Hydrological Modelling Approach Research Articles

River flow forecasting with artificial neural networks using satellite observed precipitation pre-processed with flow length and travel time information: case study of the Ganges river basin

Abstract. This paper explores the use of flow length and travel time as a pre-processing step for incorporating spatial precipitation information into Artificial Neural Network (ANN) models used for river flow forecasting. Spatially distributed precipitation is commonly required when modelling large basins, and it is usually incorporated in distributed physically-based hydrological modelling approaches. However, these modelling approaches are recognised to be quite complex and expensive, especially due to the data collection of multiple inputs and parameters, which vary in space and time. On the other hand, ANN models for flow forecasting are frequently developed only with precipitation and discharge as inputs, usually without taking into consideration the spatial variability of precipitation. Full inclusion of spatially distributed inputs into ANN models still leads to a complex computational process that may not give acceptable results. Therefore, here we present an analysis of the flow length and travel time as a basis for pre-processing remotely sensed (satellite) rainfall data. This pre-processed rainfall is used together with local stream flow measurements of previous days as input to ANN models. The case study for this modelling approach is the Ganges river basin. A comparative analysis of multiple ANN models with different hydrological pre-processing is presented. The ANN showed its ability to forecast discharges 3-days ahead with an acceptable accuracy. Within this forecast horizon, the influence of the pre-processed rainfall is marginal, because of dominant influence of strongly auto-correlated discharge inputs. For forecast horizons of 7 to 10 days, the influence of the pre-processed rainfall is noticeable, although the overall model performance deteriorates. The incorporation of remote sensing data of spatially distributed precipitation information as pre-processing step showed to be a promising alternative for the setting-up of ANN models for river flow forecasting.

A coupled hydraulic–hydrologic modelling approach to deriving a water balance model for a complex floodplain wetland system

Wetlands, particularly those in semi-arid or arid environments, are hotspots of biological diversity and productivity. Water resource managers are therefore increasing their efforts to conserve wetlands from environmental degradation. To do this, they require a thorough understanding of the wetting and drying regimes of these wetlands, and how potential land use, climate change and water resource development might affect inundation patterns. Hydrologic models can help to enhance this understanding, and to predict and assess future impacts. However, for semi-arid environments, data to assist in model construction is scarce. This paper presents a new method for developing a water balance model for a semi-arid wetland, the Narran Lakes ecosystem in eastern Australia. This method combines hydraulic (improving our understanding of water movement through a wetland) and hydrologic (improving our predictive capability for inundation levels) models and satellite imagery (acting as calibration and validation data) to produce a predictive model of wetland inundation. We show that this coupled hydraulic–hydrologic model yields inundation patterns commensurate with those that actually occurred over more than 30 years. The model results indicate that current inundation levels are at historical lows, which is most likely associated with a naturally occurring drought and increasing water resource development upstream.

Estimating the role of a ditch network in groundwater recharge in a Mediterranean catchment using a water balance approach

Water balance variables were monitored in a farmed Mediterranean catchment characterized by a dense ditch network to allow for the separate estimation of the diffuse and concentrated recharge terms during flood events. The 27 ha central part of the catchment was equipped with (i) rain gauges, (ii) ditch gauge stations, (iii) piezometers, (iv) neutron probes, and (v) an eddy covariance mast including a 3D sonic anemometer and a fast hygrometer. The water balance was calculated for two autumnal rain and flood events. We also estimated the uncertainty of this approach with Monte Carlo simulations. Results show, that although ditch area represents only 6% of the total study area, concentrated recharge appeared to be the main source of groundwater recharge. Indeed, it was 40–50% of the total groundwater recharge for autumnal events, which are the major annual recharge events. This indicate that both, concentrated and diffuse recharge should be taken into account in any hydrological modeling approach for Mediterranean catchments. This also means that, since they collect overland flow that is often largely contaminated by chemicals, ditches may be a place where groundwater contamination is likely to occur. The uncertainty analysis indicates that recharge estimates based on water balance exhibit large uncertainty ranges. Nevertheless, Monte Carlo simulations showed that concentrated recharge was higher than expected based on their area.

