Analysis of Precipitation Characteristics in Different Seasons in the Nighttime and Daytime in Sichuan in the Past 56 Years

Based on the precipitation data of 141 stations in Sichuan Province from 1961 to 2016, the spatial and temporal variations of precipitation amount and frequency during the night and day periods in four seasons are analyzed. The results show that: (1) the distribution of the precipitation account for more than 60% in four seasons in most areas of Sichuan Province are similar to frequency more than 50% at nighttime. Precipitation amount and frequency during the nighttime in four seasons in western mountainous area of Basin and parts of southeastern Sichuan are large, and in other parts of Panxi and Western Sichuan plateau the precipitation amount and frequency during the nighttime are large too. Nighttime precipitation in northeastern Sichuan is almost the same as that in daytime precipitation. (2) The climatic trend coefficients of precipitation amount at nighttime and daytime in four seasons, precipitation frequency at nighttime and daytime in spring, daytime in winter generally show a trend of increasing in Western Sichuan and decreasing in eastern Sichuan. The distribution areas of increasing and decreasing trends are different in different seasons. In addition to the weak increasing trend in some areas of the plateau, the precipitation frequency during the daytime and nighttime in autumn and nighttime in winter showed a decreasing trend in Sichuan, and the decreasing trend in autumn in eastern Sichuan and Panxi passed 99% significance test level. (3) The precipitation frequency at nighttime and daytime in the whole Sichuan area decreased linearly, but the trend of the precipitation amount is different in different seasons at nighttime and daytime. Generally speaking, the inter-decadal variation of the precipitation in the four seasons at nighttime is more obvious than that in the daytime, and the linear trend of precipitation in different seasons and different periods of the day are different. But in autumn, the precipitation amount and frequency decreased linearly before 2000 and then increased.