基于碳水通量耦合原理改进Penman-Monteith蒸散发模型

Improving the Penman-Monteith evapotranspiration model based on the coupling principle of carbon and water fluxes

陆地蒸散(ET)涵括地表和潮湿叶片的蒸发和植物的蒸散发,是陆地水循环的重要组成部分。Penman-Monteith方程是估算陆地蒸散的重要方法,方程中的叶片或冠层气孔导度是提高估算精度的关键因子。根据碳水循环的耦合原理,植物光合作用模型可用于估算叶片或冠层气孔导度。植物光合作用模型可分为三类:1)使用总冠层导度的大叶模型(BL),2)区别阴、阳叶冠层导度的双大叶模型(TBL),3)区别阴、阳叶叶片导度的双叶模型(TL)。与这三类光合作用模型相对应,衍生出基于不同导度计算方法的三种蒸散估算模型。三种蒸散模型之间的主要区别在于是否进行从叶片尺度到冠层尺度的气孔导度集成。这三种模型中,双叶模型使用叶片尺度的气孔导度,集成度最低。反之,大叶模型使用冠层尺度的气孔导度,集成度最高。由于在Penman-Monteith中,蒸腾和气孔导度之间的关系是非线性的,气孔导度的集合会导致负偏差。因此,与通量测量相比,大叶蒸散模型的估算偏差最大,而双叶蒸散模型的估算偏差最小。

Evapotranspiration(ET)is an important component of the land water cycle.It includes the evaporation of the soil surface and wet leaves and the transpiration of plants.The Penman-Monteith equation is an important method used to estimate ET.The stomatal conductance of leaves or canopies in the equation is the key factor controlling the estimation accuracy.According to the coupling principle of the carbon and water cycles,a plant photosynthesis model can be used to estimate the stomatal conductance of leaves or canopies.Plant photosynthesis models can be divided into three categories:1)the big-leaf model(BL),which uses total canopy conductance;2)the two big-leaf model(TBL),which distinguishes the canopy conductance of shaded and sunlit leaves;and 3)the two-leaf model(TL),which uses stomatal conductances of shaded and sunlit leaves.Corresponding to these three types of photosynthesis models,three evapotranspiration estimation models based on different conductance calculation methods are then derived.The main difference among the three evapotranspiration models is whether or not the stomatal conductance is integrated from the leaf scale to the canopy scale.Finally,the calculated stomatal conductance is input into the Penman-Monteith equation,so as to estimate the ET.Among them,the BL model has the highest degree of aggregation.Due to the fact that the relationship between the transpiration and stomatal conductance is nonlinear,the aggregation of stomatal conductance will lead to negative bias in ET estimation.Also,as the BL model has the largest aggregation of stomatal conductance,the bias error also the greatest.The results of previous studies show that the TL evapotranspiration model causes no significant bias error in comparison with flux measurements.