EGU23-7666, updated on 10 Jan 2024
https://doi.org/10.5194/egusphere-egu23-7666
EGU General Assembly 2023
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Interpretability of negative latent heat fluxes from Eddy Covariance measurements during dry conditions

Sinikka Jasmin Paulus1,2, Tarek Sebastian El-Madany1, Rene Orth1, Anke Hildebrandt3,2, Markus Reichstein1, Jacob A. Nelson1, Arnaud Carrara4, Gerardo Moreno5, Matthias Mauder6, Jannis Groh7,8,9, Sung-Ching Lee1, and Mirco Migliavacca1,10
Sinikka Jasmin Paulus et al.
  • 1Max Planck Institute for Biogeochemistry, Jena, Germany (spaulus@bgc-jena.mpg.de)
  • 2Friedrich-Schiller University, Jena, Germany
  • 3Helmholtz Centre for Environmental Research - UFZ, Leipzig, Germany
  • 4Fundacion Centro de Estudios Ambientales del Mediterraneo, Valencia, Spain
  • 5Universidad de Extremadura, Forest Research, Placencia , Spain
  • 6Technische Universität Dresden, Dresden, Germany
  • 7University of Bonn, Bonn, Germany
  • 8Forschungszentrum Jülich, Jülich, Germany
  • 9Leibniz Centre for Agricultural Landscape Research (ZALF), Müncheberg, Germany
  • 10now at Joint Research Center - European Comission, Ispra, Italy

Non-rainfall water can play a critical role in many ecosystems, but is understudied in most regions due to a lack of continuous, specialized measurements. One of the most commonly used techniques to quantify in situ ecosystem water fluxes is Eddy Covariance (EC). However, its use for the quantification of the two most famous non-rainfall water sources, dew and (radiation) fog, is limited because they often occur under humid conditions and nighttime stable stratification, making EC measurements particularly uncertain or non-valid.

Here we describe how a non-rainfall water input observed under dry conditions, namely water vapor adsorption by soil particles (VWA), can be monitored using existing eddy covariance datasets, giving insight into this little-studied soil water source. Unlike dew and radiation fog, atmospheric stability is not a prerequisite for WVA. Instead, WVA is driven by a highly negative soil matric potential inducing water vapor to condensate already at relative humidity < 100 %. Therefore, EC measurements may be more suitable to detect and quantify this flux than for dew and fog.

In this study, we test EC measurements for inferring WVA by comparing them to observations from large-weighing lysimeters, where the latter can be considered as a reference system for the measurement of WVA. Our aim is to explore the potential and limitations of the EC technique to detect and quantify WVA. We assess the quantitative and qualitative agreement between WVA estimated with the lysimeters and negative (downward) LE fluxes from EC. Our analysis uses four years of observations from a semi-arid tree-grass ecosystem and one year of a temperate agricultural ecosystem during the 2018 drought.

Our results show that during dry conditions the water vapor gradient between the relatively humid atmosphere and the dry soil pores leads to WVA in both ecosystems. We find a decent agreement between the timing of fluxes detected as WVA with lysimeters and with EC instruments, but the magnitudes (i.e. the amount of flux) differ. Furthermore, we aim to characterize the conditions under which negative LE fluxes from EC measurements can and should be interpreted as WVA. This way, our study expands the possibilities to investigate the relevance of WVA as a non-rainfall water source and, more generally, sheds light on a mostly overlooked aspect of land-atmosphere interaction during dry conditions in different ecosystems.

How to cite: Paulus, S. J., El-Madany, T. S., Orth, R., Hildebrandt, A., Reichstein, M., Nelson, J. A., Carrara, A., Moreno, G., Mauder, M., Groh, J., Lee, S.-C., and Migliavacca, M.: Interpretability of negative latent heat fluxes from Eddy Covariance measurements during dry conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7666, https://doi.org/10.5194/egusphere-egu23-7666, 2023.