Abstract:

Using daily average temperature of five meteorological stations in Shiyang River Basin from 1960 to 2017, we analyzed spatial and temporal distribution characteristics of negative accumulated temperature and its relationship with temperature and frozen soil by linear trend coefficient method, ANOVA cycle method, accumulative anomaly and signal-to-noise ratio method. The results showed that the negative accumulated temperature of Shiyang River Basin was affected by altitude, landform, vegetation and weather system, and had obvious regional characteristics, the average and extreme value of the negative accumulated temperature was the highest in oasis plain, followed by that in desert area and mountain area. The negative accumulated temperature of normal years was the most, the probability was over 60%, and declined rapidly to both ends. The annual and decadal negative accumulated temperature showed increasing trends, and the increasing trend was the most obvious in Gulang. Time series quasi-period of the annual negative accumulated temperature was 7-9 years. The negative accumulated temperature in Gulang had an abrupt change in 1986, and there was no abrupt climate change in other regions. The starting and ending date and the emergence period of the negative accumulated temperature had certain differences, the earliest starting date (September 2, 1972) and the latest ending date (June 9, 1969) of the negative accumulated temperature all appeared in Tianzhu. The longest negative accumulated temperature period was 258 d (1972) in Tianzhu and the shortest was 100 d (2001) in Minqin. There was a very significant positive correlation between annual negative accumulated temperature and annual temperature in Shiyang River Basin, and the rise of the negative accumulated temperature had a good synchronous with annual temperature. Response of frozen soil change to the negative accumulated temperature was sensitive in Shiyang River Basin, with the increase of the negative accumulated temperature of 100℃, the frozen soil days decreased by about 6.2 d, the average frozen soil depth decreasesd by 4.5 cm and the maximum frozen soil depth decreased by about 6.9 cm.

Key words: negative accumulated temperature, evolution characteristics, frozen soil, correlation, Shiyang River Basin