ASSESING THE IMPACT OF LAND USE / LAND COVER CHANGE ON STREAM FLOW (THE CASE OF UPPER AWASH RIVER BASIN, ETHIOPIA

Abstract

The population growth for the last 33 years caused changes in land cover of the upper Awash River basin of Ethiopia. The effect of the land cover changes has impact on the stream flow of the watershed by altering the magnitude of surface runoff and ground water flow. This study aimed at investigating the impacts of the land use/land cover change (LU/LCC) on the stream flow of the upper Awash River basin. Both meteorological and hydrological dataset was gathered and analyzed for a period of 1986 to 2018. Land use change detection was done using remote sensing techniques and the maps were processed using ERDAS Imagine 2014 in conjunction with ArcGIS10.1 software. The land use land cover maps were classified using the Maximum Likelihood Algorithm of Supervised Classification. The accuracy of the classified maps was assessed using Confusion Metrics. The result of this analysis showed that the cultivated land, water body and settlement area has expanded but forest and, grass lands has shown a substantial decline during the study period of 1986-2018. The Soil and Water Assessment Tool (SWAT) model was used to simulate the stream flow under different LU maps. The model was calibrated during a periods of (1986 to 1991), (1996 to 2001), (2006 to 2011) and validated during a periods of (1992 to 1995), (2002 to 2005), (2012 to 2015) for land use/land caver of 1986, 2002 and 2018 respectively. The results of sensitivity analysis show that fifteen flow parameters were identified to be sensitive for the stream flow. Calibration and validation on monthly stream flow is performed by dividing stream flow from (1986_1995) first class for1986 land use and land cover, (1996_2005) second class, for 2002 land use and land cover and (2006_2015) 3rd class for 2018 land use and land cover respectively. For 1986 LULC class of Calibration period, Nash-Sutcliffe simulation efficiency (ENS) of 0.78 and coefficient of determination (R2 ) of 0.84 and validation ENS value of 0.60 and R2 of 0.76 respectively. For 2002 LULC class of Calibration period, Nash-Sutcliffe simulation efficiency (ENS) of 0.81 and coefficient of determination (R2 ) of 0.86 and validation with the ENS value of 0.62 and R 2 of 0.82 respectively. For the 2018 LULC class of Calibration period, Nash-Sutcliffe simulation efficiency (ENS) of 0.85 and coefficient of determination (R2 ) of 0.89 and validation with the ENS value of 0.64 and R 2 of 0.84 respectively. The trend analysis indicated that flow during the wet months has increased by 34.4% and 10.7% between 1986 to 2002, and 2002 to 2018 respectively. While the flow during the dry months decreased by 4.6% and 6.9% between 1986 to 2002, and 2002 to 2018 respectively. Generally, the analysis indicated that flow during the wet months has increased, while the flow during the dry months decreased. The SURQ increased, while GWQ decreased from 1986 to 2018 due to the increment of cultivated land and expansion of urbanization. The model results showed that the stream flow characteristics changed due to the land cover changes during the study period