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# Sensitivity of Covered and Confined Aquifers to Climate
Forcing in Metropolitan France

Sivarama Krishna Reddy Chidepudi, Nicolas Massei, Abderrahim Jardani, Matthieu Fournier, Lisa Baulon, Asmae Ez Zahy, Augustin Thomas

► To cite this version:

Sivarama Krishna Reddy Chidepudi, Nicolas Massei, Abderrahim Jardani, Matthieu Fournier, Lisa Baulon, et al.. Sensitivity of Covered and Confined Aquifers to Climate Forcing in Metropolitan France. Journées OneWater 2025, Aug 2025, BORDEAUX, France. hal-05306224

HAL Id: hal-05306224

https://hal.science/hal-05306224v1

Submitted on 9 Oct 2025

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Public Domain
Confined groundwater aquifers and more generally aquifers under impervious sedimentary cover (CAq) are a priori rather protected from external anthropogenic and climate forcings. Within the framework of the DEESAC project, which aims to define a methodological guide for the sustainable exploitation of CAq in France, we investigate the sensitivity of CAqs across metropolitan France to large-scale and local-scale climate variability using transfer entropy analysis. Transfer entropy is used to assess information flow from climate variables to CAq groundwater levels (GWL) in terms of causal relationships and associated lag times. The approach developed allows us to identify areas involved in information flow from precipitation to GWL and may help to identify recharge or pressure pulse transfer pathways controlling GWL. In addition, the quantification of information flow from climate indices to GWL provides an assessment of large-scale/global climate variability impact on CAqs.

### Défi 3 : L'eau comme sentinelle de la santé environnementale et humaine
le long du continuum terre-eau-mer

### Projet DEESAC : Durabilité et exploitabilité des eaux souterraines des aquifères captifs ou sous couverture

## Motivation & Objectives

* To what extent are confined and covered aquifers (CAq) sensitive to climate variability?

* What methodological approaches to deploy to assess such possible links?

## Study Area & Data

* Data from confined and covered aquifers across metropolitan France with 25+ years of data and minimal gaps.

* Climate indices: describe large-scale atmospheric circulation or ocean dynamics patterns (North Atlantic: NAO, SCAND, EA, AMO; Pacific: PDO, NINO indices).

* Precipitation from ERA 5 (0.25*0.25 and 0.1*0.1 degrees) and SAFRAN grids (~0.1*0.1 degrees)

<figure><img src="image_2.png" /><figcaption>234 CAq GWL stations (Red)</figcaption></figure>

<figure><img src="image_3.png" /><figcaption>Example of GWL and selected climate indices time series</figcaption></figure>

## Assessing causality and information flow between climate and GWL

* Bivariate Transfer Entropy is computed to analyze magnitude of causal relationships between climate indices, local precipitation, and GWL

* → a statistical way to evaluate hydrological connections and to provide insights into recharge processes

* Technical:

* → **Non-linearity** accounted with the use of Kraskov estimator.

* → **Statistical significance** tested via surrogate data/randomization/permutations

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* Some indices (oceanic: AMO, PDO, NINO) indicate widespread causal relationship → relate to long-term trends affecting wide spatial areas

* Atmospheric indices → more sparse relationships to GWL (more related to atmospheric higher-frequency variability?)

Map of TE over the whole area: Arrow pointing from precipitation grid cell to GWL station at the center of the precipitation window: first step

to identifying recharge areas?

TE approach allows us to identify areas involved in information flow from precipitation to GWL

## Key takeaways and perspectives

* Large-scale oceanic climate indices (e.g., AMO, PDO, NINO) demonstrate widespread causal relationships with GWL, likely reflecting their influence on long-term trends.

* TE from precipitation grids to be compared with physics based modeling at pilot-sites and against different reanalysis datasets.

* Evaluation of the physical meaning of TE by conducting numerical experiment using synthetic cases with controlled physics (Felipe et al (generic model) / other DEESAC teams)

* Relation of TE to geochemical information (estimated residence times)

SCAN ME

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RÉPUBLIQUE
FRANÇAISE
Liberté
Egalité
Fraternité

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PROGRAMME
DE RECHERCHE
ONEWATER -
EAU BIEN COMMUN

cnrs

Géosciences pour une Terre durable
brgm

INRAO

université
de BORDEAUX

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DEESAC

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