58 research outputs found
Rice Intensification in a Changing Environment: Impact on Water Availability in Inland Valley Landscapes in Benin
This study assesses the impact of climate change on hydrological processes under rice intensification in three headwater inland valley watersheds characterized by different land conditions. The Soil and Water Assessment Tool was used to simulate the combined impacts of two land use scenarios defined as converting 25% and 75% of lowland savannah into rice cultivation, and two climate scenarios (A1B and B1) of the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios. The simulations were performed based on the traditional and the rainfed-bunded rice cultivation systems and analyzed up to the year 2049 with a special focus on the period of 2030â2049. Compared to land use, climate change impact on hydrological processes was overwhelming at all watersheds. The watersheds with a high portion of cultivated areas are more sensitive to changes in climate resulting in a decrease of water yield of up to 50% (145 mm). Bunded fields cause a rise in surface runoff projected to be up to 28% (18 mm) in their lowlands, while processes were insignificantly affected at the vegetation dominated-watershed. Analyzing three watersheds instead of one as is usually done provides further insight into the natural variability and therefore gives more evidence of possible future processes and management strategie
Modeling Spatial Soil Water Dynamics in a Tropical Floodplain, East Africa
Analyzing the spatial and temporal distribution of soil moisture is critical for ecohydrological processes and for sustainable water management studies in wetlands. The characterization of soil moisture dynamics and its influencing factors in agriculturally used wetlands pose a challenge in data-scarce regions such as East Africa. High resolution and good-quality time series soil moisture data are rarely available and gaps are frequent due to measurement constraints and device malfunctioning. Soil water models that integrate meteorological conditions and soil water storage may significantly overcome limitations due to data gaps at a point scale. The purpose of this study was to evaluate if the Hydrus-1D model would adequately simulate soil water dynamics at different hydrological zones of a tropical floodplain in Tanzania, to determine controlling factors for wet and dry periods and to assess soil water availability. The zones of the Kilombero floodplain were segmented as riparian, middle, and fringe along a defined transect. The model was satisfactorily calibrated (coefficient of determination; R2 = 0.54â0.92, root mean square error; RMSE = 0.02â0.11) on a plot scale using measured soil moisture content at soil depths of 10, 20, 30, and 40 cm. Satisfying statistical measures (R2 = 0.36â0.89, RMSE = 0.03â0.13) were obtained when calibrations for one plot were validated with measured soil moisture for another plot within the same hydrological zone. Results show the transferability of the calibrated Hydrus-1D model to predict soil moisture for other plots with similar hydrological conditions. Soil water storage increased towards the riparian zone, at 262.8 mm/a while actual evapotranspiration was highest (1043.9 mm/a) at the fringe. Overbank flow, precipitation, and groundwater control soil moisture dynamics at the riparian and middle zone, while at the fringe zone, rainfall and lateral flow from mountains control soil moisture during the long rainy seasons. In the dry and short rainy seasons, rainfall, soil properties, and atmospheric demands control soil moisture dynamics at the riparian and middle zone. In addition to these factors, depths to groundwater level control soil moisture variability at the fringe zone. Our results support a better understanding of groundwater-soil water interaction, and provide references for wetland conservation and sustainable agricultural water management
Physically-based modelling of hydrological processes in a tropical headwater catchment (West Africa) ? process representation and multi-criteria validation
International audienceThe aim of the study was to test the applicability of a physically-based model to simulate the hydrological processes in a headwater catchment in Benin. Field investigations in the catchment have shown that lateral processes such as surface runoff and interflow are most important. Therefore, the 1-D SVAT-model SIMULAT was modified to a semi-distributed hillslope version (SIMULAT-H). Based on a good database, the model was evaluated in a multi-criteria validation using discharge, discharge components and soil moisture data. For the validation of discharge, good results were achieved for dry and wet years. The main differences were observable in the beginning of the rainy season. A comparison of the discharge components determined by hydro-chemical measurements with the simulation revealed that the model simulated the ratio of groundwater fluxes and fast runoff components correctly. For the validation of the discharge components of single events, larger differences were observable, which was partly caused by uncertainties in the precipitation data. The representation of the soil moisture dynamics by the model was good for the top soil layer. For deeper soil horizons, which are characterized by higher gravel content, the differences between simulated and measured soil moisture were larger. A good agreement of simulation results and field investigations was achieved for the runoff generation processes. Interflow is the predominant process on the upper and the middle slopes, while at the bottom of the hillslope groundwater recharge and ? during the rainy season ? saturated overland flow are important processes
