Dominant atmospheric circulation patterns associated with the rapid intensification of summer flash droughts in Eastern China

Flash droughts (FDs), which are characterized by rapid intensification, occurred frequently over Eastern China, posing great challenges for drought forecasting and preparation on subseasonal timescale. However, the drivers of the rapid development of FDs are not well understood. By comparing with slow droughts (SDs), this study investigates the dominant physical processes responsible for FDs in four different regions over Eastern China through diagnosing moisture budgets and further linking them to large-scale atmospheric circulation patterns. Results reveal that the rapid intensification of FDs in the four regions are dominantly driven by stronger and more persistent subsidence than those for SDs, which suppress precipitation and heat the atmosphere, leading to rapid soil drying. Further analyses indicate that stronger and more stable atmospheric circulation systems are conductive to the rapid intensification of FDs. Specifically, in Northeast China, the persistent subsidence is strongly related to the maintenance of high over area south to Lake Baikal, which is associated with enhanced subtropical jet stream. In North China Plain, the upper-level cyclonic anomalies associated with the negative phase of the circumglobal teleconnection, together with more southward East Asia summer monsoon (EASM) rain belt, are responsible for the stronger sinking motions. In southern China, droughts can be attributed to simultaneous expansions of the South Asia high (SAH) and western Pacific subtropical high (WPSH). While the persistently joint control of the SAH and WPSH and larger area under the control of the two systems are crucial for FDs in Yangtze River basin and South China, respectively. The SDs are often related to the less organized circulation patterns and inconsistent shift of the EASM rain belt during the development phase. Our findings suggest potential source of predictability for summer FDs in Eastern China.