Change Characteristics of Precipitation in Northwest China from 1961 to 2018

The Northwest China, which is adjacent to the Qinghai-Tibet Plateau, is the largest Eurasian arid region. Its precipitation responses to the global climate changes, to the arid environment, and to the climate change in the Qinghai-Tibet Plateau region are special significance. Based on the observational data of the daily precipitations and monthly temperatures at 144 stations in Northwest China from 1961 to 2018, the characteristics and trends of the precipitation change in Northwest China are analyzed. The results showed that: (1) During nearly the last 60 years, 92% of the stations in Northwest China observed an increasing trend of annual precipitations, while less than 10% of the stations in southeastern Gansu observed a decreasing trend. (2) On the seasonal scale, precipitations at more than 75% stations showed an increasing trend in spring, summer, and autumn, however the most significant is that almost all the stations had an increasing trend of precipitations in winter. The increase of precipitations in autumn and winter was relatively small, which reflected the influence of winter wind on the precipitation in Northwest China. (3) Another feature is that since the beginning of the 21st century, the summer and annual precipitations in Northwest China have maintained a quasi-3 a cycle. The spring and autumn cycles have several stages, while the winter precipitation has a relatively stable cycle of nearly 3 a. Therefore, natural cycle changes do not contribute much to the increase of the precipitation. The precipitation in Northwest China has indeed increased over the past 60 years, especially since the beginning of 21st century when the precipitation has been continuously increasing. However, the increased precipitation amount is limited, which is not enough to change the arid and semi-arid climate characteristics in the region.