| Summary: | 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, <0, and 0.43 for NSE respectively. In general, the model shows an acceptable
performance in runoff simulation.
A land use scenario was performed to identify the effect of land use change on runoff.
Scenario of land use in 2019 was constructed by changing non-fertile land within
Yogyakarta Agglomeration into settlements. The result of the scenarios revealed that
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.
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