Temporal and spatial distributions of hourly rain intensity under the warm background in Xinjiang

It is well known that climate changes sometimes may cause natural disasters，especially the disastrous weather days，as downpour，flood，landslide and mudslide，and their derivatives disasters not only have relationship with precipitation，but also，closely with rainfall intensity. In the practice of Xinjiang disaster prevention，it’s urgent to know the temporal and spatial distributions of precipitation intensity and the maximum of precipitation intensity in different recurrence periods. In this paper，based on the observed hourly precipitation data over 16 national-standard stations during May to September from 1991 to 2013 in Xinjiang，some large-scale，multisites and long-paying observed hourly precipitation data have been used firstly together with the methods of probability distributions，statistical tests，variant difference analysis and extreme value analysis，the temporal and spatial distributions and the diurnal variation of hourly rain in summer in Xinjiang have been analyzed. The results show that the hourly rain presents high frequency in northwest and low frequency in southeast of Xinjiang. The high value center of the frequency with hourly rainfall intensity over 0.1 mm·h-1 or 4 mm·h-1 both in Western Tianshan Mountains. The frequency of heavy rainfall is increasing in places such as Ruoqiang where rains less. The high frequent periods of heavy rainfall，with hourly rainfall intensity over 4 mm·h-1，are often occurred in the afternoon，and the first and second half of the night in Northern Xinjiang，while it occurs at night in Southern Xinjiang. The hourly rain frequencies share obviously different diurnal variation in all regions of Xinjiang，where the hourly rainfall is not well-distributed. The distribution characteristic of daily rain in Northern Tacheng and Altay Prefecture is bimodal and in the rest regions of Northern Xinjiang is unimodal. Nevertheless，in Southern Xinjiang，most are in bimodal distribution. The total frequency of hourly rainfall intensity larger than 0.1 mm·h-1 or 4.0 mm·h-1 in Northern and Southern Xinjiang both appears to be an evident increase trend，and it would increase more significance in Southern Xinjiang in the 2010s. The high value region of hourly rainfall intensity occurring once in 50 or 100 years，respectively 45 mm·h-1 and 50 mm·h-1，both is in the western Aksu.