The spatiotemporal variability in precipitation gradients based on meteorological station observations in mountainous areas of Northwest China

Exploration of the spatiotemporal variability in precipitation gradients (PGs) is important for understanding the spatial differences in precipitation and optimizing hydrological process simulations. Here, the spatiotemporal distribution of precipitation and PG was analyzed in the Tianshan and Qilian Mountains based on national meteorological station data from 1961 to 2017. The relationships between PG and relative humidity and wind speed were explored. The results show that precipitation exhibits a significant increasing trend during the last decades. Precipitation in the Tianshan Mountains is greater in the north and west, the maximum precipitation height (MPH) occurs at 1942.5 m a.s.l., and the precipitation change rate is higher in the west than in the east. Precipitation in the eastern Qilian Mountains is greater, the MPH is approximately 2850 m a.s.l., and the precipitation change rate decreases from the middle to the western and eastern sections. There are noticeable differences in PG between the two mountain areas. Annually, the PG in the Tianshan and Qilian Mountains, except for the Yili Valley, has increased significantly. The PG change rate in the western Qilian Mountains is higher. Monthly, the PG increases most significantly from June to August. Precipitation is positively correlated with elevation in the Tianshan Mountains from April to October and in the western and eastern sections of the Qilian Mountains every month, while that in the middle Qilian Mountains decreases with increasing elevation from November to January. The PG in both mountain regions experienced abrupt changes around the 1970s-1980s, and most areas increased significantly after the abrupt changes, showing a clear humidification phenomenon. Except for some subregions, PG is directly proportional to relative humidity and inversely proportional to wind speed.