An interdisciplinary scenario analysis to assess the water availability and water consumption in the Upper Ouémé catchment in Benin
This paper presents an interdisciplinary scenario analysis to assess the influence of global and regional change on future water availability and water consumption in the Upper OuĂ©mĂ© catchment in central Benin. For the region three development scenarios were evolved. These scenarios are combined with climate change scenarios based on the IPCC (Intergovernmental Panel on Climate Change). In the mo-delling approach the quantification of the land use/land cover change is performed by the cellular automata model CLUE-S. The future climate scenarios are computed with the regional climate model REMO driven by the global ECHAM model. Using this data different land use and climate change scenarios can be calculated with the conceptual hydrological model UHP-HRU to assess the effects of global changes on the future water availability in Benin. <P> To analyse the future water availability also the water consumption has to be taken into account. Due to high population growth an increase in water need in the future is expected for the region. To calculate the future household water consumption data from a regional survey and demographic projections are used. Development of the water need for animal husbandry is also considered. <P> The first test run of the modelling approach was performed for the development scenario 'business as usual' combined with the IPCC scenario B2 for the year 2025. This test demonstrates the applicability of the approach for an interdisciplinary scenario analysis. A continuous run from 2000–2025 will be simulated for different scenarios as soon as the input data concerning land use/land cover and climate are available
Modelling of flood hazard extent in data sparse areas: a case study of the Oti River basin, West Africa
Study region: Terrain and hydrological data are scarce in many African countries. The coarse spatial resolution of freely available Shuttle Radar Topographic Mission elevation data and the absence of flow gauges on flood-prone reaches, such as the Oti River studied here, make flood inundation modelling challenging in West Africa. Study focus: A flood modelling approach is developed here to simulate flood extent in data scarce regions. The methodology is based on a calibrated, distributed hydrological model for the whole basin to simulate the input discharges for a hydraulic model which is used to predict the flood extent for a 140 km reach of the Oti River. New hydrological insight for the region: Good hydrological model calibration (Nash Sutcliffe coefficient: 0.87) and validation (Nash Sutcliffe coefficient: 0.94) results demonstrate that even with coarse scale (5 km) input data, it is possible to simulate the discharge along this region's rivers, and importantly with a distributed model, derive model flows at any ungauged location within basin. With a lack of surveyed channel bathymetry, modelling the flood was only possible with a parametrized sub-grid hydraulic model. Flood model fit results relative to the observed 2007 flood extent and extensive sensitivity testing shows that this fit (64%) is likely to be as good as is possible for this region, given the coarseness of the terrain digital elevation model
Translating environmental xenobiotic fate models across scales
International audienceThe classical models developed for degradation and transport of xenobiotics have been derived with the assumption of homogeneous environments. Unfortunately, deterministic models function well in the laboratory under homogeneous conditions but such homogeneous conditions often do not prevail in the field. A possible solution is the incorporation of the statistical variation of soil parameters into deterministic process models. This demands the development of stochastic models of spatial variability. To this end, spatial soil parameter fields are conceived as the realisation of a random spatial process. Extrapolation of local fine scale models to large heterogeneous fields is achieved by coupling deterministic process models with random spatial field models
IMPETUS: Implementing HELP in the Upper Ouémé basin
Regional climate models that take into account land-use changes indicate that in the future, a general decrease in rainfall, together with prominent surface heating, can be expected for sub-Saharan Africa and the region north of the Sahara until 2050. Due to high population growth, land use changes rapidly and influences water availability and water demand. In this context, the research project IMPETUS (âAn Integrated Approach to the Efficient Management of Scarce Water Resources in West Africaâ) offers a range of options for sustainable management of different components of the hydrological cycle. Target areas are the OuĂ©mĂ© basin in Benin and the DrĂąa catchment in Morocco. This paper concentrates on the OuĂ©mĂ© basin.Based on plausible scenarios of future economic, demographic, and climate developments, the effects of land use, land cover change, climate change, and demographic development on water availability and water demand are quantified. Scenarios of future water availability and water demand for the Upper OuĂ©mĂ© (Benin) catchment are discussed. To calculate water availability, the output of a regional climate model was linked to a hydrological model that also considered land use change calculated by a cellular automata model. Future water requirements were