Water vapor content is a highly important variable for ecosystem, hydrology and climate systems. It directly affects the generation of precipitation, and it has a close correlation with the whole content of water vapor in the air. Many researches have been done in water vapor conditions, sources, directions of movement and convergence regarding the formation of heavy rain, and in the relations between these factors and the rainy season and rain belts in the east, south and low-latitude regions of China. However, due to the limitation of available data and computing technologies, it was not until the 1990s that the study on water vapor in Northwest China began to be paid much attention to. Since the latter half of the 1980s, precipitation and temperature in the northern and southern regions of Qinling Mountains increased and decreased significantly, respectively, which are usually attributed to global warming and the climate changed from ‘warm and humid' to ‘warm and dry' in this region.
In this paper, based on the surface vapor content data from 47 weather stations in the northern and southern regions of Qinling Mountains between 1960 and 2011, by the methods of linear trend estimation, anomaly analysis, Spline spatial interpolation, Pettitt abrupt change test and Morlet wavelet analysis etc., we analyzed the spatial and temporal variation, mutation, periodical changes and their possible causes. The results are as following: (1)Surface water vapor presented a clear pattern that high in south and low in north, water vapor decreased from east to west, which had a good altitudinal and latitudinal zonality. The order of water vapor, according to amount of water content, was Bawu Valley(BWV), Han River Basin(HRB), northern and southern regions of Qinling Mountains(NSQ), southern slope of Qinling Mountains(SSQ) and northern regions of Qinling Mountains(NRQ), the order of seasonal water vapor was summer, autumn, spring and winter. (2)Yearly averaged water vapor pressure presented an increasing trend, the increasing rate was bigger in SSQ and HRB, while BWV had a deceasing trend. In spring, regionally averaged water vapor pressure increased insignificantly, BWV and NSQ had decreasing trend; In summer, regionally averaged water vapor pressure decreased insignificantly, only NSQ showed increasing trend; In autumn, all regions' water vapor pressure increased, the increasing rate of SSQ and BWV was relatively bigger; In winter, water vapor pressure of most stations showed increasing trend, which was more obvious in southern regions of Qinling Mountains. (3)Water vapor pressure of 53% stations experienced abrupt change in winter, which mainly located in the southern regions of Qinling Mountains and the period mainly lied between 1985 and 1988, in line with the mutation of temperature in winter. The phenomenon of mutation was not obvious in other regions. (4)Water vapor experienced 4 times dry-wet alternating change on the 21a scale, the seasonal water vapor also had similar characters. In the near future (about 10 years), water vapor content of NSQ will stand at a low level, which means the dryness will last for 10 years. (5)Water vapor pressure was affected by several meteorological factors including temperature, wind speed, sunshine etc. Water vapor pressure correlated positively with precipitation, temperature, relative humidity and sunshine hours, but it had a negative correlation relationship with wind speed. The order of influential factor was temperature, precipitation, sunshine hour and relative humidity. Except for BWV, temperature and water vapor pressure had same change trend.