# Characteristics of Summer Flash Drought and Its Effect on Maize Growth in Liaoning Province, China
## 4 Discussion  
### Identification of Summer Flash Droughts in Liaoning and Their Spatiotemporal Characteristics  
The EDDI was used to identify the occurrence of flash droughts in the present study. The IOC curve of summer flash droughts in Liaoning showed an increasing trend from 1961 to 2020. During the 60-year study period, there were 8, 10, and 31 years of large-scale, regional, and local flash droughts, respectively. The highest average range of flash droughts occurred in 2011-2020, and the lowest average range was observed in 1961-1970. The frequency of summer flash droughts was higher than 20% at 16 sites, mainly situated in Eastern and parts of Western Liaoning. The frequency of flash droughts at the remaining 36 sites was between 10% and 20%. The decades 1981-1990 and 2011-2020 experienced the highest frequencies of flash droughts, whereas 1961-1970 had the lowest frequency of flash droughts. During the 60-year period, summer flash droughts in Liaoning were dominated by exceptional droughts; the frequency of exceptional droughts in most areas ranged from 10% to 20%.  
Compared with conventional droughts, flash droughts are mostly characterized by their rapid onset and the severity of the drought. Conventional drought intensity is often classed as light drought, moderate drought, severe drought, and extreme drought, whereas a flash drought is mainly classified as severe drought or extreme drought [11; 32]. When various methods are used to identify flash drought, the deviation of the index anomaly or the percentile of the index is commonly used to indicate the severity of drought, but neither corresponds to the classes of conventional drought severity. A previous study noted that any flash drought, regardless of the category, is an extreme phenomenon [11]. In the present study, the categories of summer flash droughts in Liaoning included severe, extreme, and exceptional droughts, which were dominated by extreme and exceptional droughts, verifying the conclusion that flash droughts are extreme drought events.  
[PERSON] et al. [33] analyzed the spatiotemporal characteristics of flash droughts in agricultural regions of China from 1983 to 2015. These authors observed that the number  
Figure 22: Geopotential height (200 hpa and 500 hpa) and anomalies in summer of three typical years experiencing flash drought (**a**) 200 hpa, 1989; (**b**) 500 hpa, 1989; (**c**) 200 hpa, 1997; (**d**) 500 hpa, 1997; (**e**) 200 hpa, 2018; (**f**) 500 hpa, 2018.  
of flash droughts showed an increasing trend, especially in Northeast China, which was the region hardest hit by high-temperature-induced flash droughts, with a high frequency of incidence and a long duration of high temperatures. [PERSON] et al. conducted an analysis of the spatiotemporal characteristics of flash droughts in diverse soil types in the eastern monsoon region of China from 1979 to 2012 [34]. The peak severity of flash droughts was generally concentrated in summer, and the frequency of flash droughts was highest in Northeastern and Central China. In the present study, we observed that the extent and frequency of summer flash droughts in Liaoning showed an increasing trend, especially the occurrence of extreme and exceptional droughts. Thus, summer flash droughts in Liaoning showed a trend of increasing in frequency and intensity, which is in accordance with the findings of the aforementioned studies [33; 34].