The cloud—water resources of the Qilian Mountain were analyzed by using the observed data of eight meteorological stations from 1960 to 2002 and the NCEP／NCAR data(2．5。×2．5。)for the period of 1970—1997．Results show that the water vapor amount gradually increased from spring to summer，and then decreased；the precipitation there was concentrated in May to Septembe r which was in the proportion of 86．8％ to annual precipitation．Comparing the preceding period (1970—1986)with the succeeding period (1988—1997)of climatic change in Northwest China，the annual mean precipitation there increased more than 8．1％ in the succee—ding period (mainly in spring and summer)，which was beneficial to the ecological improvement there．The precipitation in the middle part of the Qilian Mountain was much more than that in eastern and western part．The annual water vapor input was 885．4×10 m ．which mostly cflme from the levels under 6O0 hPa，an d it divergenced over 600 hPa at most time of a year．The water vapor mainly canle from longitudinal input．
The cloud—water resources of the Qilian Mountain were analyzed by using the observed data of eight meteorological stations from 1960 to 2002 and the NCEP／NCAR data(2．5。×2．5。)for the period of 1970—1997．Results show that the water vapor amount gradually increased from spring to summer，and then decreased；the precipitation there was concentrated in May to Septembe r which was in the proportion of 86．8％ to annual precipitation．Comparing the preceding period (1970—1986)with the succeeding period (1988—1997)of climatic change in Northwest China，the annual mean precipitation there increased more than 8．1％ in the succeeding period (mainly in spring and summer)，which was beneficial to the ecological improvement there．The precipitation in the middle part of the Qilian Mountain was much more than that in eastern and western part．The annual water vapor input was 885．4×10 m ．which mostly cflme from the levels under 6O0 hPa，an d it divergenced over 600 hPa at most time of a year．Th e water vapor mainly canle from longitudinal input．
Based on the surface meteorological observation data and dust event days from X70 stations in China from 1951 to 2000,the spatial dis- tribution of dust storm,sand blowing,dust in January, April, July, events originate mainly from both the Northwest and the North of China, there arc three regions where the dust events occur frequently, which arc Hexi corridor and Alashan plateau with the center of Mingqin county; the southern edge of Tarim basin with the center of Hetian; the mid- dle part of Inner Mongolia with the center of Zhurihe. In addition, there is another region with the center of both Ningxia Yanchi and Etuokc area of Inner Mongolia, where dust storm occurred frequently too. (hhe spatial distributions of dust storm, sand blowing, dust arc basically co- incident. 'hhen, according to surface meteorological data, the relations between dust events distribution and surface meteorological elements have been studied in this paper. 'hhc rasults arc as follows;the corrclations between dust events and precipitation,rclativc humidity as well as vegeta- tion coverage rate arc obviously negative, and the correlation between dust events and evaporation is positive. "hhese facts show that the main influencing factors of dust events arc vegetation coverage rate,evaporation, precipitation,rclativc humidity. 'hhe correlation between dust events and average temperature is not obvious,and average wind speed arc weakly related with it.
According to the observational data of aerosols over Lanzhou city from June 2000 to May 2001, the concentration and size distribution of aerosols in the atmosphere including their yearly, monthly and daily variation were analyzed, and the influence of at-mosphere aerosols on human heath was discussed also. The results show that the variation tendencies of monthly mean density of PM10 and monthly mean number of persons infected with respiratory diseaseat the same period are basically coincident, they present nificant positive correlation. When aerosol concentration is on the high increase in 1-2 r avs.the number of persons infected respiratory disease will increase in 1~2 days.
According to "the criterion of surface meteorological observation"，visibility and wind speed are important targets to classify dust一stormy weather. Using the data of visibility and wind speed observed in meteorological stations，we try to construct duststormy weather index to determine the intensity of dust一stormy weather phenomenon，moreover we can measure the strong or weak state of dust一stormy weather happened anywhere. We have obtained thefollowing conclusions ahe dust一sand index can corre}ond with the intensity of dust一stormy weather ;our analysis to state of dust一stormy weather in different area is in corre}ondence with real weather facts. The correlative analysis between sand一dust index and urban airpollution index indicated their affinity. It ispossible to build urban air pollution statistical forecasting model with the sand一dust index.
