Special Column:Celebration of the 70th Anniversary of IGSNRR, CAS
QIU Xin-fa, LIU Chang-ming, ZENG Yan
Evaporation(evapotranspiration),on the one hand,is an important component in the heat and water balance of the Earth's surface,and is the component of the hydrologic cycle most directly influenced by land-use and climate change.On the other hand,evaporation(evapotran-spiration)consumes much of the water and energy that are available on the surface of the earth and therefore influence all hydrological and most meteorological processes.Basic knowledge for evaporation change over global or regional scale redounds to understand the law and causations of climate change.Up to now,studies on global climate change are,more and often,concerned with temperature and precipitation.Researches on the influence of climate change on evapora-tion(evapotranspirtation)are in small numbers.Based on observational data from1960~2000of123meteorological stations,near and in the Yellow River Basin,the spatial and temporal distri-butions of trends for pan evaporation are studied.The results show that,although the annual mean air temperature over the Yellow River Basin has,on average,increased0.6℃over the past40years,the rate of pan evaporation over the Yellow River Basin has,on average,steadily de-creased,especially in summer and spring.Compared with the1960s~1970s,the rate of annual pan evaporation of the1980s~1990s has decreased136mm or7.5%.Spatial distribution of the change rate shows that this trend is general but not universal,pan evaporation has significantly decreased over the upper and lower reaches of the Yellow River Basin,and increased in a small degree over the middle reaches of it.