Climate change data
Adaptation to climate change relies on a robust and shared assessment of physical climate risks. For local authorities and businesses alike, it is essential to understand how climate hazards will evolve in terms of intensity, frequency, and duration over different time horizons.
In France, several methods for assessing and rating climate hazards have been developed in recent years by public institutions, financial actors, and specialized consulting firms. However, these approaches use heterogeneous indicators, thresholds, and scoring systems. This methodological diversity limits the comparability of results, complicates their interpretation, and hinders the development of a coherent national framework for decision-making.
As part of the National Climate Change Adaptation Plan (PNACC 3), ADEME commissioned the Auxilia and Hydroclimat consortium to carry out a structural study aimed at harmonizing and enhancing the transparency of methods for assessing future climate hazards, ensuring their compatibility with the TRACC (Reference Warming Trajectory for Climate Change Adaptation).
The study has a dual scientific and operational purpose. On the one hand, it aims to conduct an in-depth critical review of the main existing national methods in order to analyze their scientific robustness, the relevance of the indicators used, the construction of rating thresholds, and the consistency of scoring systems. This analysis focuses in particular on references such as OCARA (Carbone 4), the Banque de France method, Bat-ADAPT (Observatoire de l'Immobilier Durable), Météo-France's Patch 4°C, and the approach developed by the Caisse des Dépôts.
The aim is also to design a harmonized set of climate risk evolution scores covering the whole of mainland France, with a view to extending it to overseas territories. The hazards studied include drought, flooding, heat waves, storms, clay shrinkage and swelling, and forest fires.
These scores must meet three major requirements. They must be scientifically robust, transparent in their construction, and directly applicable to regional adaptation efforts.
The first phase of the project consisted of establishing a shared methodological framework to ensure scientific rigor and national consistency in the work. This step is crucial in a study assessing the evolution of climate hazards, as it determines the comparability and robustness of the final results.
The framework made it possible to specify the geographical scope, centered on metropolitan France with consideration given to extending it to overseas territories, as well as the climate reference system used, namely TRACC. It also defined the time horizons for analysis, the principles of compatibility with existing reference systems, and the transparency requirements for constructing the scores.
In-depth work was carried out to establish common evaluation criteria based on four key dimensions: the scientific quality of climate indicators, their operational relevance for end users, the representativeness of the climate hazards covered, and compatibility with national and European frameworks.
This stage was based on close dialogue with the steering committee and the scientific committee to ensure methodological alignment from the outset of the study.
The second phase constitutes the analytical core of the study. It is based on an in-depth critical review of the main national methods for rating climate hazards, developed by institutional, financial, and technical actors. The objective is not to merge these methods, but to analyze their strengths, limitations, and biases in order to identify cross-cutting lessons.
The second phase constitutes the analytical core of the study. It is based on an in-depth critical review of the main national methods for rating climate hazards, developed by institutional, financial, and technical actors. The objective is not to merge these methods, but to analyze their strengths, limitations, and biases in order to identify cross-cutting lessons.
This analysis focuses in particular on the nature of the climate and hydroclimatic indicators used, their physical link to the hazard under study, the data sources used, and the calculation and aggregation methods. Particular attention is paid to the construction of rating thresholds, whether based on statistical, expert or hybrid approaches, as well as to the stability of these thresholds over time.
The consideration of uncertainties is another central focus of the critical review. Methods are examined in terms of their ability to integrate multi-model variability, the dispersion of climate projections, and sensitivity to scenario assumptions. This phase also relies on collaborative workshops. These workshops bring together method developers and relevant institutions to compare approaches and consolidate a shared understanding of methodological issues, particularly for complex hazards such as floods, soil drought, clay shrinkage-swelling, and forest fires.
Particular attention is paid to taking climate uncertainties into account, including inter-model variability, projection dispersion, and sensitivity to scenario assumptions.
The third phase of the project consists of transforming the lessons learned from the critical review into a harmonized operational framework. The aim is to design a set of climate hazard evolution scores that are compatible with TRACC, scientifically robust, and directly usable by local authorities, businesses, and financial actors.
This step involves selecting harmonized climate indicators, defining consistent aggregation principles, and determining transparent and justified thresholds. The calculations are based on public reference databases and incorporate a multi-model approach to ensure the robustness of the results. The aim is to produce scores that are comparable over time and space, while maintaining a level of clarity that is appropriate for the needs of decision-makers.
The project will result in the creation of a comprehensive, freely accessible municipal database covering the evolution of the main climate hazards until 2100. This common foundation is not intended to replace existing methods, but to provide a harmonized and interoperable framework for strengthening the national consistency of climate assessments.
By combining scientific rigor, methodological transparency, and operational requirements, these three phases structure a comprehensive approach ranging from critical analysis to the production of decision-making tools for climate change adaptation.
The study will result in the definition of a robust and transparent methodological framework for rating future climate hazards in France.
The scores produced will form a common national basis compatible with TRACC, facilitating comparability between territories and strengthening the consistency of climate assessments.
Local authorities, businesses, and financial actors will have access to scientifically validated indicators that are directly interpretable and suitable for decision-making. These tools will make it possible to prioritize adaptation actions, guide investments, and more effectively integrate climate risk into development, insurance, and financing strategies.
This study conducted for ADEME marks a key step in the development of a harmonized national framework for assessing climate change.
By ensuring compatibility with TRACC and building on existing public frameworks, the project helps to transform the complexity of climate projections into a clear, consistent, and operational tool for decision-making.
Beyond methodological harmonization, this approach sustainably strengthens the capacity of territories and organizations to anticipate the effects of climate change and develop adaptation strategies based on robust, transparent, and comparable indicators.
It thus contributes to the structuring of a national reference framework for climate resilience.
