IMPACT OF LAND USE LAND COVER CHANGE ON HYDROLOGIC RESPONSE: THE CASE OF DEME CATCHMENT, OMO-GIBE RIVER BASIN, ETHIOPIA

Abstract

Hydrologic modeling was conducted for each LULC map in three time periods (1999, 2010, 2018) in the Deme catchment using the SWAT model. Changes in streamflow and its components between three simulations by using the LULC map of 1999, 2010, and 2018 were related to the changes of LULC to quantify the impact of LULCC. The data used for analyses were streamflow of Deme catchment, satellite imageries of 1999,2010, and 2018, Digital elevation model, and meteorological data. LULC classification was carried out by using ERDAS imagine2014. Five types of LULC were identified in the Deme watersheds such as agricultural land, grassland, bushland, built-up area, and forest. The LULCC analysis depicted that there was an expansion of agricultural land and the built-up area in the catchment. Agricultural land was increased by 29.96% and 36.78% from 1999-2010 and 2010 -2018 respectively. The built-up area was also increased by 80.41% and 148.47% during the first and the second period respectively. The other LULC classes showed a continuous decrement in all periods. The performance evaluation result depicted that the SWAT model can be used for the analysis of the impact of LULCC on streamflow of the Deme catchment. During calibration, the value for NSE, R2, and PBIAS was 0.80, 0.75, and -1.2 respectively. During validation, the value for NSE, R2, and PBIAS was 0.74, 0.70, and -7.3 respectively. The LULCC had impacted the magnitude of streamflow and its components. During the driest season, mean monthly streamflow has decreased by 16.71% and 37.81% during the first and second periods respectively. But in contrast during the wettest month, the mean monthly streamflow has increased by 12.79% and 25.16% during the first and second period respectively. The contribution of mean annual surface runoff increased by 11.63mm and 15.94mm from 1999- 2010 and 2010 to 2018 respectively. While lateral flow decreased by 6.47mm and 9.96mm in both periods. Similarly, shallow groundwater recharge decreased by 3.77mm and4.67mm during the first and second periods. The decrease in lateral flow and shallow groundwater recharge and increase in surface runoff was related to the expansion of agricultural land, and built-up area, as well as decrement of forest, bushland and grass land. Therefore, Deme watershed requires the application of appropriate watershed management options to minimize the undesirable impacts on water and land resources.