A grid-based approach to assess the impacts of climate change and land-use change on the water resources of West Africa

E.L. Tate and J.R. Meigh

A novel approach is taken to the problem of estimating water scarcity at a global scale, using a realistic and consistent procedure which has been applied across many countries. Water demands, surface flows and groundwater availability are estimated on a gridded basis, and various water availability indices are derived comparing the resource with the projected demand. Surface flows are estimated using a conceptual rainfall-runoff model linking climate to runoff and, in the major river basins, the runoff estimates for individual grid cells are accumulated to give estimates for the total flows at all points of interest. Groundwater availability is derived from hydrogeological maps based on estimates of the potential yield that can be expected from a borehole and the likely maximum borehole density. Estimates of potential groundwater recharge derived from the surface water model are also taken into account. Water demands are based on current and projected population and livestock numbers, and information on irrigation schemes and industrial water use. An important application of the results of the modelling is to highlight spatial and temporal occurrences of water scarcity; most other global-scale assessments present only a time- or region-averaged view of the water availability situation. The approach is currently being applied across west Africa as part of the PROMISE project. A selection of scenarios of climate change and land-use change will be considered from other modelling groups within the project; the grid-modelling results will aid in assessing the effects of such scenarios on ground hydrology and water resources.

Key words: Climate change, land-use change, water resources modelling, water scarcity, grid-based models, water demands, west Africa.