Investigating Climate Change Impacts on the 2020 Extreme Meiyu Through Global Variable‐Resolution Ensemble Subseasonal Hindcasts

Abstract This study investigates the impact of climate change on the extreme 2020 Meiyu over the middle and lower reaches of the Yangtze River (middle‐lower Yangtze River (MLYR)) through global variable‐resolution ensemble subseasonal hindcasts. Results reveal that post‐1980 climate change enhanced the 2020 extreme Meiyu rainfall over the MLYR region by approximately 14.67% at monthly scale, while simultaneously decreasing light and moderate precipitation frequency but intensifying heavy and extreme precipitation occurrences. Climate change intensified the low‐pressure over northern China and southern China while weakening the Western Pacific subtropical high and the low‐pressure over the Indian Peninsula. The circulation pattern results in significant shear between northeasterly and northwesterly winds in the southern MLYR region, contrasting with the high‐pressure dominance in the northern MLYR region. This configuration suppressed convergence, vertical motion, and precipitation in the northern MLYR while enhancing these processes along its southern. Compared with frequently re‐initialized simulations, subseasonal hindcasts better preserve the continuous evolution of the Meiyu system and the consistency between precipitation and circulation responses, making them a more suitable framework for attribution of 2020 persistent rainfall Meiyu season. Overall, this study highlights the value of global variable‐resolution subseasonal simulations for attributing changes in Meiyu precipitation and its associated large‐scale circulation background under climate change. Future studies would benefit from improved subseasonal forecasting capabilities to enhance attribution reliability.