Investigating the impacts of climate and land use/cover changes on the Oueme Delta hydrosystem in Benin, West Africa

Hydrological modeling in deltaic regions remains challenging. This study assesses the impacts of climate change (CC) and land use/land cover change (LULC) on the Oueme Delta hydrosystem using the physics-based integrated model ParFlow-CLM. Surface runoff (SRO), evapotranspiration (ET), water table depth (WTD), and soil water content (SWC) were simulated and evaluated against ERA5 data using performance metrics such as correlation and Kling-Gupta efficiency (KGE). For historical simulations (1975, 2000, and 2013), land-use maps from the West Africa LULC Dynamics project and climate data from WFDE5 were employed. Future projections (2030, 2050, and 2085) relied on climate inputs from CMIP6 datasets, while LULC maps were extrapolated using a Markov chain approach. The model demonstrated strong performance in simulating key components of the water balance, particularly ET (daily scale: Correlation > 0.8; KGE > 0.6). Under constant climate conditions, a 20% reduction in forest cover between 1975 and 2013 showed a negligible impact on water resources. In contrast, CC exerted a substantial influence on the hydrological cycle: increased precipitation led to substantial rises in SRO and ET. Scenario-based projections indicate that LULC changes may amplify climate impacts. Specifically, a precipitation increase exceeding 50% combined with full reforestation could double SRO and increase flood risks. Conversely, a 50% decrease in precipitation coupled with complete deforestation could induce severe ecosystem water stress, reducing SWC by 3.9%. These findings highlight the need for integrated land and water management strategies and inform the development of effective policies for water resource conservation in the context of CC and LULC changes.