WP2: Interface models-data

WP2: Interface models-data

The WP2 Interface models-data aims to improve the use of observatories’ data in modeling and to promote data-models merging in order to enhance the knowledge on the Critical Zone’s functioning. The WP2 also aims at promoting, through modeling, dialogue and interactions between the OZCAR-RI’s teams, in particular between “experimenters” and “modellers”.

A multi-site approach to modeling

A lot of modeling work has been carried out on the different sites of the OZCAR-RI which, combined with data analysis, has provided some key knowledge. However, these approaches remained very site-specific and often used different modeling tools.

In the context of the OZCAR-RI, it became necessary to use a multi-site modeling approach based on the data from OZCAR-RI observatories in order to foster a comparative approach and to try to answer “big” questions on general and local functioning of the Critical Zone.

A first step was to identify the modeling tools used in OZCAR-RI and the type of observables needed/used. A synthesis was presented at the TERENO conference in October 2018. 

Towards a better dialogue between observation data and models

In order to demonstrate the added value of a data-models fusion work on a set of OZCAR-RI observatories, two posdoctoral fellows, Sylvain Kuppel (April 2019 to January 2021) and then, Julien Ackerer (since February 2021) have been recruited.

After a consultation with the teams interested in the approach, Sylvain Kuppel’s work focused on implementing the EcH2O-iso ecohydologic model on four observatories sharing a similar geology but with different climatic and land-use contexts : the Strengbach site in the Vosges (OHGE), the Kerbernez site in Brittany (AgrHys), the Ara site in Benin (AMMA-CATCH) and the Mule Hole site in India (M-TROPICS). This allowed the following scientific questions to be addressed :

  • Where do plants extract the water they consume and how does this influence water pathways in the watershed?
  • How do water flows and water residence times in the regolith (the soil’s altered area) impact the transport of major elements?

To address the second question, the EcH2O-ISO ecohydrological model was linked with the WITCH3D chemical wheathering model.

Julien Ackerer has continued this work by focusing on three metropolitan basins with contrasting geological, climatic and land use contexts: the Kervidy-Naizin (AgrHys), Auradé and Strengbach (OHGE) basins.

Strong results have been obtained for each catchment making it possible to explain the river flows observed, the groundwater levels monitored by piezometers and the evapotranspiration measured at flux towers. The simulations were also constrained by geophysical measurements (estimating the thickness of the regolith in the catchment areas, i.e. weathered material) and the satellite measurements (estimating the state oh the vegetation and land cover). The model also provides access to non-measurable variables such as water stocks in the various reservoirs and their transit times. The multi-site dimension of this project revealed the extent to which the functioning of the Critical Zone is impacted by regional specificities. These results have been summarized in an article submitted to Water Resources Research in June 2023.

In 2022, a Master 2 internship enabled the development of reactive transport modelling at the Kervidy-Naizin site/Aghrys Observatory by using the KIRMAT model.

Workshop on modelling in 2023

A workshop on Critical Zone modelling, entitled ” Modelling the Critical Zone : from local data acquisition to regional modelling ” was held on 25 and 26 Mays 2023. Around 30 people attended this workshop, half of them being on-site and was an opportunity to encourage an exchange between modellers from different sites whatever their field of expertise and also to discuss the interactions between local to regional scales and the global scale thanks to presentations of two continental surface models (SURFEX and ORCHIDEE models) used in climate modelling.

The seminar was organised into 4 parts:

– a summary of the modelling challenges by discipline (hydrology/hydrogeology, biogeochemistry, geophysics, vegetation and interactions between water, energy, carbon, sediment transport and geomorphology)

– a workshop to think about 5 questions dealing with progress that should be made in modelling as well as elements required for preparing a position paper summarising the challenges of modelling the Critical Zone in the OZCAR RI observatories

– a discussion on the possible outline of this position paper and the figures that could illustrate it

– an introduction to climate modelling and Earth system modelling with presentations of the SURFEX model used at CNRM and Météo-France by Aaron Boone (CNRM) and the ORCHIDEE model used at IPSL by Agnès Ducharne (METIS) for hydrology and Philippe Peylin (LSCE) for biogeochemistry.

Thanks to these rich and fruitful exchanges, a series of elements were collected for preparing the positioning article.

The programme of the workshop : open

A summary of developments made on the WP2 Model Data Interface is presented in the annual OZCAR newsletter. You can find the latest developments in the newsletter OZCAR 2023.