A WATER-RESOURCES PLANNING RESPONSE TO CLIMATE-CHANGE IN THE SENEGAL RIVER BASIN

The Senegal River Basin (SRB), located in the Sahel region of West Afr ica, is simultaneously undergoing fundamental environmental, hydrologi c and socioeconomic transitions. The tri-nation (Senegal, Mauritania a nd Mali) river basin development authority, the Organisation pour la M ise en Valeur du Fleuve Senegal (OMVS), is attempting to execute a shi ft to irrigated rice production for domestic consumption in the river basin in order to ease the severe foreign exchange shortfalls these ri parian nations face. With the recent completion of the Manantali and D iama dams, year-round irrigated agriculture is now possible in the SRB . The full agricultural development potential of the SRB is constraine d, however, by the basin's limited water resources. Significantly, a t ime series analysis of Senegal River hydrology has provided powerful e vidence that the prolonged Sahelian drought may be permanent. The basi c hydrologic constraint on development is revealed in a time series de composition of Senegal River annual flow volumes, which strongly sugge sts that water resources availability has been substantially curtailed since 1960. Two alternative time series mechanisms are hypothesized t o account for the decreased flow volumes in recent decades. The first time series model suggests the presence of a long-term periodicity, wh ile the second model hypothesizes an ARMA(1,1) process. The second hyp othesis provides a superior model fit. The stationary ARMA(1,1) model can be fit successfully, however, only after explicitly removing a non -stationary component by linearly detrending after 1960. The implicati on of non-stationarity in Senegal River hydrology provides analytic ev idence that the landscape degradation and desertification processes ob served in Sahelian Africa can be in part attributed to climate change effects. The negative impact of the state-imposed rice production poli cy compounds the severe effects of the drought on the river basin ecol ogy. Rice production in the arid river valley has been a financial and social failure. Irrigated rice projects suffer a high rate of abandon ment and have intensified the desertification process in the river val ley. As an alternative use of the basin's scarce water resources, an a gricultural development policy based on village-scale irrigation proje cts and intensive, irrigated agro-forestry projects has been proposed. Village-scale irrigation is dedicated to low-water-consumption cereal grain crops and is managed by traditional socio-political structures. The agroforestry production system analysed has the dual objectives o f using irrigation to re-establish a protective bio-mass cover in the desertifying river valley and of reversing the drought-induced migrati on from rural to urban areas. A comparative river system simulation st udy was conducted to analyse the effects of both the rice production d evelopment policy (policy RP) and the natural resources management pol icy (policy NRM) on the SRB's full agricultural development potential. The simulation study compared three alternative hydrologic scenarios using, (1) the pre-drought era, (2) the 1970s level drought and (3) th e 1980s level drought. Principles of dynamic programming were applied to Manantali reservoir management to optimize water allocation in each scenario. All the hydrologic scenarios generated showed that the lowe r overall water-demand pattern exerted by policy NRM allows a higher f ull agricultural development potential than does policy RP. (C) 1997 A cademic Press Limited