Impact of Climate Change on Water Resources in Eastern Africa

Indices Of Water Resources Stress

There are many possible indices of water stress, considering different aspects of use and availability. The basic measure used in the Comprehensive Assessment is the ratio of the amount of withdrawals to the renewable resources available in a country, including runoff imported from upstream regions. In the absence of consistent data at more local scales, the indices are calculated using national population and water resource statistics. Baseline estimates of national water resources, both generated internally and imported from upstream, are taken from data prepared for the Comprehensive Assessment, as are figures for current withdrawals. Future withdrawals of water will increase with population. It is assumed that the per capita use will remain constant over the next few decades although this is perhaps unrealistic, because in practice, use would change as economic development changes, water use efficiency increases and irrigation use increases at different rates compared to population. Climate change might also have an effect on the demand for water.

It is generally accepted that water resources become a constraint on development when use exceeds 20% of the total resources potentially available (Falkenmark 1989). In countries prone to severe problems during drought years in absence of secure supplies through investment in supply facilities, development opportunities are constrained. Countries using less than 20% of total potential resources are not immune to water stress and may experience severe problems in some regions and at some times.