Assessment of water availability and demand in Huruluwewa Catchment, Sri Lanka: case study focusing on trans-basin water management

Abstract

Many river basins are increasingly vulnerable to extremely high or low flows due to climate change. Transbasin water transfers offer a sustainable solution, mitigating uneven water distribution by redirecting surplus water to deficit areas. This study focused on the impact of climate change on water resources and the applicability of trans-basin water transfer in Sri Lanka's dry zone. Future precipitation and temperature data were generated using the CNRM-CM6-1-HR model, downscaled with LARS-WG software. Projected inflow to the Huruluwewa reservoir was simulated using HEC-HMS software. The study shows that trans-basin water transfer reduced the water deficit from 20.7 MCM to 4.2 MCM during the 2018-2019 water year. Findings indicate an expected increase in annual rainfall by 6.4% and 5.5% during the 2030-2049 period under SSP1-2.6 and SSP5-8.5 scenarios, respectively. Both monsoonal rainfall patterns show an upward trend under these scenarios. However, projections indicate a decreasing trend in monthly average rainfall during the dry season, suggesting even drier future conditions. Rising temperatures will lead to higher evapotranspiration rates, resulting in a projected 27% decrease in annual inflow to the reservoir. Consequently, the required annual trans-basin water transfer is projected to increase to 24.7 MCM and 29.4 MCM under SSP1-2.6 and SSP5-8.5, respectively.