Showing papers by "Mike Hulme published in 1990"

The changing rainfall resources of Sudan

Abstract: Rainfall is one of the key resources of Sudan. This requires detailed measurement and monitoring of rainfall availability to enable its effective management. The changing nature of rainfall supply in Sudan during the twentieth century is examined using historical annual, monthly and daily data back to 1900. Rainfall depletion has been most severe in semi-arid central Sudan where between 1921-50 and 1956-85 annual rainfall has declined by 15 per cent, the length of the wet season has contracted by three weeks, and rainfall zones have migrated southwards by between 50 km and 100 km. This depletion has been due more to a reduction in the frequency of rain events rather than to a reduced rainfall yield per rain event. Effective resource management requires timely and accurate information about the current and future state of the resource. Three aspects of Sudan rainfall information availability are discussed in the light of recent developments: historical archived data, automatic, near real-time rainfall monitoring, and both seasonal and decadal rainfall forecasting. The measurement and monitoring of rainfall are not ends in themselves and it is important that such information is used in the climate management process.

Global climate change and the Nile Basin.

Abstract: Introduction Precipitation over the Nile Basin, and consequently Nile discharge, has fluctuated both historically and pre-historically. Precipitation zones have migrated latitudinally over the middle Nile by as much as 600 km over the last 20,000 years. Within the twentieth century, decadal precipitation changes have been up to 20 per cent of these Holocene changes. Our current understanding of precipitation over the Nile Basin suggests its sensitivity to a variety of factors operating on different time and space scales. These factors include changes in the Earth's orbit, global ocean temperature anomalies, migrations of the Inter-Tropical Convergence Zone, and land-cover changes within the African continent. Future global climate, however, may be subject to a new anthropogenic forcing, the impact of which on precipitation over northeast Africa, and hence Nile discharge, is still poorly understood, namely, progressive increases in the global atmospheric concentration of greenhouse gases. This chapter presents a range of climate scenarios specifying the likely magnitudes and rates of change in Nile Basin precipitation over the next few decades. These scenarios are constructed from historical analogues, recent instrumental data, and General Circulation Model experiments. It is suggested that twentieth century precipitation characteristics are unlikely to be a reliable guide to twenty-first century precipitation. Relative contributions to Nile discharge from the Blue and While Niles may change, and increased evaporative water loss may be as important for assessing future Nile discharge as changes in precipitation.