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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/hess-2020-95
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2020-95
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  16 Mar 2020

16 Mar 2020

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A revised version of this preprint was accepted for the journal HESS and is expected to appear here in due course.

Imprints of evaporation and vegetation type in diurnal temperature variations

Annu Panwar, Maik Renner, and Axel Kleidon Annu Panwar et al.
  • Biospheric Theory and Modeling group, Max Planck Institute for Biogeochemistry, Jena, 07745, Germany

Abstract. Diurnal temperature variations are strongly shaped by the absorption of solar radiation, but evaporation, or the latent heat flux, also plays an important role. Generally, evaporation cools. Its relation to diurnal temperature variations, however, is unclear. This study investigates the diurnal response of surface and air temperatures to evaporation for different vegetation types. We used the warming rate of temperature to absorbed solar radiation in the morning under clear-sky conditions and evaluated how the warming rates change for different evaporative fractions. Results for 51 FLUXNET sites show that the diurnal variation of air temperature carries very weak imprints of evaporation across all vegetation types. However, surface temperature warming rates of short vegetation decrease significantly by ~ 23 × 10−3 K/W m−2 from dry to wet conditions. Contrarily, warming rates of surface and air temperatures are similar at forest sites and carry literally no imprints of evaporation. We explain these contrasting patterns with a surface energy balance model. The model reveals a strong sensitivity of the warming rates to evaporative fraction and aerodynamic conductance. However, for forests the sensitivity to evaporative fraction is strongly reduced by 74 % due to their large aerodynamic conductance. The remaining imprint is reduced further by ~ 50 % through their enhanced aerodynamic conductance under dry conditions. Our model then compares the individual contributions of solar radiation, evaporation and vegetation types in shaping the diurnal temperature range. These findings have implications for the interpretation of land-atmosphere interactions and the influences of water limitation and vegetation on diurnal temperatures, which is of key importance for ecological functioning. We conclude that diurnal temperature variations may be useful to predict evaporation for short vegetation. In forests, however, the diurnal variations in temperatures are mainly governed by their aerodynamic properties resulting in no imprint of evaporation in diurnal temperature variations.

Annu Panwar et al.

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Annu Panwar et al.

Annu Panwar et al.

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Short summary
Here we quantify and demonstrate how do solar energy, surface water availability and vegetation types shape the diurnal variation of surface and air temperature. We found stronger imprints of evaporation in diurnal surface temperature for short vegetation. Contrarily, taller vegetations like forest reduce the diurnal variation and its responses to evaporation drastically due to their stronger aerodynamic conductance. Surprisingly, the diurnal air temperature has no imprints of evaporation.
Here we quantify and demonstrate how do solar energy, surface water availability and vegetation...
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