How crucial is it to account for the antecedent moisture conditions in flood forecasting? Comparison of event-based and continuous approaches on 178 catchments

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.

A Modeling Approach to Water Quality Management of an Agriculturally Dominated Watershed, Kansas, USA

Impairment of water quality is a major concern for streams and rivers in the central USA. Total maximum daily loads (TMDLs) establish a watershed framework and set management targets to alleviate pollution from both point and nonpoint sources. For this study, we have used a hydrologic modeling approach to holistically examine the effect of land use management, urban development, and agricultural practices on sediment and nutrient loadings in an agricultural watershed. Annualized Agricultural Nonpoint Source (AnnAGNPS) simulation indicates that while point source dischargers contribute 8% of total nitrogen (TN) and 24% of total phosphorus (TP) loadings to the Marmaton River, agricultural nonpoint sources are the leading pollution source contributing 55% of TN and 49% of TP loading. Based on TMDL analysis and model simulation, 3% of the watershed area (3,244 ha) needs to be targeted to control TN loading whereas 1% of the total area (1,319 ha) is required for TP reduction management. Managing the TN areas alone can achieve a 57% reduction in the TP load required for the TMDL, whereas managing the targeted TP areas can only provide 30% of the required TN reduction. Areas required both TN and TP management comprise 469 ha. Targeting these areas can achieve approximately 22% of the required TN reduction and 29% of the required TP reduction. Overall, 4,094 ha will require management to achieve water quality goals. This study demonstrates that a modeling approach is needed to effectively address TMDL issues and help identify targeted areas for management.

Influence of landscape aggregation in modelling snow-cover ablation and snowmelt runoff in a sub-arctic mountainous environment

Appropriate representation of landscape heterogeneity at small to medium scales is a central issue for hydrological modelling. Two main hydrological modelling approaches, deductive and inductive, are generally applied. Here, snow-cover ablation and basin snowmelt runoff are evaluated using a combined modelling approach that includes the incorporation of detailed process understanding along with information gained from observations of basin-wide streamflow phenomena. The study site is Granger Basin, a small sub-arctic basin in the mountains of the Yukon Territory, Canada. The analysis is based on the comparison between basin-aggregated and distributed landscape representations. Results show that the distributed model based on “hydrological response” landscape units best describes the observed magnitudes of both snow-cover ablation and basin runoff, whereas the aggregated approach fails to represent the differential snowmelt rates and to describe both runoff volumes and dynamics when discontinuous snowmelt events occur.

A land surface data assimilation framework using the land information system: Description and applications

The Land Information System (LIS) is an established land surface modeling framework that integrates various community land surface models, ground measurements, satellite-based observations, high performance computing and data management tools. The use of advanced software engineering principles in LIS allows interoperability of individual system components and thus enables assessment and prediction of hydrologic conditions at various spatial and temporal scales. In this work, we describe a sequential data assimilation extension of LIS that incorporates multiple observational sources, land surface models and assimilation algorithms. These capabilities are demonstrated here in a suite of experiments that use the ensemble Kalman filter (EnKF) and assimilation through direct insertion. In a soil moisture experiment, we discuss the impact of differences in modeling approaches on assimilation performance. Provided careful choice of model error parameters, we find that two entirely different hydrological modeling approaches offer comparable assimilation results. In a snow assimilation experiment, we investigate the relative merits of assimilating different types of observations (snow cover area and snow water equivalent). The experiments show that data assimilation enhancements in LIS are uniquely suited to compare the assimilation of various data types into different land surface models within a single framework. The high performance infrastructure provides adequate support for efficient data assimilation integrations of high computational granularity.

