Assessment of Extreme Precipitation Events over the Nile Basin and their Impact on Downstream Countries
Abstract
Surface water levels in Lake Nasser peaked (>182 m.a.m.s.l) twice (1998 to 2002) and (2019 to present) during the past two decades and excess Lake Nasser water had to be channeled through spillways towards the depressions within the Eocene limestone plateau bounding the lake from the west forming the Tushka Lakes (area: 1580 km2). Using a surface-water model calibrated against lake stages the total volume of water diverted (late 1998 to early 2002) from Lake Nasser to five major depressions was estimated at 27.4 km3, 40% of which was lost to evaporation by 2012, and over 90% by 2018. Knowing the maximum areal extent and the maximum surface water levels of the individual Tushka Lakes during the second, high lake level period, we estimate a minimum volume of 17.4 km3 was diverted to the Tushka Lakes during this period. This estimate does not consider losses to evaporation and infiltration. We investigated the nature of these high lake level events using temporal precipitation data (1979 to 2021), GRACE (2003 to 2017) and GRACE-FO (2018 to 2021) CSR mascon solutions, and stream flow data over the Blue Nile, White Nile, and Atbara basins. Findings indicate the two high lake level events were preceded by one or more of the following: (1) increased precipitation over the Blue Nile, Atbara subbasins, and occasionally over the White Nile, for a period of 5-7 years, (2) progressively increasing GRACETWS, Lake Nasser levels, and stream flow rates over a period of 3-7 years. Findings suggest that excess Lake Nasser waters should not be left to evaporate in the Tushka Lakes (past and current practices), but instead it should be used to develop sustainable agricultural communities in the Dakhla subbasin. This could be accomplished by channeling the excess waters across the western plateau, and artificially recharging the Nubian Sandstone Aquifer System (NSAS) that underlies the Western Desert of Egypt (area: 680,000 km2) and crops out at the foothills of the plateau. The NSAS is largely formed of non-renewable fossil waters that were recharged in previous wet climatic periods, and is currently being utilized in a non-sustainable manner. The advocated suggestion would replenish the NSAS and put an end to these undesired practices.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.H25H1113B