By Tekleab Shibru (PhD)
Associate Professor of Geomatics,
Chicago State University
June 8, 2020
Ever since Ethiopia embarked on Grand Ethiopian Renaissance Dam (GERD), to generate electricity that would light 60% of 114 million Ethiopia’s population, Egypt has engaged in an inexorable diplomatic campaign of decrying Ethiopia’s right to use its natural resources. This rather fabricated victimhood is resonating with the larger international community given Egypt’s desertic climate. The notion that the annual average 100 mm rainfall is the only source of water for Egypt’s 100 million, if not for Nile river, is refuted in the part I of this article. This part of the article compares the Nile river basins of the two countries focusing on the portion of rainfall that is exiting the watershed through surface run-off water (i.e., stream water outflow). Accordingly, Ethiopia’s Nile river sub-basin loses 12.8 BCM of water through the Tekeze-Atbara river; 54.4 BCM of water through Blue Nile river, and 13.6 BCM of water through the Baro-Akobo-Sobat river a total of 81 BCM; while Egypt’s sub-basin is losing none. Therefore, defining Ethiopia as country with plentiful water resources, based on the rainfall data alone, without accounting the portion of the rainfall that is actually exiting the Ethiopia to drain into Egypt’s, is inconclusive. It is, therefore, about time for the international community to examine the alleged predicament with scientifically verified evidences and hold a moral ground that is fitting to the standard.
Keywords: Stream water outflow, Watershed hydrology, Water budget, Grand Ethiopian Renaissance Dam (GERD), Egypt, Ethiopia
In the Part I hydrologic inputs component of the overall water budget of the Nile river sub-basins in Egypt and Ethiopia was discussed. The discussion enumerated all possible sub-basins’ hydrologic inputs and exposed the flaw in the global perception of Ethiopia’s water plentiful. This article reviews, part of the other component of the water budget, stream outflow of hydrologic outputs. Hydrologic outputs, as pathways by which a particular watershed loses the water resources encompasses, stream water outflow, evaporation and transpiration. Additionally, pathways, such as groundwater recharges, subsurface outflow, evaporation from streams and water exports are also considered, though due to the lack of sufficient date, these components are omitted from consideration.
The stream water outflow is water exiting sub-basins through runoffs water. Run-off is a part of rainfall water in excess of soil infiltration, direct evaporation and seepage to recharge groundwater. This excess water often flows down a landscape gradient as surface runoff. Generally, such surface run off from a landscape is a function of meteorological and bio-physical factors. Meteorologically, factors controlling run-off water are mainly rainfall amount and intensity, while the biophysical factors are topography, soils types and drainage condition, land cover, etc… Surface run off is high on a landscape experiencing intense rainfall over short time span, degraded soils with low vegetation cover, and topographies with steeply-slop gradient.
Ethiopia mountainous land system exhibit a critical physical setting of both rainfall and surface run-off formation. First, the physical setting of the Ethiopia’s highland enhances orographic uplift of prevailing airmasses and the creation of torrential rainfall system, thereof. Secondly, it facilitates a condition where the torrent rainfalls coupled with the inherently rugged and sloppy landscape generate surface runoffs, which form streams or rivers upon funneled into channelized topographies carrying running water. Nightly seven percent of these streams/rivers are transboundary, and only 3% remains within the country; a phenomenon which earned Ethiopia a status of “water towers Africa” (Fig. 1).
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