EGU General Assembly 2020
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the Creative Commons Attribution 4.0 License.

High accuracy measurement system for dew and fog water quantification in temperate grassland ecosystems

Andreas Riedl, Yafei Li, Nina Buchmann, and Werner Eugster
Andreas Riedl et al.
  • ETH Zürich, Institute of Agrictultural Sciences, Departement of Environmental Systems Science, Zürich, Switzerland (

Dew and fog occur rather frequently in ecosystems all over the world. Still, water from dew and fog is often not considered in ecohydrological budgets. One reason is that there is no reference standard instrument to measure those water inputs into ecosystems. Another reason is that the water input from dew and fog is, compared to the water input from precipitation, a rather small amount at most locations, which makes it difficult to be measured accurately.

We developed a custom-made measurement system for quantifying dew and fog water inputs to temperate grassland ecosystems. The system consists of three high accuracy weighing micro-lysimeters composed of a plant pot which stands on a weighing platform with additional sensors. The weighing micro-lysimeters were designed to quantify even small water gains caused by dew formation on grasses with unprecedented accuracy.  Some former studies on micro-lysimeter design for dew measurements used small-size plant or bare-soil pots in combination with low capacity load cells, which allowed high accuracy measurements, but these systems were not able to mimic natural field conditions in terms of thermal behaviour and plant development. Other studies used large lysimeter systems which were better capable to simulate natural conditions, but required substantial infrastructure for installation and often showing too low accuracy, because of a trade-off between load cell accuracy vs. capacity.

Inside the micro-lysimeter plant pots, we installed soil moisture and temperature sensors to compare thermal and moisture conditions inside the plant pots with sensors installed in a control field plot at 1 m distance. A further component of the measurement system is a visibility sensor which allows to determine if water inputs originate solely from dew or from dew and fog in combination (fog: horizontal visibility < 1000 m). A leaf moisture sensor gives a redundant measurement to sense if leaves are really wet and for how long they stay wet. 

We set up a measuring network with the beforementioned system at eight sites in Switzerland and an additional site in South Tyrol (Italy). The sites were selected to gain representative measurements over an extended elevational gradient (from 500 to 2000 m a.s.l), within areas prone to fog (Swiss Plateau) and rather unlikely fog occurrence (Alps), as well as with low and high precipitation amounts (from 500 up to over 1500 mm/year).

Measuring dew and fog water inputs is expected to be important, as grassland species are able to take up water via foliar water uptake. Thus, dew and fog water can be important water inputs, especially in dry periods during fair weather summer conditions.

How to cite: Riedl, A., Li, Y., Buchmann, N., and Eugster, W.: High accuracy measurement system for dew and fog water quantification in temperate grassland ecosystems , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4535,, 2020

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Display material version 1 – uploaded on 05 May 2020
  • CC1: Comment on EGU2020-4535, Maurizio Mencuccini, 06 May 2020

    dear Andreas,
    very interesting setup. It seems to be accurate and sensitive at the same time. I was not clear from the slides how you separate condensation on the plant vs the soil. Good work... is it published yet?

    • AC1: Reply to CC1, Andreas Riedl, 06 May 2020

      Dear Maurizio,

      Thanks for your comment and interest.

      We can't seperate condensation from soil and plant canopy. However, both, condensation on leaves and on soils provides water to plants. Uptake can occur via roots or via foliar water uptake. Dew formation on soils is rare (Agam and Berliner 2004, DOI: 10.1175/1525-7541(2004)005<0922:DWCCIT>2.0.CO;2). Thus, we hypothesize that most of the water input from dew stems from condensation on leaves. This is also in line with the positive correlation between leaf area index and dew water yield.

      We are currently working on a publication on the topic.



      • CC2: Reply to AC1, Maurizio Mencuccini, 06 May 2020

        thanks for your answer. I have learnt something today!

  • CC3: Occurrence of dew vs occurrence of soil adsorption, Sinikka Paulus, 06 May 2020

    Hi Andreas,

    really great work and simple but very good idea to combine the different techniques to differentiate the processes! Since there was no time left in the life chat now here- can you say something about the amount and occurrence of leaf surface wetting events vs. the soil adsorption? Did you see any kind of seasonality in the processes?

    Thanks in advance for taking your time, cheers, Sinikka