Climatic Factors Modulating Nile River Flow

Abstract

This chapter presents a review of climatic factors modulatingvariability of Nile River flow. Through composite analysis of seasonswith high and low flow, the Atlantic zonal overturning atmosphericcirculation is seen as a dominant feature. When upper easterlies andlower westerlies prevail, convection is enhanced over the highlands ofNortheast Africa. This atmospheric cell is shown to be coupled with thePacific Ocean thermocline oscillation that comprises the El NinoSouthern Oscillation. At the event scale, floods are produced by anenhanced southerly monsoon over the West Indian Ocean that is reflectedback toward Northeast Africa by an Arabian ridge. Diurnal forcing isevident in surface heating and a mid-day strengthening of northwesterlywinds over Sudan. During the 1970s and early 1980s, droughts caused theNile River flow to decline. This appears related to a multi-year coolphase in the North Atlantic and a southward retreat of thenear-equatorial trough. Sympathetic responses of rainfall extend fromEthiopia to India and across the West African Sahel, suggesting thatclimatic variability in the Nile catchment is part of a global pattern.Although some predictability is uncovered, more than half of thevariance in Nile River flow is apparently random and unresolved byeither statistical or numerical models. Thus coping mechanisms andstrategies for resource switching in wet and dry phases are needed, toput countries bordering the Nile on sound economic footing.