bluuebunny/crossref_metadata_2025 huggingface dataset:
Dying to find the source – the quantitative use of rhodamine WT as a proxy for soluble point source pollutants in closed pipe surface drainage networks
Authors: Mines C. H. , Ghadouani A. , Ivey G. N.
Published: April 2010

Abstract. Rhodamine WT (RWT), a xanthene dye, may serve as a proxy for soluble pollutants within quantitative tracing studies investigating point source contaminant transport. This study quantified the effects of altering the concentration, pH, temperature and salinity of a RWT solution on the detected fluorescence of RWT within the laboratory prior to a field release of RWT within a closed pipe urban drainage network. All RWT solutions exhibited stability and <10% variation from the expected concentration over a thirteen hour laboratory study period; pH related quenching of RWT fluorescence of up to 14.9% was observed for solutions with pH <3.9; and increasing salinity of RWT solution was found to have a negligible quenching effect. In direct contrast to previous studies RWT fluorescence was found to directly correlate with temperature of solution, and a temperature correction factor was determined and tested. If these effects were combined in an additive manner, the maximum potential underestimation and overestimation of RWT concentration are approximately 30% and 20% respectively. The field release study succeeded in detecting RWT at concentrations two orders of magnitude greater than background fluorescence, and RWT peak concentration prediction using longitudinal dispersion theory was achieved within 10% of the observed peaks.
The effect of changes in rainfall on the response of the water table to a major alley farming experiment
Authors: Noorduijn S. L. , Smettem K. R. J. , Vogwill R. , Ghadouani A.
Published: April 2010

Abstract. Widespread clearing of native vegetation in Southwest Western Australia has led to land degradation associated with rising groundwater, secondary salinisation and waterlogging. Land degradation can be controlled by re-establishing native deep rooted perennial vegetation across parts of the landscape. Alley farming is an agroforestry practice where multiple perennial tree belts are planted in alternation with traditional agricultural crops. To identify the best configuration (belt width verses alley width) for controlling rising groundwater levels and providing viable economic returns, a large scale experiment was established in 1995. The experiment contains seven different alley farming designs, each with transects of piezometers running across tree belts into adjacent alleys to monitor changes in the groundwater level. Two control piezometers were also installed in an adjacent paddock. At the site groundwater is shallow (<3 m) and of poor quality (pH 3–5, Ec 2.1–45.9 mS cm−1) and so root water uptake from the saturated zone is limited. Simple hydrograph analysis did not identify any treatment effects on the water table response. Subsequent statistical analysis revealed that 20–30% of the variability in the water table data over the 12 year period was attributable to the alley farming experiment. It was hypothesized that a climate trend (reducing annual rainfall over time) may be obscuring the effect of the experiment. To further investigate the effect of the experiment on groundwater response, further hydrograph analysis was conducted to compare the trends in the control piezometers in relation to those located within the belts. A difference of 0.9 m was observed between the mean groundwater levels in the control piezometers and the mean levels in the perennial belt piezometers. For a mean specific yield of 0.03 m3 m−3 this equates to a small additional water use of 27 mm yr−1 by the perennial agroforestry system. It is concluded that declining annual rainfall is the principal control on hydrograph response at the site. Perennial biomass development and perennial root development (both laterally and vertically) exert only a small influence on water table depth. The implications of this study indicate that alley farming has a limited ability to control a rising water table in low lying areas with a shallow saline water table.
Calibration analysis for water storage variability of the global hydrological model WGHM
Authors: Werth S. , Güntner A.
Published: April 2010

Abstract. This study contributes to an improved global simulation of continental water storage variations by calibrating the WaterGAP Global Hydrology Model (WGHM) for 28 of the largest river basins worldwide. Five years (01/2003–12/2007) of satellite-based estimates of total water storage changes from the GRACE mission are combined with river discharge data in a multi-objective calibration framework of the most sensitive WGHM model parameters. The uncertainty and significance of the calibration results is analyzed with respect to errors in the observation data. An independent simulation period (01/2008–12/2008) is used for validation. The contribution of single storage compartments to the total water budget before and after calibration is analyzed in detail. A multi-objective improvement of the model states is obtained for most of the river basins, with mean error reductions up to 110 km3/month for discharge and up to 24 mm of a water mass equivalent column for total water storage changes, as for the Amazon basin. Errors in phase and signal variability of seasonal water mass changes are reduced. The calibration is shown to primarily affect soil water storage in most river basins. The variability of groundwater storage variations is reduced at the global scale after calibration. Structural model errors are identified from a small contribution of surface water storage including wetlands in river basins with large inundation areas, such as the Amazon or the Mississippi. The results demonstrate the value of GRACE data and the multi-objective calibration approach for improvements of large-scale hydrological simulations, as they constitute a starting-point for improvements of model structure. The integration of complimentary observation data to further constrain the simulation of single storage compartments is encouraged.
Extracting statistical parameters of extreme precipitation from a NWP model
Authors: Eliasson J. , Rögnvaldsson Ó. , Jonsson T.
Published: April 2010

