Simultaneous increase in temperature and dry days in West African transboundary Benue River Basin

This study examines the spatial and temporal changes in temperature and precipitation extremes from 1951 to 2020 in the West African transboundary Benue River Basin, which frequently experiences impacts from extreme events. The existing studies in the region have relied on sparse observation data, hindering a comprehensive understanding of the spatial variability of climate extremes. High-resolution gridded climate data can be used to explore how climate extremes vary spatially and temporally across transboundary river basins. This study is the first attempt to employ 0.25° × 0.25° daily ERA5 temperature and precipitation data to comprehensively assess spatiotemporal changes of climatic extremes in a West African transboundary river basin. The study applied the non-parametric Mann-Kendall test and Sen’s slope method to analyze temperature and precipitation extremes in the Benue River Basin. Results show a significant increase in mean maximum temperature (Tmax) of approximately ≥ 2 °C, indicating rising mean Tmax. Analysis of temperature indices reveals significant positive trends, with the number of warm days (TX90p) increasing by 8%. In contrast, evaluations of maximum 1-day (RX1day) and 5-day (RX5day) precipitation exhibit widespread reductions of 22.5% and 45%, respectively, indicating decreasing rainfall over most areas. Examinations of consecutive dry days (CDD) display higher mean changes in the northern basin extending to western Chad (70 to ≥ 110 days), revealing a link between lower annual precipitation and increased temperatures. However, we also found a basin-wide decrease in CDD ranging from ≤-2 to ≥-10 days. Overall, this study shows that the maximum temperature increases faster than the minimum temperature in the study area and that extreme temperature changes are more pronounced than extreme precipitation. These findings hold crucial implications for understanding the evolving climate dynamics in this vulnerable basin, emphasizing the urgency for adaptive measures in the face of escalating climate challenges.