Warm-sector heavy rainfall over the eastern China plains: identification, characteristics, and precursor dynamic signals

Abstract

Warm-sector heavy rainfall (WSHR) poses forecasting challenges, while its contribution to regional heavy rainfall and short-term precursors remain poorly quantified. Drawing on 2021–2025 warm-season (June–September) observations from 493 surface rain gauges, ERA5 reanalysis, and a radar wind profiler (RWP) mesonet across the eastern China plains, we build an objective identification framework integrating automated front detection, warm-sector mask, and station-specific 99th-percentile hourly rainfall thresholds to separate WSHR from other heavy rain events. We detect 477 station-based WSHR events alongside 6002 other heavy rainfall events. WSHR is spatially scattered, peaks in July–August, and preferentially begins at 20:00–03:00 Beijing Time (BJT). Accounting for merely 5 %–10 % of annual heavy rainfall occurrences, WSHR has shorter durations yet comparable median rainfall accumulations and heavier extreme rainfall tails. Among the 297 stations recording at least one WSHR event, the mean station-level contribution of WSHR to heavy-rainfall accumulation is 13.8 %, with a maximum of 48.1 %. Composite ERA5 fields show that WSHR initiates within an 850 hPa moist tongue of high pseudo-equivalent potential temperature south of the front, superimposed on strengthening low-level moisture flux convergence. RWP composites of 62 WSHR events show increasing low-level jet (LLJ) occurrence and enhanced low-level ascent shortly before rainfall onset. Comparison with 271 warm-sector non-heavy rainfall events indicates a more pronounced late increase in LLJ occurrence and a stronger upper tail of ascent speeds at 1–2 km in WSHR, although the distributions overlap substantially. These observations identify candidate kinematic indicators whose event-level predictive skill remains to be evaluated.