Temporal and Spatial Distribution Characteristics of Short-Duration Heavy Rainfall in Ganzi Prefecture of Eastern Slope of Tibetan Plateau

Abstract

 Short term heavy rainfall is often caused by small and medium-sized systems, and its occurrence and development are very rapid, with strong locality, drastic changes, and complex causes. Monitoring, forecasting, and early warning of it have always been a hot and difficult point in meteorological forecasting services. Using hourly precipitation observation data from 18 benchmark (basic) meteorological stations and 489 regional meteorological stations in Ganzi Prefecture from April to October 2012 to 2021, the spatial and temporal distribution characteristics of short-term heavy precipitation in Ganzi Prefecture on the western Sichuan Plateau were statistically analyzed. The results showed that: 1) The total frequency of short-duration heavy rainfall during the flood season in Ganzi Prefecture from 2012 to 2021 was 1906 times, with an average of 190.6 times per year, and the frequency decreased exponentially with increasing magnitude, with 15-25mm/h short-term heavy precipitation accounting for more than 84%. 2) The diurnal variation of short-duration heavy rainfall showed a bimodal pattern, with the peak occurring from 20:00 to 22:00 Beijing time, and the highest peak at 22:00, followed by 20:00. Short-duration heavy rainfall is more likely to occur from the afternoon to the first half of the night. The monthly variation showed a unimodal pattern, with the most occurrences in July (30.16%), followed by June and August. The interannual variation was uneven, with an average total frequency of 190 occurrences per year. The frequency of short-duration heavy rainfall in 2012 was the lowest, with only 38 occurrences, while in 2020, it was the highest, with 336 occurrences. 3) The frequency of short-duration heavy rainfall was higher in the southern and eastern regions compared to the northern and western regions, indicating an uneven spatial distribution.The highest frequency occurred in the southern part of Luding County, followed by the southern part of Jiulong County, which are the high-incidence areas of short-duration heavy rainfall in the entire prefecture. Short-duration heavy rainfall mainly occurred at an altitude of 1100-3900m, with the most occurrences at an altitude of 1100-1900m, and the maximum peak rainfall intensity of 63.3mm/h occurred in the altitude range of 1100-1300m. Short-duration heavy rainfall in Ganzi Prefecture is closely related to altitude, which is the result of the interaction between complex terrain and regional circulation.