Characteristics of Winter–Spring Drought in Yunnan, China and Their Connection to Extratropical South Pacific Sea Surface Temperature Anomalies

Abstract

ABSTRACT Drought events are increasingly frequent and severe in Yunnan, affecting the livelihoods and economies of millions of people across the province. To mitigate the associated impacts, understanding the characteristics of drought and discussing its possible causes has become a crucial research focus. This study, therefore, analyzes the drought characteristics and the underlying influence of extratropical sea surface temperature (SST) over the South Pacific Ocean (SPO) from 1961 to 2022 during the winter–spring period. Findings indicate an increase in drought incidents after the 21st century, with a significant rise in the central‐eastern parts of the study region. A large portion of the Yunnan Province is affected by distinct drought categories, except for extreme drought, which frequently affects the border areas of the province. The drought characteristics suggest that most areas of Yunnan experienced frequent mild to moderate droughts, with a frequency reaching at least 60% and longer durations exceeding 3.5 months. Extreme drought features the highest intensity, whereas moderate drought comes with strong severity in most parts of the province. It is further found that the Yunnan drought is significantly and positively related to an SPO Dipole (SPOD) SST anomaly, independent of the El Niño‐Southern Oscillation effect. The positive phase of the SPOD, with anomalous warm SST off eastern New Zealand and cold SST centered around 65° S, 100° W in high latitudes, induces an upper‐level anticyclonic anomaly at middle latitudes. The eastern flank of this anomalous anticyclone triggers southeasterly winds that traverse from the mid‐latitudes of the South Pacific to Yunnan Province. This anomalous circulation favours the formation and development of an anomalous anticyclone associated with descending and divergent moist conditions at the low level over the province, which is conducive to precipitation deficits and drought conditions. The findings from this study add a valuable contribution to winter–spring drought prevention and mitigation measures in Yunnan.