computed by linking population growth and per capita water demand, which was derived from a regional survey. Furthermore, the need for water for animal husbandry was considered.The results of the âbusiness as usualâ scenario, combined with IPCC Scenarios A1B and B2, through the year 2045 are presented. The results reveal a significant decrease in water availability (surface water and groundwater) due to a decrease in rainfall and a significant increase in evapotranspiration. Although total water consumption increases strongly, it represents only about 0.5% of the yearly renewable water resources. Comparing these data, it may be concluded that water scarcity is not a problem in Benin. However, water availability shows high temporal variations due to the rainy and the dry seasons. Even if physical water scarcity is not a limiting factor, access to water in some parts of the catchment is limited due to economic factors.Keywords: HELP, IMPETUS, Benin, Morocco, Decision Support Systems, global change, information systems, loosely coupled models, problem clusters, scenario development, water availability, water deman
Impact of climate change on hydrological conditions in a tropical West African catchment using an ensemble of climate simulations
This study evaluates climate change impacts on water resources using an
ensemble of six regional climate models (RCMs)âglobal climate models (GCMs)
in the Dano catchment (Burkina Faso). The applied climate datasets were
performed in the framework of the COordinated
Regional climate Downscaling
Experiment (CORDEX-Africa) project.After evaluation of the historical runs of the climate models' ensemble, a
statistical bias correction (empirical quantile mapping) was applied to daily
precipitation. Temperature and bias corrected precipitation data from the
ensemble of RCMsâGCMs was then used as input for the Water flow
and balance Simulation Model (WaSiM) to simulate
water balance components.The mean hydrological and climate variables for two periods (1971â2000 and
2021â2050) were compared to assess the potential impact of climate change on
water resources up to the middle of the 21st century under two greenhouse gas
concentration scenarios, the Representative Concentration Pathways (RCPs) 4.5
and 8.5. The results indicate (i) a clear signal of temperature increase of
about 0.1 to 2.6âŻÂ°C for all members of the RCMâGCM ensemble;
(ii)Â high uncertainty about how the catchment precipitation will evolve over
the period 2021â2050; (iii) the applied bias correction method only affected
the magnitude of the climate change signal; (iv)Â individual climate models
results lead to opposite discharge change signals; and (v)Â the results for
the RCMâGCM ensemble are too uncertain to give any clear direction for
future hydrological development. Therefore, potential increase and decrease
in future discharge have to be considered in climate change adaptation
strategies in the catchment. The results further underline on the one hand
the need for a larger ensemble of projections to properly estimate the
impacts of climate change on water resources in the catchment and on the
other hand the high uncertainty associated with climate projections for the
West African region. A water-energy budget analysis provides further insight
into the behavior of the catchment.</p
Multivariate Prediction of Total Water Storage Changes Over West Africa from Multi-Satellite Data
West African countries have been exposed to changes in rainfall patterns over the last decades, including a significant negative trend. This causes adverse effects on water resources of the region, for instance, reduced freshwater availability. Assessing and predicting large-scale total water storage (TWS) variations are necessary for West Africa, due to its environmental, social, and economical impacts. Hydrological models, however, may perform poorly over West Africa due to data scarcity. This study describes a new statistical, data-driven approach for predicting West African TWS changes from (past) gravity data obtained from the gravity recovery and climate experiment (GRACE), and (concurrent) rainfall data from the tropical rainfall measuring mission (TRMM) and sea surface temperature (SST) data over the Atlantic, Pacific, and Indian Oceans. The proposed method, therefore, capitalizes on the availability of remotely sensed observations for predicting monthly TWS, a quantity which is hard to observe in the field but important for measuring regional energy balance, as well as for agricultural, and water resource management.Major teleconnections within these data sets were identified using independent component analysis and linked via low-degree autoregressive models to build a predictive framework. After a learning phase of 72 months, our approach predicted TWS from rainfall and SST data alone that fitted to the observed GRACE-TWS better than that from a global hydrological model. Our results indicated a fit of 79 % and 67 % for the first-year prediction of the two dominant annual and inter-annual modes of TWS variations. This fit reduces to 62 % and 57 % for the second year of projection. The proposed approach, therefore, represents strong potential to predict the TWS over West Africa up to 2 years. It also has the potential to bridge the present GRACE data gaps of 1 month about each 162days as well as aâhopefullyâlimited gap between GRACE and the GRACE follow-on mission over West Africa. The method presented could also be used to generate a near real-time GRACE forecast over the regions that exhibit strong teleconnections
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