Abstract. Precipitation simulations in an 8×8 km grid by the PSU/NCAR Mesoscale Model MM5 are used to find the M5 and Ci statistical parameters in order to support the M5 map used for flood estimates by Icelandic engineers. It is known a priori that especially wind anomalies do occur on a considerably smaller scale than 8 km. The simulation period used is 1962–2005 and 73 meteorological stations do have records long enough in this period to provide an observation value set. Of these only 1 is in the central highlands, so the highland values of the existing M5 map are estimations. The comparison between the simulated values and the observational value set show a M5 average difference (observed-simulated) of −5 mm/24 h with standard deviation 17 mm, 3 outliers excluded. This is within expected limits, computational and observational errors considered. Suggested correction procedure brings these values down to 4 mm and 11 mm.
An evaluation of the canadian global meteorological ensemble prediction system for short-term hydrological forecasting
Authors: Velázquez J. A. , Petit T. , Lavoie A. , Boucher M.-A. , Turcotte R. , Fortin V. , Anctil F.
Published: April 2010

Abstract. Hydrological forecasting consists in the assessment of future streamflow. Current deterministic forecasts do not give any information concerning the uncertainty, which might be limiting in a decision-making process. Ensemble forecasts are expected to fill this gap. In July 2007, the Meteorological Service of Canada has improved its ensemble prediction system, which has been operational since 1998. It uses the GEM model to generate a 20-member ensemble on a 100 km grid, at mid-latitudes. This improved system is used for the first time for hydrological ensemble predictions. Five watersheds in Quebec (Canada) are studied: Chaudière, Châteauguay, Du Nord, Kénogami and Du Lièvre. An interesting 17-day rainfall event has been selected in October 2007. Forecasts are produced in a 3 h time step for a 3-day forecast horizon. The deterministic forecast is also available and it is compared with the ensemble ones. In order to correct the bias of the ensemble, an updating procedure has been applied to the output data. Results showed that ensemble forecasts are more skilful than the deterministic ones, as measured by the Continuous Ranked Probability Score (CRPS), especially for 72 h forecasts. However, the hydrological ensemble forecasts are under dispersed: a situation that improves with the increasing length of the prediction horizons. We conjecture that this is due in part to the fact that uncertainty in the initial conditions of the hydrological model is not taken into account.
Deriving a global river network map at flexible resolutions from a fine-resolution flow direction map with explicit representation of topographical characteristics in sub-grid scale
Authors: Yamazaki D. , Oki T. , Kanae S.
Published: April 2010

Abstract. This paper proposes an improved method to convert a fine-resolution flow direction map into a coarse-resolution river network map for the use in global river routing models. The proposed method attempts to preserve the river network structure of an original fine-resolution map in upscaling procedures, which has not been achieved by previous methods. It is found that the problem in previous methods is mainly due to the traditional way of describing downstream cells of a river network map with a direction toward one of the eight neighboring cells. Instead in the improved method, the downstream cell can be flexibly located onto any cells in the river network map. The improved method is applied to derive global river network maps at various resolutions. It succeeded to preserve the river network structure of the original flow direction map, and consequently realizes automatic construction of river network maps at any resolutions. This enables both higher-resolution approach in global river routing models and inclusion of sub-grid scale topographic features, such as realistic river meanderings and catchment boundaries. Those advantages of the proposed method are expected to enhance ability of global river routing models, providing ways to represent surface water storage and movement such as river discharge and inundated area extent in much finer-scale than ever modeled.
Less rain, more water in ponds: a remote sensing study of the dynamics of surface waters from 1950 to present in pastoral Sahel (Gourma region, Mali)
Authors: Gardelle J. , Hiernaux P. , Kergoat L. , Grippa M.
Published: April 2010

Abstract. Changes in the flood regime of ponds in the Gourma region from 1950 to present are studied by remote sensing, in the general context of the current multi-decennial Sahel drought. The seasonal and interannual variations of the areas covered by surface water are assessed using multi-date and multi-sensor satellite images (SPOT, FORMOSAT, LANDSAT-MSS, -TM, and -ETM, CORONA, and MODIS) and aerial photographs (IGN). Water body classification is adapted to each type of spectral resolution, with or without a middle-infrared band, and each spatial resolution, using linear unmixing for mixed pixels of MODIS data. The high-frequency MODIS data document the seasonal cycle, with an abrupt rise early in wet season and a progressive decrease in the dry season. They also provide a base to study the inter-annual variability of the flood regime, with sharp contrasts between dry years such as 2004 (low and early maximal area) and wetter years such as 2001 and 2002 (respectively high and late maximal area). The highest water level reached annually greatly depends on the volume, intensity and timing of rain events. However, the overall reduction by 20% of annual rains of the current period, compared to the 50' and 60', is concomitant with an apparently paradoxical large increase in the area of surface water, starting from the late 1980's. Spectacular for the two study cases of Agoufou and Ebang Mallam, for which time series covering the 1954-present period exist, this increase also reaches 98% between 1975 and 2002 for 92 ponds identified in central Gourma. Ponds with turbid waters and no aquatic vegetation are responsible for this increase, more pronounced to the north of the study zone. Possible causes of this change in surface water volume and regime are discussed based on differential changes in ponds dynamics related to the specifics in topography, soil texture and vegetation cover over the watershed. Changes in rain pattern and in ponds sedimentation are ruled out, and the impact of changes in land use, limited in the area, is found secondary, as opposed to what has often been advocated for in cultivated Sahel. Instead, major responsibility is attributed to increased runoff triggered by the lasting impact of the 1970–1980's droughts on the vegetation and on the hydric system over shallow soils.
Soil bio-engineering for risk mitigation and environmental restoration in a humid tropical area
Authors: Petrone A. , Preti F.
Published: April 2010

