Studies of 21st‐century precipitation trends over West Africa

Abstract

West Africa includes a semi-arid zone between the Sahara Desert and the humid Gulf of Guinea coast, approximately between 10°N and 20°N, which is irrigated by summer monsoon rains. This article refers to the region as the Sahel. Rain-fed agriculture is the primary sustenance for Sahel populations, and severe droughts (in the 1970s and 1980s), therefore, have devastating negative societal impacts. The future frequency of Sahel droughts and the evolution of its hydrological balance are therefore of great interest. The article reviews 10 recent research studies that attempt to discover how climate changes will affect the hydrology of the Sahel throughout the 21st century. All 10 studies rely on atmosphere-ocean global climate model (AOGCM) simulations based on a range of greenhouse gas emissions scenarios. Many of the simulations are contained in the Intergovernmental Panel on Climate Change archives for Assessment Reports #3 and #4. Two of the studies use AOGCM data to drive regional climate models. Seven studies make projections for the first half of the 21st century and eight studies make projections for the second half. Some studies make projections of wetter conditions and some predict more frequent droughts, and each describes the atmospheric processes associated with its prediction. Only one study projects more frequent droughts before 2050, and that is only for continent-wide degradation in vegetation cover. The challenge to correctly simulate Sahel rainfall decadal trends is particularly daunting because multiple physical mechanisms compete to drive the trend upwards or downwards. A variety of model deficiencies, regarding the simulation of one or more of these physical processes, taints models' climate change projections. Consequently, no consensus emerges regarding the impact of anticipated greenhouse gas forcing on the hydrology of the Sahel in the second half of the 21st century.

A review of droughts on the African continent: a geospatial and long-term perspective

“…Large uncertainties exist in these findings and thus require caution in making regional or continental conclusions. Druyan (2011) reviewed 10 studies which are based on the simulations of atmosphere-ocean global climate models on future climate of Sahel. Some studies projected wetter conditions and some projected more frequent droughts, thus, no consensus was observed.…”

Multimodel ensemble simulations of present and future climates over West Africa: Impacts of vegetation dynamics

“…The region's high dependency on rain-fed agriculture has left the population highly susceptible to droughtinduced famine. Since the societal sustainability of the region is acutely sensitive to climate, development of future adaptation strategies depends on reliable prediction of climate trends [Druyan, 2011;Patricola and Cook, 2010;Wang et al, 2016]. Climate models, however, provide a rather uncertain outlook for the future rainfall in the region, leaving the question of ''drier or wetter Sahel?''…”

“…Climate models, however, provide a rather uncertain outlook for the future rainfall in the region, leaving the question of ''drier or wetter Sahel?'' a topic of continued debate [Druyan, 2011;Biasutti et al, 2008;Giannini et al, 2008aGiannini et al, , 2008b.…”

Hydro-climatic changes in the Niger basin and consistency of local perceptions

“…For future conditions, no coherent projection for either decreasing or increasing precipitation emerges from global climate model (GCM) products (Druyan 2011). This lack of consensus among GCM projections was attributed to the unclear West African monsoon precipitation response to anthropogenic climate change (Biasutti and Giannini 2006;Douville et al 2006;Giannini et al 2008).…”