1971-2014年青藏高原参考蒸散变化及其归因

研究参考蒸散时空变化格局并辨识其驱动因子，是认识区域水文过程及其对气候变化响应的重要途径。基于修正的FAO 56 Penman-Monteith公式和青藏高原75个台站逐日气象观测资料，分析了1971—2014年高原参考蒸散变化的转折特征，并探讨转折前后的年际与季节变化趋势及其主导因素。结果表明：1971—1996年青藏高原参考蒸散呈急剧下降态势〔-27.07 mm·(10a)^-1〕，而1997—2014年高原参考蒸散增加趋势显著〔40.16 mm·(10a)^-1〕，尤以33°N以南区域最为突出。这与影响参考蒸散变化的气候因子变化趋势的年际转折密切相关。其中，风速变小是1971—1996年高原年参考蒸散减少的主要因素，特别是在高原北部；相对湿度降低则极大地促进了1997—2014年高原主体(除高原北缘外)参考蒸散的显著增加。此外，从季节上看，春、秋、冬季参考蒸散变化的最大贡献因子由之前的风速减小转变为1997—2014年的相对湿度下降；影响高原夏季参考蒸散的主导因子是1971—1996年相对湿度的增加，之后则转变为1997—2014年日照时数的增加。

Change and Attribution of Reference Evapotranspiration over the Tibetan Plateau during the Period of 1971-2014

It is indispensable to explore the spatiotemporal variation of reference evapotranspiration over the Tibetan Plateau and its driving factors so as to deepen the understanding of regional hydrological process and its response to climate change. The daily data from 75 meteorological stations over the plateau were utilized to analyze the spatiotemporal change of evapotranspiration based on the modified formula of FAO 56 Penman-Monteith, and the contribution of climatic factors to the variation during the period of 1971-2014 was discussed. The main conclusions are summarized as follows: Annual reference evapotranspiration over the Tibetan Plateau tended to an increase, especially in the region south from 33°N from 1997 to 2014 with an average linear trend of 40.16 mm·(10a)^-1. It, however, decreased remarkably at the rate of -27.07 mm·(10a)^-1 from 1971 to 1996, and the dominant climatic factor resulting in the decrease was the reduction of wind speed, especially in Northern Plateau. Reduction of relative humidity played a crucial role in increasing the reference evapotranspiration from 1997 to 2014. In addition, the biggest contribution factor to the seasonal variation of reference evapotranspiration shifted from the reduction of wind speed (from 1971 to 1996) to the decrease of relative humidity (from 1997 to 2014) and the dominant factor to the summer variation of reference evapotranspiration shifted from the increase of relative humidity (from 1971 to 1996) to the increase of annual mean relative sunshine duration (from 1997 to 2014).