Analysis on Variation Characteristics of Areal Rainfall in Yalong River Basin in 1981-2017

By using the daily precipitation data of 18 weather stations in Yalong river basin during 1981 to 2017, areal rainfall and the spatial and temporal distribution characteristics of rainy season in Yalong river basin were analyzed through arithmetic mean method, moving average method and linear regression method. The results showed the areal rainfall in Yalong river basin fluctuated obviously with the month, and the annual variation was unimodal. The spring areal rainfall in the basin showed increasing trend. The summer areal rainfall in the upper reaches showed a stable trend and the lower reaches showed a decreasing trend. The autumn areal rainfall in the middle reaches and the lower reaches showed a decreasing trend. The winter areal rainfall showed no obvious change. The average annual areal rainfall in the basin increased gradually from north to south, and showed rising trend in upper and middle reaches and downtrend in lower reaches. The start date of rainy season in the basin was in advance. The end date of rainy season in upper and lower reaches was delay, and had no obvious change in middle reaches. The heavy rainfall mainly appeared during June to September. The maximum value of areal rainfall in the basin was in July and minimum value was in January. The heavy rainfall in upper reaches had no correlation with middle reaches and lower reaches, and the correlation between middle reaches and lower reaches was 23.3%.