Quantitative Assessment of Regional Heavy Rainfall Process in Guangdong and Its Climatological Characteristics

Using daily precipitation data of 86 meteorological stations in Guangdong from 1961 to 2017, the standard of regional heavy rainfall process is defined. Assessment methods on composite intensity of regional heavy rainfall process in Guangdong are constructed, which take duration, range, maximum daily precipitation and maximum accumulated precipitation during the process into consideration. Characteristics and changes of the frequency, intensity and rain-waterlogging years of regional heavy rainfall process in Guangdong in recent 57 years are studied. 1211 regional heavy rainfall processes are captured, and the annual average frequency is 21.2 times. There are obvious interannual and interdecadal variations, the highest frequency occurs in 2016 (30 times), and the lowest occurs in 1963 (13 times). The annual frequency of regional heavy rainfall process in Guangdong increases at a rate of 0.08/(10 a) in recent 57 years, though not quite significant. The regional heavy rainfall process in Guangdong mainly occurs from April to September, accounting for 81.9% in the year, among which 45.4% processes occur in the first flood season (April-June), and 36.5% processes occur in the second flood season (July-September). The average duration of single regional heavy rainfall process in Guangdong is 2.3 d, and the longest is 17 d (9-25 June 1968). The average range of a single process covers 20.3 stations, and the process occurring on 28 January 2016 is observed by the most stations (83). The regional heavy rainfall process with the maximum composite intensity index occurs during 12-24 June 2005, reaching 1385.1 mm (Longmen), and this coincides "05.6" torrential rains and floods in Guangdong. The frequency and strength of the regional heavy rainfall process in Guangdong have intermonth, interannual and inter-decade variations, the frequency in May is the highest, and the strength in June is the highest. The annual harvest index of the rain waterlogging in Guangdong increases obviously at a rate of 0.17/(10 a) in recent 57 years. Regional heavy rainfall processes of relatively strong and strong class increase significantly, while those of relatively weak class decrease obviously in recent 57 years. Evaluation results show that there are five heavy rain waterlogging years, i.e., 2008, 2001, 1973, 1994, 1993.