Analysis of the characteristics of torrential rain and short-duration heavy rainfall in Yanjin County, Yunnan Province

Located at the border of Yunnan and Sichuan Provinces, Yanjin County is highly prone to rainstorm-induced floods, which often trigger secondary disasters such as mudslides and landslides. This study systematically analyzed the spatiotemporal distribution characteristics of torrential rain and short-duration heavy rainfall in Yanjin County, compared them with the high-incidence periods of flood disasters, and derived the rainfall intensity formula, employing methods such as trend analysis, hierarchical statistics, and extreme value estimation. The analysis was based on flood disaster records from 2013 to 2022, annual precipitation, and torrential rain frequency data from the Yanjin National Meteorological Station (1993—2022), hourly precipitation data from 29 regional stations (2020—2022), and annual maximum precipitation values across 11 durations from the station’s minute-level records at the Yanjin National Meteorological Station (1981—2022). The results are as follows. (1) The monthly variations in torrential rain and short-duration heavy rainfall are consistent with those of flood disaster frequency. (2) Over the past 30 years, Yanjin’s average annual precipitation has been similar to Yunnan’s long-term average with no significant trend. The torrential rain processes predominantly occur in summer and early autumn, occasionally occur in spring, and are never observed in winter. (3) Short-duration heavy rainfall events are most frequent from April to September, with a pronounced nocturnal peak, dominated by 20—30 mm·h⁻¹ events (67.5% of cases), while ≥50 mm·h⁻¹events are occasional; spatially, their distribution is uneven, with high-frequency stations scattered sporadically and lower overall frequency in central regions. (4) An extreme 1-hour precipitation of 82.3 mm for a 100-year return period is estimated from the derived rainstorm intensity formula, offering a critical reference for urban stormwater drainage design.