Spatiotemporal characteristics of cloud water resources in Northwest China from 2000 to 2019

In order to understand the characteristics of cloud water resource in Northwest China and scientifically plan the layout of air water resource for artificial rainfall development, the 1°×1° cloud water resources observation diagnostic evaluation dataset in China from 2000 to 2019 is used to statistically analyze the distribution and evolution of cloud water resource (CWR) in Northwest China. The linear fitting and empirical orthogonal decomposition methods are employed. The results show that: (1) Over the entire area, physical quantities related to cloud water resource (including state quantity, plain discharge, total amount and precipitation efficiency) are mainly the highest in summer, followed that that in spring and autumn, and the lowest in winter. Among them, the total cloud water resource in spring is about 173.6 billion tons (equivalent to about 51.2 mm column water), which is close to that in summer. The precipitation efficiency of hydrometeors in spring is 48.7%, and the development potential of cloud water resource is greater than that in autumn. (2) Calculation results in the 1°×1° grids of the region indicate that spatial distributions of annual total cloud water resource, annual total water vapor and annual total hydrometeors in the past 20 years are characterized by a "two highs and one low" pattern due to the influences of terrain and circulations. The high values are located in the marginal regions affected by the westerly jet and monsoon, while the low values are mainly distributed in the plateau climate region. (3) In the past 20 years, the annual total cloud water resource at the 1°×1° grids in the northwest has been increasing at an average rate of 23.6 mm/a, and the increase trend is the most significant in spring with a growth rate of 8.5 mm/a. In terms of seasonal distribution, the CWR is the highest in summer, followed by that in spring and autumn, and the least in winter. The precipitation efficiency of hydrometeors is high in summer, low in spring and autumn, and lowest in winter. (4) The contribution rate of the first EOF decomposition mode (EOF1) of CWR is about 78.2%. The distribution feature is that the eastern part of the region is relatively high. An interannual turning point occurred in 2008, when the distribution pattern of more CWR in the east and less in the west began to change. (5) In typical areas of Northwest China, the average annual total CWR and precipitation efficiency of hydrometeors in Tianshan mountains are higher than those in Qilian mountains. CWR is increasing in Qilian Mountain area and decreasing in Tianshan mountain area.