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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. Full article

Potential impacts of climate change on the streamflow of the Bernam River Basin in Malaysia are assessed using ten Global Climate Models (GCMs) under three Representative Concentration Pathways (RCP4.5, RCP6.0 and RCP8.5). A graphical user interface was developed that integrates all of the common procedures of assessing climate change impacts, to generate high resolution climate variables (e.g., rainfall, temperature, etc.) at the local scale from large-scale climate models. These are linked in one executable module to generate future climate sequences that can be used as inputs to various models, including hydrological and crop models. The generated outputs were used as inputs to the SWAT hydrological model to simulate the hydrological processes. The evaluation results indicated that the model performed well for the watershed with a monthly R², Nash–Sutcliffe Efficiency (NSE) and Percent Bias (PBIAS) values of 0.67, 0.62 and −9.4 and 0.62, 0.61 and −4.2 for the calibration and validation periods, respectively. The multi-model projections show an increase in future temperature (t_max and t_min) in all respective scenarios, up to an average of 2.5 °C for under the worst-case scenario (RC8.5). Rainfall is also predicted to change with clear variations between the dry and wet season. Streamflow projections also followed rainfall pattern to a great extent with a distinct change between the dry and wet season possibly due to the increase in evapotranspiration in the watershed. In principle, the interface can be customized for the application to other watersheds by incorporating GCMs’ baseline data and their corresponding future data for those particular stations in the new watershed. Methodological limitations of the study are also discussed. Full article