Projection of cold and wet compound events in the Yangtze River Basin based on NEX-GDDP-CMIP6 downscaling simulations

Abstract The Yangtze River Basin (YRB), as an important economic belt and ecological security barrier in China, is threatened by compound cold and wet events (CWCEs) that not only impact socioeconomic and ecological systems but also affect clean energy production and grid transmission and distribution, thereby constraining the scientific formulation of climate change response policies. This study utilizes high-resolution downscaling simulations from NEX-GDDP-CMIP6 (0.25° × 0.25°) to systematically assess the spatiotemporal distribution characteristics of winter CWCEs in the YRB during the historical analysis period (1961–2013) and projects future changes under four Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5). The results indicate that during the historical analysis period, high-frequency areas of CWCEs were mainly located in the southern part of the YRB, with local frequencies exceeding 1 event/year. The frequency of CWCEs in the YRB has shown an overall downward trend over the past 50 years, with the most pronounced decrease in the southern YRB, and parts of Sichuan province. NEX-GDDP-CMIP6 performs well in simulating the observed spatial distribution and variability of CWCEs but poorly in simulating the distribution of trends. In future periods, CWCE frequency decreases significantly under all scenarios, with the magnitude of decrease increasing along with CO2 emissions and the length of the projection period. Under the SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 scenarios, the changes in CWCE frequency in the YRB at the end of this century relative to the 1981–2010 reference period are − 0.21/year (-0.30/year to -0.16/year), -0.24/year (-0.28/year to -0.20/year), -0.25/year (-0.29/year to -0.23/year), and − 0.29/year (-0.31/year to -0.27/year), respectively.