Temporal and spatial distribution characteristics of flash heavy rain in Henan during rainy season

Based on the hourly rainfall data from dense automatic weather stations over Henan between May and September from 2010 to 2015, we have analyzed temporal and spatial distribution characteristics of flash heavy rain (FHR) in this province during rainy season. Major results are as follows. FHR occurs most frequently in July, followed by August. According to regional difference of FHR in amount, contribution rate and frequency, there are four high value centers of FHR, i.e. the north of the Yellow River in the northern Henan, the Shangqiu in the eastern Henan, the piedmont region involved with the south and east of Funiu Mountains in the southwest Henan, and the basins along Hwai River and its south in the southern Henan. Terrain has a significant effect on the increase of precipitation, which is mainly achieved by increasing the frequency of FHR. The diurnal variation of FHR frequency shows obviously a double peak structure, and FHR occurs mostly in the period from nightfall to wee hours of the morning. The diurnal variation of FHR frequency differs among the four high value centers mentioned above. For example, in the north of the Yellow River, it shows a single peak characteristic and its amplitude is large, while in the basins along Hwai River and its south, it shows a persistent and active characteristic and its amplitude is small. Most of FHR events are accompanied by continuous precipitation whose durations are between 1 h and 8 h, and those lasting longer than 3 h occur more in the two high value centers related closely to terrain, i.e. the bell mouthed terrain in the east of Funiu Mountains and the basins along Hwai River and its south.