MODELING HYDROLOGICAL RESPONSES TO LAND USE AND LAND COVER CHANGE IN MEGECHA RIVER CATCHMENT OMO-GIBE BASIN, ETHIOPIA

Abstract

Land use/ land cover change has been one of factors responsible for altering the stream flow of the watershed on the Megecha River Catchment OMO-GIBE basin leading to impacting river flows. The study mainly focused on to evaluate the impact of land use land cover change on streamflow. Land use change detection was done using remote sensing techniques and the maps were processed through maximum likelihood algorithm of supervised classification using ERDAS Imagine 2014 and ArcGIS 10.4 software. A physical based, semi –distributed hydrological model, SWAT was used to investigate the impact of land cover change on streamflow, of Megecha River Catchment OMO-GIBE Basin. From the land cover change analysis result it was found that there has been a substantial decline of sparse and moderate forest, grass land, bare land and water body. The cropland in the watershed increased from 68.80% in 1996 to 71.13 in 2016. Similarly shrub land and settlement shows increase. This is mainly because of the population growth that caused the increase in demand for new agricultural land and rural settlements which in turn resulted shrinking on other types of land use and land cover of the area. Results have revealed that there is substantial increase in surface runoff volume from 94.34mm to 125.97mm for the LULC map of year1996 and 2016 respectively. The model evaluation statistics for stream flow provided a very good result since NSE >0.75 and R2 >0.75. The change in LU/LC ensued in augmented stream flow and in which the expansion of agriculture has also resulted an increase of surface run off, but decreased the ET of river catchment. Therefore, curving the trends of LU/LC towards increasing vegetation covers is very important so as to reduce the seasonal flow and surface runoff, on the other hand to increase ground water flow. One way of increasing vegetation cover in the river catchment is through controlling the expansion of agriculture at the expense of other land covers and improving the productivity of existing farm lands through the provision of improved production inputs and livelihood diversification