基于水热耦合平衡的长江源实际蒸散变化研究

Variations of actual evapotranspiration in the Yangtze River headwater region based on coupled water-energy balance

采用1960~2012年长江源地区8个气象站的气象数据和直门达站的径流数据,基于流域水热耦合平衡方程计算了长江源区实际蒸散(ET),采用云模型、Mann-Kendall检验、Pettitt检验和Sen趋势度等方法分析了ET的时空变化特征,并通过敏感性分析确定了影响ET的主要气候因子。结果表明:1)1960~2012年长江源区多年平均ET为277.6mm/a,呈显著上升趋势(99%置信度),上升速率为6.27mm/10a,并在1997年发生突变(99%置信度)。2)年均ET从西北向东南递增,且上升速率从西北向东南递减。熵值En和超熵He分别呈西高东低和西北高东南低的分布规律。ET均值大的区域年ET随时间变化较为均匀且稳定性较强。3)源区年ET变化对降水最为敏感,其后依次是相对湿度、日照时数、最高气温、风速、最低气温和平均气温。降水量上升对ET的增加起主要贡献作用,其次是气温与日照时数的上升和相对湿度的下降。

Based on the daily meteorological data from 8 stations and runoff data from Zhimenda during 1960 ~2012 in the Yangtze River headwater region,annual ET were calculated and tested by coupled water-energy balance equation. The spatio-temporal variation characteristics of ET were analyzed by cloud model,Mann-Kendall test,Pettitt test and Sen slope,and the key climate variables were determined by sensitivity analysis.The results showed that：（ 1） The annual ET increased significantly（ 99% confidence level）,with an average of277. 6 mm/a and an increasing rate of 6. 27 mm/10 a. The change-point occurred in 1997（ 99% confidence level）.（ 2） The distribution of average annual ET increased from northwest to southeast with an increasing rate decreasing from northwest to southeast. The distributions of entropy En and super entropy He were ＂ high in west and low in east＂ and ＂ high in northwest and low in southeast＂ respectively. ET changed with greater uniformity and stronger stability over time in the area of large mean ET.（ 3） ET was the most sensitive to precipitation,followed by relative humidity,sunshine duration,maximum air temperature,wind speed,minimum air temperature and mean air temperature. The dominant reason for ET increase was precipitation increase,followed by air temperature increase,sunshine duration increase and relative humidity decrease.