High-Resolution Simulation of Future Runoff Variability and Extremes Across China

As the third-largest country in the world by land area, with highly diverse climatic regions and major river basins, China serves as a critical case study for examining large-scale hydrology under climate change. However, few studies have comprehensively investigated future runoff variability and extreme events across the entire region at high spatial resolution. This study analyses future runoff changes across China at 0.25-degree resolution under medium (SSP245) and high (SSP585) emission scenarios, using the Joint UK Land Environment Simulator (JULES), which has been calibrated and validated for simulating hydrological processes in China. The Global Climate Models (GCMs) are downscaled and bias-corrected using the bias-correction and spatial disaggregation (BCSD) method to drive the model. The results highlight significant regional imbalances in annual runoff, with an increase of 41.45 mm/decade in the Southeast basin under SSP585, compared to 7.30 mm/decade at the national scale. Seasonal patterns reveal contrasting trends, including wetter summers and drier winters in the south, while the northwest is expected to experience the opposite pattern. Projected changes indicate a rise in extreme high runoff in over 56% of regions, particularly in the south, and increased extreme low runoff in over 40% of China, notably in the central Yangtze River basin. Both extreme high and low runoff are projected to intensify in the far future, with SSP585 indicating more severe impacts. This study identifies spatial disparities and trends critical for sustainable water resource management and targeted adaptation strategies in response to climate change.