Dominance of terrestrial moisture supply for the record-breaking extreme precipitation in Hubei, China on August 12, 2021

A record-breaking heavy rainfall swept across Suizhou of Hubei province in China on August 12, 2021. It was characterized by suddenness and extremeness and caused severe socio-economic losses. To deepen the understanding of such an urban rainstorm and to improve the forecasting ability, this study revealed the dominant atmospheric circulation and moisture sources for this event. We performed a Lagrangian model FLEXPART to understand this event in terms of moisture sources and transport trajectories. Three key circulation systems affecting this extreme event were identified, including the western Pacific subtropical high (WPSH), the low-level southwesterly jet and an anticyclone over northern China. The low-level jet was lifted along the northern dry and cold air mass to form a front, resulting in the heavy rain. The moisture sources located on land contributed about 64% of the moisture. The development of the low-level southwesterly jet in southern China was strengthened near the time of the precipitation occurrence, providing the main moisture supply. Southern China (23°–32.5°N, 98°–122°E) was the most important source region, which contributed the most to the precipitation (43.6%). The results highlight the prominent role of the terrestrial water cycle in this extreme precipitation event over Hubei.