Partitioning of evapotranspiration based on flux variance similarity theory for an urban forest land

Partitioning of evapotranspiration(ET) into its components (ET; the sum of vegetation transpiration [T] and soil evaporation [E])from urban forest land is important for guiding precise irrigation decisions in urban areas and assessing the impact of urbanization on the urban hydrological cycle. So far, the variability of T/ET in natural ecosystems has been extensively discussed, few studies have examined under urban. In this study, high frequency (10 Hz) time series eddy covariance observations collected from January 2020 to December 2021 in an urban forest land located in Tianjin, China. We observed changes in water vapor and carbon dioxide fluxes and the flux variance similarity (FVS) theory based on five water use efficiency(WUE) algorithms was applied to partition ET into E and T. We also combined with oxygen and hydrogen isotopes to verifies the partition results. The results indicated that the partitioning was partially consistent with the isotope-based approach. The growing season average T/ET ranges from 0.68 to 0.96, which can be described well as a function of leaf area index (LAI). Finally, we further discussed the characteristics, uncertainties and applicability of five WUE algorithms in urban forest land.