Spatial and temporal variations of actual soil water repellency and their influence on surface runoff

AbstractThe increase of surface runoff at the plot scale caused by soil water repellency is a generally accepted phenomenon. However, to improve the understanding of the effect of water repellency on runoff at the catchment scale, spatio‐temporal dynamics of water repellency have to be analysed in more detail.The experimental setup of this study allowed the investigation of the relationship between water repellency and runoff generation on Quaternary and Tertiary sandy substrates while ensuring similar conditions in terms of terrain characteristics, meteorological and vegetation‐free conditions on both areas. Measurements of water drop penetration time and contact angle were carried out over a period from September 2003 to December 2005. Spatial variability of actual soil water repellency was related to heterogeneity of substrate and geomorphologic units, variations in time were related with the seasons and their meteorological conditions. To relate variable degrees of actual water repellency to surface runoff generation, both variables were measured in parallel at the plot scale (1 m × 1 m) and at the hillslope scale from September 2004 to December 2005. Soil water repellency of the Tertiary sands showed a temporal variability depending on the season, with the highest degree during summer and autumn. Variation of hydrophobicity between the seasons caused higher runoff coefficients in summer and autumn. Spatial heterogeneity of the soil water repellency revealed lower values in fine‐textured erosion rills and higher values for interrills and top areas. The measured runoff coefficients decreased from the scale of microplots to the hillslope scale due to infiltration in hydrophilic rills on the hillslope.The results suggest that improved hydrological modelling approaches on water‐repellent soils can be based on a geomorphological subdivision of the catchment area and seasonally varying infiltration parameters. Copyright © 2007 John Wiley & Sons, Ltd.

Rainforest conversion in Central Sulawesi, Indonesia: recent development and consequences for river discharge and water resources

Summary: The present land cover of humid tropical catchment areas mainly regulates the flow of vapour to the atmosphere.Therefore land use decisions play an important role for the water balance of a tropical catchment. Studies that relate land coverchanges with river discharge changes for humid tropical catchment areas at the mesoscale level are rare. This article applies anintegrated remote sensing and hydrological modelling approach to analyse the impact of land cover changes on the water resources of a mesoscale humid tropical catchment. First, a change detection analysis of Landsat/ ETM + satellite images wascarried out to quantify land cover changes of the mesoscale Gumbasa River catchment in Central Sulawesi, Indonesia. There-after the distributed hydrological model WASIM-ETH was calibrated and validated for the current Landsat/ ETM + scene.The historical Landsat/ ETM + scene was integrated for the hydrological model application as a historical land cover scenario.Further hypothetical total-change scenarios were carried out. The results of the hydrological model scenario application clearlydemonstrate a strong relationship between deforestation rates and increasing discharge variability. Especially a significant increase of high water discharges was simulated for the applied scenarios. With regard to the high deforestation rates of the research catchment, one can expect further changes of the water balance.

The response of precipitation and surface hydrology to tropical macro‐climate forcing in Colombia

AbstractIn tropical South America, weather and climate are affected by the meridional oscillation of the inter‐tropical convergence zone, the Pacific and Atlantic oceans, the Amazon basin, and the Andes Mountains. The dominant mode of the inter‐annual climate variability in the tropical Pacific is the El Niño/Southern Oscillation (ENSO) phenomenon. Colombia is among the South American countries that experiences large climate anomalies because of ENSO. However, the hydrologic response in Colombia to a particular ENSO event is highly complex and non‐linear.To describe this complex, non‐linear hydro‐climatic response to large‐scale atmospheric forcing in Colombia, a one‐way coupled atmospheric‐land surface hydrologic modelling approach is implemented whose main components are Colorado State University's Regional Atmospheric Modelling System (RAMS) and the Swedish Hydrologiska Byråns Vattenbalansavdelning‐Hydrologic Modelling System (HBV‐HMS). RAMS is implemented in a two‐nested grid domain for seasonal simulations and a four‐nested grid domain for daily simulations. Seasonal simulations emphasize the annual cycle at regional scales, while daily simulations focus on describing the diurnal cycle for specific watersheds. The HBV‐HMS is implemented for a specific watershed and used to examine its response at daily time scales.Results of the seasonal simulations reproduce quite well the observed spatial and temporal patterns of the hydro‐climatic variables: simulated temperature, pressure, wind velocity, and precipitation distributions show good agreement with observations. Results also show that the 1992 warm phase of ENSO led to a generalized decrease of precipitation along the Andes ranges and that the low lands of Colombia received more precipitation than during the 1989 cold ENSO phase. Similarly, daily‐simulated fields show good agreement with observed values. However, the simulated diurnal cycle of precipitation exhibits a temporal phase lag of several hours and simulated precipitation tends to underestimate both the total amount of precipitation and the duration of precipitation events. Despite these discrepancies, the results of the modelling effort clearly demonstrate the ability of this approach to capture the non‐linear and complex interactions of large‐scale atmospheric forcing and local characteristics as indicated by the satisfactory simulation of stream flow responses for a set of small watersheds. Copyright © 2006 John Wiley & Sons, Ltd.

