Impact of the Zonal Position of La Niña on Summer Precipitation over China

Based on the monthly Extended Reconstructed Sea Surface Temperature dataset (ERSST.v5) provided by the National Oceanic and Atmospheric Administration (NOAA), this study investigates how the zonal position of La Niña affects summer precipitation over eastern China during its developing phase from 1950 to 2023, along with the underlying physical mechanisms. The results show that when the La Niña cold center shifts eastward, a meridional dipole precipitation anomaly pattern tends to emerge over southern China, featuring increased rainfall over the Yangtze River Basin and decreased rainfall over South China. In contrast, no significant precipitation anomalies are observed in eastern China when La Niña shifts westward. Further analysis reveals that eastward-shifted La Niña events are often accompanied by positive sea surface temperature anomalies (SSTAs) in the equatorial western Pacific, which strengthen the zonal SSTA gradient and enhance equatorial easterly wind anomalies. These changes favor the development of an anomalous anticyclonic circulation near the Maritime Continent, transporting more moisture toward the Yangtze River Basin and suppressing convection over South China through its subsiding branch. Conversely, westward-shifted La Niña events feature a weaker zonal SSTA gradient and insignificant atmospheric circulation responses, thus exerting little influence on precipitation in eastern China. This study highlights the crucial role of La Niña’s zonal position in shaping summer rainfall patterns over China and provides new physical insights into the ENSO–precipitation relationship, with important implications for improving flood-season precipitation prediction.