Characteristics of 2016 severe convective weather and extreme rainfalls under the background of super El Niño

Abstract

The strongest El Nino event that has been ever seen since observation records started in 1951 occurred in 2015/2016. This paper analyzes the characteristics of the severe convective weather and extreme rainfalls that were experienced from January to August, 2016, which are then compared to those found for the corresponding periods since 1981. The findings are summarized as follows. (1) Severe convective weather, especially thunderstorm gales and short-time rainstorms, occurred much more in 2016 than normal, resulting in the most serious severe convective disasters in the recent years and the most extreme precipitation events since 2000. (2) The interannual variation of the severe convective weather and extreme rainfalls since 1981 reveals that in the years (1982/1983, 1997/1998, 2015/2016) when super El Nino events ended the extreme rainfalls and severe convective weather occurred much more than those during the normal El Nino years, when there are not very obvious features of high frequency of such weather events. (3) In 1983, thunderstorm gales and hails occurred frequently, but the extreme rainfall days were similar with those in normal years except in the Yangtze River valley. (4) In 1998, extreme precipitation days over the whole country were the most since 1981, and the frequency of short-time heavy precipitation ( ³ 20 mm/h) was only second to that in 2016 while the disaster-inducing short-time rainstorms ( ³ 50 mm/h) was the most since 1981. (5) In 2016, severe convective weather was mainly reflected by frequent thunderstorm gales and short-time rainstorms, which were more than the climatic averages over the Yangtze River valley and its south regions. Especially, the fierce thunderstorm gales stronger than 25 m/s were the most in the recent five years, about 3–4 times of those in the other years. However, hail events were still in the decreasing trend as the result of the remarkable decrease in hail over the northern part of China. Comparatively, the days of extreme rainfalls in North China were the second most since 1981, of which the nationwide rainfall amount in the 18–20 July severe precipitation event with the North China region as the heavy rainfall center exceeded the precipitation in the corresponding period in history. (6) In the years when the three super El Nino events ended, extreme rainfalls occurred more frequently than normal, but difference existed in different regions. In 2016, the frequency ratio of extreme rainfalls was the highest since 2000 no matter whether it was for the nationwide, or the Yangtze River valley and North China. The extreme rainfall days that appeared nationwide and the Yangtze River valley in 1998 was the highest since 1981 while such days in 1983 were found more only in the Yangtze River valley.