ASSESSING THE EFFECTS OF LAND USE CHANGE ON RUNOFF CASE STUDY OF BEDOG SUB WATERSHED IN YOGYAKARTA PROVINCE, INDONESIA

The study was to assess the effects of land use change on runoff in the Bedog sub watershed, Yogyakarta, Indonesia which role both as centre of economics activities and source of rice production. Remote sensing and Geographic Information System (GIS) were tools employed to identify land use and its changes. Soil and Water Assessment Tool-Water Balance (SWAT-WB) was a hydrological modeling used to predict runoff for years of 2001, 2006, and 2010. Land use in the study area has rapidly changed in last few decades due to agglomeration process in Yogyakarta City. Coverage of mixed garden decreased during period of 2001- 2010 despite still as predominant land use in total. On the other side, change detection analysis revealed that there was an increase of settlements coverage from 9.51% to 13.79% in the same period. Land use datasets, soil datasets, and weather data were main inputs provided to SWAT-WB in predicting runoff. Sensitivity analysis revealed that soil properties were the most sensitive parameters on runoff generation. Calibration was performed for years of 2001, 2006, and 2010. The results of calibration on monthly basis were 0.7, 0.57, and 0.51 for R 2 respectively and 0.64,