中文摘要：

通过分析西藏西北部潜在蒸散量的时空分布以及影响潜在蒸散的气候因素。结果表明：1西藏西北部潜在蒸散呈现从西北向东南减少的分布特征,最大潜在蒸散出现在夏季,春季次之,冬季最小。近30 a来,除冬季潜在蒸散呈略微增加趋势外,其余均呈减少趋势。气温、相对湿度和降水量呈增加趋势,平均风速和日照时数呈减少趋势;潜在蒸散与气温、风速、日照时数呈正相关,与相对湿度、降水量呈负相关。2影响潜在蒸散的主要气象要素为相对湿度、平均气温和日照时数,风速对冬季潜在蒸散的影响最为显著;近30 a来,风速减小、日照时数减少、相对湿度增加是导致潜在蒸散量减少的主要气象影响因子。西藏西北部地区潜在蒸散的变化存在＂蒸发悖论＂现象,即在气温升高〔0.55℃·（10a）（-1）〕的背景下,潜在蒸散呈下降趋势〔10.02 mm·（10a）（-1）〕。

英文摘要：

As a continuous process in a quite complex system,evapotranspiration（ ET_p） includes not only water vapor evaporation from the earth surface and the plant surface,but also the water transpiration in plants. Therefore,ET is an important point in the process of water cycle and one of the key components for energy and water balance of the earth surface. Consequently,an accurate estimation of ET is required in applications,such as the irrigation management,weather forecasting,climate model simulation and the accurate understanding in mechanism of landatmosphere interaction. In this paper,the spatiotemporal distribution of potential evapotranspiration（ ET_p） and its affecting meteorological factors in northwest Tibet were analyzed based on the monthly meteorological data during the period of 1980- 2009 using the Penman-Monteith equation. Results showed that the ET_pdecreased from the northwest to the southeast of Tibet. The highest ET_poccurred in summer,than in spring,and the value was the lowest in winter. The annual and seasonal ET_pvalues were in a decrease except a slight increase in winter in recent 30 years.Air temperature,relative humidity and precipitation were in an increase trend,but wind speed and sunshine duration were in a decrease one during the period of 1980- 2009. The ET_pwas positively related to the air temperature,wind speed and sunshine duration,but it negatively related to the relative humidity and precipitation. The partial correlation coefficients revealed that the relative humidity,mean air temperature and sunshine duration were the main meteorological factors affecting the variation of ET_p,and the effect of wind speed on ET_pin winter was the most significant. The decrease of ET_pin recent 30 years was mainly caused by the decrease of wind speed and sunshine duration and the increase of relative humidity.