An Evaluation of Model-Based Partitioning of Eddy Covariance Terrestrial Latent Heat Observations into Wet Evaporation and Transpiration.

了解决定陆地表面蒸发速率的过程是研究气候变化对天气、气候、水资源、农业和生态系统功能影响的重要重点。冠层的蒸发水分损失包括冠层和土壤表面的湿蒸发，以及冠层内通过叶片气孔失去的蒸腾作用，以换取大气中的二氧化碳。有了一种从陆地表面蒸发观测中区分这两种成分的方法，将能够研究与湿蒸发和蒸腾有关的冠层过程。该项目将开发一种方法，将植物冠层上方蒸发水分损失的涡旋协方差观测分离为湿蒸发和植物蒸腾分量。该方法基于这样一个事实，即当潮湿时，植物树冠以潜在的蒸发率疏松水分，而当干燥时，由于气孔对蒸腾通量的限制，水分损失速率略有减少。自然降雨引起的湿润和干燥事件导致观测到的蒸发水分损失在这两种情况下发生变化。如果可以指定表面的湿度程度，则这提供了执行分区所需的信息。采用一种简单的建模方法，这种湿度是由降雨输入和湿蒸发输出之间的差值确定的。该项目将使用蒸发水损失的涡旋协方差观测结合卫星微波数据来评估这一方法，卫星微波数据包含关于地表湿度的信息。然后，这一方法将应用于广泛的生物群落，其中涡动协方差蒸发失水数据保存在一个名为FLUXNET的中央数据库中。通过这样做，这将使研究这些植物树冠的用水策略与其相应的气候和水预算限制有关。

Understanding the processes that determine the rate of evaporation from the land surface is an important focus for research into the effects of climate change on weather, climate, water resources, agriculture and ecosystem function. The evaporative water loss from canopies is comprised of both wet evaporation from the canopy and soil surfaces and transpiration derived from within the leaves of the canopy lost via leaf stomata in exchange for atmospheric CO2. Having a methodology for separating out these two components from observations of land surface evaporation will enable research on the canopy level processes associate with wet evaporation and transpiration. This project will develop a method for separating eddy covariance observations of evaporative water loss made above plant canopies into their wet evaporation and plant transpiration components. The methodology turns on the fact that when wet, plant canopies loose water at the potential rate of evaporation whilst when dry the rate of water loss is somewhat reduced due to stomatal limitations imposed on the transpiration flux. Natural rainfall induced wetting and drying events cause the observed evaporative water loss to change between these two conditions. This provides the necessary information to perform the partitioning if the degree of wetness of the surface can be specified. Using a simple modelling approach this wetness is determined by the difference between rainfall inputs and wet evaporation outputs. This project will evaluate this approach using eddy covariance observations of evaporative water loss combined with satellite microwave data which contain information on surface wetness. The methodology will then be applied to a wide range of biomes for which eddy covariance evaporative water loss data are held on a central database called FLUXNET. In doing so, this will enable a study of the water use strategies of these plant canopies in relation to their corresponding climate and water budget constraints.