Analysis Of Meteorological Elements And Study On The Reason Of Variation Of Evaporation In Changjing River Basin In Recent 50a

Water is always moving in geographical environment. Each kind of water body is unceasingly circulating and transforming, from one state into another state. It makes importantly theory and practice sense to research evaporation in basin, because evaporation is the most important link in water cycle. The report of IPCC indicated that the air temperature has gone up by 0.4～0.8℃, during the past 100 years in the 20 century, reaching the highest value in the recent 1000 years. It is considered that evaporation will increase as a result of the temperature rise. But, on the contrary, during the past half century, pan evaporation measured by pan evatorimeters has decreased over some areas. The decline in pan evaporation is at odds with the expectation that global warming caused by increasing emission of greenhouse gases would increase potential evaporation. What is the reason of the phenomena? It is very important for the meteorologists and hydrologist to resolve them.Under the background, based on the daily observation data of meteorological elements (pan evaporation, the maximum air temperature, the mean air temperature, the minimum air temperature, the ground temperature, the relative humidity, the cloud, the wind speed, the sunlight time, the average atmospheric press and the average vapor press) from 115 stations in Changjiang River Basin from 1951～2000, Characteristics of the trends of Climate in Changjiang River Basin are statistically investigated by calculating climate tendency with least square method and the relations between pan evaporation and kinds of meteorological elements are also analyzed. These results show that for recent 50 years in Changjiang River Basin:(1)Characteristics of Spatial-Temporal Variability of kinds of meteorological elements are analyzed in subareas in Changjiang River Basin.(2)The reference evapotranspiration is estimated with standard FAO Penman-Monteith method. The result is satisfied by comparing it with the observation data though calculating coefficient; Also, it was found that k_Rs is affected by the site of water, topography, time and regional environment, and dT_dew is relating to geographical environment, such as topography, altitude and meteorological elements such as wind speed, precipitation.(3)The pan evaporation has declined in 4 subareas in Changjiang River Basin, of the 4 subareas, it has declined significantly in the midriver.(4)The most possible reason that causes the decline of pan evaporation in SG is the average vapor press. The most possible reasons that cause the decline of pan evaporation in SP is the ground temperature and the sunlight time. The most possible reason that causes the decline of pan evaporation in midriver and downriver is the sunlight time.