Assessing freshwater availability in Africa under the current and future climate with focus on drought and water scarcity

Abstract

Droughts can have devastating effects on water supply, crop production, food security and many other aspects of human livelihood. The impact is particularly severe in Africa where subsistence farming dominates the food production and where political, social and economic systems are often inadequately prepared to cope with disasters. The recurrence of droughts in the past decades has triggered many famines in the continent. The severity of droughts and their impacts is projected to increase as a consequence of climate change. By applying a semi-distributed hydrological model SWAT (Soil and Water Assessment Tool), this study estimates the different freshwater components (i.e., green and blue water) for the whole African continent at the subbasin level. The spatial and temporal distributions of water resources are assessed. The presented model is then used to project the water resources availability under the future climate change in Africa for the period 2020-2040. Particular attention is made to the dry periods and their implications for water supply and food production. The simulation under the current climate shows that on a continental and annual basis, Africa has abundant water resources but the problem is the large spatial and temporal variability within and between African countries and river basins. The simulation of the impact of the future climate change on water resources is conducted with the projected climate data from 5 global circulation models (GCMs) under the four IPCC emission scenarios. The projected climate data are fed into the SWAT model calibrated under the current climate situation. The results show that for Africa as a whole, the mean total quantity of water resources is likely to increase. For individual subbasins and countries, variations are substantial. Although uncertainties are high in the simulated results, it is found that in many regions/countries, most of the climate scenarios projected the same direction of changes in water resources, suggesting a relatively high confidence in the projections. The assessment of the number of dry days and the frequency of their occurrences suggests an increase in the drought events and their duration in the future. This poses additional challenge to the agriculture in dry regions where water shortage is already severe while irrigation is expected to become more important to stabilize and increase food production.