Interannual variation trend of hail days in hail prone areas in Xinjiang

Hail causes significant agricultural losses in Xinjiang every year, and the study of interannual variation of hail days and its causes can provide a climatic background for hail warning and defense. This study analyzes the trends and abrupt changes in the interannual variability of hail days in the areas with frequent hail using linear trend analysis and abrupt climate change detection methods, and explains the climatic causes of these trends using atmospheric stability. The results show that areas with frequent hails in Xinjiang are located on both sides of the Tianshan Mountains and their adjacent areas, and area with the most to the fewest hail days are in the following order: Zhaosu and Bayinbruck on the Alpine Platform, Aksu region on the south side of the Tianshan Mountains, and Bortala and Kuy-Ma Basin on the north side of the Tianshan Mountains. The interannual variation of hail days in Aksu region, Bortala and Kuy-Ma Basin from 1961 - 2016 shows a linear increasing trend, but the increase is small, only 0.2 - 0.4 d per 10 a, which is contrary to the conclusion of previous studies where the number of hail days in the Chinese region showed a decreasing trend; whereas the Alpine Platforms shows a linear decreasing trend with a larger decrease of 2.5 d per 10 a. The annual number of hail days on the Alpine Platform changed abruptly in 1993 and in the Aksu region in 1978. The linear increase (decrease) in the interannual variation of the warm season modified total index leads to a linear increase (decrease) in the number of hail days on both sides of the Tianshan Mountains and on the Alpine Platform. The trend of interannual variation in the number of hail days in the hail-prone areas in Xinjiang depends on the altitude of the elevation, with a decreasing trend at higher elevations and an increasing trend at lower elevations.