Spatiotemporal Variation of Water Availability under Changing Climate: Case Study of the Upper Girna Basin, India

The present study quantifies the variation in water balance components of the semiarid Upper Girna basin (UGB), Maharashtra, India, and the flow quantiles of a dam downstream of the UGB under changing climate using the semidistributed hydrologic model Soil and Water Assessment Tool (SWAT). The SWAT model was developed using digitized actual ground-surveyed data (1971-1979) spanning 4,730 km2; it was calibrated (1991-1998) and validated (2006-2010) using hydrometeorological data. The water balance components of UGB as simulated by the calibrated SWAT model for the historical observed period (1981-2010) have water yield and evapotranspiration contributions of 17% and 56%, respectively, out of the total 100% precipitation input to the system. All the water balance components as simulated by SWAT for all future climate scenarios [for two representative concentration pathways (RCPs) 4.5 and 8.5 W/m2 under three time slices 2011-2040, 2041-2070, 2071-2100] represented by CMIP5 general circulation models (GCMs) are lower than those historically observed. Additionally, based on the yearlong and monsoon month flow duration curves, a significant change is observed in simulated streamflow between the historical climate and future climate scenarios. The variation in the magnitudes of all the flow indexes between the CMIP5 GCMs for the early and midcentury time slices is less than the variation for the late century time slice, as demonstrated from dispersed flow duration curves. The present case study is the first of its kind to carry out climate change impact analysis for the UGB; according to the spatiotemporal maps of precipitation and other water balance components, Subbasins 2 and 5 in the UGB are plausible for severe depletion of water resources. The present work provides significant insights for resource managers and policy makers for efficient water resources planning and management in the UGB. (c) 2020 American Society of Civil Engineers.