ASSESSING THE IMPACT OF LAND USE AND LAND COVER CHANGE ON HYDROLOGY OF KESEM WATERSHED IN AWASH BASIN, ETHIOPIA

Abstract

Within Kesem watershed land use is undergoing major changes due to pressures of human activities. Changes in land use have potentially large impacts on water resources by causing more surface runoff, decreased water retention capacity, loss of wetland and drying of river. In this study, both the Soil and Water Assessment Tool (SWAT) model and Mann-Kendall (MK) statistical time series analysis for measured streamflow were applied to understand the streamflow variability and land use dynamics effect on hydrology of Kesem watershed. Land use change detection was done using remote sensing techniques and the maps were processed using ERDAS Imagine 2014 and ArcGIS10.1 software. From the land cover change analysis results it was found that there has been a substantial decline of forest lands, shrub lands, grass lands and drastic expansion of agricultural land. The SWAT modeling results showed that an increase of streamflow by 23.2% comparing the two land use maps (1993 versus 2005). The analysis also revealed that flow during the wet months has increased by 16.1% while the flow during the dry season decreased by 0.8%. The MK test has been applied to mean annual, seasonal, 1- and 7-days annual minimum and maximum flows. The MK- test demonstrates that in the case of 1-day maximum flow, no significant trend is noticeable; however, the extreme low flows indicators (e.g. 1D minimum, 7D minimum) and dry seasonal flows exhibited statistically significant decreasing trends. Generally, the combined results of the SWAT model and the statistical tests revealed that land use change has caused a significant increase on mean annual streamflow and decreasing dry season flows of the studied watershed during the last three decades. The identified result is important to inform optimal water resource management and to plan and manage water resources development within the watershed in a sustainable manner