Changes in precipitation over Northwest China from 1973 to 2019: Variation characteristics and relationships with climatic factors

The Shaanxi-Gansu-Ningxia (SGN) region in Northwest China has been challenged by drought and water shortage for decades. The present study systematically assessed the spatio-temporal variation of precipitation and relationship with climatic factors in SGN region, and clarified the differences between the climate transition zone and other regions. Analyzed the precipitation and different climate factors at 30 weather stations from 1973 to 2019, and developed an analysis framework of precipitation recirculation. The results showed that precipitation at annual scale had decreased significantly (P < 0.01) at the rate of 1.46 mm/10a during 1973–2019, and precipitation had a pattern of northwest-southeast spaced distribution in spatial distribution. In terms of seasonal precipitation, the summer precipitation variability was more concentrated and contributes the most to annual precipitation variation, while winter had a limited effect on annual precipitation variability due to less precipitation. The correlation analysis showed that annual precipitation had significant associations with RH (R = 0.623, P < 0.01) and T max (R =-0.294, P < 0.05) from 1973 to 2019. We therefore suggest that decreased air humidity and elevated extreme temperature are probably important factors for the significant decreasing trend of precipitation in SGN region over the past 50 years.