Effect of spring soil moisture over the Indo-China Peninsula on the following summer extreme precipitation events over the Yangtze River basin

Extreme precipitation events (EPEs) over the Yangtze River basin (YRB) exert widespread impacts on regional ecological environment and people's life. Using observed precipitation, atmospheric reanalysis, and land assimilation datasets, the present study explores the relationship between the summer EPEs over the YRB and the Meiyu front and their possible linkages with the preceding spring soil moisture anomalies over the Indo-China Peninsula (ICP). The analyses show that both the frequency and intensity of summer EPEs over the YRB are closely associated with the mean intensity of the Meiyu front, which exhibits a significant negative correlation with the soil moisture anomalies in the preceding spring over the ICP. An abnormally drier soil over the ICP in spring would evidently raise air temperature by suppressing local evapotranspiration, and vice versa. Owing to a strong memory of the ICP soil moisture, the persistent anomalous heating would elevate local geopotential height in summer, inducing an excessive westward extension of the Western Pacific subtropical high. Accordingly, a strengthened southwesterly wind at the lower troposphere brings abundant warm-wet air to the YRB, intensifying the mean Meiyu front. This is also verified by the diagnosis of vertical motion (omega) equation. As a result, the risk of summer EPEs (both the frequency and intensity) over the YRB would increase (decrease) with an abnormally drier (wetter) ICP soil during the preceding spring. For the summer EPEs over the YRB, our results suggest that the spring ICP soil moisture can be used as an important seasonal predictor.