Assessment of Water Availability in Kalu Ganga Catchment under Climate Change Effects

Kalu Ganga, a major right-bank tributary of Amban Ganga, is one of the perennial rivers of Sri Lanka. Kalu Ganga Dam is a large gravity dam and a vital component of the complex Moragahakanda-Kalu Ganga Project built at Pallegama in the Matale District over the Kalu Ganga. A study was carried out to investigate and evaluate the present and future water availability of the Kalu Ganga reservoir. The present water availability is calculated using historical weather data, and the future water availability is estimated using predicted data extracted from downscaled climate change models. The study employed two Representative Concentration Pathway (RCP) scenarios, RCP 4.5 and RCP 8.5, of six climate models. Before being used, the climate change-predicted rainfall and temperature data were bias-corrected. Subsequently, the water availability was calculated using the rainfall-runoff model, Soil Water Assessment Tool (SWAT). The SWAT model was calibrated and validated using observed flow series at Laggala stream gauge on the Kalu Ganga. Using the same calibration settings, the SWAT model was then used to evaluate the potential impacts of climate change on streamflow in future scenarios. The SWAT, HEC-ResSim models and the climate change forecasted data have been shown to be useful tools for identifying climate change-driven water availability challenges, which can help with strategic water resources planning.