the past discharge assimilation system on a set of 49 independent stations.Tue, 24 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1595/2010/<b>The ability of a GCM-forced hydrological model to reproduce global discharge variability</b><br /><br />Hydrology and Earth System Sciences, 14, 1595-1621, 2010<br /><br />Author(s): F. C. Sperna Weiland, L. P. H. van Beek, J. C. J. Kwadijk, and M. F. P. Bierkens<br /><br />Data from General Circulation Models (GCMs) are often used to investigate hydrological impacts of climate change. However GCM data are known to have large biases, especially for precipitation. In this study the usefulness of GCM data for hydrological studies, with focus on discharge variability and extremes, was tested by using bias-corrected daily climate data of the 20CM3 control experiment from a selection of twelve GCMs as input to the global hydrological model PCR-GLOBWB. Results of these runs were compared with discharge observations of the GRDC and discharges calculated from model runs based on two meteorological datasets constructed from the observation-based CRU TS2.1 and ERA-40 reanalysis. In the first dataset the CRU TS 2.1 monthly timeseries were downscaled to daily timeseries using the ERA-40 dataset (<i>ERA6190</i>). This dataset served as a best guess of the past climate and was used to analyze the performance of PCR-GLOBWB. The second dataset was created from the ERA-40 timeseries bias-corrected with the CRU TS 2.1 dataset using the same bias-correction method as applied to the GCM datasets (<i>ERACLM</i>). Through this dataset the influence of the bias-correction method was quantified. The bias-correction was limited to monthly mean values of precipitation, potential evaporation and temperature, as our focus was on the reproduction of inter- and intra-annual variability. <br><br> After bias-correction the spread in discharge results of the GCM based runs decreased and results were similar to results of the ERA-40 based runs, especially for rivers with a strong seasonal pattern. Overall the bias-correction method resulted in a slight reduction of global runoff and the method performed less well in arid and mountainous regions. However, deviations between GCM results and GRDC statistics did decrease for <i><span style="border-top: 1px solid #000; color: #000;">Q</span></i>, <i>Q90</i> and IAV. After bias-correction consistency amongst models was high for mean discharge and timing (<i>Qpeak</i>), but relatively low for inter-annual variability (IAV). This suggests that GCMs can be of use in global hydrological impact studies in which persistence is of less relevance (e.g. in case of flood rather than drought studies). Furthermore, the bias-correction influences mean discharges more than extremes, which has the positive consequence that changes in daily rainfall distribution and subsequent changes in discharge extremes will also be preserved when the bias-correction method is applied to future GCM datasets. However, it also shows that agreement between GCMs remains relatively small for discharge extremes. <br><br> Because of the large deviations between observed and simulated discharge, in which both errors in climate forcing, model structure and to a lesser extent observations are accumulated, it is advisable not to work with absolute discharge values for the derivation of future discharge projections, but rather calculate relative changes by dividing the absolute change by the absolute discharge calculated for the control experiment.Thu, 19 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1581/2010/<b>Changes in flood frequencies in Switzerland since 1500</b><br /><br />Hydrology and Earth System Sciences, 14, 1581-1594, 2010<br /><br />Author(s): P. Schmocker-Fackel and F. Naef<br /><br />In northern Switzerland, an accumulation of large flood events has occurred since the 1970s, preceded by a prolonged period with few floods (Schmocker-Fackel and Naef, 2010). How have Swiss flood frequencies changed over the past 500 years? And how does the recent increase in flood frequencies compare with other periods in this half millennium? We collected historical flood data for 14 Swiss catchments dating back to 1500 AC. All catchments experienced marked fluctuations in flood frequencies, and we were able to identify four periods of frequent flooding in northern Switzerland, lasting between 30 and 100 years (1560–1590, 1740–1790, 1820–1940 and since 1970). The current period of increased flood frequencies has not yet exceeded those observed in the past. We tested whether the flood frequency fluctuation could be explained with generalised climatic indices like solar activity or the NAO. The first three periods of low flood frequency in Switzerland correspond to periods of low solar activity. However, after 1810 no relationship between solar activity and flood frequency was found, nor could a relationship be established between reconstructed NAO indices or reconstructed Swiss temperatures. We found re-occurring spatial patterns of flood frequencies on a European scale, with the Swiss periods of frequent flooding often in phase with those in the Czech Republic, Italy and Spain and less often with those in Germany. The pattern of flooding in northern Switzerland and the Czech Republic seem to be rather similar, although the individual flood events do not match. This comparison of flooding patterns in different European countries suggests that changes in large scale atmospheric circulation are responsible