Assessment of current and projected runoff in the Sabarmati river basin using CMIP6 climate projections and hydrological modelling

Rapid change in the regional hydrological state of a river basin under current and future climatic scenarios affects the availability of freshwater resource threatening food and water security. It is imperative to understand the present and future streamflow projections at a river basin scale for effective water resource management. In the present study, we integrate the SWAT model and CMIP6 rainfall projections to simulate present (2001–2020) and future (2021–2049) runoff in the Sabarmati River Basin (SRB). SWAT model was calibrated and validated with in-situ discharge estimates using the SUFI2 algorithm. SWAT model performed well during the calibration period (2001–2012) with NSE 0.69 and R2 0.7 indicating that the data inputs for the model can simulate the streamflow accurately. To evaluate the CMIP6 model projections, we derived historical rainfall (2001–2014) estimates from 6 CMIP6 models. It was observed that five out of the six models underestimated monthly rainfall for the Indian Summer Monsoon. Future runoff projections indicated highest runoff during October and January attributed to model uncertainty and anthropogenic influences. Changes in streamflow indicate that water management policies need to incorporate future climate scenarios and stringent research on model output dataset for simulation of future streamflow.