Hydroclimatic Impact Assessment Using the SWAT Model in India—State of the Art Review

The Soil and Water Assessment Tool (SWAT) has been widely employed to assist with decision making and management planning for assessing and mitigating the impact of climate change. This model has gained popularity in India as the country is facing increasing water issues under projected climate changes. However, a systematic review of the literature that discusses the applicability of the model, the impact assessment process, and the interpretation of the modeling results in India remains lacking. We synthesized and reviewed 110 recent SWAT modeling studies (published from 2012 to 2022) that evaluated the impact of future climate change on water resources in India to identify research gaps that need to be filled to advance SWAT modeling practices for impact assessments. The review revealed that the SWAT model provided acceptable accuracy statistics in most (90%) of the studies reviewed. Half of these studies identified the base curve number (CN2) as the parameter to which the water balance is the most sensitive; thus, this parameter was included in the calibration process. The accuracy of SWAT modeling is closely associated with the accuracy of the weather data fed to the model. However, extreme events, including heavy storm events and severe droughts, were rarely considered in climate change impact assessments using the SWAT model. Most studies downscaled global-scale climate modeling outputs to local weather stations when applying the SWAT model using various methods, such as the delta change method, multiple linear regression method, gamma–gamma transformation, fitted histogram equalization, and quantile mapping. Further, most studies investigated the performance of the SWAT model before applying the model to quantify the future hydrological consequences of projected climate change in a subsequent scenario analysis. This review suggests that further evaluations of the characteristics and development processes of existing climate data products are needed to effectively consider extreme events in impact assessments. In addition, this review finds that climate change impact modeling has been improved with advances in climate projection preparation, including ensemble averaging, bias correction, and downscaling methods. This regional review of current SWAT modeling practices for climate change impact assessments can be used to create reliable future hydrological projections in India