Characteristics of dynamic evaporation and thermal evaporation in North China

Based on the observed meteorological data from 1957 to 2002,an analysis was made of seasonal and annual variations of dynamic evaporation and thermal evaporation,their differences,and their contributions to the total amount of evaporation of 5 regions in North China,as well as the trend of their variations for recent 20 years under the condition of global warming.The results show that there are obvious differences between seasonal variations of dynamic evaporation and thermal evaporation in different regions,the former being double-peak distributed,while the latter being single-peak distributed,and that obvious differences also exist between annual variations of dynamic evaporation and thermal evaporation,and the differences become more evident under the condition of global warming.It is also demonstrated that the contribution of average annual thermal evaporation to the total amount of evaporation is greater than that of average annual dynamic evaporation,while the situation is quite different in different seasons: in warm season,thermal evaporation is of greater contribution to the total amount of evaporation of these regions,however,apart from the fourth region,the dynamic evaporation is of greater contribution to the total amount of evaporation in cold season.