An Analysis of Heat and Water Balances in West Africa

Abstract

UD URING the last two decades the literature on heat and water balances has multiplied considerably. This enormous body of work results from the realization that the study of heat and water balances has practical applications to a number of problems such as climate indexing and water-resource planning. In spite of the importance of heat and water balance studies, this branch of climatology is still in its infancy in West Africa. The only pioneering studies available about this region are those by Benjamin J. Garnier, Charles W. Thornthwaite and John R. Mather, John A. Davies, J. Cocheme and P. Franquin, Simeon 0. Ojo, and G. 0. P. Obasi.' Only the works of Garnier, Thornthwaite and Mather, and Ojo cover the whole of West Africa. Until now, the extent and the detailed nature of aridity in West Africa has not received major attention. The devastating effects of the 19681973 drought in the Sahelian region of West Africa, however, gave rise to concerns about the state of water resources in this region. The prime objective of this study is to portray the main features of the surface heat and water balances in West Africa south of 25?N. The various components of the surface net radiation are calculated first, followed by the computation of potential evapotranspiration. The month-by-month progress of the components of the water balance are derived next. Finally annual totals of the main components are computed, and the main hydroclimatological ratios are derived. The outputs of these four steps are presented in map form, with an accompanying discussion. This study uses the long-term records of 110 climatic stations in West Africa. Only stations with records longer than ten years were used. From these series, monthly averages were then calculated. The stations were chosen so as to be representative of the major circulation features governing the weather in West Africa, and, in particular, to include the entire annual range of the movement of the InterTropical Discontinuity.