Observed and d4PDF-Simulated Impacts of Different El Niño Transition Types on Summer Precipitation and Tropical Cyclone-Associated Precipitation Around Japan

Abstract El Niño–Southern Oscillation (ENSO) significantly influences East Asian summer precipitation, and its impacts vary with transition types from winter to the following summer. However, most previous studies have focused on mean precipitation, and effects on extreme precipitation and their linkage to tropical cyclones (TCs) remain unclear. Here we investigate how El Niño transition types modulate summer mean precipitation (Pav) and summer maximum daily precipitation (Rx1d) around Japan, focusing on TC roles, using JRA-3Q reanalysis and 60-km global large-ensemble simulations from d4PDF. JRA-3Q reanalysis shows that Pav generally exhibits positive anomalies across all transition types, but separating TC- and non-TC-associated components reveals clear transition-type dependence: TC-associated precipitation increases during developing summers and decreases during post-El Niño summers, consistent with TC frequency changes. In contrast, Rx1d is strongly controlled by TC activity, indicating that extreme precipitation is predominantly controlled by TC-related processes. d4PDF simulations reproduce these observed features. The main results are robust even when September is included. Under future climate conditions, transition-type-dependent anomalies relative to future climatology remain comparable to those in the present climate. Relative to present climatology, however, both Pav and Rx1d increase overall, mainly due to enhanced non-TC-associated precipitation.