EGU2020-17901
https://doi.org/10.5194/egusphere-egu2020-17901
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Large Aperture Scintillometer measurements above a large green roof to assess the evapotranspiration flux

Leydy Alejandra Castellanos Diaz1, Pierre Antoine Versini1, Ioulia Tchiguirinskaia1, Olivier Bonin2, and David Ramier3
Leydy Alejandra Castellanos Diaz et al.
  • 1HM&Co, Ecole des Ponts ParisTech, Champs-sur-Marne, France (leydy.castellanos@enpc.fr)
  • 2LVMT, Ecole des Ponts ParisTech, Champs-sur-Marne, France (olivier.bonin@enpc.fr)
  • 3Cerema, Equipe-projet TEAM, Trappes, France (david.ramier@cerema.fr)

The challenges induced by the continuous urbanization and the climate change effects, such as extreme events (e.g. flooding or heat waves) or the intense increase of the urban temperatures (Urban Heat Island), encourage the implementation of Blue and Green Solutions (BGS). These solutions are inspired by the nature, favouring natural process in the cities like water infiltration or evapotranspiration (ET), reducing air temperature during heatwaves events.

Characterize the thermal behavior governing a BGS is necessary to promote their implementation. Consequently, this research studies the energy fluxes –and particularly the evapotranspiration one- of a 1 ha wavy-shape green roof located in Champs-Sur-Marne (France), called Blue Green Wave (BGW). Therefore, a Large Aperture Scintillometer MKI, a CNR4 radiometer and 4 Type K thermocouples were installed on the BGW to measure the sensible heat flux of convection, the net radiation and the heat conduction into the soil substrate. The latent heat flux of ET was deduced from the energy balance.

Each LAS unit was placed on the highest locations of the roof with about 100 m of distance between them. Diaphragms for short-range applications were placed in front of the units. The measurements were conducted on sunny and randomly days during the 2019 summer over an average time period of 7 hours.

It appears that LAS sensible heat flux measurements on completely sunny days follow the net radiation flux trend. However, on cloudy days important flux fluctuations are noticed. Therefore, a sensitivity analysis was carried out to illustrate the significant correlation between the wind and the sensible heat flux during short time periods. In parallel, the heat conduction was analysed through a thermal gradient of temperature and a Fourier analysis demonstrating a poor conduction rate mainly on drier conditions of the BGW.

Finally, the deduced latent heat was compared with the measurements of a dynamic evaporation chamber, confirming a significant over estimation of the latent heat computed from the energy balance. This can be explained by the sum of uncertainties related to each energy flux component, in addition to the restraint conditions of LAS measurement operation on the BGW (application over the limits of MOST theory). A multifractal analysis to determinate the temporal and spatial scaling behaviour of latent heat flux is ongoing.

How to cite: Castellanos Diaz, L. A., Versini, P. A., Tchiguirinskaia, I., Bonin, O., and Ramier, D.: Large Aperture Scintillometer measurements above a large green roof to assess the evapotranspiration flux, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17901, https://doi.org/10.5194/egusphere-egu2020-17901, 2020

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Presentation version 1 – uploaded on 05 May 2020
  • CC1: Comment on EGU2020-17901, Hamideh Nouri, 06 May 2020

    Very interesting research. Could you please explain whether you use any of available energy balance models like SEBAL or SEBS?

    • AC1: Reply to CC1, Leydy Alejandra Castellanos Diaz, 06 May 2020

      Thanks for your comment. We didn’t use one of these models or remote sensing datasets. Even if the evapotranspiration is the residual of energy balance like in these models, the soil and sensible heat flux are calculated from local measurements.

      A radiometer was used to measure incoming and outgoing short and longwave radiation.

      The soil heat flux is estimated using Fourier’s law heat conduction equation: 4 thermocouples were placed at different depths on the substrate (separated 2-3cm) to measure the soil thermal gradient and the thermal conductivity parameter was chosen from the scientific literature in function of the soil moisture conditions.

      The sensible heat flux was calculated using Monin-Obukhov similarity theory (MOST) from Cn2 LAS measurements. Additional weather data is necessary to apply MOST functions.