Abstract: Based on the meteorological data from 1961 to 2010 in Qinghai province, the spatial and temporal distributions and the trend of the pan evaporation were analyzed. The major climate factors affecting the pan evaporation were also studied by methods of a partial correlation and a principal component analysis. The results show that the pan evaporation is in a decreasing trend in the recent 50 years in Qinghai plateau, which is caused by thermodynamic, water and dynamic factors together. Among three factors, the dynamic and water factors have greater impact on the pan evaporation than thermodynamic factor. Regional analysis suggests that the major factors influencing pan evaporation are wind speed and relative humidity in the eastern agricultural areas and Qaidam Basin and relative humidity in three rivers source areas respectively, while the main impacting factor is diurnal temperature range in Tangula areas. It is negative correlation between evapotranspiration and surface water resource by analyzing both relationships. Summer evapotranspiration has a significant effect on the mean flow, while the response of mean autumn flow to evapotranspiration is the most sensitive.

Key words: font-family: "Times New Roman", mso-font-kerning: 1.0pt, mso-ansi-language: EN-US, mso-fareast-language: ZH-CN, mso-bidi-language: AR-SA, mso-bidi-font-size: 12.0pt, Potential evapotranspiration')">mso-fareast-font-family: 宋体">Potential evapotranspiration, Mean flow, Mann-Kendall test