Abstract
Predicting freshwater resources is a major concern in West Africa, where large parts of the population depend on rain-fed subsistence agriculture. However, a steady decline in the availability of in-situ measurements of climatic and hydrologic variables makes it difficult to simulate water resource availability with hydrological models. In this study, a modeling framework was set up for sparsely-gauged catchments in West Africa using the Soil and Water Assessment Tool (SWAT), whilst largely relying on remote sensing and reanalysis inputs. The model was calibrated using two different strategies and validated using discharge measurements. New in this study is the use of a multi-objective validation conducted to further investigate the performance of the model, where simulated actual evapotranspiration, soil moisture, and total water storage were evaluated using remote sensing data. Results show that the model performs well (R2 calibration: 0.52 and 0.51; R2 validation: 0.63 and 0.61) and the multi-objective validation reveals good agreement between predictions and observations. The study reveals the potential of using remote sensing data in sparsely-gauged catchments, resulting in good performance and providing data for evaluating water balance components that are not usually validated. The modeling framework presented in this study is the basis for future studies, which will address model response to extreme drought and flood events and further examine the coincidence with Gravity Recovery and Climate Experiment (GRACE) total water storage retrievals.
Highlights
The availability of freshwater is a major concern in West Africa, directly influencing food security, human health, and economic development [1]
While Soil and Water Assessment Tool (SWAT)-ready climate input files based on the National Centers for Environmental Prediction (NCEP) climate forecast system reanalysis data (CFSR) [52] are readily available, as discovered in Poméon et al [23], CFSR precipitation information compares worse to other products in the region
Total water storage (TWS): Gravity Recovery And Climate Experiment (GRACE) TWS retrievals were used for further model validation
Summary
The availability of freshwater is a major concern in West Africa, directly influencing food security, human health, and economic development [1]. Bormann studied the results of two process-based (SIMULAT-H and TOPLATS) and one conceptual hydrological model (UHP) applied to the upper Ouémé basin [5] Another approach was employed by Wagner et al, who downscaled meteorological fields and remote sensing data over the White Volta basin for water balance estimation [6]. Calibrating global hydrological models against long-term annual discharge may lead to poor temporal performance [1] Considering these constraints, Schuol et al employed the semi-distributed, physically-based hydrological SWAT (Soil & Water Assessment Tool) model to estimate freshwater resources of. We set up a modeling framework by calibrating and validating a SWAT model covering the major West African river basins for the period of 1998–2013, using freely available remote sensing and reanalysis products including new climatological, land use, and soil datasets. Africa using freely available data, (ii) to assess which simulation quality can be obtained using these datasets, (iii) to perform a multi-objective validation, and (iv) to evaluate the potential and limitations of this approach for assessing water availability at the sub-continental scale
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