THE IMPACT OF LAND USE-LAND COVER CHANGE ON WATER AVAILABILITY IN THE KULFO WATERSHED

Abstract

A change in land cover/use is altering the hydrologic system of many watersheds. It is also a scientific challenge to predict their effects on water availability. The main objective in this study is to evaluate water availability under a changing land cover/use in Kulfo watershed in Southern Ethiopia by integrating satellite remote sensing data and a rainfall-runoff model. To address this concern, the selected model must be able to represent the impact of land cover/use on various runoff components. The land cover/use change was evaluated properly using latest techniques of Remote Sensing to Landsat images; thematic mapper (TM), Enhanced thematic mapper plus (ETM+) and Operational land imager (OLI) with the aid of historical trends and recent ground based data. The land cover/use maps of the year 1986, 1996, 2010 and 2017 were produced. The accuracies of the maps were found within the acceptable ranges in literature. The change detection analysis showed that Kulfo catchment experienced an increase in crop land, plantation and bare land (by 8.34%, 1.9%, and 1.5% respectively) over the past three decades. However, shrub and grass land were decreased (by 8% and 3.5%) in the same period. The fully spatially distributed hydrologic model (WetSpa) was applied to identify the contribution of LULC change to any historical changes in water availability. The model closely relates runoff with catchment physical properties in a distributed manner and allows operating at different spatio-temporal scales. The calibrated WetSpa model reasonably reproduced the volume (Model Volumetric efficiency of 0.69%) and pattern (Nash-Sutcliffe model efficiency of 0.52) of the observed hydrograph. The watershed had undergone significant change in stream flow in the study period. The direct runoff had progressively increased by 12.78% and interflow and ground water flow were reduced by 4.84% and 7.46% respectively. Changes in surface runoff were largest for the main rainy season (increased by 39.3%) and short rain season Bega (increased by 37 %). However, the interflow and ground water flow were highly reduced in the dry season reduced by 14.77% and 10.39 % respectively. These changes could be attributed to spatial increases in crop land, bare land in the expense of shrub and grass land over the study period.