Was the Extremely Wet Spring of 2022 in Southwest China Driven by La Niña?

Abstract

Abstract In the spring of 2022, an excessive amount of rainfall fell in Southwest China (SWC) under the background of frequent droughts in history. This extreme event occurred in the decaying phase of a second-year of a double/triple dip La Nina event, and thus, presumably La Niña played a role in this extreme event. In this work, based on observational diagnoses and model forecasts, we examine the atmospheric circulation anomalies, contributions of external forcing, and the predictability of this event. It is suggested that La Niña and the upper-tropospheric warming over the Tibetan Plateau are two major factors leading to the extreme event. In addition to the recognized impact of La Niña, the upper-tropospheric warming over the Tibetan Plateau modulates the Asian atmospheric circulation by inducing a northwest-southeast wave pattern extending from the Ural Mountains to the Indochina Peninsula via the western Tibetan Plateau. The meridional heat contrast with the upper tropospheric warming over the Tibetan Plateau favors upward motion and excessive rainfall in SWC. The connection between the SWC spring rainfall anomaly and the northwest-southeast wave pattern is confirmed by a climate model forecast. The model captured the wet pattern in SWC in spring 2022 in short (1–3 months) lead real-time predictions though there are biases in the area and severity probably due to that the model did not well capture the atmospheric circulation anomalies at the middle and high latitudes associated with the upper-tropospheric warming over the Tibetan Plateau. These results indicate that such an event is predictable to some extent if both the ENSO evolution and heat condition over the Tibetan Plateau can be well captured.