Investigating Climate Change Impacts on the 2020 extreme Meiyu Through Global Variable-Resolution Ensemble Subseasonal Hindcasts

This study investigates the impact of climate change on the extreme 2020 Meiyu over the middle and lower reaches of the 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 17.19% 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. Comparison between frequently re-initialized and subseasonal simulations further demonstrates that subseasonal simulations, by allowing full development of interactions between regional systems and large-scale circulation, more realistically represent climate change impacts on Meiyu season. In contrast, the frequently updated initial conditions in re-initialized simulations constrain such feedback processes. This study highlights the importance of utilizing global variable-resolution simulations at subseasonal-scale for climate attribution studies. Future studies would benefit from improved subseasonal forecasting capabilities to enhance attribution reliability.