Forests and natural hazards in mountain areas are closely related. In the Pyrenees, erosion makes soils more fragile. More than 560 French towns are at risk for avalanches, rockslides, erosion, flash floods, and landslides. To combat these hazards, starting in 1860, the French government replanted unstable areas: river basins, stream banks, dams, etc.
As part of public forest management, the Mountain Land Restoration service of the National Forest Office (ONF-RTM) intervenes as such in more 11,000 hectares of at-risk land in southwest France. It is also important that the action taken by stakeholders involved in the ‘Natural hazard’ line of action of the project take into account the scale of the Pyrenees.
Flooding events and more frequent extreme weather phenomenon can impact geological structures leading to an increase in natural hazards. Floods, landslides, rock falls, and avalanches are the main risks affecting the entire mountain range.
Given the important role forests play in mitigating these natural hazards, the actions undertaken within the project in the ‘Forests’ and ‘Natural hazards’ lines of action shall be dealt with separately.
Work carried out under the ‘Natural hazards’ line of action shall serve to implement certain indicators to better understand the evolution of natural hazards in the Pyrenees (floods, avalanches, landslides, and rockfalls). In terms of climate change, it shall also analyse the role of the forest in relation to these natural hazards and address how climate change may influence the protective role played by mountain forests.
The objective is to determine the geomorphology of ‘intervention sites’, better understand the evolution of natural hazards (floods, avalanches, landslides, and rockslides) in response to climate change, analyse the role the forest plays against these natural hazards, and address how aforementioned changes may influence the protective role played by mountain forests.
- synthetic identification of natural hazards that exist in mountain areas; reconcile vocabulary used by different French and Spanish stakeholders;
- technical exchange; determine a common mapping methodology to be applied in reference zones (7 or 8 zones at the basin level distributed throughout the Pyrenees mountain region);
- shared mapping at a 1/50,000 scale (even 1/30,000) for reference zones;
- foster awareness among local stakeholders and those responsible for protecting forest populations;
- propose a network of permanent tracking plots to monitor the effects of climate change;
- define a shared methodology and perform geomorphological, bioclimatic, forestry, ecological, and socioeconomic diagnostics at different scales (certain variables may refer to reference zones, intervention sites, as well as tracking plots inside and outside intervention sites (or even outside reference zones));
- propose forest intervention techniques against natural hazards;
- create a common tracking protocol for indicators; identify climate change indicators;
- define criteria for managing mountain forests that take ‘climate change’ into account;
- develop guidelines for forest management based on different contexts and ‘climate change’.
- adapt and align methods for bioclimatic diagnosis;
- technical reports.
1. Historical, policy, and regulatory report on types of protection forests.
2. Consideration criteria for natural hazards associated with mountain forests.
3. Select reference zones, intervention sites, and tracking plots.
4. Parameters, diagnostics, and context description, particularly geological in nature, for the reference zones that have been identified.
5. Develop a common methodology for mapping natural hazards as well as reference zones (spatial characterization of hazards, strong points, and forest cover + geological input, susceptibility to landslides, relevance of hydrogeological characterization).
6. Characterise hydrogeological context of basins at 4 intervention sites:
- assess hydrogeological functioning of existing groundwater layers (suitability of land for run-off or infiltration, recharge estimation, changes in water levels and/or flow);
- provide river basins with instruments adapted to different geological contexts (hydrometric stations, automatic recording of water levels, measurement of land permeability, soil moisture, etc.), and implement tracking activities adapted to the context of each selected site;
- geotechnical analysis for landslide measurement.
7. Analyse and commence intervention techniques against natural hazards: the forest in terms of strong point (storms, fire, forest diseases, animal life) and in terms of influence over hazards (flooding, avalanche, landslides and rock fall).
8. Operational implementation of tools and methods to track climate change indicators (common tracking protocol in plots); inventory of initial state (data, measurements).
9. Exchange, define criteria to manage mountain forests, and develop management guidelines based on contexts.
10. Propose solutions to consolidate and protect strong points to reduce the risk associated with landslide (bibliography, assessment).
11. Draft final report for the landslide section of the priority topic ‘Natural hazards’ to include geological mapping and hydrogeological and hydrological studies.
Climate change indicators (within the OPCC framework)
Preselected indicator to track CC
Actions for implementation
Map changes in territories subject to major natural hazards
Mapping hazards proposes certain reference zones and constitutes a snapshot in time T. Climate evolution enables the behaviour of soils to be evaluated with respect to vegetation and climate change (change mainly in water factor)
Changes in natural /restored surface water flow
Certain reference zones are or shall be the object of a study to assess their hydrogeological resources and it will be necessary to measure flow rates and engage in long-term monitoring activities.
Piezometric tracking of groundwater
If reference zones are already equipped with piezometers, the quality of data attained must be checked. In other cases, a sector may need to be equipped. In all cases, selected piezometers shall be part of the Pyrenees tracking network yet to be created.
For this action, BRGM and partners, GEIE FORESPIR, along with a network of forest stakeholders (see ‘Forest’ line of action) composed of overseers, forest engineers, consultants, and experts in natural hazards in mountain areas shall ensure proper action implementation.
Crédit photos : RTM
• Bureau de Recherches Géologiques et Minières de Midi-Pyrénées