Model-Based Characterization and Monitoring of Runoff and Soil Erosion in Response to Land Use/land Cover Changes in the Modjo Watershed, Ethiopia

The Modjo watershed has experienced significant land use/land cover (LULC) change and soil erosion. This study examines changes in surface runoff generation and soil erosion in response to the LULC dynamics. To simulate runoff and sediment yield, the geographic information system-interfaced Soil and Water Assessment Tool (SWAT) model was used. Model sensitivity, calibration and validation analyses were carried out, and the efficiency of the model was evaluated using simulated and measured discharge data. The two scenario model simulation goodness-of-fit measures verified that the SWAT model performed very well during calibration and validation periods for daily and monthly time steps (Nash-Sutcliffe efficiency>079 and root mean square error-observation standard deviation ratio<04). Although the computed values of per cent bias fulfilled a satisfactory standard (greater than -118%), the model results tended to overestimate discharge. Consequent to the LULC change, an overall increase in the amount of surface runoff (142%) and sediment yield (37%) was observed relative to the baseline (1973) simulation scenario. Mean annual soil loss rate was estimated at 242Mgha(-1)y(-1). Nearly 952% of the watershed is experiencing moderate to severe soil loss rates ranging from 147 to 375Mgha(-1)y(-1). In the remaining parts of the watershed, soil loss rates range from 44 to 147Mgha(-1)y(-1). Surface runoff generation and soil erosion varied widely by soil, LULC types and slope positions. The observed environmental change would lead to further land degradation, with negative implications on the livelihoods of local people unless appropriate conservation measures are implemented. Copyright (c) 2014 John Wiley & Sons, Ltd.