Localized revision and application of assessing indices for regional heavy rainfall events in Hubei Province

Based on the operational provisions of important regional weather event monitoring and evaluation issued by CMA in 2019, in terms of the monitoring and evaluation method for regional heavy rainfall event within, also for being easy to compare the different regional heavy rainfall events, we have conducted a localized revision to the relative indices, and applied the corrected assessing indices to the assessment of regional heavy rainfall events in Hubei province. Firstly, using daily precipitation data at 81 national weather stations in Hubei from 1961 to 2018, the regional heavy rainfall day and the regional heavy rainfall event in Hubei were defined. Secondly, average heavy rainfall intensity, average covering area and duration of a regional heavy rainfall event were selected as the assessing factors by which the synthesizing assessing index is established for the regional heavy rainfall events in Hubei, and then the synthesizing intensity grades were divided by percentile method to simulate the intensity recurrence interval of regional heavy rainfall process by the normal distribution function. Thirdly, the frequency and intensity and the climatic change characteristics of regional heavy rainfall events were analyzed in the recent 50 years in Hubei. The validity of assessment was verified by the loss data of main regional heavy rainfall events. The results show that the 723 regional heavy rainfall events occurred in the recent 50 years in Hubei, and there are from 9 times to 23 times a year, with their annual change tendency being not significant, according to the localized criterion of monitoring index. But after the mid-1990s, the events lasting 1 or 2 days have an increasing trend, while those lasting more than 3 days have a decreasing trend. After 21st century, the extra strong and strong regional heavy rainfall events in Hubei tend to decrease, and the events being ordinary and weak tend to increase. The top 10 events in Hubei happened mainly in 20th century. The monitoring and evaluation indices to provincial regional heavy rainfall events issued by CMA in 2019 can be used in the monitoring and assessing such events in Hubei after the localized revising.