Abstract. The use of soil bio-engineering techniques in developing countries is a relevant issue for disaster mitigation, environmental restoration and poverty reduction. Research on authochtonal plants suitable for this kind of works and on economic efficiency is essential for the divulgation of such techniques. The present paper is focused on this two issues related to the realization of various typologies of soil bio-engineering works in the humid tropic of Nicaragua. In the area of Río Blanco, located in the Department of Matagalpa, soil bio-engineering installations were built in several sites. The particular structures built were: drainages with live fascine mattress, a live palisade, a vegetated live crib wall for riverbank protection, a vegetative covering made of a metallic net and biotextile coupled with a live palisade made of bamboo. In order to evaluate the suitability of the various plants used in the works, monitorings were performed, one in the live palisade alongside an unpaved road and the other on the live crib wall along a riverbank, collecting survival rate and morphological parameters data. Concerning the economic efficiency we proceed to a financial analysis of the works and once the unit price was obtained, we converted the amount in EPP Dollars (Equal Purchasing Power) in order to compare the Nicaraguan context with the Italian one. Among the used species we found that Madero negro (Gliricidia sepium) and Roble macuelizo (Tabebuia rosea) are adequate for soil-bioengineering measure on slopes while Helequeme (Erythrina fusca) reported a successful behaviour only in the crib wall for riverbank protection. In the comparison of the costs in Nicaragua and in Italy, the unit price reduction for the Central American country ranges between 1.5 times (for the vegetative covering) and almost 4 times (for the fascine mattress) if it's used the EPP dollar exchange rate. Conclusions are reached with regard to hydrological-risk mitigating actions performed on a basin scale and through naturalistic (live) interventions: not only are they socially and technically attainable, even in hardship areas (by maximizing the contribution of the local labor force and minimizing the use of mechanical equipment), but they are also economically sustainable.
Variability of the groundwater sulfate concentration in fractured rock slopes: a tool to identify active unstable areas
Authors: Binet S. , Spadini L. , Bertrand C. , Guglielmi Y. , Mudry J. , Scavia C.
Published: April 2010

Abstract. Water chemical analysis of 100 springs from the Orco and the Tinée valleys (Western Italy and Southern France) and a 7 years groundwater chemistry monitoring of the 5 main springs were performed. All these springs drain crystalline rock slopes. Some of these drain currently active gravitational slope deformations. The pyrite nuclei contained in crystalline rock materials were found in the fractures to be covered superficially by iron oxide coatings. Potentially, the infiltration of oxidigenated waters leads to the dissolution of iron(II) sulfides associated with precipitation of insoluble iron(III) oxides and with a consequent release of sulfate ions to solution, such as observed. All the waters flowing through unstable slopes show anomalies in the sulfate concentrations compared to stable aquifers. A sulfate concentrations increasing was observed repeatability after five consecutive landslides and suggest that the mechanical deformation is the origin of changes of the water composition and of the superficial mineralogy in the fractures. Moreover, the long-term observation of changes in water chemistry, rock mineral composition and associated calculation shows that sliding acceleration and chemical composition are closely related. Such signatures is produced even from slow (mm/yr) and low magnitude deformations. This result opens interesting perspective for the follow-up of sliding dynamic in landslides or in (a)seismic events and for the eventual prediction of catastrophic ruptures.
Growth of a high-elevation large inland lake, associated with climate change and permafrost degradation in Tibet
Authors: Liu J. , Kang S. , Gong T. , Lu A.
Published: April 2010

