Potential impacts of 1.5 °C and 2 °C global warming on rainfall onset, cessation and length of rainy season in West Africa

Abstract

This study examines the potential impacts of 1.5 °C and 2 °C global warming (GWL15 and GWL20) on rainfall onset dates (RODs), rainfall cessation dates (RCDs), and length of the rainy season (LRS) in West Africa under RCP4.5 and RCP8.5 scenarios. Nineteen multi-model multi-ensemble simulation datasets from eight regional climate models that participated in the Coordinated Regional Climate Downscaling Experiment were used for the study. The ability of the model ensemble mean to reproduce the characteristics of RODs, RCDs and LRS for past climate were evaluated using two observed datasets. The impacts of GWL15 and GWL20 on each parameter were quantified and compared. The models reproduce the characteristics of RODs, RCDs, and LRS as observed in the historical climate over West Africa though with few biases. The models projected the western and eastern Sahel as hot-spots for a delayed ROD and reduced LRS in the 1.5 °C and 2 °C warmer climate under RCP4.5 and RCP8.5 scenarios. A delayed RCD and longer LRS are projected over the western part of the Guinea coast. The uncertainties associated with the projections are high for RCD but lower for ROD and LRS. While an increase in global warming from 1.5 °C–2 °C enhances late ROD over the entire West Africa under the RCP4.5, it fosters early ROD over the Sahel zone under the RCP8.5. It also encourages a decrease in the LRS over the Guinea zone and an increase in LRS over the Sahel zone, but produces opposite results under RCP8.5. The results of the study have application in reducing the impacts of global warming over West Africa.