Many studies have shown that the precipitation in the arid region of northwest China has shown a significant increasing trend in the last 50 years, which is considerably different from that of other areas in China that exhibit slightly rising trends or even downward trends for the same period. However, the causes of the significant rising trend in precipitation of northwest China from 1960 to 2010 are unclear. This topic requires further investigation to elucidate the reasons for this period. Furthermore, studies are also needed to analyse the influence of water vapour sources on precipitation from the perspective of atmospheric dynamics.  

To identify the possible cause for the regional precipitation change in northwest China, a researcher team led by Prof. CHEN Yaning detected the precipitation variations in northwest China for the period of 1960-2010 and investigated the relationships between precipitation changes and eleven modes of atmospheric circulations based the monthly and annual precipitations from 74 meteorological stations.  

Precipitation exhibited an increasing trend (0.61 mm/year) in northwest China during 1960-2010, especially after 1987. From 1987 to 2010, precipitation variations in spring, summer, autumn and winter accounted for 21.6%, 42.4%, 18.4% and 17.6% of the annual change, respectively. The annual precipitation in northwest China has a strong and significant correlation with the annual West Pacific Subtropical High (WPSH, P<0.001) and the North America Subtropical High (NASH, P<0.001).  

They hypothesize that the water vapour in the arid region of northwest China mainly originates from the Atlantic, followed by the western Pacific, with a small amount from the Indian Ocean. Researchers found that NASH and WPSH have great influences on precipitation in spring, summer and winter, and they are probably important factors influencing the precipitation change in the arid region of northwest China over the past 50 years. In general, the stronger the NASH and WPSH are, the higher the precipitation is. 

This study was published in Atmospheric Research in January 2016.