Dominant Modes of Spring Drought Variability in Southern China During 1979–2022 and the Associated Drivers

Utilizing the Standardized Precipitation Evapotranspiration Index (SPEI) and ERA5 reanalysis data, this study investigates the variability of spring drought in southern China from 1979 to 2022 and its associated drivers. The results indicate that southern China experienced interdecadal changes in SPEI over the past several decades, which can be concluded that drought severity intensified from 1979 to 2010, whereas a transition shift towards increased wetness occurred from 2010 to 2022. The first Empirical Orthogonal Function (EOF1) mode of SPEI variability in southern China accounts for 44.37% of the total variance, reflecting a uniform variation of SPEI across the region. In contrast, the second Empirical Orthogonal Function (EOF2), which explains 24.41% of the total variance, reveals a west-east dipole pattern in SPEI variability. Further analysis indicates that the positive phase of EOF1 is primarily driven by warm sea surface temperature anomalies (SSTAs) in the tropical eastern Pacific. These anomalies induce an anomalous anticyclone over the Philippine Sea, enhancing water vapor transport to southern China during spring. The positive phase of EOF2 is jointly influenced by warm SSTAs in the tropical Indian Ocean and the central Pacific; the latter induces anticyclonic anomalies over the Philippine Sea, which enhance water vapor transport from the western Pacific and increase precipitation in the eastern part of southern China. However, the warm SSTAs in the tropical Indian Ocean trigger an anomalous anticyclone over South Asia, inhibiting water vapor transport from the Bay of Bengal to the western part of southern China and thus reducing precipitation there.