Investigating future low-flow variations under changing climate conditions in Padiyathalawa river basin

Abstract

Climate change exerts profound changes to the low-flow regime in river basins worldwide, with potentially dire consequences expected in regions already vulnerable to water stress, such as dry zone areas. This study aims to assess the changing climate condition’s impact on future low-flow variations in the Maduru Oya river basin in Sri Lanka. The section extending up to the Padiyathalawa stream-gauge station was simulated using a lumped model approach, employing the HEC-HMS rainfall-runoff model. The future precipitation was projected under two Shared Socioeconomic Pathways (SSP2-4.5 and SSP5-8.5) for the CNRM-CM6-1 Global Climate Model (GCM) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) and downscaled using the LARS-WG 8.0. To forecast future river flows, the HEC-HMS model was employed with downscaled rainfall time series. To evaluate future low-flow, 7Q10 and flow-duration indices were used. Model results show that the annual total precipitation would change by -16% to 21% in three future periods between 2021-2080 compared to the baseline (1997-2019) average. Despite negative changes in annual total rainfall, low-flow may increase during future periods. The results are anticipated to aid in proactive water resource planning by predicting possible changes in low-flow within the Maduru Oya river basin.