Articles | Volume 21, issue 3
Hydrol. Earth Syst. Sci., 21, 1809–1825, 2017
https://doi.org/10.5194/hess-21-1809-2017
Hydrol. Earth Syst. Sci., 21, 1809–1825, 2017
https://doi.org/10.5194/hess-21-1809-2017

Research article 28 Mar 2017

Research article | 28 Mar 2017

A site-level comparison of lysimeter and eddy covariance flux measurements of evapotranspiration

Martin Hirschi1, Dominik Michel1, Irene Lehner1,a, and Sonia I. Seneviratne1 Martin Hirschi et al.
  • 1Institute for Atmospheric and Climate Science, ETH Zurich, Universitätstrasse 16, 8092 Zurich, Switzerland
  • apresent address: Centre for Environmental and Climate Research (CEC), University of Lund, Lund, Sweden

Abstract. Accurate measurements of evapotranspiration are required for many meteorological, climatological, ecological, and hydrological research applications and developments. Here we examine and compare two well-established methods to determine evapotranspiration at the site level: lysimeter-based measurements (EL) and eddy covariance (EC) flux measurements (EEC). The analyses are based on parallel measurements carried out with these two methods at the research catchment Rietholzbach in northeastern Switzerland, and cover the time period of June 2009 to December 2015. The measurements are compared on various timescales, and with respect to a 40-year lysimeter-based evapotranspiration time series. Overall, the lysimeter and EC measurements agree well, especially on the annual timescale. On that timescale, the long-term lysimeter measurements also correspond well with catchment water-balance estimates of evapotranspiration. This highlights the representativeness of the site-level lysimeter and EC measurements for the entire catchment despite their comparatively small source areas and the heterogeneous land use and topography within the catchment. Furthermore, we identify that lack of reliable EC measurements using open-path gas analyzers during and following precipitation events (due to limitations of the measurement technique under these conditions) significantly contributes to an underestimation of EEC and to the overall energy balance gap at the site.

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Short summary
We compare lysimeter and eddy covariance (EC) flux measurements of evapotranspiration at a research catchment in Switzerland. The measurements are compared on various timescales, and with respect to a 40-year long-term lysimeter time series. Overall, the lysimeter and EC measurements agree well, especially on the annual timescale. Furthermore, we identify that lack of reliable EC data during/after rainfall events significantly contributes to an underestimation of EC evapotranspiration.