Study of Statistical Characteristics of wet Season Hourly Rainfall at Hulu Watershed with Γ Function in Qilian Mountains

The probability distribution of the wet season hourly precipitation is the important basis for the study of the precipitation distribution, especially in mountainous areas. Hulu watershed is the study area located in the upper reaches of Heihe River, Qilian Mountains. By adopting the maximum likelihood estimation, the shape parameter α and scale parameter β of 6 stations were obtained with observed wet season (May to September) half hourly data, and different intensity precipitation probability density distribution, cumulative probability density and probability of precipitation and elevation and precipitation relationship were analyzed. The shape parameter α and scale parameter β is significantly negatively correlated, shape parameter α and average hourly precipitation distribution is consistent. Local topography is also an important factor to affect the precipitation redistribution and the probability distribution of precipitation in Hulu watershed. In addition to the increase of precipitation events, the probability of 1~3 mm mm/h precipitation increases with the altitude, which is the main reason for the increase of precipitation with altitude.