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一个重要重点。从冠层的蒸发水分损失包括从冠层和土壤表面的湿蒸发和来自冠层的叶片内通过叶片气孔损失的蒸腾作用，以交换大气中的CO2。有一种方法，分离出这两个组成部分的观测陆面蒸发，将使冠层过程的研究与湿蒸发和蒸腾。本计画将发展一种方法，将植物冠层上方的蒸发水分损失的涡度相关观测值分离成湿蒸发和植物蒸腾成分。该方法基于这样的事实，即当潮湿时，植物冠层以潜在的蒸发速率释放水分，而当干燥时，由于对蒸腾通量施加的气孔限制，水分损失的速率有所降低。自然降雨引起的湿润和干燥事件导致所观察到的蒸发水分损失在这两种情况之间变化。如果可以指定表面的湿度，则这提供了执行分区的必要信息。使用一个简单的建模方法，这种湿度是由降雨量输入和湿蒸发输出之间的差异确定的。该项目将利用蒸发水损失的涡动协方差观测值，结合含有地表湿度信息的卫星微波数据，对这一方法进行评价。然后，该方法将被应用到一个广泛的生物群系，涡度协方差蒸发水分流失数据被保存在一个中央数据库，称为FLUXNET。在这样做的过程中，这将使这些植物冠层的用水策略的研究，其相应的气候和水预算的限制。

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.