The Indonesian Geographers Association ASSESSING THE EFFECTS OF LAND USE CHANGE ON RUNOFF IN BEDOG SUB WATERSHED YOGYAKARTA

The study was to assess the effects of land use change on runoff in the Bedog sub watershed. Soil and Water Assessment Tool-Water Balance (SWAT-WB) hydrological modeling was used to predict runoff for years of 2001, 2006, and 2010. Land use in Bedog 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. Sensitivity analysis revealed that soil properties were the most sensitive parameters on runoff generation. Calibration was performed for years of 2001, 2006, and 2010 and the result shows an acceptable performance in runoff simulation. Changes in land use were responsible for an increase in the annual runoff between 3.42 % – 4.67%. This study showed that dynamics of runoff can be predicted by forecasting and simulating future land use