Abstract. This study analyzed satellite images and long term climate variables from a high-elevation meteorological station (4730 m) and streamflow records to examine hydrological response of Nam Co Lake (4718 m), the largest lake on the Tibetan Plateau, over the last 50 years. The results show the lake area extended by 51.8 km2 (2.7% of the total area) when compared with the area in 1976. This change is associated with an annual precipitation increase of 65 mm (18.6%), annual and winter mean temperature increases of 0.9°C and 2.1°C respectively, an annual runoff increase of 20% and an annual pan evaporation decrease of about 2%, during the past 20 years. The year of the change point in annual precipitation, air temperature, annual pan evaporation and runoff occurred in 1971, 1983, 1997 and 1997, respectively. The timing of the lake growth corresponds with the abrupt increase in annual precipitation and runoff since the mid-1990s. This study suggests a strong positive water balance in the largest inland lake on the Tibetan Plateau.
Modelling field scale water partitioning using on-site observations in sub-Saharan rainfed agriculture
Authors: Makurira H. , Savenije H. H. G. , Uhlenbrook S.
Published: April 2010

Abstract. Smallholder rainfed farming systems generally realise sub-optimal crop yields which are largely attributed to dry spell occurrences during crop growth stages. However, with improved farming practices, it seems possible to significantly increase yield levels even with little and highly variable rainfall. The presented results follow research conducted in the Makanya catchment in northern Tanzania where gross rainfall amounts to less than 400 mm/season which is insufficient to support staple food crops (e.g. maize). Alternative cultivation techniques such as runoff harvesting and in-field micro-storage structures are compared. These techniques aim to reduce soil and nutrient loss from the field but, more importantly, promote in-field infiltration and water retention. Water balance components have been observed in order to study water partitioning processes under different cultivation techniques. Based on rainfall, soil evaporation, transpiration, runoff and soil moisture measurements, a water balance model has been developed to simulate soil moisture variations over the growing season. It appears that about 50% of the diverted water leaves the root zone through deep percolation. Modelling shows that during the field trials the average productive transpiration flow ranged between 1.1–1.4 mm d−1 in the trial plots compared to 0.7–1.0 mm d−1 under traditional tillage practice. Productive transpiration processes accounted for 23–29% while losses to deep percolation accounted for 33–48% of the available water. Conclusions from the research are that the innovations tested are effective in enhancing soil moisture retention at field scale and that diversions allow crop growth moisture conditions to be attained with early rains. It is also concluded that there is more scope for efficient utilisation of the diverted runoff water if storage structures could be installed to regulate water flow to the root zone when required.
A simple two layer model for simulation of adsorbing and nonadsorbing solute transport through field soils
Authors: Akhtar M. S. , Mohrlok U. , Stüben D.
Published: April 2010

Abstract. While rapid movement of solutes through structured soils constitutes the risk of groundwater contamination, simulation of solute transport in field soils is challenging. A modification in an existing preferential flow model was tested using replicated Chloride and Lithium leachings carried out at constant flow rates through four soils differing in grades and type of structure. Flow rates generated by +10 mm, −10 mm, −40 mm, and −100 mm water heads at the surface of 35 cm diameter 50 cm height field columns. Three well-structured silty clay soils under ponding had concurrent breakthrough of Chloride and Lithium within a few cm of drainage, and a delayed and reduced peak concentration of Lithium with decrease in flow rate controlled by the negative heads. Massive sandy loam soil columns had delayed but uniform breakthrough of the solutes over the flow rates. Macropore flow in well-structured silty clay/clay loam soils reduced retardation, R (1.5 to 4.5) and effective porosity, θe (0.05 to 0.15), and increased macropore velocity, vm (20 to 30 cm cm−1 drainage) compared to the massive sandy soils. The existing simple preferential flow equation (single layer) fitted the data well only when macropore flow was dominant. The modified preferential flow equations (two layers) fitted equally well both for the adsorbing and nonadsorbing solutes. The later had high goodness of fit for a large number of solute breakthroughs, and gave almost identical retardation coefficient R as that calculated by two-domain CDE. With fewer parameters, the modified preferential flow equation after testing on some rigorous model selection criteria may provide a base for future modeling of chemical transport.
Selection of an appropriately simple storm runoff model
Authors: van Dijk A. I. J. M.
Published: April 2010

Abstract. Alternative conceptual storm runoff models, including several published ones, were evaluated against storm flow time series for 260 catchments in Australia (23–1902 km2). The original daily streamflow data was separated into baseflow and storm flow components and from these, event rainfall and storm flow totals were estimated. For each tested model structure, the number of free parameters was reduced in stages. The appropriate balance between simplicity and explanatory power was decided based on Aikake's Final Prediction Error Criterion and evidence of parameter equivalence. The majority of catchments showed storm recession half-times in the order of a day, with more rapid drainage in dry catchments. Overland and channel travel time did not appear to be an important driver of storm flow recession. A storm runoff model with two free parameters (one related to storm event size, the other to antecedent baseflow) and a fixed initial loss of 12 mm provided the optimal model structure. The optimal model had some features similar to the Soil Conservation Service Curve Number technique, but performed an average 12 to 19% better. The non-linear relationship between event rainfall and event runoff may be associated with saturated area expansion during storms and/or the relationship between storm event size and peak rainfall intensity. Antecedent baseflow was a strong predictor of runoff response. A simple conceptual relationship between groundwater storage and saturated catchment area proved adequate and produced realistic estimates of saturated area of <0.1% for the driest and >5% for the wettest catchments.
Hydroperiod and hydraulic loading for treatment potential in urban tidal wetlands
Authors: Eaton T. T. , Yi C.
Published: April 2010

