Simulation of Streamflow in the Upper Bernam River Basin in Malaysia Using SWAT Model and CMIP6 Projection Scenarios

Abstract

Water resource management, irrigated agriculture, and flood mitigation in Malaysia have emphasized the significance of the Upper Bernam River Basin (UBRB). Anticipation of future streamflow patterns of the UBRB is essential for sustainable irrigation management, particularly under climate change conditions for the Integrated Agricultural Development Area (IADA), Selangor. The Soil and Water Assessment Tool (SWAT) coupled with Coupled Model Intercomparison Project phase 6 (CMIP6) climate scenarios under SSP126, SSP245, SSP370, and SSP585 is used in this study to evaluate streamflow responses. The results of this study revealed that the streamflow in the UBRB is projected to decline during the off season (January–June) across all SSP scenarios, with a mean decrease of 15.9% under SSP585, 12.8% under SSP126, and 9.7% under SSP370 by the 2020s due to higher temperature and evapotranspiration. The annual streamflow change during the off season is also expected to decline by 0.7% to 13.4% (2020s–2040s) but increase by 1–37.1% during the main season (2050s–2080s), except for SSP126 (10.7–1.4%). The highest increase of the streamflow (37.1%) is expected to occur under SSP370 in the 2080s. However, the streamflow decreases in January–June and increases in August–December, with a transition in July. In general, the streamflow of UBRB will increase chronologically under most SSPs, with SSP370 exceeding SSP585, highlighting the need for adaptive water management to address future irrigation and hydrologic challenges.