Assessing the Impacts of Land Use and Land Cover Change on Stream Flow Using SWAT+ Model. A Case of Mormora River Catchment, Genale Dawa River Basin, Ethiopia

Abstract

Because it has a considerable impact on stream flow, land use and land cover change (LULC) is a very important topic in terms of global dynamics and their reactions to hydrological features and soil and water management of a watershed. Using the QSWAT+ model, this study seeks to evaluate the effects of changing land use and land cover on stream flow. Spatial and weather data are the main input data for the SWAT+ model. The land use and land cover data were gathered from USGS Earth Explore and created using the ERDAS IMAGINE 2015 program utilising the maximum likelihood of supervised classification approaches for the land use and land cover maps of 2001, 2011, and 2021.Based on the result the significant changes were occurred in each study period and between 2001 and 2011 Forest decreased by 17.92%, and Agriculture increase by 38.2% and between 2011 and 2021 Forest, Grass land and water body minimize by 20.19%, 10.155% and 0.035% respectively but agriculture and settlement increased by 29.69% and 0.697%. Using the MOLUSCE plugin and QGIS 2.8, a map of predicted future land use and land cover (LULC) for the year 2031 was created and Forest, grass land water body were decreased by 3.94%, 2.185% and 0.005% but agriculture and settlement was increased by 5.54% and 0.525% as compared with 2021. The effects of LULC on the hydrological response of the Mormora watershed were simulated using the physical-based semi-distributed hydrological QSWAT+ model. Using the SWAT plus-Tool box v1.0.1 software, the performance of the SWAT+ model was assessed through sensitivity analysis, calibration, and validation. The calibration result demonstrates good agreement between monthly observed and monthly simulated streamflow, with coefficient of determination (R2 ) values of 0.7761, 0.7921, 0.8024, and 0.7903; Nash-Sutcliffe coefficients (NSE) of 0.75, 0.77, 0.79, and 0.75 and PBIAS of 13.73, 11.32, 8.16 and 11.723 for the calibration of the LULC maps for 2001, 2011, 2021 and 2031; and coefficients of determination (R2 ) values of 0.7451, 0.7438, 0.7417, and 0.7416, NSE of 0.73, 0.72, 0.71 and 0.71, and PBIAS of 5.042, 5.279, 5.77, and 5.80 for the validation of the LULC maps for 2001, 2011, 2021, and 2031. According to the study's findings, the average seasonal stream flow for the wet seasons, increased from 41.34 m3/s to 41.70 m3/s and 56.72 m3/s to 57.19 m3/s for the calibration and validation periods, the average seasonal stream flow for the dry season increased from 0.690 m3/s to 0.702 m3/s and 2.010 m3/s to 2.026 m3/s for the calibration and validation periods. From the study's overall findings, it can be deduced that increased stream flow during the wet and dry seasons is caused by the growth of the settlement area and the predominance of agricultural land.