The Upper Brantas Watershed (DAS Brantas Hulu) in Batu City plays a vital role in the hydrological system of East Java. However, it is currently classified as critical due to extensive land use changes. Over the past five years, the increasing frequency of floods including 18 events in a single month in 2023 indicates severe environmental degradation. This study aims to analyze land use changes in 2012, 2016, 2020, and 2024; and examine the correlation between these changes and the increase in surface runoff discharge. The methodology involves spatial analysis of land use change using ArcGIS 10.8 and calculation of surface runoff discharge using the SCS-CN hydrograph method. Curve Number (CN) values were determined based on land cover characteristics and soil types, while rainfall data were processed through frequency analysis, consistency testing, and probability distribution fitting. The results indicate a significant reduction in natural infiltration areas, such as primary forest (−3.3%) and secondary forest (−5.6%), along with an increase in impervious surfaces, including settlements (+30.9%) and industrial areas (+63.2%). These changes contributed to higher CN values and increased surface runoff, thereby elevating flood risks in the Upper Brantas Watershed. The findings emphasize the urgent need to control land conversion as part of sustainable spatial planning and disaster mitigation strategies.
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