基于站点观测和水量平衡的四种蒸散发产品在我国的评估与对比

Verification and comparison of four evapotranspiration products based on eddy covariance observations and water balance method

【目的】蒸散发是陆面水循环的关键环节,蒸散发产品的评估与对比能够为产品运用和改进提供参考。【方法】对4种全球蒸散发产品分别进行了站点尺度和流域尺度的精度分析,在此基础上就产品蒸散发时空格局进行了对比。【结果】结果显示:与全国12个站点通量观测数据对比中,PML_V2产品的精度最高,其后依次是ERA5-Land、EB-ET和MOD16A2;在农田类通量观测数据对比中PML_V2表现最好,自然植被类(草地、森林)通量观测数据对比中ERA5-Land表现最好;与基于水量平衡法计算的中国九大流域多年平均蒸散发比较,4种产品的决定系数为0.89~0.96,表现最好的是EB-ET产品,4种产品有各自适用的流域。蒸散发时空格局对比结果表明,ERA5-Land与其它3个产品差异最大,ERA5-Land模拟的全国年均蒸散发最大且有逐年下降趋势,多年平均蒸散发在西北干旱区农田和我国东部分别出现低估与高估。【结论】结果表明:4种产品在不同下垫面条件下的精度有明显区别;在流域等大尺度应用中能够符合精度要求,但在时空格局方面仍有较大差异。

[Objective]Terrestrial evapotranspiration(ET)is a key process of the water cycle.The evaluation and comparison of ET products can provide reference for their application and improvement.[Methods]In this study,we compare 4 global ET products at site-pixel scale and watershed scale,respectively,and the temporal and spatial patterns of average ET are compared.[Results]The results show that PML_V2 has the highest accuracy,followed by ERA5-Land,EB-ET and MOD16A2 in comparison with the flux observation data of 12 stations across the country.In the comparison of farmland flux observation data,PML_V2 performs best,and in the comparison of natural vegetation(grassland,forest)flux observation data,ERA5-land performs best.In comparison with the multi-year average ET calculated by the water balance method in nine major river basins,the correlation of determination of four products are between 0.89 and 0.96,and EB-ET has the best performance.The four products are applicable to their respective river basins.The comparison of spatial and temporal patterns of ET over many years shows that ERA5-Land is the most different from the other three products.The national annual average ET simulated by ERA5-Land is the largest and has a downward trend year by year.It is underestimated and overestimated in arid farmland of northwest China and eastern China,respectively.[Conclusion]The accuracy of the four products is obviously different under different land cover types.The four products can meet the accuracy requirements in large-scale applications such as river basin,but there are still great differences among them in the spatial and temporal patterns of ET.