Abstract. Conventional methods of estimating water quality improvement due to wetland treatment are not well suited to the dynamic water level and wetted area fluctuations observed in coastal settings. We present a new method to quantify hydroperiod and hydraulic loading at different elevations in a coastal wetland profile in which the principal inflows and outflows are due to tides. We apply our method to an urban coastal setting (part of the New York-New Jersey Harbor Estuary) where a major water quality problem persists due to fecal coliform contamination from combined sewer overflow (CSO) discharges. Based on three types of simplified hydrograph, we show how such an approach and conceptual model of a terraced tidal wetland with constant mean slope can be used to assess hydrologic constraints for wetland vegetation species and the potential treatment effectiveness for adjacent impaired coastal waters. Resulting hydroperiods and hydraulic loading values decrease approximately exponentially with elevation along the wetland profile with considerable variation in overall slope depending on the hydrograph pattern. Application of a first-order contamination reduction model using our calculated hydraulic loadings indicates that such tidal treatment wetlands could reduce average fecal coliform concentrations in the range of 27% to 94% depending on the pattern of water level fluctuation, wetland surface elevation and vegetation density. Our analysis shows the performance potential for tidal wetlands to treat adjacent coastal waters. Restoration of existing salt marshes, and construction of new tidal wetlands would therefore be a promising part of an ecohydrologic strategy to improve water quality in contaminated urban coastal settings like the New York-New Jersey Harbor Estuary.
Multi-model comparison of a major flood in the groundwater-fed basin of the Somme River (France)
Authors: Habets F. , Gascoin S. , Korkmaz S. , Thiéry D. , Zribi M. , Amraoui N. , Carli M. , Ducharne A. , Leblois E. , Ledoux E. , Martin E. , Noilhan J. , Ottlé C. , Viennot P.
Published: April 2010

Abstract. The Somme River Basin is located above a chalk aquifer and the discharge of the somme River is highly influenced by groundwater inflow (90% of river discharge is baseflow). In 2001, the Somme River Basin suffered from a major flood causing damages estimated to 100 million Euro (Deneux and Martin, 2001). The purpose of the present research is to evaluate the ability of four hydrologic models to reproduce flood events in the Somme River Basin over an 18-year period, by comparison with observed river discharge and piezometric head as well as satellite-derived extents of the flooded area. The models used differ in their computation of the surface water budget and in their representation of saturated and unsaturated zones. One model needed structural modification to be able to accurately simulate the riverflows of the Somme river. The models obtained fair to good simulations of the observed piezometric heads, but they all overestimate the piezometric level after flooding, possibly because of a simplistic representation of the deep unsaturated flow. Models differ in their annual partition of the infiltration of water within the root zone (mostly driven by simulated evapotranspiration), but these differences are attenuated by water transfers within the saturated and unsaturated zone. As a consequence, the inter-model dispersion of the computed annual baseflow is reduced. The aquifer overflow areas simulated during flooding compare well with local data and satellite images. The models showed that this overflow occurs almost every year in the same areas (in the floodplain), and that the flooding of 2001 was characterized by an increase in the quantity of the overflow and not much by a spreading of the overflow areas. Inconsistencies between river discharge and piezometric levels suggest that further investigation are needed to estimate the relative influence of unsaturated and saturated zones on the hydrodynamics of the Somme River Basin.
Towards understanding hydroclimatic change in Victoria, Australia – why was the last decade so dry?
Authors: Kiem A. S. , Verdon-Kidd D. C.
Published: April 2010

Abstract. Since the mid-1990s Victoria, located in southeast Australia, has experienced severe drought conditions characterized by streamflow that is the lowest on record in many areas. While severe decreases in annual and seasonal rainfall totals have also been observed, this alone does not seem to explain the observed reduction in flow. In this study, we investigate the large-scale climate drivers for Victoria and demonstrate how these modulate the regional scale synoptic patterns, which in turn alter the way seasonal rainfall totals are compiled and the amount of runoff per unit rainfall that is produced. The hydrological implications are significant and illustrate the need for robust hydrological modelling, which takes into account insights into physical mechanisms that drive regional hydroclimatology, in order to properly understand and quantify the impacts of climate change (natural and/or anthropogenic) on water resources.
Technical Note: Comparing and ranking soil-moisture indices performance over Europe, through remote-sensing of vegetation
Authors: Peled E. , Dutra E. , Viterbo P. , Angert A.
Published: April 2010

