Assessing the Water Resources Potential of the Nile River Based on Data, Available at the Nile Forecasting Center in Cairo

Abstract

This paper estimates the monthly values of mean areal precipitation (MAP) and discharge data (Q) over significant sub-catchments of the Nile River watershed on the basis of daily and monthly gridded data (resolution of about 25 km2) available at the Nile Forecast Center (NFC) in Cairo. On this basis, the author proceeds with an analysis of the MAP, Q, and annual runoff ratio for each sub-catchment, an analysis of the covariance of the basic temporal modes of the inter-annual variation of the MAP and Q between the Blue Nile and the White Nile, and an analysis of the resilience of a well-managed Aswan High Dam facility to historical climate variability. The main conclusions are: a) similar behaviour of the basic mode variability exists throughout the Nile sub-catchments, although the inter-annual basic mode variability overlarge areas is small; b) there is a dominant 44-month cycle for MAP, and 9 and 20 year cycles for total Nile Basin runoff at Aswan; c) the correlation coefficient between annual Q and MAP is low in the Equatorial Lakes and the marshlands of the White Nile and is much higher for areas in and downstream of the Blue Nile; d) in the past, the White Nile including the Sobat River has contributed an average of approximately 30% of the inflow to Lake Nasser (1912–1995 data) but with its contribution ranging from about 25% in the early years of the 20th century to 40% in the 1960's and a steady decreasing trend in recent years; e) assuming that irrigation demand in Egypt remains at present day levels, improved management of the High Aswan waters through the modern forecast-control system should be able to accommodate the historical climatic variability without significant detrimental effects for the Egyptian water supply (period of record 1872–1998); and f) for an increase of 8 km3 in upstream water consumption and for the same climate variability of the inflows to the Aswan High Dam as in the past 128 years, the forecast-control scheme ensures the minimum of the current irrigation demand for Egypt. It is carefully pointed out throughout the analysis that data is not uniformly available throughout the Nile Basin and the analysis contains errors that are not homogeneous over the entire Nile watershed; furthermore, the historical climatic variability is likely not to be repeated in the area as evidenced by the behaviour in the 1960's (one event in this long record).