Modeling groundwater and heat fluxes to quantify streamwater temperature spatiotemporal heterogeneity

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INRAE presentation

The French National Research Institute for Agriculture, Food, and Environment (INRAE) is a major player in research and innovation. It is a community of 12,000 people with 272 research, experimental research, and support units located in 18 regional centres throughout France. Internationally, INRAE is among the top research organisations in the agricultural and food sciences, plant and animal sciences, as well as in ecology and environmental science. It is the world’s leading research organisation specialising in agriculture, food and the environment. INRAE’s goal is to be a key player in the transitions necessary to address major global challenges. Faced with a growing world population, climate change, resource scarcity, and declining biodiversity, the Institute has a major role to play in building solutions and supporting the necessary acceleration of agricultural, food and environmental transitions.

Work environment, missions and activities

Context
The effects of global warming are now measurable in French rivers (Seyedhashemi, et al., 2022), particularly the steady rise in their temperatures. This warming is disrupting ecological balances: a reduction in viable aquatic habitats, thermal stress for fish, loss of biodiversity, and deterioration in water quality. It also affects critical uses, such as electricity generation and drinking
water supply.
 

Among the key processes influencing river temperatures are the exchanges between groundwater and river water (Figure 1.A). With more moderate seasonal temperature variability (warmer in winter and cooler in summer), groundwater — when it contributes significantly to a watercourse — can mitigate temperature extremes and play a vital buffering role for ecosystems. However, these interactions are still poorly understood, which limits our ability to map these thermal anomalies for conservation purposes - e.g., use as thermal refuges - (Kurylyk, et al., 2026). This thesis will aim to better account for these key interactions and thereby improve our ability to simulate river temperatures and propose strategies to enhance the resilience of hydrosystems.
 

Across the Saône catchment (France), geological and geomorphological heterogeneity creates significant contrasts in groundwater-river interactions (Figure 1.B). The headwaters of the Saône (~100 km²) are therefore an ideal study area for
better characterizing these groundwater-river interactions in contrasting hydrogeological contexts and quantifying their impact on river temperature, which is essential for:
 – identifying thermal refuge zones;
 – understanding their spatial extent and temporal stability;
 – developing decision-support tools for climate change adaptation.
In particular, this thesis will provide river managers with information to help them best preserve thermal refuges in the context of global change.
 

Thesis Research Question and Objectives
You will conduct a thesis aimed at quantifying the impact of groundwater on river temperature. Applied to medium-sized watersheds (~100 km²) located in the Saône watershed, this thesis aims to make general progress on the following questions: where does groundwater primarily contribute to river flow? What is the temperature of these inflows, given the characteristicsof the relevant water bodies and the groundwater pathways contributing to them? How stable are these inflows over time (seasonally, interannually)?
The research question of this thesis can therefore be stated as follows: How can we quantify the spatiotemporal dynamics of underground water and heat inflows into headwater streams, and then incorporate this knowledge into an
operational thermal model ?
 

The thesis will focus on three objectives:
1. Quantify groundwater inflows to the river (Qgw) at watershed heads representative of different hydrogeological contexts.
2. Estimate the temperature of groundwater inflows (Tgw) and the associated heat fluxes using combined data/model approaches.
3. Integrate these flows into the TNET/J2000 coupling to simulate the thermal heterogeneity of watercourses at high resolution, particularly during critical periods (low water levels, heat waves)

Methodology
Your research will involve developing hydrogeological models of watersheds and quantifying their ability to represent the spatiotemporal heterogeneity of groundwater inflow into watercourses. These models will be developed and calibrated in a parsimonious manner to fit the available data. In a second phase, these models will be expanded to include groundwater thermal modeling in order to quantify not only water flows but also heat flows from the aquifer to the watercourse.
 

This thesis will be organized into three stages:
1. Learn to use the MODFLOW model with the HydroModPy library and adapt it to the watersheds to be modeled (Abhervé, et al., 2023; Gauvain, et al., 2026).
2. Conduct a literature review on heat transport to develop methods based on processes (Briggs, et al., 2018) or on data (Marteau, et al., 2022; Johnson, et al., 2024) to infer heat fluxes from aquifers to watercourses (Kurylyk, et al., 2026).
3. Integrate the computational codes developed previously with the T-NET river thermal model to create an integrated model that combines surface hydrology and hydrogeology.

Work environment
You will be based at the RiverLy research unit (INRAE Villeurbanne), which conducts multidisciplinary research on the functioning of hydrosystems. RiverLy brings together expertise in ecology, microbiology, ecotoxicology, environmental
chemistry, hydrology, and hydraulics. It has a staff of approximately 130 people, including 70 permanent employees.
You will be supervised by:
     -Jean Marçais (UR RiverLy), hydrogeologist and modeler. Jean works on estimating the contribution of groundwater to river flow and its impact on river water ages.
     - Florentina Moatar (UR RiverLy), a specialist in the interactions between hydrology, water quality, climate, and anthropogenic pressures. She is responsible for developing the T-NET model, which is used in Step 3 (see methodology).
     - Ronan Abhervé (UMR SAS, INRAE Rennes), hydrogeologist and modeler. Ronan is an expert in MODFLOW. He focuses on intermittent rivers and the characterization of hydrogeological properties based on river networks.
This dissertation will be part of the ThermieFrance project, coordinated by Florentina Moatar. This project brings together a
broad academic and operational consortium (INRAE, CNRS, BRGM, Météo-France, EDF, Mines Paris PSL, etc.). The dissertation
will benefit from privileged access to the project’s databases, opportunities for exchange among doctoral students, and
interdisciplinary training.
Proposed collaborations:
  - Barret Kurylyk, Dalhousie University, New Brunswick, Canada, a hydrogeologist specializing in groundwater-river
exchange and its impact on river temperature.

Training and skills

We are looking for a candidate who is curious about environmental issues, creative, and meticulous, with a strong interest in environmental modeling.
- Recommended education: MS in hydrology, geosciences, or environmental sciences.
- Desired knowledge: Hydro(geo)logy.
- Desired skills: Strong interest in modeling, knowledge of the Python and R and/or MATLAB programming languages.
   Independence. Strong writing skills.

INRAE's life quality

By joining our teams, you benefit from (depending on the type of contract and its duration):

- up to 30 days of annual leave + 15 days "Reduction of Working Time" (for a full time);
- parenting support: CESU childcare, leisure services;
- skills development systems: training, career advise;
- social support: advice and listening, social assistance and loans;
- holiday and leisure services: holiday vouchers, accommodation at preferential rates;
- sports and cultural activities;
- collective catering.

How to apply

I send my CV and my motivation letter