Comparative Analysis of Precipitation Extremes in Two Major Rainstorm Events at the Edge of the Subtropical High

This study conducts a systematic comparative analysis of two extreme heavy rainfall events in Gansu Province, occurring in July 2022 (‘7·15’) and July 2024 (‘7·22’), using multi-source observational data and reanalysis datasets combined with various diagnostic methods.The key findings are as follows: (1) The two events differed in 24-h cumulative precipitation, hourly rainfall intensity, and frequency of short-duration heavy rainfall.The ‘7·15’ event had greater cumulative rainfall and stronger instantaneous intensity, but its spatial extent of extreme rainfall (≥50 mm) and frequency of short-duration heavy precipitation were significantly lower than those of ‘7·22’.(2) Both events exhibited extreme characteristics.The ‘7·15’ event broke historical records for short-duration rainfall intensity at more stations than ‘7·22’, whereas the latter showed higher cumulative precipitation totals and more frequent short-duration heavy rainfall events.(3) Significant differences existed in short-duration precipitation metrics.The ‘7·15’ event had substantially higher proportions of moderate and heavy rainfall (44.55% and 10.68%, respectively), with maximum 5-min and 1-h sliding precipitation reaching 30.9 mm and 93.6 mm.In contrast, ‘7·22’ was dominated by light rainfall (60.70%), with only 8.68% heavy precipitation events and maximum 5-min/1-h accumulations of 15.3 mm and 83.6 mm.The ‘7·15’ event demonstrated more extreme precipitation characteristics and greater disaster potential.(4) The two events exhibited both similarities and differences in their dominant weather systems, moisture convergence, and thermodynamic/dynamic lifting conditions.Both were warm-sector convective heavy precipitation events triggered by the coupling of upper- and lower-level systems including the subtropical high, mid-to-low-level vortex shear, and surface convergence lines.While the ‘7·15’ event showed significantly weaker values than‘7·22’ in moisture convergence intensity, vertical convergence depth, moist layer thickness, frontogenesis, vertical updraft intensity, and CAPE, it demonstrated greater precipitable water throughout the atmospheric column at the rainfall core, stronger convective instability during intense precipitation, and higher vertical ascent heights during peak rainfall periods.