Comparing different methods for determining forest evapotranspiration and its components at multiple temporal scales

Qiang Tie; Hongchang Hu; Fuqiang Tian; N Michele Holbrook

doi:10.1016/j.scitotenv.2018.03.082

Comparing different methods for determining forest evapotranspiration and its components at multiple temporal scales

Sci Total Environ. 2018 Aug 15:633:12-29. doi: 10.1016/j.scitotenv.2018.03.082. Epub 2018 Mar 20.

Authors

Qiang Tie¹, Hongchang Hu², Fuqiang Tian³, N Michele Holbrook⁴

Affiliations

¹ Department of Hydraulic Engineering, State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China; Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA.
² Department of Hydraulic Engineering, State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China.
³ Department of Hydraulic Engineering, State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China. Electronic address: tianfq@tsinghua.edu.cn.
⁴ Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA.

PMID: 29571042
DOI: 10.1016/j.scitotenv.2018.03.082

Abstract

Accurately estimating forest evapotranspiration and its components is of great importance for hydrology, ecology, and meteorology. In this study, a comparison of methods for determining forest evapotranspiration and its components at annual, monthly, daily, and diurnal scales was conducted based on in situ measurements in the subhumid mountainous forest of North China. The goal of the study was to evaluate the accuracies and reliabilities of the different methods. The results indicate the following: (1) The sap flow upscaling procedure, taking into account diversities in forest types and tree species, produced component-based forest evapotranspiration estimate that agreed with eddy covariance-based estimate at the temporal scales of year, month, and day, while soil water budget-based forest evapotranspiration estimate was also qualitatively consistent with eddy covariance-based estimate at the daily scale; (2) At the annual scale, catchment water balance-based forest evapotranspiration estimate was significantly higher than eddy covariance-based estimate, which might probably result from non-negligible subsurface runoff caused by the widely distributed regolith and fractured bedrock under the ground; (3) At the sub-daily scale, the diurnal course of sap flow based-canopy transpiration estimate lagged significantly behind eddy covariance-based forest evapotranspiration estimate, which might physiologically be due to stem water storage and stem hydraulic conductivity. The results in this region may have much referential significance for forest evapotranspiration estimation and method evaluation in regions with similar environmental conditions.

Keywords: Catchment water balance; Eddy covariance; Forest evapotranspiration; Sap flow; Soil water budget; Subhumid mountainous forest.