Persistent Meteorological Drought in the Yangtze River Basin during Summer-Autumn 2022: Relay Effects of Different Atmospheric Internal Variabilities

During the summer-autumn (July-October, Jul-Oct) period of 2022, the Yangtze River Basin (YRB) of China experienced an extreme meteorological drought, with Jul-Oct containing the lowest precipitation in the YRB since 1979. The possible causes of this drought were analyzed in the present study. Surprisingly, unlike many previous drought events, we found that this event was not characterized by a consistent atmospheric circulation anomaly regime throughout the entire drought period. Instead, two distinct circulation patterns were responsible for the precipitation deficit in two different stages, i.e., July-August (Jul-Aug) and September-October (Sep-Oct). In Jul-Aug, the YRB precipitation deficit primarily resulted from an intensified and northward-shifted East Asian subtropical jet, which allowed for an extremely northwestward shift of western Pacific subtropical highs, leading to an anomalous descending motion. Such circulation patterns in Jul-Aug originated from the dispersion of Rossby waves upstream from central Asia and Europe. Meanwhile, in Sep-Oct, the YRB drought was primarily attributed to a low-level cyclonic anomaly over the western North Pacific, which was closely associated with frequent tropical cyclones traveling across this region. Observational analysis and a model ensemble hindcast suggest that atmospheric internal variabilities dominated the drought process, while the SSTA, particularly the La Nina event, played a limited role. Therefore, this long-lasting extreme YRB meteorological drought was largely driven by the relay effects of different atmospheric internal variabilities in Jul-Aug and Sep-Oct, respectively, which shows limited model predictability and poses a great challenge for operational climate predictions.