Impact of agricultural land-use change to the surface run-off: a case study of Cereng catchment area, Kulon Progo Regency, Special Region of Yogyakarta

Agricultural land-use changes can cause a reduction in the green open space area, thereby reducing infiltration and increase surface run-off. One of the phenomena in agricultural land-use changes as indicated by the addition of the percentage of irrigation paddy fields in Cereng Catchment Area (CA) by 2.31%, 2.94%, and 4.39%, respectively, in 1995, 2008, and 2018. Besides, the addition of the settlement area and the plantation area's reduction were also phenomena of land-use change. The impact of these changes is associated with curve number (CN) and direct run-off. The analysis conducted on the relationship between effective design rainfall and response to the land-use changes to produce direct run-off volume in 2, 5, 10, 20, and 50 years-return period, respectively, in 1995, 2008, and 2018 using the HEC-HMS model. The result showed that have addition to CN that were 81.85, 85.82, and 86.66, respectively, in 1995, 2008, and 2018. This addition caused an increase in the percentage of direct run-off volume from 1995 to 2018; those values were 24.28%, 16.8%, 13.76%, 11.61%, and 9.53%, respectively, at the 2, 5, 10, 20, and 50-years return period. The increase in the value of direct run-off volume causes a high possibility of a flood.