我国蒸发研究的概况与展望

A REVIEW: EVAPORATION STUDY IN CHINA

蒸发既是地球表面热量平衡的组成部分,又是水量平衡的组成部分,而地表面热量、水分收支状况在很大程度上决定着地理环境的形成和演变,因此蒸发的研究是地理环境研究中的一个内容。蒸发与许多国民经济中的实际问题有关,那是显而易见的,水的问题已成为目前全世界所共同关注的问题之一,而几乎所有水的实际问题的解决,都离不开蒸发的研究。

This paper sums up evaporation study in China under three headings. ( 1 ) measuring evaporation, (2) calculating evaporation., (3)potential and actual evaporation. With reference to the progresses of this field in the world, achievement of the last three decades in China is gathered, and prospect is presented.Much work on measuring evaporation was undertaken during the period from mid 1950’s to mid-1960’s. The research on evaporation from water tank and/or pan was carried out in some evaporation stations which were established under the guidance of the Ministry of water Conservancy and power and its local authorites. A number of measurements were made with accuracy, and on the basis of data some formulas were obtained. The detemination of evapotranspiration from agricultural field was performed in some experimental stations due to the need of scheduling irrigation. The water balance method was applied to the detemina tion of evapotranspira tion. Mo.it of the results by using it we-re not very satisfactory, because of the accuracy of measurement of water ele ments and limitation of observation aites.A type of lysimelers, which is mainly used for the relation of rain to infiltration and fluctuation of groundwater, was installed by organizations of the Ministry of Geology, but it is quite difficult to have good results of evapotranspiration under natural conditions. More comprehensive studies on evaporation which include various methods with exception of eddy correlation method were carried out by some institutions, but desirable results did not reach because of difficulties of both theory and practice. In view of deficiencies of evaporation studies in the past, a great effort has to be made towards the experimental direction.On the contrary,much more work has been done in calculating evaporation. Various formulas were produced to meet the urgent need of evaporation information, and some maps of evaporation distribu tion were presented by some authors. The articles on evaporation calculation are still increasing. There is a motley collection of results. It is a good idea to compare the calculation values with experimental data in order to judge which is better or worse.As for potential and actual evaporation, first of all, a variety of definitions of potential evaporation was analysized. In common sense it was regarded as evapotranspiration which occurs under the condition of sufficient water or when water is not a limiting factor in evaporation process. Differences of definition appeared when otherlimiting factors were added to specify potential evaporation under a particular condition. The variance of it was not justified in our country so far, therefore it is difficult to use the estimation of potential evaporation by existing formula. Once actual evaporation was looked over, it was kept in mind that our knowledge about it was too little. In order to improve it experimental study in representative catchments and development of models should be put into action.