The Effect of Climate Change and Land Use Change Scenarios on the Design Flood Discharge and the Curve Number: The Case of the Noelmina and Benanain Watersheds, Indonesia

Abstract

Climate change substantially alters watershed hydrology, primarily through increased flood discharge. This study uses the Hydrologic Engineering Center’s Hydrologic Modeling System (HEC-HMS) to assess how climate change and land-use change scenarios affect the design flood discharge and Curve Number (CN) for the Noelmina and Benanain watersheds in East Nusa Tenggara, Indonesia. The Representative Concentration Pathways (RCPs) 2.6 and 8.5 were applied for the periods 2041-2060 and 2081-2100. The simulated flood discharge increased progressively over time, most notably under the high-emission RCP 8.5 scenario towards the end of the century. Compared with the discharge from observed rainfall in 2024, the 25-year design flood under RCP 8.5 (2081-2100) increased by 35.6% in Noelmina and 32.6% in Benanain, while the 50-year flood increased by 36.3% and 30.7%, respectively. A land-use analysis conducted between 2015 and 2024 revealed the conversion of vegetated land into residential and agricultural areas. This raised the composite CN from 83.19 to 83.73 in Noelmina and from 85.99 to 86.82 in Benanain. This indicates a reduction in infiltration capacity and an increase in surface runoff. The combined effects of climate change and land use are likely to exacerbate future flood risk, highlighting the need for integrated watershed management and adaptive mitigation strategies.