Abstract. Climate change induces long-term changes in soil-moisture. These changes can have important effects on the terrestrial biosphere, which can feedback into the climate system. In the past years there have been many attempts to produce and improve global soil-moisture datasets, however, comparing and validating these various datasets is not an easy task. Here, interannual variations in indices of soil moisture are compared to interannual changes in vegetation, as captured by NDVI. By comparing the correlations of the different indices with NDVI we evaluated which soil moisture index provides the most reliable soil moisture representation. We showed that NDVI can be used as an external validation dataset to soil moisture indices, in areas that are classified as warm temperate climate with hot or warm dry summers. Using the best performing index, NSM (Normalizes Soil Moisture), and the ICA (Independent Component Analysis) technique, we analyzed the response of vegetation to temperature and soil-moisture stresses over Europe.
An experiment on the evolution of an ensemble of neural networks for streamflow forecasting
Authors: Boucher M.-A. , Laliberté J.-P. , Anctil F.
Published: April 2010

Abstract. We present an experiment on fifty multilayer perceptrons trained for streamflow forecasting on four watersheds. This type of neural network is common in hydrology and using multiple training repetitions (ensembling) is a popular practice: the information issued by the ensemble is then aggregated and considered to be the final output. Some authors proposed that the ensemble could serve the calculation of confidence intervals around the ensemble mean. In the following, we are interested in the reliability of confidence intervals obtained in such fashion and in tracking the evolution of the ensemble of neural networks during the training process. For each iteration of this process, the mean of the ensemble is computed along with various confidence intervals. The performance of the ensemble mean is evaluated based on the mean absolute error. Since the ensemble of neural networks resemble an ensemble streamflow forecast, we also use ensemble-specific quality assessment tools such as the Continuous Ranked Probability Score to quantify the forecasting performance of the ensemble formed by the neural networks repetitions. We show that while the performance of the single predictor formed by the ensemble mean improves throughout the training process, the reliability of the associated confidence intervals starts to decrease shortly after the initiation of the training process. While there is no moment in the training process where the reliability of the confidence intervals is perfect, we show that it is best after approximately 5 to 10 iterations, depending on the basin. We also show that the Continuous Ranked Probability Score and the logarithmic score do not evolve in the same fashion during the training, due to a particularity of the logarithmic score.
On the role of the runoff coefficient in the mapping of rainfall to flood return periods
Authors: Viglione A. , Merz R. , Blöschl G.
Published: April 2010

Abstract. While the correspondence of rainfall return period TP and flood return period TQ is at the heart of the design storm procedure, their relationship is still poorly understood. The purpose of this paper is to shed light on the controls on this relationship examining in particular the effect of the variability of event runoff coefficients. A simplified world with block rainfall and linear catchment response is assumed and a derived flood frequency approach, both in analytical and Monte-Carlo modes, is used. The results indicate that TQ can be much higher than TP of the associated storm. The ratio TQ/TP depends on the average wetness of the system. In a dry system, TQ can be of the order of hundreds of times of TP. In contrast, in a wet system, the maximum flood return period is never more than a few times that of the corresponding storm. This is because a wet system cannot be much worse than it normally is. The presence of a threshold effect in runoff generation related to storm volume reduces the maximum ratio of TQ/TP since it decreases the randomness of the runoff coefficients and increases the probability to be in a wet situation. We also examine the question which runoff coefficients produce a flood return period equal to the rainfall return period if the design storm procedure is applied. For the systems analysed here, this runoff coefficient is always larger than the median of the runoff coefficients that cause the maximum annual floods. It depends on the average wetness of the system and on the return period considered, and its variability is particularly high when a threshold effect in runoff generation is present.
Estimation of permafrost thawing rates in a sub-arctic catchment using recession flow analysis
Authors: Lyon S. W. , Destouni G. , Giesler R. , Humborg C. , Mörth M. , Seibert J. , Karlsson J. , Troch P. A.
Published: April 2010

Abstract. Permafrost thawing is likely to change the flow pathways taken by water as it moves through arctic and sub-arctic landscapes. The location and distribution of these pathways directly influence the carbon and other biogeochemical cycling in northern latitude catchments. Direct observations of permafrost depth are difficult to perform at scales larger than a local scale. Using recession flow analysis, it may be possible to detect and estimate the rate of permafrost thawing based on a long-term streamflow record. We demonstrate the application of this approach to the sub-arctic Abiskojokken catchment in northern Sweden. Based on recession flow analysis, we estimate that permafrost in this catchment may be thawing at an average rate of about 0.9 cm/yr during the past 90 years. This estimated thawing rate is consistent with direct observations of permafrost thawing rates, ranging from 0.7 to 1.3 cm/yr over the past 30 years in the region.
Parameterization of the coupling CO2 and H2O gas exchange model at the leaf scale of Populus euphratica tree
Authors: Zhu G. , Li X. , Su Y. , Huang C.
Published: April 2010

