Impact of precipitation and temperature changes on hydrological responses of small-scale catchments in the Ethiopian Highlands

Tatenda Lemann,Vincent Roth,Gete Zeleke

doi:10.1080/02626667.2016.1217415

Abstract

ABSTRACT The hydrological response of catchments with different rainfall patterns was assessed to understand the availability of blue and green water and the impacts of changing precipitation and temperature in the Ethiopian Highlands. Monthly discharge of three small-scale catchments was simulated, calibrated, and validated with a dataset of more than 30 years. Different temperature and precipitation scenarios were used to compare the hydrological responses in all three catchments. Results indicate that runoff reacts disproportionately strongly to precipitation and temperature changes: a 24% increase in precipitation led to a 50% increase in average annual runoff, and an average annual rainfall–runoff ratio that was 20% higher. An increase in temperature led to an increase of evapotranspiration and resulted in a decrease in the rainfall–runoff ratio. But a comparison of combined results with different climate change scenarios shows that downstream stakeholders can expect a higher share of available blue water in the future.

Highlights

Until recently, 99% of agriculture in the highlands of Ethiopia was rain-fed, using almost exclusively green water (Hagosa et al 2011)
One reason for “no discharge” may be water supply for agricultural or residential use, which was not taken into account in this study, or a very high infiltration rate of the dry soils, which could not be modelled with Soil and Water Assessment Tool (SWAT); another may be that discharge was not consistently measured outside the major rainy season
The eventuality of deep percolation has been included in the simulations with the ranges of the parameters used for calibration (Table 4) such as RCHRG_DP, GWQMN, or GW_REVAP (Groundwater “revap” coefficient)

Summary

Introduction

99% of agriculture in the highlands of Ethiopia was rain-fed, using almost exclusively green water (Hagosa et al 2011). A rapidly growing population and economy have led to an increase in the number and size of dams, as demand for blue water for agricultural and industrial use rises. This development is being observed closely by downstream countries in the Nile Basin, which have limited precipitation and are highly dependent on blue water coming from the Ethiopian Highlands (Hurni et al 2005). These hydrological differences pose one of the main challenges for Ethiopia’s water resource management, making it imperative to improve understanding of the impact of the above-mentioned parameters (Taye et al 2015). We modelled long-term hydrological responses of three small-scale catchments with different rainfall patterns, and processed scenarios with comparable temperatures and amounts of precipitation

Methods

Results

Conclusion