for the flood frequency fluctuations.Tue, 17 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1567/2010/<b>A method for parameterising roughness and topographic sub-grid scale effects in hydraulic modelling from LiDAR data</b><br /><br />Hydrology and Earth System Sciences, 14, 1567-1579, 2010<br /><br />Author(s): A. Casas, S. N. Lane, D. Yu, and G. Benito<br /><br />High resolution airborne laser data provide new ways to explore the role of topographic complexity in hydraulic modelling parameterisation, taking into account the scale-dependency between roughness and topography. In this paper, a complex topography from LiDAR is processed using a spatially and temporally distributed method at a fine resolution. The surface topographic parameterisation considers the sub-grid LiDAR data points above and below a reference DEM, hereafter named as topographic content. A method for roughness parameterisation is developed based on the topographic content included in the topographic DEM. Five subscale parameterisation schemes are generated (topographic contents at 0, ±5, ±10, ±25 and ±50 cm) and roughness values are calculated using an equation based on the mixing layer theory (Katul et al., 2002), resulting in a co-varied relationship between roughness height and topographic content. Variations in simulated flow across spatial subscales show that the sub grid-scale behaviour of the 2-D model is not well-reflected in the topographic content of the DEM and that subscale parameterisation must be modelled through a spatially distributed roughness parameterisation. Variations in flow predictions are related to variations in the roughness parameter. Flow depth-derived results do not change systematically with variation in roughness height or topographic content but they respond to their interaction. Finally, subscale parameterisation modifies primarily the spatial structure (level of organisation) of simulated 2-D flow linearly with the additional complexity of subscale parameterisation.Tue, 17 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1551/2010/<b>On the reproducibility and repeatability of laser absorption spectroscopy measurements for δ²H and δ¹⁸O isotopic analysis</b><br /><br />Hydrology and Earth System Sciences, 14, 1551-1566, 2010<br /><br />Author(s): D. Penna, B. Stenni, M. Šanda, S. Wrede, T. A. Bogaard, A. Gobbi, M. Borga, B. M. C. Fischer, M. Bonazza, and Z. Chárová<br /><br />The aim of this study was to analyse the reproducibility of off-axis integrated cavity output spectroscopy (OA-ICOS)-derived δ²H and δ¹⁸O measurements on a set of 35 water samples by comparing the performance of four laser spectroscopes with the performance of a conventional mass spectrometer under typical laboratory conditions. All samples were analysed using three different schemes of standard/sample combinations and related data processing to assess the improvement of results compared with mass spectrometry. The repeatability of the four OA-ICOS instruments was further investigated by multiple analyses of a sample subset to evaluate the stability of δ²H and δ¹⁸O measurements. <br></br> Results demonstrated an overall agreement between OA-ICOS-based and mass spectrometry-based measurements for the entire dataset. However, a certain degree of variability existed in precision and accuracy between the four instruments. There was no evident bias or systematic deviations from the mass spectrometer values, but random errors, which were apparently not related to external factors, significantly affected the final results. Our investigation revealed that analytical precision ranged ±from ±0.56&permil; to ±1.80&permil; for δ²H and from ±0.10&permil; to ±0.27&permil; for δ¹⁸O measurements, with a marked variability among the four instruments. The overall capability of laser instruments to reproduce stable results with repeated measurements of the same sample was acceptable, and there were general differences within the range of the analytical precision for each spectroscope. Hence, averaging the measurements of three identical samples led to a higher degree of accuracy and eliminated the potential for random deviations.Fri, 13 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1537/2010/<b>Integrated response and transit time distributions of watersheds by combining hydrograph separation and long-term transit time modeling</b><br /><br />Hydrology and Earth System Sciences, 14, 1537-1549, 2010<br /><br />Author(s): M. C. Roa-García and M. Weiler<br /><br />We present a new modeling approach analyzing and predicting the Transit Time Distribution (TTD) and the Response Time Distribution (RTD) from hourly to annual time scales as two distinct hydrological processes. The model integrates Isotope Hydrograph Separation (IHS) and the Instantaneous Unit Hydrograph (IUH) approach as a tool to provide a more realistic description of transit and response time of water in catchments. Individual event simulations and parameterizations were combined with long-term baseflow simulation and parameterizations; this provides a comprehensive picture of the catchment response for a long time span for the hydraulic and isotopic processes. The proposed method was tested in three Andean headwater catchments to compare the effects of land use on hydrological response and solute transport. Results show that the characteristics of events and antecedent conditions have a significant influence on TTD and RTD, but in general the RTD of the grassland dominated catchment is