Exploratory SWAT assessment of recent land-use change and simulated hydrological responses in the ungauged tropical river basin.

Small tropical urban basins are often managed with limited hydrological records despite rapid land-use change and increasing pollution risk. This study provides an exploratory assessment of recent land-use/land-cover (LULC) change and associated simulated hydrological responses in the ungauged Kuang River Basin, Malaysia. LULC maps for 2019 and 2023 were compared using post-classification comparison, and class-level landscape metrics were used to examine sub-basin patterns. ArcSWAT was configured as a scenario-screening tool using global terrain, soil, and climatological inputs. Because continuous discharge records were unavailable, model evaluation was limited to internal water-balance checks and dry- and wet-season spot discharge observations rather than formal calibration and validation. Agriculture remained the dominant class but declined by 21.83% between 2019 and 2023, whereas rangelands and barren land increased by 36.24% and 28.03%, respectively. Across 27 sub-basins, barren land expansion was associated with higher simulated changes in surface runoff (86 mm yr⁻¹), agricultural expansion with reductions in simulated baseflow (up to 4.7 mm yr⁻¹), and agricultural and grassland changes with changes in simulated sediment yield (- 1.89 to + 0.19 t ha⁻¹ yr⁻¹). These findings are hypothesis-generating rather than predictive because the basin is ungauged and climate forcing relied on monthly climatology through the SWAT weather generator.