Numerical Investigation of Flux Partitioning Methods for Water Vapor and Carbon Dioxide

The partitioning of ecosystem evapotranspiration and carbon dioxide fluxes into their plant and ground components is a critical research priority to better understand the water cycle and ecosystem function. Despite advances in different measurement techniques and partitioning models in the last decades, much is still unknown regarding the importance of different components of H₂O and CO₂ fluxes in ecosystems. In this work, we compare three partitioning methods that are based on analysis of conventional high frequency eddy-covariance (EC) data: the flux variance similarity method, the modified relaxed eddy accumulation method, and the conditional eddy covariance method. To this end, we developed an approach to simulate these fluxes in large eddy simulations, where time series were generated and further used to probe the performance, assumptions, and relative skill of the three methods. We also investigated the influence of canopy configuration, such as canopy sparseness, on the results. Our findings indicate that the methods’ performance depends on the flux magnitude of the different components. Moreover, it is also influenced by the turbulent mixing directly caused by different canopy arrangements. Overall, our numerical study allows the development of best partitioning practices for the implementation of each method.