Climate Elasticity of Runoff in Kalu and Kelani River Basins in the Wet Zone of Sri Lanka

This study estimates the climate elasticity of runoff concerning precipitation and evaporation, in Kalu and Kelani river basins in the wet zone of Sri Lanka. The Ellagawa subbasin of Kalu river and Hanwella subbasin of Kelani river were selected for the assessment. The non-parametric estimator was selected based on the simplicity to assess the climate elasticity of runoff in the selected wet zone basins under current climate scenarios. The rainfall elasticity and evaporation elasticity were estimated for prevailing climate conditions. At the same time, the climate elasticity under synthetic climate change scenarios was assessed using a hydrological model. The HEC-HMS rainfall-runoff model was selected based on the accessibility, flexibility, reliability, and data requirements to simulate streamflow. According to the model results, climate change results in causing -41% to 31% change in runoff in the Kalu river basin and -49% to 23% change in runoff in the Kelani river basin under synthetic climate change scenarios that have been developed for the period of 2016-2035 considering the predicted precipitation and evaporation changes comparative to the baseline period of 1986-2005.