To provide a technique for assessing water scarcity problems caused by rapid increases in population, urbanisation and industrial development and which are further complicated by variability in climate and climate change adding uncertainty to projection on future availability and distribution of water resources.

Improved methods of quantifying the availability of water on a global scale were developed and incorporated into user-friendly software displaying such results. The study aimed at a realistic and consistent methodology, in particular combining surface and groundwater sources and accounting for temporal and spatial variability in both water availability and demands.

Surface flows, groundwater yield and water demands were examined on a 0.50 x 0.50 grid. The measures of availability, particularly surface water, take account of the time-varying nature of river flows and thus provide a true indication of the water that is actually available for use. Within each grid cell the comparison of surface and groundwater availability to water demands provides an index of water resources availability or scarcity for that cell; by using a grid to cover the study area, regional variability in supply and demand is taken into account.

The area studied so far is eastern and southern Africa, including the whole of the 20 countries from Egypt to South Africa, with a total land area of 12.8 million km2 and covering a wide range of resource constraints. Results are presented for present conditions and for a range of future scenarios for the years 2025 and 2050. For present conditions it was found that there is more than adequate water availability over much of the region, even in some of the drier areas which might be thought of to be more problematic. However, some areas have substantial shortfalls, such as those with dense populations, substantial industrial demands or very extensive irrigation development.

Presentation of such assessment techniques using GIS and software provides a much more visual index of water availability or scarcity in different regions and also provides a flexible range of options for examining the results in different ways.

Meigh, J.R. et al. 1998. Assessment of global water resources - phase II: estimates of present and future water availability for eastern and southern Africa. DFID Report 98/4, Institute of Hydrology, Wallingford.

Email: jrm@mail.nwl.ac.uk