Analysis of future climate variability under CMIP6 scenarios based on a downscaling method considering wet days in the upper Yangtze River basin, China

Abstract According to recent studies, the past decade was the hottest on record, and climate change is accelerating. As part of the Yangtze River Basin, the largest river basin in China, the Upper Yangtze River Basin (UYRB) plays a crucial role as the primary source of hydropower. However, the UYRB is also one of the most climate-sensitive regions within the basin, making the impact of climate change on this area particularly critical. We downscaled CMIP6 GCMs’ outputs of precipitation (including wet/dry spells sequence correction), and temperature projections (2024–2100), under four typical Shared Socioeconomic Pathways (SSPs), and we pursued a trend analysis upon these potential future climate series. We found significant upward trends in temperature across all SSPs in August, but no significant trends in precipitation for the same month. Additionally, for SSP370 and SSP585, there are significant upward trends in temperature in December, while precipitation showed no significant trends during that month. This may result in drier winters than now, increased potential evapotranspiration, and reduced surface (snow) water storage, impacting water resources availability. Consecutive dry/wet days at station, and basin scale show spatial-temporal heterogeneity, but generally wet spells are longer, and dry spells shorten moving from South-East to North-West.