A tale of two futures: contrasting scenarios of future precipitation for West Africa from an ensemble of regional climate models

Alessandro Dosio,Bruce Hewitson,Alain T Tamoffo,Richard G Jones,Christopher Lennard,Grigory Nikulin,Andrew G Turner,Laurent Terray,Mouhamadou Bamba Sylla

doi:10.1088/1748-9326/ab7fde

Abstract

The results of a large ensemble of regional climate models lead to two contrasting but plausible scenarios for the precipitation change over West Africa, one where mean precipitation is projected to decrease significantly over the Gulf of Guinea in spring and the Sahel in summer, and the other where summer precipitation over both regions is projected to increase.Dry and wet models show similar patterns of the dynamic and thermodynamic terms of the moisture budget, although their magnitudes are larger in the dry models. The largest discrepancies are found in the strength of the land-atmosphere coupling, with dry models showing a marked decrease in soil moisture and evapotranspiration.Some changes in precipitation characteristics are consistent for both sets of models. In particular, precipitation frequency is projected to decrease in spring over the Gulf of Guinea and in summer over the Sahel, but precipitation is projected to become more intense.

Highlights

West Africa, with a fast population growth and an economy reliant on rain-fed agriculture, is one of the regions most affected by climate variability (Sultan and Gaetani 2016, Sylla et al 2018)
Large differences exist amongst Regional Climate Models (RCMs) in the simulated position, extension and intensity of the band of high rainfall; when models are compared to a large ensemble of observational datasets, the uncertainty in both ensembles is remarkably similar, especially during the rainy season from May through October
Over the Gulf of Guinea, RCMs show the largest uncertainty in projected mean precipitation change during the early phase of the rainy season (April– July): based on this finding, we separate model results into two classes, namely ‘wet’, i.e. those projecting an increase in mean precipitation, and ‘dry’, i.e. those projecting a decrease

Summary

Introduction

West Africa, with a fast population growth and an economy reliant on rain-fed agriculture, is one of the regions most affected by climate variability (Sultan and Gaetani 2016, Sylla et al 2018). The annual cycle of precipitation over the region is linked to the passage of the West African Monsoon (WAM), which produces annual rainfall up to around 2500 mm (Raj et al 2019). In the Sahel, in particular, the WAM accounts for about 80% of annual precipitation (Steinig et al 2018). West Africa is vulnerable to the impact of future climate change (Niang et al 2014). A comprehensive effort has been undertaken by the scientific community to portray future precipitation behaviour over West Africa.

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Conclusion