Type Analysis of Precipitation Diurnal Variation in Dali Region, the Tibetan Plateau Southeast Margin

The precipitation diurnal variations at 12 stations in Dali region were analyzed by using the harmonic analysis. The results show that the diurnal variations of rainfall at 12 stations, may be fi tted by the fi rst three harmonics, and the harmonic was signif i cant when its variance contribution rate was bigger than 30%. Four types were found: Only one single peak in night in the Erhai basin, with rainfall events occurred usually 3 hours or more. Two peaks at the night and afternoon respectively in the valley of the western of Mount Ailao and Diancang: the rainfall at the night peak may last for 6 hours and is 6 times of that of that at the afternoon peak. Two peaks in afternoon and night in the Northern area of alpine valleys: rainfall may lasts 10 hours at the afternoon peak and was 1.5 times of that at the night peak which lasts for 4 hours or more. Two peaks at afternoon and night in Southern and western regions: rainfall events at the afternoon peak and the night peak, were all last around 4-5 hours The differences between these types are mainly due to the lake-land wind and the hill-valley wind caused by the diurnal change of solar radiation and the complex terrain factors.