Water resources data
The Orb, Libron and Hérault river basins are already highly exposed to flood risks from river overflow, surface runoff and coastal flooding. In a changing climate, the intensity of extreme rainfall, soil dryness, changes in flood events and sea-level rise could alter the nature and scale of these risks.
The EPTB Fleuve Hérault and EPTB Orb Libron have therefore launched a forward-looking study of flood risks under climate change across the entire Orb Libron Hérault SLGRI area, covering 256 municipalities and 17 intermunicipal authorities.
The objective is to develop plausible scenarios for 2050 to help elected officials and technical teams understand what could change. More specifically, the study aims to assess the potential consequences of these changes and identify the adaptation measures that can be anticipated today.
Climate change does not only affect temperatures. It also alters the water cycle and can change the frequency, intensity and seasonality of precipitation.
This issue is particularly important in the Mediterranean region. According to Météo-France, Mediterranean rainfall events exceeding 200 mm in 24 hours are now twice as frequent as they were in the 1960s. Observations therefore show an intensification of heavy rainfall and an increase in the frequency of the most intense events. (Source : Météo-France – Quel est l’impact du changement climatique sur les épisodes méditerranéens ?)
Across the Orb, Libron and Hérault river basins, several phenomena therefore need to be considered together: extreme rainfall, surface runoff, river flooding, soil drought, wildfires, changes in land use and sea-level rise along the coastline.
The challenge is to understand how these factors may interact and reshape flood risk by 2050.
The study aims to better prepare the Orb, Libron and Hérault areas for the potential impacts of climate change on flooding.
In particular, it seeks to identify the territory’s vulnerability, highlight the main levers for reducing it in the short, medium and long term, and help elected officials and technical teams understand and prepare for these changes.
The approach has one important feature: rather than attempting to predict a specific event, it uses prospective scenario planning to explore realistic situations by 2050 and assess their potential consequences for the territory.
Prospective scenario planning does not seek to predict precisely which climate event will occur in 2050, on what date or with what intensity. Instead, it involves developing several plausible future situations consistent with the available scientific knowledge and then analysing their potential consequences for the territory.
Unlike an approach focused on a specific event, such as modelling the consequences of a particular flood, prospective scenario planning combines several changes that may occur simultaneously: more intense rainfall, soil drought, changes in flood flows, surface runoff, sea-level rise and changes in the territory’s vulnerability.
The first phase consists of consolidating the available knowledge on climate change, hydrology and flood risks.
PAPI assessments, the Hérault 2050 and Orb 2050 studies, existing hydraulic modelling, climate and hydrological data, as well as scientific research on the Mediterranean region, are reviewed and analysed.
The objective is to critically assess this information in order to identify sufficiently robust data to characterise the territory’s vulnerabilities and inform the prospective scenarios.
Building on this foundation, several prospective flood scenarios for 2050 are developed with elected officials and technical teams.
They are based on estimates of potential changes in factors such as intense rainfall, flood flows, sea level, flood dynamics and the potential extent of flood-prone areas.
The approach also takes cascading effects into account. A succession of droughts can, for example, weaken soils and vegetation, while a wildfire can increase a catchment’s susceptibility to surface runoff during subsequent rainfall events.
Four territorial workshops are used to develop scenarios tailored to different local contexts: urban, rural, agricultural and coastal areas, as well as floodplains and upstream parts of the river basins.
The scenarios are then used to identify flood risk adaptation measures that can be implemented today or introduced progressively over time.
In the short term, these may include reducing vulnerability, improving warning systems or strengthening crisis management. Over the longer term, considerations may focus on land-use planning, flood expansion areas, the natural functioning of rivers or the adaptation of flood protection infrastructure.
The objective is to identify measures that remain robust across several possible futures and can inform future local strategies, particularly PAPI, SAGE and the SLGRI.
The final phase consists of transforming scientific findings and prospective insights into information that can be directly understood and used by local stakeholders.
The co-developed scenarios, their potential consequences and the associated adaptation measures are presented in several formats: a comprehensive report, a summary brochure, educational materials and local stakeholder meetings.
This phase helps build a shared understanding of future flood risks and facilitates their integration into public policies and land-use planning decisions.
Anticipating climate change means no longer relying solely on events observed in the past.
A territory may simultaneously face more intense rainfall, drier soils that can increase certain types of surface runoff, faster flood events, or sea-level rise that limits water drainage along the coast. The technical specifications specifically identify these interactions as factors to be explored through the prospective scenarios.
Météo-France also highlights that climate change tends to intensify extreme rainfall and that Mediterranean rainfall events are affected by this trend.
Prospective analysis therefore enables local authorities to adapt before an event occurs. It helps identify vulnerabilities, assess the robustness of existing measures, and prioritise actions for flood prevention and climate change adaptation.
The study is expected to provide a shared and operational understanding of how flood risk may evolve by 2050 across the three river basins.
The EPTBs will have access to a consolidated knowledge base, prospective scenarios developed with local stakeholders, and an identification of the main adaptation levers. A comprehensive report and a brochure aimed at elected officials will also help disseminate the study’s key findings more widely.
The ultimate objective is to move from climate change knowledge to action: anticipating future risks in order to strengthen the resilience of territories to flooding today.
