How could climate change affect the magnitude, duration and frequency of hydrological droughts and floods in West Africa during the 21st century? A storyline approach

In recent decades, West Africa has been increasingly exposed to hydrological droughts and floods. However, the extent to which these changes are related to climate change and are likely to persist during the 21st century remains poorly understood. To address this gap, this study integrates plausible regional climate change storylines, derived from the 6th phase of the Coupled Model Intercomparison Projects (CMIP6), into physically based hydrological modelling experiments utilising the latest high-resolution setup of Open Source LISFLOOD (OS-LISFLOOD). Despite some limitations over the Sahelian region, OS-LISFLOOD shows good performances in representing the hydrological cycle and specific characteristics of hydrological droughts and floods. While CMIP6 models consistently project warming temperatures over West Africa, greater zonal contrasts and model discrepancies are found in projected rainfall changes. Overall, CMIP6 models tend to project more (less) rainfall, as well as more (less) intense rainfall, over the eastern (western) region of West Africa. However, wetter (drier) conditions are projected over larger regions in CMIP6 models simulating weaker (stronger) warming in the North Atlantic and Mediterranean temperatures. Future changes in hydrological droughts and floods mirror changes in precipitation. In the 21st century, we find robust significant increases (decreases) in the magnitude (duration) of floods. Meanwhile, reduced (increased) intensity of shorter (longer) duration hydrological droughts are found in the eastern (western and coastal) regions of West Africa. Our study stresses the importance of considering future changes in hydrological droughts and floods for effective water resource management and risk reduction across this highly vulnerable region.