concentrated in the shorter time spans and has a higher cumulative TTD, while the forest dominated catchment has a relatively higher response distribution and lower cumulative TTD. The catchment where wetlands concentrate shows a flashier response, but wetlands also appear to prolong transit time.Fri, 13 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1527/2010/<b>Extraction of thalweg networks from DTMs: application to badlands</b><br /><br />Hydrology and Earth System Sciences, 14, 1527-1536, 2010<br /><br />Author(s): N. Thommeret, J. S. Bailly, and C. Puech<br /><br />To study gully spatial patterns in the badlands using a continuous thalweg vector network, this paper presents methods to extract the badlands' thalweg network from a regular grid digital terrain model (DTM) by combining terrain morphology indices with a drainage algorithm. This method will delineate a thalweg only where the DTM denotes a significant curvature with respect to DTM accuracy and relies on three major steps. First, discontinuous concave areas were detected from the DTM using morphological criteria, either the plan curvature or the convergence index. Second, the concave areas were connected using a drainage algorithm, which provides a continuous, thick, tree-structured scheme. We assumed that these areas were physically significant and corresponded to a gully floor. Finally, the thick path was reduced to its main course and vectorised to obtain a thalweg network. The methods were applied to both virtual and actual DTM cases. The actual case was a LiDAR DTM of the Draix badlands in the French Alps. The obtained networks were quantitatively compared, both with a network obtained using the usual drainage area criteria and with a reference network mapped in the field. The CI-based network showed the great potential for thalweg network extraction.Tue, 10 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1509/2010/<b>Soil moisture modelling of a SMOS pixel: interest of using the PERSIANN database over the Valencia Anchor Station</b><br /><br />Hydrology and Earth System Sciences, 14, 1509-1525, 2010<br /><br />Author(s): S. Juglea, Y. Kerr, A. Mialon, E. Lopez-Baeza, D. Braithwaite, and K. Hsu<br /><br />In the framework of Soil Moisture and Ocean Salinity (SMOS) Calibration/Validation (Cal/Val) activities, this study addresses the use of the PERSIANN-CCS¹database in hydrological applications to accurately simulate a whole SMOS pixel by representing the spatial and temporal heterogeneity of the soil moisture fields over a wide area (50×50 km²). The study focuses on the Valencia Anchor Station (VAS) experimental site, in Spain, which is one of the main SMOS Cal/Val sites in Europe. <br><br> A faithful representation of the soil moisture distribution at SMOS pixel scale (50×50 km²) requires an accurate estimation of the amount and temporal/spatial distribution of precipitation. To quantify the gain of using the comprehensive PERSIANN database instead of sparsely distributed rain gauge measurements, comparisons between in situ observations and satellite rainfall data are done both at point and areal scale. An overestimation of the satellite rainfall amounts is observed in most of the cases (about 66%) but the precipitation occurrences are in general retrieved (about 67%). <br><br> To simulate the high variability in space and time of surface soil moisture, a Soil Vegetation Atmosphere Transfer (SVAT) model – ISBA (Interactions between Soil Biosphere Atmosphere) is used. The interest of using satellite rainfall estimates as well as the influence that the precipitation events can induce on the modelling of the water content in the soil is depicted by a comparison between different soil moisture data. Point-like and spatialized simulated data using rain gauge observations or PERSIANN – CCS database as well as ground measurements are used. It is shown that a good adequacy is reached in most part of the year, the precipitation differences having less impact upon the simulated soil moisture. The behaviour of simulated surface soil moisture at SMOS scale is verified by the use of remote sensing data from the Advanced Microwave Scanning Radiometer on Earth observing System (AMSR-E). We show that the PERSIANN database provides useful information at temporal and spatial scales in the context of soil moisture retrieval. <br><br> <br><br> ¹Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Cloud Classification System – <a href="http://chrs.web.uci.edu/persiann"target="_blank">http://chrs.web.uci.edu/persiann</a>Tue, 10 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1499/2010/<b>Accurate LAI retrieval method based on PROBA/CHRIS data</b><br /><br />Hydrology and Earth System Sciences, 14, 1499-1507, 2010<br /><br />Author(s): W. J. Fan, X. R. Xu, X. C. Liu, B. Y. Yan, and Y. K. Cui<br /><br />Leaf area index (LAI) is one of the key structural variables in terrestrial vegetation ecosystems. Remote sensing offers an opportunity to accurately derive LAI at regional scales. The anisotropy of canopy reflectance, variations in background characteristics, and variability in atmospheric conditions constitute three factors that can strongly constrain the accuracy of retrieved LAI. Based on a hybrid canopy reflectance model, a new hyperspectral directional second derivative method (DSD) is proposed in this paper. This method can estimate LAI accurately through analyzing the canopy anisotropy. The effect of the background can also be effectively removed. With the aid of