IMPACT OF LAND USE/LAND COVER DYNAMIC ON HYDROLOGY REGIME: A CASE STUDY IN THE UPPER BARO BASIN, GAMBELLA, SOUTHWEST ETHIOPIA

Abstract

The principal driving forces for land use/land cover change(LULCC) are rapid increases of population and forest clearing. Those are important factors that influence the hydrological condition of a catchment. Land use/land cover change can also result in change of flood frequency, increase peak flows, base flow, and annual mean discharge. To reverses such kind of problems, assessment of hydrological condition in relation to LULC and finding solution at a watershed level is necessary. The objective of this study was to assess the impacts of LULC change on the hydrology of Upper Baro Basin using Soil and Water Assessment Tool model. The LULC change analysis was performed by using supervised classification method using ERDAS imagine 2014. The accuracy of the classified maps was assessed using error matrix of each selected period. Consequently, 92.14%, 94.63% and 95.63% were found for LULC classification of 1987 ,2002 and 2017 study years, respectively. The result show that there was a drastic decreased of grass land by15.64 % and an increase of agricultural land and settlement by 18.01% and 13.01%, respectively over period. SWAT model was adopted to perform simulation of the main hydrological component in order to finding the effect of LULCC using in 1987,2002 and 2017 and also calibration, validation and uncertainty analysis were performed using sequential uncertainty fitting (SUFI-2). The result showed that there was a reasonable agreement between observed and simulated streamflow with coefficient of determination (R2) and Nash-Sutcliffe efficiency values 0.87 and 0.76 for calibration periods 1990-2002 and 0.77and 0.72 for validation period of 2003 to 2010 respectively. Further, the model was predicting the impact of LULC change on streamflow for period 1987,2002 and 2017. Evaluation of hydrologic response unit (HRU) due to LULCC showed that mean monthly streamflow was increased by 35.8% in wet months and decreased by 21.05% in dry months between the years 1987 and 2002. While betwee 2002 and 2017, it was increased by 47.1% and 3.49% for wet and dry months, and the year 2017 and 1987, it was increased by 82.9% and 15.54% for wet and dry months respectively. InVEST model was used to assess the total soil loss potential for each LULCC, these result show that increased from 276462.8 in 1987 to 391741.2 ton/year in 2017 and the mean annual soil loss was also increased from 67.67ton/ha/year in 1987 to 70.84ton/ha/year in 2017. The trend of soil loss and sediment export indicates that an increase in LULCC. Deforestation and soil erosion problems need to be give attention urgently to maintain the stability and resilience of the ecosystem