Simulating hydrological response and flow regime dynamics to land cover changes in sub-watershed

Abstract

Land degradation in tropical forest regions due to anthropogenic activities and land cover change poses a serious challenge to the hydrological stability of watersheds.This study aims to (1) analyze the dynamics of land cover change in the Mangguliling sub-watershed, South Sulawesi, during the 2020-2024 period, and (2) evaluate the hydrological stability of the area based on the river regime coefficient (RRC) values through the soil and water assessment tool (SWAT) model simulation.The methods used include Landsat 8 OLI image interpretation for land cover analysis and hydrological modeling using SWAT by dividing the watershed into hydrologic response units (HRUs).Land classification validation was conducted using the confusion matrix method, which resulted in an overall accuracy rate above 97%.Watershed health indicators were assessed based on the river regime coefficient and runoff coefficient in accordance with Ministry of Forestry regulations.The results show that the Mangguliling sub-watershed has a high level of ecological resilience against deforestation pressure.Primary Dryland Forest remained stable at 915.65 ha (47.97%) throughout the observation period.Positive vegetation dynamics occurred in the form of an increase in Secondary Dryland Forest by 5.11 ha through natural succession processes from open land.Other land-use changes included the conversion of paddy fields into mixed dryland agriculture covering 23.24 ha.Hydrologically, the area is in a stable condition as reflected by the constant average curve number (CN) value (~60.13) and the dominance of lateral flow over surface runoff.Despite extreme rainfall anomalies in 2024 that increased maximum discharge, baseflow availability remained well-maintained.In conclusion, the preservation of primary forest cover in the upstream area is crucial for maintaining water regulation functions and mitigating the risk of hydrometeorological disasters in the Mangguliling sub-watershed.

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