The sensitivity of Sahel rainfall to global warming: implications for scenario analysis of future climate change impact

Inter-decadal rainfall variability in the Sahel during the course of the present century has been large and, on occasions, its impacts on environment and society have been catastrophic. Our understanding of the causes of this variability has progressed substantially over the last 25 years. The roles of land cover change, ocean circulation, and atmospheric aerosol concentrations have been stressed by various authors and in recent years there has been the establishment of an embryonic seasonal forecasting capability for Sahel rainfall. This paper explores the ability of the latest generation of Global Climate Models (GCMs) to simulate historic Sahelian rainfall variability and evaluates the sensitivity of simulated Sahel rainfall to future changes in greenhouse gas and sulphate aerosol concentrations under different emissions assumptions. Results from the suite of experiments performed by the UK Hadley Centre in 1995 and 1996 using the HADCM2 model, including ensemble simulations, are used. The implications of this analysis for scenarios of future rainfall change in the Sahel are highlighted and suggestions made about the conduct of future regional climate change impact assessments on environmental resources such as water and agriculture.