Estimation of rainfall elasticity of streamflow in Australia

Estimates of rainfall elasticity of streamflow in 219 catchments across Australia are presented. The rainfall elasticity of streamflow is defined here as the proportional change in mean annual streamflow divided by the proportional change in mean annual rainfall. The elasticity is therefore a simple estimate of the sensitivity of long-term streamflow to changes in long-term rainfall, and is particularly useful as an initial estimate of climate change impact in land and water resources projects. The rainfall elasticity of streamflow is estimated here using a hydrological modelling approach and a nonparametric estimator. The results indicate that the rainfall elasticity of streamflow (ϵ P ) in Australia is about 2.0–3.5 (observed in about 70% of the catchments), that is, a 1% change in mean annual rainfall results in a 2.0–3.5% change in mean annual streamflow. The rainfall elasticity of streamflow is strongly correlated to runoff coefficient and mean annual rainfall and streamflow, where streamflow is more sensitive to rainfall in drier catchments, and those with low runoff coefficients. There is a clear relation-ship between the ϵ P values estimated using the hydrological modelling approach and those estimated using the nonparametric estimator for the 219 catchments, although the values estimated by the hydrological modelling approach are, on average, slightly higher. The modelling approach is useful where a detailed study is required and where there are sufficient data to reliably develop and calibrate a hydrological model. The nonparametric estimator is useful where consistent estimates of the sensitivity of long-term streamflow to climate are required, because it is simple to use and estimates the elasticity directly from the historical data. The nonparametric method, being model independent, can also be easily applied in comparative studies to data sets from many catchments across large regions.

Comparison of two model approaches in the Zambezi river basin with regard to model reliability and identifiability

Abstract. Variations of water stocks in the upper Zambezi river basin have been determined by 2 different hydrological modelling approaches. The purpose was to provide preliminary terrestrial storage estimates in the upper Zambezi, which will be compared with estimates derived from the Gravity Recovery And Climate Experiment (GRACE) in a future study. The first modelling approach is GIS-based, distributed and conceptual (STREAM). The second approach uses Lumped Elementary Watersheds identified and modelled conceptually (LEW). The STREAM model structure has been assessed using GLUE (Generalized Likelihood Uncertainty Estimation) a posteriori to determine parameter identifiability. The LEW approach could, in addition, be tested for model structure, because computational efforts of LEW are low. Both models are threshold models, where the non-linear behaviour of the Zambezi river basin is explained by a combination of thresholds and linear reservoirs. The models were forced by time series of gauged and interpolated rainfall. Where available, runoff station data was used to calibrate the models. Ungauged watersheds were generally given the same parameter sets as their neighbouring calibrated watersheds. It appeared that the LEW model structure could be improved by applying GLUE iteratively. Eventually, it led to better identifiability of parameters and consequently a better model structure than the STREAM model. Hence, the final model structure obtained better represents the true hydrology. After calibration, both models show a comparable efficiency in representing discharge. However the LEW model shows a far greater storage amplitude than the STREAM model. This emphasizes the storage uncertainty related to hydrological modelling in data-scarce environments such as the Zambezi river basin. It underlines the need and potential for independent observations of terrestrial storage to enhance our understanding and modelling capacity of the hydrological processes. GRACE could provide orthogonal information that can help to constrain and further enhance our models. In the near future, other remotely sensed data sources will be used to force modelling efforts of the Zambezi (e.g. satellite rainfall estimates) and to identify individual storage components in the GRACE observations (e.g. altimeter lake levels and microwave soil moisture). Ultimately, this will create possibilities for state updating of regional hydrological models using GRACE.

