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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/hess-2020-104
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2020-104
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  24 Mar 2020

24 Mar 2020

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This preprint is currently under review for the journal HESS.

Modelling of water and energy exchanges over a sparse olive orchard in semi-arid areas

Wafa Chebbi1,2, Vincent Rivalland2, Pascal Fanise2, Aaron Boone3, Lionel Jarlan2, Hechmi Chehab4, Zohra Lili Chabaane1, Valérie Le Dantec2, and Gilles Boulet2 Wafa Chebbi et al.
  • 1Université de Carthage/INAT/LR GREEN-TEAM, 43 avenue Charles Nicole, Tunis 1082, Tunisie
  • 2CESBIO, Université de Toulouse, CNES/CNRS/INRA/IRD/UPS, Toulouse, France
  • 3Centre National de Recherches Météorologiques, Toulouse, France
  • 4l'institut de l'olivier, Unitéspécialisée de Sousse, Rue Ibn Khaldoun, Sousse 4061, Tunisie

Abstract. In the Mediterranean basin, olive orchards occupy a large fraction of agricultural lands due to its sustainability to harsh conditions, drought in particular. Since most modeling tools to simulate vegetation functioning are not meant to represent very sparse crops (i.e., rainfed olive trees have a vegetation fraction cover ranging from 2 to 15 %), computing the water needs and the vulnerability to drought of an olive orchard is a challenge. There is indeed a very high contribution of the bare soil signal to the total fluxes, and it is difficult to decipher the contribution of the tree from that of the entire surface. In this context, in an attempt to study the olive tree hydrological functioning at field scale (38 ha), an experimental site was setup and a Soil–Vegetation–Atmosphere (SVAT) model has been applied. To represent the orchard soil–plant–atmosphere interactions, a simulation with default settings was assessed using parameters derived from both the literature and ground measurements. In this default configuration, neither the predicted actual nor the potential transpiration could reach the observed transpiration acquired during the wet season (R2 = 0.67, the Root Mean Square Error (RMSE) = 5.63 mm week−1). We show that the model fails to reproduce the relevant leaf surface that transpires. To address this issue and to improve the estimate of the year-to-year variability of the olive tree transpiration, we propose guidance on how a SVAT model can be modified to more appropriately represent the hydrological functioning of a sparse orchard. Once the tree transpiration is accurately simulated (R2 = 0.93, RMSE = 1.62 mm week−1), we evaluated whether the fully coupled (single patch) or a fully uncoupled (two patch) system better reproduced the total fluxes and their components. Owing to the independent characteristics of the soil columns inherent in the assumption of the 2-patch version, the bare soil column shows a deficiency if the topsoil root extraction is not accounted for. We deduced that we cannot accurately reproduce the soil evaporation in this configuration. This study open perspectives for a better representation of water fluxes over sparse tree crops into both hydrological and SVAT models.

Wafa Chebbi et al.

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Wafa Chebbi et al.

Wafa Chebbi et al.

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