Human Impact on the Nile Basin: Past, Present, Future

Abstract

The gradual spread of plant and animal domestication throughout the Nile valley was associated with widespread deforestation, accelerated soil erosion and an exponential increase in the human population. The climate in the Nile basin during the first half of the Holocene was wetter than today. The advent of drier conditions began about 5,000 years ago and further accelerated the land degradation resulting from the spread of agriculture into the upland headwaters of the Blue and White Nile. A severe drought 4,200 years ago is evident in the strontium isotopic records from Lake Albert in Uganda as well as the Nile delta, and was associated with famine and severe social distress during Old Kingdom times. Deforestation in the Ethiopian highlands has led to accelerated soil loss from the Ethiopian headwaters of the Blue Nile/Abbai and Atbara/Tekezze rivers, with concomitant rapid rates of sedimentation in reservoirs downstream. By 1996, the capacity of the Roseires reservoir on the Blue Nile had been reduced by almost 60% through silt accumulation and that of the Khasm el Girba reservoir on the Atbara by nearly 40%. Historic fluctuations in Nile flood levels are in part related to El Niño Southern Oscillation (ENSO) events, with years of low flow often synchronous with years when the Southern Oscillation Index (SOI) is strongly negative. (The SOI is a measure of the surface atmospheric pressure difference between Darwin and Tahiti). Since over 300 million people will depend upon the waters of the Nile for their livelihood by the year 2020, a clear understanding of present land use and Nile flood history is essential for future planning.