Debunking Ethiopia’s Plentiful Water Resources: Evapotranspiration (Part III)

Debunking Ethiopia’s Plentiful Water Resources vis-à-vis Egypt: A Closer Look at the Hydrologic Outputs – Evapotranspiration

Evapotranspiration _ Nile _ Ethiopia _ Egypt
Abbay (Nile)River

By  Tekleab Shibru (PhD) 
Associate Professor of Geomatics 
Chicago State University
June 20,2020

Abstract

Evapotranspiration is among critical ecosystem processes, which facilitates water movements in hydrologic cycle and its redistribution on the earth’s surface. However, evapotranspiration is also a mechanism by which available water on the surface and subsurface, is lost from the ecosystem into unavailable water form. Such loss of water is a critical fraction of hydrologic inputs (i.e., precipitation, stream inflow, groundwater extraction, etc..) of a basin. This article assessed the evapotranspiration of Egypt’s and Ethiopia’s sub-basins to resolve the quantities of sub-basins’ water losses and the resultant water resources of the two countries. Accordingly, the Ethiopia’s Nile river sub-basin and Lake Tana together lose a total of 353.3 BCM of water through the evaporation and evapotranspiration; while Egypt loses 51 BCM water from its arable lands of the sub-basin. This Ethiopia’s water loss is, approximately, 7-folds and 600% more than a loss from the Egypt’s sub-basin, an accounting that is ignored from the alleged Ethiopia’s possession of plentiful water resources. Therefore, in the interest of rational and reasonable deliberation, it is imperative that this component of hydrologic outputs is appraised and made available for debates and inform the settlements on the Nile basin water resources sharing. 

Keywords: Evaporation, Evapotranspiration, Water budget, Grand Ethiopian Renaissance Dam (GERD), Egypt, Ethiopia

  1. Introduction

Evaptranspiration is a critical process in a hydrologic cycle of a watershed or landscape. When the input component of hydrologic cycle, a rainfall event land a landscape, it has one of the following three fates. These are run-off, evaporation, and infiltration into soils. Run-off, which discussed in Part II of this article, is a fraction a rainfall event, excess of infiltration, that flows down-slope a basin or landscape. This run-off water concentrates into channelized rivers or streams for eventual discharge of rainfall water into inland lakes or ocean. Conversely, infiltration is a fraction of a rainfall event that soaks the soil to constitute soil-water available for plant growth. Some infiltration water further percolates deep into subsurface saturated zone to recharge the groundwater. The third is evaporation, a fraction that evaporates to atmosphere in gaseous form.

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