Based on the daily maximum, daily minimum and average air temperature data of 24 meteorological stations from 1961 to 2017, 12 extreme air temperature indices recommended by the CCl/CLIVAR climate change monitoring and indices expert group were used to analyze the temporal and spatial variations of extreme air temperature indices in Qilian Mountains and the characteristic of the temporal and spatial variations are explained. The results showed that:The spatial distribution of warm indices increases to the periphery with the central and eastern part of Qilian Mountains as the region with smaller warming range. The spatial distribution of cold indices decreases from the south to the north. In contrast to warm extremes, indices that related to cold extremes showed warmer trend. The warming range of night indices is larger than day indices, which is consistent with the significant decrease of diurnal temperature range. The length of growing season length was significantly longer. The number of ice days and frost days significantly decreased, and the areas with large reduction were concentrated in the south of Qilian Mountains. After 1985, especially during the 1990s, the warming trend of Qilian Mountains accelerated. After 2000, the warming trend slowed down, and after 2010, the warming rate increased significantly. The extreme temperature indices have a good correlation with altitude. The higher altitude, the greater warming of extreme temperature indices. In the high-altitude area (>2500 m), the extreme temperature cold indices changes significantly, while in the low altitude area (< 2500 m), the extreme temperature warm indices changes significantly. The effect of the circulation index of Atlantic multidecadal Oscillation, Tropical Northern Atlantic Index, Tropical Southern Atlantic Index, North Tropical Atlantic SST Index, Caribbean SST Index on the extreme temperature warm index was stronger than that of extreme temperature cold index. Central Tropical Pacific SST mainly affects the extreme temperature cold indices, while South China Sea Summer Monsoon Index mainly affects the extreme temperature warm indices.
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