New study reveals precursors for forecasting summer clustered extreme precipitation events in Northeast China

Against the background of accelerated global warming, the atmospheric moisture content has increased significantly and the hydrological cycle has intensified, leading to pronounced rises in both the frequency and intensity of extreme precipitation events globally. Northeast China, a region highly sensitive to climate change, has experienced increasing occurrence of clustered extreme heavy precipitation events in recent years. Improved knowledge of synoptic regimes and moisture accumulation responsible for clustered extreme heavy precipitation events (CEPEs) is essential for enhancing short-term forecasting skill and disaster prevention and mitigation.

Researchers from Nanjing University of Information Science and Technology, China, have revealed the antecedent evolutions of synoptic regimes and the net moisture budget from the pre-event phase to the occurrence days of CEPEs over Northeast China. The results have recently been published in Atmospheric and Oceanic Science Letters.

According to this study, four synoptic patterns contribute to summer CEPEs over Northeast China: eastward-moving low-altitude vortex (Pattern 1); southwesterlies (Pattern 2); a locally intense low-altitude vortex (Pattern 3); and northward-moving tropical cyclones (Pattern 4). The former two patterns are primarily driven by northward extension of the western North Pacific subtropical high (WNPSH) and northeastward extension of the South Asian high (SAH) from 24 hours before CEPEs. Pattern 3 is predominantly influenced by westward WNPSH extension and eastward SAH extension 24 hours prior to CEPEs. Pattern 4 is promoted by eastward WNPSH retreat and westward SAH extension.

In addition, the net meridional influx increases considerably 24 hours before CEPEs under all synoptic patterns, peaking six hours earlier under Patterns 1 and 2, and twelve hours earlier under Patterns 3 and 4, respectively.

"For short-term forecasting of clustered extreme heavy precipitation events, it is necessary to comprehensively understand the coordinated configurations of multilevel weather systems, as well as the cumulative effects of moisture budgets across different vertical levels and transport pathways", explains Dr. Tingting Han, a climatologist from Nanjing University of Information Science and Technology, the first author of the paper. "This study provides a robust assessment of prerequisite conditions for the occurrence of clustered extreme heavy precipitation events."