The influence of Mount Merapi eruption on the water balance in Kali Kuning sub-watershed

The national park area has a function in conserving the water in the catchment area. This study aimed to compare the changes of the water balance before and after the eruption and to analyse the drought index. This study uses Thornwaite and Mather water balance analysis by calculating the amount of water input and output. The results showed that the water balance in the Kali Kuning sub-watershed was surplus in the wet months, namely January-April and November-December. Meanwhile, the deficit occurs during the dry months, namely May-October. The condition of the water balance in the Kali Kuning sub-watershed before and after the eruption changes but was not significant due to factors of land use, rainfall and temperature before and after the explosion did not change significantly. Before the outbreak (2006-2010), the drought index tended to decrease due to high rainfall every year, while after the explosion (2011-2019) it tended to increase due to changes in land use conditions. Mount Merapi eruption resulted some part of the forest in the Kali Kuning sub-watershed turned into open land. © 2021 Published under licence by IOP Publishing Ltd.