Context and challenges of assessing the climate change impacts
The Argoat-Trégor-Goëlo SAGE territory, located in the north-west of Brittany, is geographically diverse, combining coastal areas, agricultural valleys and natural wetlands. It is criss-crossed by numerous coastal rivers and is heavily dependent on water resources for its many uses. It faces a number of growing challenges linked to the availability and quality of water resources.
The major issues concern the supply of drinking water for the local population, farming activities, mainly livestock and fodder crops, the agri-food industries, which consume large quantities of water, and the functioning of aquatic environments (wetlands, rivers, biodiversity). Reconciling these uses makes the balanced management of this resource particularly complex, especially during periods of low water or extreme events
Against a backdrop of climate change, the region is already experiencing signs of increased pressure on its water resources, which are likely to increase over the course of the 21st century: longer and more intense periods of summer drought, reduced low-water flows putting pressure on aquatic environments and priority uses, and changes in the seasonal distribution of rainfall, with a risk of more marked summer deficits.
These developments increase the risk of structural imbalances between supply (available resources) and demand (human and ecological needs), particularly in summer, with repercussions not only for uses but also for natural environments and aquatic biodiversity. Faced with these challenges, an evaluation of climate change impacts on water resources is a priority for the region.
Objective of the evaluation of climate change impacts
As part of an approach to sustainable, shared management of water resources, the Local Water Commission (CLE) of the Argoat-Trégor-Goëlo SAGE has launched a study to assess the impacts of climate change using the HMUC (Hydrology, Environments, Uses, Climate) approach, with a cross-sectional approach to all aspects of the region’s socio-hydrological system. The ‘Climate’ part of this study aims to:
- Establish a climatological diagnosis of the region based on historical meteorological data, whether observed or derived from reconstructions;
- Analyse the anticipated impacts of climate change on surface and groundwater resources, on different temporal and spatial scales;
- Understand the consequences of these changes on human uses (drinking water, agriculture, industry) and ecological balances (functioning of aquatic environments, hydrological continuity, biodiversity).
The aim of this study is to provide input for a coherent and operational regional strategy for adapting to climate change in order to help manage water resources. The study will help inform the long-term planning of actions under the SAGE, in conjunction with the other components of the HMUC (Hydrology, Environments, Uses) study.
Phase 1: Literature review on climate change
The first phase of the evaluation of climate change impacts aims to establish a common base of scientific knowledge on climate change, prior to the specific analyses carried out on the Argoat-Trégor-Goëlo SAGE territory. It is an essential step in laying the methodological foundations for assessing the impact of climate change on water resources, by mobilising recognised references at global, national and regional levels.
This bibliographical summary is based on the most recent and robust publications available to date, in particular the IPCC reports, the data and analyses disseminated via the DRIAS – Climate Futures portal, the contributions of the Observatoire de l’Environnement en Bretagne, and the studies produced as part of the Explore 2 and TRACC projects.
It provides a structured presentation of the fundamental mechanisms of climate change, such as the greenhouse effect, radiative forcings, and the uncertainties associated with climate projections. It also introduces the main tools used in prospective studies, namely :
- global climate models (GCM) and regional climate models (RCM),
- greenhouse gas emission scenarios (RCP/SSP),
- as well as climate narratives, enabling the hypotheses to be contextualised within plausible socio-economic trajectories.
In addition to scientific rigour, this phase adopts a popular educational approach, with the aim of making these complex concepts accessible to all the local players involved. In this way, it promotes a shared understanding of the climatic issues and an appropriation of the modelling hypotheses used in the rest of the study.
In this sense, this summary helps to anchor the HMUC study in a dynamic of consultation and climate acculturation, an essential prerequisite for the construction of an ambitious and coherent adaptation strategy on a regional scale. It is a necessary step in the evaluation of the climate change impacts
Phase 2: Analysis of the reference climate - past and present
This phase of the evaluation of the climate change impacts is based on the use of historical meteorological data available locally in the Argoat-Trégor-Goëlo SAGE area. Several measuring stations, such as Ploumanac’h, Saint-Brieuc and Kerpert, have been used to build up climate records over several decades, covering key parameters such as rainfall, temperature and evapotranspiration.