a widely-accepted atmospheric model, the influence of atmospheric conditions can be minimized as well. Thus the inversion precision and the dynamic range can be markedly improved, which has been proved by numerical simulations. As the derivative method is very sensitive to random noise, we put forward an innovative filtering approach, by which the data can be de-noised in spectral and spatial dimensions synchronously. It shows that the filtering method can remove random noise effectively; therefore, the method can be applied to hyperspectral images. The study region was situated in Zhangye, Gansu Province, China; hyperspectral and multi-angular images of the study region were acquired via the Compact High-Resolution Imaging Spectrometer/Project for On-Board Autonomy (CHRIS/PROBA), on 4 June 2008. After the pre-processing procedures, the DSD method was applied, and the retrieved LAI was validated by ground reference data at 11 sites. Results show that the new LAI inversion method is accurate and effective with the aid of the innovative filtering method.Tue, 10 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1487/2010/<b>Analysis of the energy balance closure over a FLUXNET boreal forest in Finland</b><br /><br />Hydrology and Earth System Sciences, 14, 1487-1497, 2010<br /><br />Author(s): J. M. Sánchez, V. Caselles, and E. M. Rubio<br /><br />The imbalance in the surface energy budget, when using eddy-covariance techniques to measure turbulent fluxes, is still an unresolved problem. Important progresses have been reported in recent years identifying potential reasons for this lack of energy balance closure. In this paper we focus on the data collected in a FLUXNET boreal forest site in Sodankylä, Finland. Using one month half-hourly data, an average Energy Balance Ratio (EBR) of 0.72 is obtained. The inclusion of the heat storage terms in the energy budget yields an improvement of about 6% in the total closure. The sensitivity of the energy balance closure to the turbulence intensity is analysed in terms of the friction velocity, and atmospheric stability/instability conditions. Significant better closure is obtained for high values of the friction velocity and unstable conditions. The mismatch in variable footprints for different fluxes is checked by analysing the dependence of the closure on wind direction. The inhomogeneities of the emplacement surrounding the flux tower induce a critical decrease in the EBR of up to 30% for specific wind directions. After filtering all unfavourable conditions, EBR=0.94. This is a reasonable good result for the energy balance closure. However there is still a 6% of the available energy unaccounted. Part of this remaining imbalance could be justified as the impossibility of the 30 min averaging time to capture the low frequency flux contributions, since the closure is improved by a 5% when the averaging time is expanded to 2 h.Fri, 06 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1477/2010/<b>Stream depletion rate with horizontal or slanted wells in confined aquifers near a stream</b><br /><br />Hydrology and Earth System Sciences, 14, 1477-1485, 2010<br /><br />Author(s): P.-R. Tsou, Z.-Y. Feng, H.-D. Yeh, and C.-S. Huang<br /><br />Pumping in a vertical well may produce a large drawdown cone near the well. In this paper, the solution is first developed for describing the groundwater flow associated with a point source in a confined aquifer near a stream. Based on the principle of superposition, analytical solutions for horizontal and slanted wells are then developed by integrating the point source solution along the well axis. The solutions can be simplified to quasi-steady solutions by neglecting the exponential terms to describe the late-time drawdown, which can provide useful information in designing horizontal well location and length. The direction of the well axis can be determined from the best SDR subject to the drawdown constraint. It is found that hydraulic conductivity in the direction perpendicular to the stream plays a crucial role in influencing the time required for reaching quasi-steady SDR. In addition, the effects of the well length as well as the distance between the well and stream on the SDR are also examined.Fri, 06 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1465/2010/<b>Using flushing rate to investigate spring-neap and spatial variations of gravitational circulation and tidal exchanges in an estuary</b><br /><br />Hydrology and Earth System Sciences, 14, 1465-1476, 2010<br /><br />Author(s): D. C. Shaha, Y.-K. Cho, G.-H. Seo, C.-S. Kim, and K. T. Jung<br /><br />Spring-neap and spatial variations of gravitational circulation and tidal exchanges in the Sumjin River Estuary (SRE) were investigated using the flushing rate. The flushing rate was calculated between multiple estuarine segments and the adjacent bay to examine the spatial variation of two exchanges. The strength of gravitational circulation and tidal exchanges modulated significantly between spring and neap tides, where stratification alternated between well-mixed and highly-stratified conditions over the spring-neap cycle. Tide-driven dispersive flux of salt dominated over gravitational circulation exchange near the mouth during spring tide due to the larger tidal amplitude that caused well-mixed conditions and rapid exchange. In contrast, the central and inner regimes were found to be partially stratified during spring tide due to the reduction in tidal amplitude where both gravitational