Offer Description
The Nouvelle-Aquitaine region, which has the largest forest area in France, is particularly vulnerable to climate change. Its consequences, which are already being felt, include an increase in periods of drought and greater susceptibility of forests to fires. Climate change influences the flammability of most plant species by altering their physiology, particularly the volatile organic compounds they emit in response to stress. As a result, mega-fires, extreme fires, and high-power fires are becoming the norm and can overwhelm the capacity of operational personnel. It is necessary to realize experience feedback on cases for which extinguishing, means were insufficient and find new indicators, notably biochemical, to better estimate the potential firepower in case of ignition. The final goal will be to adapt the air and ground extinguish means to the estimated firepower with tactical and security issues to retain control over the wildfires.
In addition, soil organic matter (SOM), which constitutes an essential interface between the atmosphere, the biosphere, and aquifers, is very likely to be impacted by these mega-fires. SOM can retain organic and mineral pollutants, thus limiting their migration, but, likely, its degradation by high temperatures or by smoldering fires spreading in peat soils will cause pollutants to be released into surface or groundwater through leaching or washing. Knowledge and monitoring of this SOM are therefore essential. Furthermore, SOM, which forms an essential interface between the atmosphere, the biosphere, and aquifers, is very likely to be impacted by these mega-fires. It can retain organic and mineral pollutants, thereby limiting their migration, but likely, degradation by high temperatures or smoldering fires spreading in peat soils will release pollutants into surface or groundwater through leaching or washing. Knowledge and monitoring of this SOM is therefore essential to preserve the quality of shallow and therefore vulnerable aquifers in Gironde.
In this context, the objectives of this thesis are:
-to assess the impact of forest fires on the SOM and therefore their ability to protect water resources.
-to propose a decision-making tool to determine the power of the fire and the hydraulic resources to be deployed at the scale of the Landes de Gascogne forest.
Methodology and implementation:
We propose to begin by studying the changes in the organic matter of these soils after a vegetation fire.
This initial objective will be addressed through several tasks:
-Reproducing the thermal conditions of a fire on soil columns with and without vegetation, on a laboratory scale in a fire chamber at the PERICLES platform of the Institut PPRIME,
– Compare the physicochemical characteristics of control and burned soils (pH, % OM, C/N ratio, particle size distribution), chemical composition (lipid and humic fractions), and biological activity through the identification of biomarkers.
- sample soils after (i) a controlled fire in the Pinail reserve and (ii) a forest fire, as well as control soil, and carry out the same measurements,
-correlate the above values with data collected by geographic information systems (GIS) and with information on groundwater and surface water quality,
-Model the transport of pyrogenic compounds in soil columns reconstructed in the laboratory.
The objective of the second part is to propose a decision-making tool to determine the fire intensity and the hydraulic resources to be deployed across the entire Landes de Gascogne forest, particularly for maritime pine forests, taking into account water management, intervention tactics, personnel safety, and the anticipation of extreme fires. This second objective will be achieved through the following actions:
-Feedback by analyzing cases of capacity breakdowns and regular exchanges with the various stakeholders: operational (firefighters, foresters, town halls, DRAFT, ONF), Ministry of Agriculture, DREAL, and the South-West General Staff, which initiated this request
-Identifying indicators and critical parameters (type, density and height of vegetation/trees, dead/living plants ratio, weather, humidity, age of trees, pruning/clearing/uprooting, topography, etc.)
-Adjust the methods of control based on the fire’s power and behavior, as determined by the indicators and small-scale experiments mentioned above.
Where to apply
E-mail: laurent.lemee@univ-poitiers.fr
