Water balance components of the potential agricultural grabens along the Rift Valley in northern Ethiopia

Abstract

Region: Ethiopia’s Rift Valley. Focus: matching agricultural water demand and supply is a growing policy challenge in drylands. We investigated the water balance components in Raya (3507 km2) and Ashenge (80.5 km2) grabens. The rainfall depth, river discharge, abstraction, climate and soil data (2015–2017) were used to address the research question.New hydrological insights: the average annual rainfall of the graben’s escarpment and its bottom was 806 ± 162 and 508 ± 110 mm, respectively. Heavy rains produce floods up to 732 m³ s−1 in the rivers that flow into the Raya graben. Moreover, greater runoff and river discharges volumes were recorded at the graben escarpments than at the graben bottom outlets (p < 0.001) due to the greater contributing area (p < 0.001, R2 = 0.98) and headwater elevation (p < 0.001, R2 = 0.98). About 24% of the water entering both graben bottoms comes from the runoff from the adjacent slopes, and about 40% of the runoff reaching the Raya graben bottom flowed out at the outlet. About 76% and 77.5% of the annual rainfall was lost through evapotranspiration from the Raya and Ashenge grabens, respectively. So about 16% and 33% of the average annual inflows infiltrated into the sediments in the Raya and Ashenge grabens, respectively. These insights provided by this study into the water balance in grabens along the Rift Valley can be used to help achieve sustainable agricultural development. Keywords: Erratic rainfall, Flash flood, Evapotranspiration, Recharge, Rift Valley, Ethiopia