Impact of climate change on the water resources of Awash River Basin, Ethiopia

Vol. 12: 91–96, 1999

CLIMATERESEARCH

Clim Res

Published August 27

Impact of climate change on the water resources

of Awash River Basin, Ethiopia

Kinfe Hailemariam*

National Meteorological Services Agency, PO Box 1090, Addis Ababa, Ethiopia

ABSTRACT: An attempt was made to investigate the sensitivity of water resources to climate change inthe Awash River Basin in Ethiopia. The climate of the basin varies from humid subtropical to arid. Thebasin was divided into 3 subcatchments for better resolution in calibration and simulation. Station-based meteorological data were processed to obtain areal averages necessary for the simulation. Different sets of temperature and rainfall scenarios were developed using GCM (both transient andCO2doubling) and incremental scenarios. The IIASA integrated water balance model (WatBal) wasused to estimate runoff under a changed climate. The model represents the water balance among sur-face outflow, subsurface outflow, and evapotranspiration. The model was calibrated using a 10 yrperiod (1971 to 1980), validated with the next 6 yr period (1981 to 1986), and then applied for differentclimate scenarios. Results of the impact assessment over the basin showed a projected decrease inrunoff, which ranged from –10 to –34%, with doubling of CO2and transient scenarios of CO2increase(GFD3, CCCM, GF01). Sensitivity analysis based on incremental scenarios showed that a drier andwarmer climate change scenario results in reduced runoff.

KEY WORDS: Awash River Basin · Climate change · General circulation models (GCMs)

1. INTRODUCTION

Scientific evidence indicates that due to increasedconcentration of greenhouse gases in the atmosphere,the climate of the Earth is changing; temperature isincreasing and the amount and distribution of rainfallis being altered (Houghton et al. 1996). The IPCCScientific Assessment suggests that global averagetemperature may increase between 1.5 and 4.5°C, witha ‘best estimate’ of 2.0°C, in the next century with adoubling of the CO2concentration in the atmosphere(Houghton et al. 1996).

By affecting certain components of the hydrologicalcycle, especially precipitation and runoff, a change inclimate can alter the spatial and temporal availabilityof water resources. Climate change that reduces eitherthe overall quantity of water or the timing of whenwater is available for use will have important effects onagriculture and industrial and urban development.

*E-mail: nmsa@http://www.wendangwang.com.et© Inter-Research 1999

Increasing variability alone would enhance the pro-bability of both flood and drought (William 1988).Theclimatic impact on the water regime may alsoexacerbate other environmental and social effects ofwater management. For instance, reduced river runoffcan concentrate the effects of pollutants or exacerbatethe spread of water-borne disease. Climate fluctua-tions can also affect the use of agricultural land asso-ciated with irrigation systems. Climate change willgreatly complicate the design, operation, and manage-ment of water-use systems (Gleick & Shiklomanov1989). On the other hand, climate change thatincreases overall water availability could either bebeneficial or could increase the risk of flooding.Regions with an arid and semi-arid climate could besensitive to even insignificant changes in climaticcharacteristics (Linz et al. 1990). The impact of climatechange on water resources is so integrated into dif-ferent sectors, such as agriculture, health, urbani-zation, fisheries, and so forth, that it has motivatedmany to conduct studies using different approachesand come up with a variety of results (Beven 1989,