Climatic Factors Modulating Nile River Flow

Abstract

This chapter presents a review of climatic factors modulating variability of Nile River flow. Through composite analysis of seasons with high and low flow, the Atlantic zonal overturning atmospheric circulation is seen as a dominant feature. When upper easterlies and lower westerlies prevail, convection is enhanced over the highlands of Northeast Africa. This atmospheric cell is shown to be coupled with the Pacific Ocean thermocline oscillation that comprises the El Niño Southern Oscillation. At the event scale, floods are produced by an enhanced southerly monsoon over the West Indian Ocean that is reflected back toward Northeast Africa by an Arabian ridge. Diurnal forcing is evident in surface heating and a mid-day strengthening of northwesterly winds over Sudan. During the 1970s and early 1980s, droughts caused the Nile River flow to decline. This appears related to a multi-year cool phase in the North Atlantic and a southward retreat of the near-equatorial trough. Sympathetic responses of rainfall extend from Ethiopia to India and across the West African Sahel, suggesting that climatic variability in the Nile catchment is part of a global pattern. Although some predictability is uncovered, more than half of the variance in Nile River flow is apparently random and unresolved by either statistical or numerical models. Thus coping mechanisms and strategies for resource switching in wet and dry phases are needed, to put countries bordering the Nile on sound economic footing.