Decadal strengthening of the preceding-winter ENSO influence on subsequent pre-flood-season precipitation over southern China. Part II: Strengthened La Niña teleconnection due to slower decay and enhanced WES feedback

Abstract In Part I, we documented a marked mid-1990s strengthening of the ENSO influence on pre-flood-season (PFS; April–June) rainfall over southern China (SC) and identified the dominant mechanism for the strengthened El Niño teleconnection. Here we focus on La Niña and examine why its influence on SC PFS rainfall strengthens after the mid-1990s. Observations show that La Niña events during 1996–2021 (P2) exhibit a slower decay than those during 1959–1995 (P1), allowing cold sea surface temperature (SST) anomalies to persist into AMJ over the Niño4 region and more strongly suppressing central-Pacific convection. The resulting Matsuno–Gill response induces more pronounced low-level wind anomalies over the western North Pacific (WNP). Together with intensified wind–evaporation–SST (WES) coupling in P2, these wind anomalies more effectively modulate surface latent heat fluxes and amplify local SST and convection anomalies over the WNP, exciting a stronger cyclonic circulation spanning the South China Sea and WNP. The associated northeasterly anomalies enhance cold–dry advection over SC, favoring anomalous subsidence and reduced moisture supply and thereby intensifying SC rainfall deficits during La Niña decay years in P2. CMIP6 historical simulations provide complementary support: models with a stronger WES coupling show a stronger La Niña–SC PFS linkage. These results show that the strengthened La Niña teleconnection arises from the combined effects of slower La Niña decay and enhanced WES coupling, providing a phase-dependent counterpart to the El Niño mechanism identified in Part I and highlighting the importance of accurately representing ENSO evolution and WNP air–sea coupling in seasonal prediction of SC PFS rainfall.