Recent Rainfall Changes and Their Impact on Hydrology and Water Supply in the Semi- Arid Zone of the Sudan

Abstract

1980s, with 1984 the driest year on record and all annual rainfalls from 1980 to 1987 well below the long-term mean. In White Nile Province annual rainfall in 1965-84 was 40 per cent below 1920-39 levels; wet season length has contracted by 39-51 per cent; and the frequencies of both large and minor daily rainfalls have declined by up to 51 per cent. Hydrological consequences in North West White Nile have included reduced frequencies of wadi flows and overland flow; a major decline in shallow aquifer recharge and perched water-table levels in wadi bed and inselberg front locations (but little effect on deep regional aquifer levels); and earlier exhaustion in the dry season of shallow wells, surface pools and reservoirs. The significant decline in large rainstorm frequency has outweighed any tendency of land degradation (via reductions in infiltration capacity due to overgrazing, mechanized agriculture and deforestation) to enhance run-off levels. In some other parts ofthe Sudan, however, the reverse is true. In order to be useful, models of the hydrological impact of rainfall decline must take into account local physical and human conditions, changes in a range of rainfall parameters, and different types of human response to drought.