Abstract: The observation data of pan evaporation and other meteorological factors from 36 meteorological stations at different terrains (the river valleys, Qaidam Basin and Qingnan Plateau) in Qinghai Province during the period of 1961-2003 were applied in the study. Results showed that the pan evaporation at the most selected stations was in an obvious decrease trend, especially at the stations in the basin and valleys. The change trend of pan evaporation at the stations in the Qingnan Plateau was different, and the decrease was not so significant. In the river valleys, the pan evaporation was decreased due to the effects of mountains, emission of air pollutant, increase of aerosol particles, weakened direct solar radiation and mountain breeze circulation, and decrease of sunshine and daily temperature range. Under the global increase of greenhouse gases and aerosols, in the Qaidam Basin the pan evaporation was decreased due to the increase of cloud cover and precipitation, and decrease of wind speed, sunshine duration and daily temperature range, and the decrease of pan evaporation in the western part of the Qaidam Basin was more significant than that in the central and eastern parts. The Qingnan Plateau is located in the main part of the Qinghai-Tibet Plateau, where the change of pan evaporation was different from different stations.    

Key words: font-size: 10.5pt, mso-bidi-font-family: 宋体, mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, terrain')">mso-bidi-language: AR-SA" lang="EN-US">terrain, pen evaporation, change trend, Qinghai Province