Hydrological impacts of climate and land-use change in Western Ghats, India

The West Flowing River Basins from Tadri to Kanyakumari (WFRB-2), India, is a highly complex hydrological system witnessing hydrological extremes frequently. In this study, the impacts of climate/Land Use Land Cover (LULC) changes on hydrology in WFRB-2 are investigated on a 0.25° spatial scale for a historic (1979–2018) time period. Six major river basins are chosen in the upper, middle and lower regions of WFRB-2 and the variable infiltration capacity (VIC) model is calibrated using SCE-UA (Shuffle Complex Evolution) algorithm. The linear trend analysis showed a significant increase in premonsoon/monsoon rainfall in the lower region and a 13% increase in the percentage of very wet years, while dry years completely disappeared in the recent past. Sensitivity analysis shows that annual mean surface runoff (SR) increases by 125 mm and evapotranspiration (ET) decreases by 562 mm when a fully forested grid was transformed into a fully built-up grid. Similarly, sensitivity towards rainfall alone is showing an increase of SR and ET by 54 mm (6%) and 64 mm (6%) respectively. Overall impact results in a reduction in the annual mean total runoff by 48 mm in the upper and 100 mm in the middle and a rise of 53 mm in the lower regions. This shows that in the lower region, with an increase in precipitation coupled with increasing urbanization, there is a possibility of greater magnitude flood peaks. This study is useful to understand the complex hydrological impacts due to climate/LULC changes for management decisions on a regional scale.