Strengthened Influence of Preceding Winter ENSO on the Following Early Autumn Precipitation in Southeast China since the Early 2000s

Autumn precipitation in Southeast China (SC) exhibits substantial interannual variability, yet it has received considerably less attention compared to boreal summer precipitation. This study identifies a significant interdecadal shift in the teleconnection between the El Niño-Southern Oscillation (ENSO) and the SC autumn climate. We find that the influence of preceding winter ENSO on the subsequent early autumn precipitation in SC was weak and statistically insignificant during the late 20th century, but has become robustly positive since the early 2000s. Our analysis reveals that in the post-2000s period, El Niño events tend to decay more rapidly and transition into a developing La Niña phase by the following summer. This accelerated decay, coupled with persistent cold sea surface temperature anomalies (SSTA) in the eastern Pacific, sustains the Western North Pacific Anticyclone (WNPAC) from summer into autumn. Moreover, due to the “seesaw pattern” in the developing La Niña phase, the warming central Indo-Pacific triggers a meridional contraction of the local Hadley circulation and contributes to the cyclonic circulation over SC. This circulation change induces anomalous subsidence over the South China Sea and significant ascending motion over inland SC. Consequently, a distinct anticyclone-cyclone dipole emerges after the early 2000s, which provides both the anomalous moisture transport and the dynamical lifting necessary for enhanced precipitation. These findings offer critical insights for improving seasonal forecasting and climate model evaluation for East Asian autumn hydroclimate.