| The observed data in this paper were based on the large lymister during June 2004 to May 2005. The daily variation, seasonal variation and year variation of dewfall and the soil evaporation in semi-arid were studied, the impact factor of dewfall and soil evaporation was analyzed. Following understanding were obtained by statistic disposal on experimentation data,by analysising on the interrelation between dewfall amount in semi-arid and corresponding meteorological factors.1.Dewfall in semi-arid is an extreme complicated physical procedure. Many kinds of meteorological factors influence dewfall amount. Among all these factors, the surface air humidity and temperature were the basic factors which impact the dewfall. While other factors Play a role by decorating two factors. The diurnal variation was obvious which mainly appeared in P.M.22 to A.M.09, while there was nearly no dewfall in any other time. The maximum amount of dewfall change with seasons, which delay with time. The time segment in which dewfall appeared in autumn was longest, the summer and the winter took the second place , and the spring was the shortest. The total dewfall amount in autumn was much more than other seasons, which reached 3.59mm, while spring and winter took the second place, summer was the minimum. Dewfall mainly concentrated in September to December, while February and June was the minimum. The dewfall amount in clear day was much more than that in overcast. The dewfall amount after rainfall was much more than in which the day before and the following two days. 2. Soil adsorption mainly occured in P.M.18 to A.M.7. The soil adsorption amount in winter was the largest, while the autumn took the second place and the summer was the minimum. The total soil adsorption amount in a year was 61.40mm, which mainly concertrated in October and Feburary. The primary factors which affected the soil adsorption were soil water content and the soil property.3. The occurred time of Rainfall,dewfall, soil adsorption and fog-water were different, the amount of rainfall and soil adsorption were much more than the dewfall and fog. The rainfall made the greatest contribution to the land surface moisture, the soil adsorption took the second place and the fog was the minimum. Fog mainly occurred in autumn, and it rarely occurred in other seasons. While the fog mainly occurred the day after the dewfall, and always occurred in overcast. The amount of fog was tiny, only reached 0.61mm.4. The formation of soil evaporation and evaporation intensity were affected by those factors such as direct solar radiation,temperature,humidity,wind speed,pressure and so on. While the amount and distribution of soil water content affected the evaporation too. The daily variation of soil evaporation change obviously, which mainly appear in A.M.10 to P.M.5. While the soil evaporation in other time was much less. The amount and frequency of evaporation in summer was largest, spring took the second place, winter was the minimum. The total evaporation amount in that year reached 571.7mm. The distribution of soil evaporation mainly occurred in April to next October. The evaporation in evaporator changed obviously with seasons, and the evaporation mainly occurred in spring and summer, winter was the minimum. The total amount of the year reached 1251.1mm. Character curve of evaporator was parabola, with up direction. The minimum amount occurred in December and January, the evaporation in April was the maximum. The character cure was monotone decreasing in May to December, while in February to April was monotone increasing. The evaporation was affected by the factors such as temperature,ground temperature,wind speed,relative humidity and so on,while the soil water content didn't show a clear relationship.
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