Contribution of the Tibetan Plateau Snow Cover to the Record-breaking Rainfall Over the Yangtze River Valley in June 2020

Abstract

ABSTRACT In June 2020, the Yangtze River Valley (YRV) experienced the most severe and long-persisting rainfall in past decades, causing hundreds of people’s death and huge property loss. Based on the high-resolution MODIS/Terra snow cover data for the 2000–2021 period and the linear baroclinic model (LBM), this study investigates the dynamic influence and the potentially predictable source from the Tibetan Plateau (TP) snow cover (TPSC) on this record-breaking YRV rainfall. The TPSC anomalies in the critical area (76°−83°E, 28°−35°N) can persist for more than six months and induce a Rossby wave train propagating northeastward. For the excessive TPSC, barotropic negative geopotential height anomalies prevail over northern East Asia and positive geopotential height anomalies over the northwestern Pacific. Such a circulation configuration favours a deepened cold vortex over Northeast China and the westward-developing western Pacific subtropical high, which leads to an intensified Meiyu-Baiu-Changma front and rich Meiyu rainfall. The LBM sensitive experiments can reproduce the above physical processes associated with the TPSC anomalies, realistically. Moreover, the quantitative contributions of the indices representing the TPSC and the three oceans (Pacific, Indian Ocean, and Atlantic) to the record-breaking Meiyu rainfall are examined, and the TPSC index explains most of the total variance of the rainfall anomaly among the indices, reaching 42.75%. This highlights the importance of the TP thermal forcing to the extreme climate conditions in June 2020.