Assessment of climate change impacts on the hydrological response of a watershed in the savanna region of sub‑Saharan Africa

Abstract

In this study, the applicability of ensemble mean from Coordinated Regional Climate Downscaling Experiment_Regional Climate Models (CORDEX_RCMs) for climate change impact assessment on Niger Central Hydrological Area (NCHA) was evaluated. Thereafter, the Soil and Water Assessment Tool (SWAT) model was successfully calibrated at the Kaduna sub-basin. The SWAT model was then forced with the CORDEX_RCMs at four specific global warming levels (GWLs) (i.e., 1.5 °C, 2.0 °C, 2.5 °C, and 3.0 °C) and the baseline (1971–2000). The water balance components (WBCs) generated at GWLs were compared with the baseline. The results indicate that the CORDEX_RCMs effectively simulated climate variables. The past and future projections (1950–2100) show an increase in annual streamflow of 4.7%, 5.9%, 3.4%, and 3.5% at 1.5 °C, 2.0 °C, 2.5 °C, and 3.0 °C, respectively, over the baseline. Similarly, with respect to baseline, changes are expected in average annual rainfall (+ 1.91%, + 2.64%, + 2.33%, and + 2.41%), runoff (+ 1.37%, + 3.81%, + 1.17%, and + 3.26%), potential evapotranspiration (+ 2.85%, + 4.09%, + 6.54%, and + 6.60%), and evapotranspiration (− 2.15%, − 2.62%, − 4.00%, and − 4.33%) under 1.5 °C, 2.0 °C, 2.5 °C, and 3.0 °C, respectively. Monthly streamflow for the dry and early rainy seasons is projected to decrease, while the late rainy season is expected to increase with an increase in GWLs. The implication is that while there may be a lack of water in the early rainy season, the flood event presently being witnessed in the late rainy season may become aggravated. Hence, adaptation strategies that take care of water deficit in the early rainy season and excess in the late rainy season should be put into consideration.