circulation and tidal exchanges were important in transporting salt. The combined contributions of two fluxes were also found during neap tide along the SRE due to the significant reduction in vertical mixing that accompanied strong stratification. Gravitational circulation exchange almost entirely dominated in transporting salt at the upstream end during spring and neap tides.Thu, 05 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1449/2010/<b>The potential for remote sensing and hydrologic modelling to assess the spatio-temporal dynamics of ponds in the Ferlo Region (Senegal)</b><br /><br />Hydrology and Earth System Sciences, 14, 1449-1464, 2010<br /><br />Author(s): V. Soti, C. Puech, D. Lo Seen, A. Bertran, C. Vignolles, B. Mondet, N. Dessay, and A. Tran<br /><br />In the Ferlo Region in Senegal, livestock depend on temporary ponds for water but are exposed to the Rift Valley Fever (RVF), a disease transmitted to herds by mosquitoes which develop in these ponds. Mosquito abundance is related to the emptying and filling phases of the ponds, and in order to study the epidemiology of RVF, pond modelling is required. In the context of a data scarce region, a simple hydrologic model which makes use of remote sensing data was developed to simulate pond water dynamics from daily rainfall. Two sets of ponds were considered: those located in the main stream of the Ferlo Valley whose hydrological dynamics are essentially due to runoff, and the ponds located outside, which are smaller and whose filling mechanisms are mainly due to direct rainfall. Separate calibrations and validations were made for each set of ponds. Calibration was performed from daily field data (rainfall, water level) collected during the 2001 and 2002 rainy seasons and from three different sources of remote sensing data: 1) very high spatial resolution optical satellite images to access pond location and surface area at given dates, 2) Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Digital Elevation Model (DEM) data to estimate pond catchment area and 3) Tropical Rainfall Measuring Mission (TRMM) data for rainfall estimates. The model was applied to all ponds of the study area, the results were validated and a sensitivity analysis was performed. Water height simulations using gauge rainfall as input were compared to water level measurements from four ponds and Nash coefficients >0.7 were obtained. Comparison with simulations using TRMM rainfall data gave mixed results, with poor water height simulations for the year 2001 and good estimations for the year 2002. A pond map derived from a Quickbird satellite image was used to assess model accuracy for simulating pond water areas for all the ponds of the study area. The validation showed that modelled water areas were mostly underestimated but significantly correlated, particularly for the larger ponds. The results of the sensitivity analysis showed that parameters relative to pond shape and catchment area estimation have less effects on model simulation than parameters relative to soil properties (rainfall threshold causing runoff in dry soils and the coefficient expressing soil moisture decrease with time) or the water loss coefficient. Overall, our results demonstrate the possibility of using a simple hydrologic model with remote sensing data to track pond water heights and water areas in a homogeneous arid area.Wed, 04 Aug 2010 00:00:00 +0200http://www.hydrol-earth-syst-sci.net/14/1435/2010/<b>Explicit simulations of stream networks to guide hydrological modelling in ungauged basins</b><br /><br />Hydrology and Earth System Sciences, 14, 1435-1448, 2010<br /><br />Author(s): S. Stoll and M. Weiler<br /><br />Rainfall-runoff modelling in ungauged basins is still one of the greatest challenges in hydrological research. The lack of discharge data necessitates the establishment of new innovative approaches to guide hydrological modelling in ungauged basins. Besides the transfer of calibrated parameters from similar gauged catchments, the application of distributed data as a hydrological response in addition to discharge seems to be promising. A new approach to guide hydrological modelling based on explicit simulation of the spatial stream network was tested in four different catchments in Germany. In a first step we used a simplified version of the process-based model Hill-Vi together with regional climate normals to simulate stream networks. The calculation of gravity driven lateral subsurface and groundwater flow is used to identify patterns of stream cells, which were compared to reference stream networks and their degree of spatial agreement was evaluated. Significant differences between good and poor simulations could be distinguished and the corresponding parameter sets relate well with the hydrogeological properties of the catchments. The optimized parameters were subsequently used to simulate daily discharge using an observed time series of precipitation and air temperature. The performance was evaluated against observed discharge and water balance. This approach shows some promising results but also some limitations. Although the model's parsimonious model structure could be further improved regarding discharge recession and evapotranspiration, the performance was similar to regionalisation methods. Stream network modelling, which has minimal data requirements, seems to be a reasonable alternative for model development and parameter evaluation in ungauged basins.Wed, 04 Aug 2010 00:00:00 +0200