ASSESSMENT OF LAND USE LAND COVER CHANGE IMPACT ON STREAM FLOW: THE CASE OF UPPER BILATEWATERSHED, ETHIOPIA

Abstract

The hydrologic systems of many watersheds are undergoing changes in land use and land cover. A difficult topic for the scientific community is predicting the effect of land use and land cover change on stream flow. The main objective of this study is to assess the impact of land use and cover changes on the stream flow of the Upper Bilate watershed in southern Ethiopia by integrating satellite remote sensing data with a SWAT model. In this study, the Soil and Water Assessment Tool (SWAT) model was selected to address the impact of land use and land cover dynamics on the hydrology of the Upper Bilate watershed. The land use land cover change detection was properly evaluated using latest techniques of Remote sensing to Landsat images; Thematic mapper (TM), Enhanced thematic mapper plus (ETM+) and Operational land imager (OLI) with the help of historical trends and ground-based data. The land use and land cover maps for the years 1999, 2008, and 2017 were produced. The accuracy of the maps was found to be within acceptable ranges. i.e., the Kappa coefficient and overall accuracy were greater than 80%. The change detection analysis showed that the Upper Bilate catchment experienced an increase in settlement, water bodies, and cultivated land over the past three decades. But, forest, grassland, shrub land, and bare land have decreased. The model was calibrated for the period from 1999-2008 and validated for the period from 2009-2013. Statistical measures with values of R2, NSE, PBIAS, and RSR of 0.84, 0.77, less than 14.8, and 0.48, respectively, were used to assess the SWAT model's performance. According to the SWAT modeling results, stream flow increased between the two land use maps from 1999 and 2008 by 37.93% and between the two maps from 1999 and 2017 by 41.40%. Depending on the determined result, planning and management of water resources in the upper Bilate watershed as well as ideal management of water resources are necessary.