THE IMPACT OF LAND USE LAND COVER CHANGE ON WATERSHED HYDROLOGY (A CASE STUDY OF UPPER AWASH BASIN)

Abstract

Land use and land cover change is one factor which has impact on watershed hydrology by changing the magnitude and pattern of stream flow. The main objective of this study is to assess the impact of land use and land cover change on stream flow of Upper Awash Basin. The land cover dynamics was identified by land use and land cover maps generated through classification of satellite images using ERDAS imagines software. SWAT model was used in concert with GIS to assess the impact of land cover dynamics on stream flow for years from 1986 to 2009. Result of image classification showed that the watershed experienced significant land use and land cover change. Land cover under agriculture was significantly increased in expenses of other land covers during the study period. SWAT model was calibrated and validated for sensitivity of stream flow parameters. Consequently, ten parameters were identified to be sensitive. The result of calibration and validation showed that there was a reasonable agreement between observed and simulated stream flow with Percent BIAS (PBIAS), coefficient of determination (R 2 ) and Nash-Sutcliffe efficiency (ENS) values -9.15, 0.98 and 0.97 for calibration, and -6.16, 0.98 and 0.97 for validation respectively. The evaluation of SWAT model hydrologic response due to land use and land cover change showed that, monthly stream flow was increased by 134.21m 3 /s in wet months and decreased by 12.92m 3 /s in dry months between the years 1986 and 2000. While between the year 2000 and 2009, it was increased by 10.05m 3 /s and 7.85m 3 /s for wet and dry months respectively due to land use and land cover change. Surface runoff was increased from 24.88mm to 39.42mm while GWQ was decreased from 38.4mm to 24.52mm for year 1986 and 2000 land use and land cover map respectively. Also surface runoff was increased from 39.42mm to 43.62mm and GWQ was increased from 24.52mm to 28.74mm for year 2000 and 2009 land use and land cover map respectively.