Comparison of different efficiency criteria for hydrological model assessment

Abstract. The evaluation of hydrologic model behaviour and performance is commonly made and reported through comparisons of simulated and observed variables. Frequently, comparisons are made between simulated and measured streamflow at the catchment outlet. In distributed hydrological modelling approaches, additional comparisons of simulated and observed measurements for multi-response validation may be integrated into the evaluation procedure to assess overall modelling performance. In both approaches, single and multi-response, efficiency criteria are commonly used by hydrologists to provide an objective assessment of the "closeness" of the simulated behaviour to the observed measurements. While there are a few efficiency criteria such as the Nash-Sutcliffe efficiency, coefficient of determination, and index of agreement that are frequently used in hydrologic modeling studies and reported in the literature, there are a large number of other efficiency criteria to choose from. The selection and use of specific efficiency criteria and the interpretation of the results can be a challenge for even the most experienced hydrologist since each criterion may place different emphasis on different types of simulated and observed behaviours. In this paper, the utility of several efficiency criteria is investigated in three examples using a simple observed streamflow hydrograph.

Assessing the hydrological effects of Landuse changes using distributed hydrological modelling and GIS

A distributed hydrological modelling and GIS approach was applied for the assessment of landuse changes in the Alzette basin, Grand‐duchy of Luxembourg. The assessment focused on the potential impact of landuse changes on the hydrological processes. Three scenarios were established and investigated. The first scenario considered a realistic increase of urbanisation, while the other scenarios were hypothetical, i.e. forest was converted to agricultural land or the opposite. Comparison of the results for each scenario showed that although the overall changes in the total evapotranspiration and river discharge remained small, that change observed in the different component of the discharge was important. Urbanisation could increase floods by 26% and deforestation increased peak discharges, but to a lesser extent. The afforestation scenario reduced peak flows by as much as 5.3%. Moreover, the afforestation scenario increased soil moisture and base flow.

Using SSURGO data to improve Sacramento Model a priori parameter estimates

As it transitions to smaller scale, distributed hydrologic modeling approaches, the National Weather Service (NWS) is improving methods of estimating parameters for the Sacramento Soil Moisture Accounting model (SAC-SMA). This is the major hydrologic model used for flood forecasting at most of the 13 river forecasting centers throughout the United States. A physically based approach based on the nationally available State Soil Geographic Database (STATSGO) has been developed (Koren, V.I., Smith, M., Wang, D., Zhang, Z., 2000. Use of soil property data in the derivation of conceptual rainfall–runoff model parameters. Proceedings of the 15th Conference on Hydrology, AMS, Long Beach, CA, pp. 103–106; Koren, V., Smith, M., Duan, Q., 2003. Use of a priori parameter estimates in the derivation of spatially consistent parameter sets of rainfall–runoff models. In: Duan, Q., Sorooshian, S., Gupta, H., Rosseau, H., Turcotte, H. (Eds.), Calibration of Watershed Models, Water Science and Applications 6, AGU, pp. 239–254), leading to objective, spatially consistent parameter estimates. This paper shows that a better representation of basin physical properties and potential improvements in hydrologic simulation performance can be obtained by basing parameter estimates on a finer-scale database of soils data, the Soil Survey Geographic Database (SSURGO), combined with high-resolution land use/land cover data. Results also suggest that an intermediate level of improvement may be obtained by combining detailed land cover data with STATSGO to refine current parameter estimates. This latter finding is significant because the SSURGO data are not yet available for the entire country.

Development of distributed time-variant gain model for nonlinear hydrological systems

In this paper, a rainfall-runoff modeling system is developed based on a nonlinear Volterra functional series and a hydrological conceptual modeling approach. Two models, i.e. the time-variant gain model (TVGM) and the distributed time-variant gain model (DTVGM) that are built on the platform of Digital Elevation Model (DEM), Remote Sensing (RS) and Unit Hydro-logical Process were proposed. The developed DTVGM model was applied to two cases in the Heihe River Basin that is located in the arid and semiarid region of northwestern China and the Chaobai River basin located in the semihumid region of northern China. The results indicate that, in addition to the classic dynamic differential approach to describe nonlinear processes in hy-drological systems, it is possible to study such complex processes through the proposed sys-tematic approach to identify prominent hydrological relations. The DTVGM, coupling the advan-tages of both nonlinear and distributed hydrological models, can simulate variant hydrological processes under different environment conditions. Satisfactory results were obtained in fore-casting the time-space variations of hydrological processes and the relationships between land use/cover change and surface runoff variation.