From these time series, climatological indicators were calculated to characterise past patterns and detect signals of change. A statistical analysis of the trends in these indicators was carried out in order to highlight :
- changes in average seasonal and annual temperatures,
- the frequency and intensity of extreme events (heat waves, droughts, intense rainfall),
- any seasonal shifts, indicating a change in the local weather pattern.
These results make it possible to characterise recent climate dynamics at the regional level and provide a reference for assessing future climate scenarios. By identifying the trends that have already been observed, this phase enhances our understanding of the region’s vulnerabilities and feeds into the evaluation of the climate change impacts on water resources.
Phase 3: Future climate projections
This phase of the evaluation of the climate change impacts aims to describe the likely evolution of the climate at the scale of the Argoat-Trégor-Goëlo SAGE territory. This description is produced on the basis of regionalised climate projections and territorialised climate narratives, in line with the work carried out as part of the TRACC (Trajectoires d’Adaptation au Changement Climatique) project.
For each time horizon (2030, 2050, 2100) and TRACC warming level, key climate indicators have been calculated: changes in precipitation, air temperature, evapotranspiration, frequency of heat waves, intensity of droughts, etc. These elements make it possible to anticipate critical periods for water availability, and to identify the major trends that could affect uses and environments. These elements make it possible to anticipate critical periods for water availability, and to identify the major trends that could affect uses and environments.
Particular attention is paid to popularising the uncertainties associated with the models and scenarios, in order to make them understandable to local stakeholders. This approach aims to encourage local ownership of the results and to contribute to the construction of adaptation trajectories that are consistent with the objectives of the SAGE.
Phase 4: Analysis of impacts on hydrology, environments and uses
The aim of this final phase is to translate projected climate change into concrete impacts on hydrological functioning, aquatic environments and water uses in the Argoat-Trégor-Goëlo SAGE area.
The data from the climate scenarios have been integrated into regional hydrological models (including SMASH, EROS Bretagne and the Explore 2 project tools) in order to simulate :
- changes in river flows,
- modification of future low-water levels,
- changes in groundwater recharge periods,
- and the increased risk of water shortages.
This modelling enables the impacts of climate change to be assessed according to local hydrogeographic characteristics.
Particular attention is paid to :
- small, ungauged rivers, which are often more sensitive to climatic variations,
- the coastal fringe, which is subject to growing tensions between uses and environments,
- aquatic environments that are already under pressure, with an increased risk of imbalance.
The analysis makes it possible to identify the most vulnerable Management Units (UG), in order to prioritise adaptation at a territorial level. These results form an essential basis for guiding the SAGE’s actions in terms of quantitative management, preservation of the environment and securing uses.
Making the most of results and supporting decision-making
The results of the evaluation of the climate change impacts will provide a strategic decision-making tool for the Local Water Commission (CLE) and local authorities involved in the sustainable management of water resources. By providing objective information on changes in climate, hydrological regimes and uses, the study will make it easier to anticipate and adapt public policies.
In particular, it will serve as a technical and forward-looking basis for :
- Readjust the volumes that can be abstracted by use (drinking water, agriculture, industry) and by Management Unit (MU), depending on the vulnerabilities identified;
- Integrate climate issues into town and country planning documents (PLUi, SCOT, PCAET, etc.);
- Prioritise the investments needed, such as reinforcing interconnections, creating storage facilities or securing supply;
- Raise awareness among all local players (elected representatives, technicians, users) of the reality of future developments and the growing limits of the resource.
By taking a regional, multi-stakeholder and forward-looking approach, this study is fully in line with an adaptive planning approach that meets the challenges posed by climate change and the growing pressure on water resources.
Conclusion
Based on robust data, updated scientific references and a rigorous methodology, this climate study for the Argoat-Trégor-Goëlo SAGE provides a framework for anticipating the impacts of climate change on water resources.
It improves detailed knowledge of the region, identifies the most vulnerable areas and provides practical decision-making tools for balanced, sustainable management. By integrating the climatic, hydrological, ecological and socio-economic dimensions, it contributes to the construction of a shared vision of the future of water in the region.
This evaluation of climate change impacts thus foreshadows a territorial transition on water uses, based on adaptation, resilience and consultation, and provides an essential basis for guiding public policies and investments in the face of the climate challenges of the XXIᵉ century.