Assessing the hydrological response of the Vamanapuram river basin to climate change and land use alterations using SWAT model: A case of tropical mountainous Western Ghats River, Southern India

The hydrological components are highly sensitive to both climate change and land use/land cover (LULC) changes. The Vamanapuram River Basin (VRB) is one of the tropical, west-flowing Western Ghats River in Southern India which is facing extreme climate events and rapid socio-economic transformation. This study evaluates the hydrological components of the VRB by examining both individual and combined effects of climate and LULC changes using the Soil and Water Assessment Tool (SWAT) model. The model showed strong agreement between simulated and observed streamflow, achieving Nash-Sutcliffe Efficiency (NSE) and coefficient of determination (R²) values exceeding 0.7 during both calibration (1993–2007) and validation (2008–2014) periods. Further, climate change impacts have been assessed using the projected climate data of 9 different General Circulation Models (GCM) from 2015 to 2100 years under two different emission scenarios, SSP 2-4.5 and SSP 5-8.5. The coarse GCM climate data has been regridded to 0.5 o and bias-corrected in the CMHyd using the linear scaling method to improve accuracy. In order to study the LULC change impacts, three hypothetical LULC change scenarios involving increasing the built-up areas by 10%, 20%, and 28% has been used. The results are as follows; (1) under climate change only scenario, the SSP 2-4.5 ensemble average of all the 9 GCM models indicate that evapotranspiration (ET) and water yield (WYLD) are projected to increase slightly by 7% and 21% while the SSP 5-8.5 are projected to increase significantly by 14% and 49%, (2) while the LULC detects 5–18% increase in surface runoff and 5–17% decrease in percolation, there were no significant changes detected in ET, and WYLD. The combined scenario of climate and LULC changes analysis revealed that (3) climate change has a more pronounced impact on the hydrological response than LULC changes with results similar to climate change scenarios. The study emphasises the need for enhanced hydrometeorological observations, improved predictive modelling, and early warning systems to ensure effective water resource management and planning.