How useful are gridded water resources reanalysis and evapotranspiration products for assessing water security in ungauged basins?

Abstract

Abstract. Achieving water security in ungauged basins is critically hindered by a lack of in situ hydrometeorological data to assess past, current and future evolution of water resources in those areas. To overcome this challenge, there has been a shift toward the use of freely available satellite and reanalysis hydrometerological products. However, due to inherent bias and uncertainty, these secondary sources require careful evaluation to ascertain their performance before being applied in ungauged basins. The objectives of this study were to evaluate the performance of nine gridded water resources reanalysis (WRR), and eight evapotranspiration (ET) products and to estimate the relative uncertainties in monthly basin-scale water balance evapotranspiration (ETWB) in eight river basins located in Central-West Africa. Evaluation results highlight strengths and weaknesses of the different WRR and ET products in simulating discharge dynamics and ET estimates respectively across the basins. Analyses further revealed that the relative uncertainties in monthly ETWB range from 4–25 % with a significant increase in magnitude during the rainy season while river discharge is the dominant source of uncertainty. Our results further revealed that the performance of land surface models (LSMs) and global hydrological models (GHM) in simulating river discharge is strongly influenced by the model structure, input data and spatial resolution. Differences in ET estimates from the different ET products may be attributed to model structure and the input data used in driving the models. Results from this study suggest that gridded WRR and ET products are a useful source of data for assessing water security in ungauged basins. However, given the plethora of products available, it is imperative to evaluate their performance in representative gauged basins to identify products that can be applied in each region.