Abstract. The following two models were combined to predict simultaneously CO2 and H2O gas exchange at the leaf scale of Populus euphratica: a Farquhar et al. type biochemical sub-model of photosynthesis (Farquhar et al., 1980) and a Ball et al. type stomatal conductance sub-model (Ball et al., 1987). The photosynthesis parameters, Vcmax, Jmax, TPU, and Rd (maximum carboxylation rate allowed by ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco), rate of phosynthetic electron transport, triose phosphate use, and day respiration) at the measurement temperature were determined by using the genetic algorithm (GA) method based on A/Ci data sets. The stomatal conductance sub-model was calibrated independently. Prediction of net photosynthesis by the coupled model agreed well with the validation data, but the model tended to underestimate rates of transpiration. Overall, the combined model generally captured the diurnal patterns of CO2and H2O exchange resulting from variation in temperature and irradiation.
HESS Opinions "A random walk on water"
Authors: Koutsoyiannis D.
Published: April 2010

Abstract. According to the traditional notion of randomness and uncertainty, natural phenomena are separated into two mutually exclusive components, random (or stochastic) and deterministic. Within this dichotomous logic, the deterministic part supposedly represents cause-effect relationships and, thus, is physics and science (the "good"), whereas randomness has little relationship with science and no relationship with understanding (the "evil"). We argue that such views should be reconsidered by admitting that uncertainty is an intrinsic property of nature, that causality implies dependence of natural processes in time, thus suggesting predictability, but even the tiniest uncertainty (e.g., in initial conditions) may result in unpredictability after a certain time horizon. On these premises it is possible to shape a consistent stochastic representation of natural processes, in which predictability (suggested by deterministic laws) and unpredictability (randomness) coexist and are not separable or additive components. Deciding which of the two dominates is simply a matter of specifying the time horizon of the prediction. Long horizons of prediction are inevitably associated with high uncertainty, whose quantification relies on understanding the long-term stochastic properties of the processes.
Radar rainfall estimation for the post-event analysis of a Slovenian flash-flood case: application of the mountain reference technique at C-band frequency
Authors: Bouilloud L. , Delrieu G. , Boudevillain B. , Zanon F. , Borga M.
Published: April 2010

Abstract. This article is dedicated to radar rainfall estimation for the post-event analysis of a Slovenian flash flood that occurred on 18 September 2007. The utility of the Mountain Reference Technique is demonstrated to quantify rain attenuation effects that affect C-band radar measurements in heavy rain. Maximum path-integrated attenuation between 15 and 20 dB were measured thanks to mountain returns for path-averaged rain rates between 10 and 15 mm h−1 over a 120-km path. The proposed technique allowed estimation of an effective radar calibration correction factor, assuming the reflectivity-attenuation relationship to be known. Screening effects were quantified using a geometrical calculation based on a digitized terrain model of the region. The vertical structure of the reflectivity was modelled with a normalized apparent vertical profile of reflectivity. Implementation of the radar data processing indicated that: (1) attenuation correction using the Hitschfeld Bordan algorithm allowed obtaining satisfactory radar rain estimates (Nash criterion of 0.8 at the event time scale); (2) due to the attenuation equation instability, it is however compulsory to limit the maximum path-integrated attenuation to be corrected to about 10 dB; (3) the results also proved to be sensitive on the parameterization of reflectivity-attenuation-rainrate relationships. The convective nature of the precipitation explains the rather good performance obtained. For more contrasted rainy systems with convective and stratiform regions, the combination of the vertical (VPR) and radial (attenuation, screening) sources of heterogeneity yields a still very challenging problem for radar quantitative precipitation estimation at C-band.
Towards automatic calibration of 2-dimensional flood propagation models
Authors: Fabio P. , Aronica G. T. , Apel H.
Published: April 2010

Abstract. Hydraulic models for flood propagation description are an essential tool in many fields, e.g. civil engineering, flood hazard and risk assessments, evaluation of flood control measures, etc. Nowadays there are many models of different complexity regarding the mathematical foundation and spatial dimensions available, and most of them are comparatively easy to operate due to sophisticated tools for model setup and control. However, the calibration of these models is still underdeveloped in contrast to other models like e.g. hydrological models or models used in ecosystem analysis. This has basically two reasons: first, the lack of relevant data against the models can be calibrated, because flood events are very rarely monitored due to the disturbances inflicted by them and the lack of appropriate measuring equipment in place. Secondly, especially the two-dimensional models are computationally very demanding and therefore the use of available sophisticated automatic calibration procedures is restricted in many cases. This study takes a well documented flood event in August 2002 at the Mulde River in Germany as an example and investigates the most appropriate calibration strategy for a full 2-D hyperbolic finite element model. The model independent optimiser PEST, that gives the possibility of automatic calibrations, is used. The application of the parallel version of the optimiser to the model and calibration data showed that a) it is possible to use automatic calibration in combination of 2-D hydraulic model, and b) equifinality of model parameterisation can also be caused by a too large number of degrees of freedom in the calibration data in contrast to a too simple model setup. In order to improve model calibration and reduce equifinality a method was developed to identify calibration data with likely errors that obstruct model calibration.
Experimental investigation of the predictive capabilities of data driven modeling techniques in hydrology – Part 2: Application
Authors: Elshorbagy A. , Corzo G. , Srinivasulu S. , Solomatine D. P.
Published: April 2010

