Abstract: Based on observational data on the monthly surface water vapor pressure and other meteorological factors from 9 meteorological stations in Weifang from 1961 to 2015,the temporal and spatial distribution characteristics of surface water vapor pressure and their influencing factors were analyzed using climate tendency rate,EOF,M-K abrupt change test and correlation coefficient statistical methods,which provides a theoretical basis for the rational development of cloud water resource.The results show that in the past 55 years,the water vapor pressures in spring,autumn and winter and annual average in Weifang show an increase trend,especially in spring,while its value in summer is in a decrease trend.Interdecadal variation of surface vapor pressure in Weifang is obvious and the lowest value appears in 1980s.In addition,annual pattern of monthly mean water vapor pressure presents an obvious single peak distribution with the maximum and minimum values in July and January,respectively.Besides,the water vapor pressure in Weifang shows an increasing trend after an abrupt change occurring in 1989.The spatial distribution of annual and seasonal water vapor pressure in Weifang all indicate increasing characteristics from the northwest to the southeast and the lowest and highest values all appear in Qingzhou and Zhucheng,respectively,which is affected by the geographical position and altitude.A spatial characteristic of reverse distribution in water vapor pressure from northwest to southeast in Weifang is reflected by the feature vector.Moreover,the surface water vapor pressure is affected by many meteorological factors and has significant positive correlation with relative humidity,temperature and precipitation,and significant negative correlation with sunshine,evaporation and wind speed.

Key words: Water vapor pressure, Climate tendency rate, Empirical Orthogonal Function (EOF), Abrupt change, Correlation analysis