Flux parameterization in the representative elementary watershed approach: Application to a natural basin

An integrated hydrological modeling approach based on the discretization of a watershed into spatial units called representative elementary watersheds (REWs) has been introduced in earlier publications. Global balance laws were formulated at the spatial scale of a REW by integrating the point‐scale conservation equations over particular control volumes. The choice of the control volumes is subject to the specific flow behavior to be described and is dependent on the hydrological characteristics of the spatial regions. These include the unsaturated subsurface flow, groundwater flow, and overland and channel flow. The REW‐scale balance laws constitute generally valid governing equations for environmental flows encountered in hydrological systems and are applicable, in contrast to point‐scale equations, independently from the chosen spatial and temporal scale of representation. This paper presents a first application of the REW approach to a complex hydrological system and shows how a theory that has so far only been used for synthetic cases is applicable to real‐world situations. In this context the most challenging research effort remains the formulation of appropriate closure schemes for mass and momentum (and energy) fluxes at the REW scale. It is recognized that the schemes proposed for the closure of the fluxes in this paper are subject to limitations but are sufficient to expose the philosophy and the essential working principles. The advantages of the particular spatial discretization and the current limitations of the closure schemes are highlighted. In this context it is pointed out which way future research should go to consolidate the REW approach as a more general and scale‐independent modeling philosophy for hydrological systems.

Assessing land use impacts on flood processes in complex terrain by using GIS and modeling approach

A distributed hydrologic modeling and GIS approach is applied for the assessment of land use impact in the Steinsel sub-basin, Alzette, Grand-Duchy of Luxembourg. The assessment focuses on the runoff contributions from different land use classes and the potential impact of land use changes on runoff generation. The results show that the direct runoff from urban areas is dominant for a flood event compared with runoff from other land use areas in this catchment, and tends to increase for small floods and for the dry season floods, whereas the interflow from forested, pasture and agricultural field areas contributes to the recession flow. Significant variations in flood volume, peak discharge, time to the peak, etc., are found from the model simulation based on the three hypothetical land use change scenarios.

Neotropical wetlands: New instruments in ecosystem management

The management of wetland ecosystems in the neotropics is a challenging task due to the ecological, geographical and socio-political complexity of these areas. These difficulties are compounded by an incomplete knowledge of system dynamics and the potential impacts that economic activities may have on wetland ecosystem functioning. There is a growing body of potential tools that can be utilized to study and monitor these large complex ecosystems. These include the use of remote sensing information, in situ hydrological and microclimate sensors with long-term dataloggers, hydrological and ecological modelling approaches based on limited historical data, energy-based models, ecological-economic indicators of wetland resource use and others. We tested some of these approaches in an international research project dedicated to the study of a large Argentine wetland, the “Esteros del Ibera” (www.unisi.it/wetland). The study focused on examining and developing instruments for the management of Latin American wetlands. Local and regional decision makers are now using project-generated instruments to make decisions for wetland resource management. The creation of innovative decision-making tools for sustainable wetland-resource utilization is an important challenge for the future.

A continental scale hydrological model using the distributed approach and its application to Asia

AbstractContinental scale hydrological models are important for improving the land surface scheme of the General Circulation Model (GCM) and for downscaling applications of GCM predictions for regional water resources assessment. A grid‐based distributed hydrological modelling approach cannot be applied at a continental scale by simply increasing the grid size due to factors such as the spatial heterogeneity and nonlinear nature of soil–vegetation–atmosphere transfer processes. Sub‐grid parameterization is required to capture the spatial variability of hydrological behaviour within a large grid. On the other hand, water resources management is usually implemented at the basin scale. The methodology presented in this study expands a grid‐based distributed hydrological model to the continental scale, and addresses both sub‐grid hydrological parameterization and basin‐based water resources assessment. A continental scale model with a 0·5° spatial resolution is developed based on a number of available global data sets. The model performance is examined through application to the Asian Continent. The regional and temporal variability of hydrological characteristics and water resources is discussed in this paper. Copyright © 2003 John Wiley & Sons, Ltd.