Abstract. In this second part of the two-part paper, the data driven modeling (DDM) experiment, presented and explained in the first part, is implemented. Inputs for the five case studies (half-hourly actual evapotranspiration, daily peat soil moisture, daily till soil moisture, and two daily rainfall-runoff datasets) are identified, either based on previous studies or using the mutual information content. Twelve groups (realizations) were randomly generated from each dataset by randomly sampling without replacement from the original dataset. Neural networks (ANNs), genetic programming (GP), evolutionary polynomial regression (EPR), Support vector machines (SVM), M5 model trees (M5), K nearest neighbors (K-nn), and multiple linear regression (MLR) techniques are implemented and applied to each of the 12 realizations of each case study. The predictive accuracy and uncertainties of the various techniques are assessed using multiple average overall error measures, scatter plots, frequency distribution of model residuals, and the deterioration rate of prediction performance during the testing phase. Gamma test is used as a guide to assist in selecting the appropriate modeling technique. Unlike the two nonlinear soil moisture case studies, the results of the experiment conducted in this research study show that ANNs were a sub-optimal choice for the actual evapotranspiration and the two rainfall-runoff case studies. GP is the most successful technique due to its ability to adapt the model complexity to the modeled data. EPR performance could be close to GP with datasets that are more linear than nonlinear. SVM is sensitive to the kernel choice and if appropriately selected, the performance of SVM can improve. M5 performs very well with linear and semi linear data, which cover wide range of hydrological situations. In highly nonlinear case studies, ANNs, K-nn, and GP could be more successful than other modeling techniques. K-nn is also successful in linear situations, and it should not be ignored as a potential modeling technique for hydrological applications.
The hydrological response of the Ourthe catchment to climate change as modelled by the HBV model
Authors: Driessen T. L. A. , Hurkmans R. T. W. L. , Terink W. , Hazenberg P. , Torfs P. J. J. F. , Uijlenhoet R.
Published: April 2010

Abstract. The Meuse is an important river in western Europe, and almost exclusively rain-fed. Projected changes in precipitation characteristics due to climate change, therefore, are expected to have a considerable effect on the hydrological regime of the river Meuse. We focus on an important tributary of the Meuse, the Ourthe, measuring about 1600 km2. The well-known hydrological model HBV is forced with three high-resolution (0.088°) regional climate scenarios, each based on one of three different IPCC CO2 emission scenarios: A1B, A2 and B1. To represent the current climate, a reference model run at the same resolution is used. Prior to running the hydrological model, the biases in the climate model output are investigated and corrected for. Different approaches to correct the distributed climate model output using single-site observations are compared. Correcting the spatially averaged temperature and precipitation is found to give the best results, but still large differences exist between observations and simulations. The bias corrected data are then used to force HBV. Results indicate a small increase in overall discharge for especially the B1 scenario during the beginning of the 21st century. Towards the end of the century, all scenarios show a decrease in summer discharge, partially because of the diminished buffering effect by the snow pack, and an increased discharge in winter. It should be stressed, however, that we used results from only one GCM (the only one available at such a high resolution). It would be interesting to repeat the analysis with multiple models.
Uncertainty in acquiring elemental fluxes from subtropical mountainous rivers
Authors: Lee T. Y. , Huang J. C. , Carey A. E. , Hsu S. C. , Selvaraj K. , Kao S. J.
Published: April 2010

Abstract. Mountainous watersheds in high standing islands of the western tropical and subtropical Pacific have received great international attention regarding its high physical and chemical weathering rates caused by cyclone invasion, friable lithology and high tectonic activity. Since mountainous region is usually difficult to assess, particularly, during severe weather conditions, hydrological responses of elements against full-scale of water discharge (often >2 orders of magnitude) are rarely reported. In this study, we conducted discrete sampling (~3 day interval) throughout four seasons and intensive sampling (hourly) during typhoon floods from three upstream watersheds in Taiwan during 2002–2005. These observations revealing various elemental responses are taken as complete dataset (i.e. reference flux) to evaluate flux uncertainty among constituents caused by different sampling frequency, sample size and estimators. Five constituents are analyzed, including nitrate (NO3), sulfate (SO4), dissolved organic carbon (DOC), calcium (Ca), and silicate (Si). Each has specific environmental and geological implications. Direct average, flow-weighted and rating curve methods were applied. Basing on statistical analyses, flow-weighted method is the most conservative method, and is recommended to use for all constituents if few samples are available. The rating curve method is suggested, only when water samples in high-flows are available. Direct average method is only appropriate for stable constituents, such as Si. These findings, such as concentration-discharge variation, sampling frequency effect, and flux estimator assessment, offer fundamental knowledge while estimating geochemical fluxes from small mountainous rivers in Oceania region.