The variation of precipitation and rain days for different intensity classes during the rainy season in the Qilian Mountains, Northwest China

As an important indicator of climate change, precipitation variability is critical to the ecological environment in arid and semi-arid mountains. This study examined the variability and trends of precipitation and rain days in the Qilian Mountains based on meteorological station data during the rainy seasons of 1960–2017 using a non-parametric method. The results revealed the following. (1) Many major precipitation events occurred during the rainy season (precipitation amount and number of rain days accounted for > 80% and > 70% of the annual total, respectively) and the proportion of precipitation increased significantly with altitude. (2) The distribution of different intensity classes of precipitation was complex in different months and at different altitudes. The distribution of rain days of different intensity classes was similar to that of precipitation. Variation of precipitation and rain days was significant (not significant) in central and eastern parts (western parts and in the Hexi Corridor on the northern slopes) of the Qilian Mountains. Regions with significant (non-significant) increasing trends for both light and moderate rain were distributed above the upper portion, i.e., 2600–3200 m (in the Hexi Corridor on the northern slopes) of the Qilian Mountains. (3) Mutations of light rain and rain days occurred before the mid-1980s above the upper portion but late in the first decade of the twenty-first century in the lower portion (2000–2600 m). Mutations of moderate rain and moderate rain days occurred earlier than for light rain and light rain days; the abrupt change points occurred later with decreasing altitude.