Wildfire

A high-resolution Wildfire Risk projections dataset based on the Fire Weather Index is under development. We have now completed the first projection of 1 out of 5 climate models and for one emissions scenario (Shared Socioeconomic Pathway 5-8.5  or SSP5-8.5). The other 4 models and second scenario (SSP1-2.6) are under way. The full high-resolution wildfire risk projections dataset will be available early 2023 to be used in forward looking physical risks assessments under climate change.

Product update (February 2023): Wildfire risk index now available, check Fire Weather Index projections at high-resolution now available.

What is wildfire risk ?

Wildfire risk refers to the potential likelihood and impacts of wildfires occurring in a given area. Wildfires are uncontrolled fires that spread quickly, engulfing vegetation, wildlife, and potentially human settlements. The risk of wildfires is influenced by several factors, each contributing to the likelihood of ignition and the severity and spread of fires when they do occur. Here are the primary components that contribute to wildfire risk:

1. Fuel Availability: The presence of combustible materials, including dry vegetation, trees, grasses, and even homes, can act as fuel for wildfires. The amount, type, and condition of these materials significantly affect the risk.
2. Climate and Weather Conditions: Hot, dry, and windy conditions can create an environment conducive to wildfires. Drought conditions can dry out vegetation, making it more flammable, while high temperatures and winds can help ignite and spread the fire more rapidly.
3. Topography: The landscape can influence wildfire behavior. Fires typically move faster uphill and can be difficult to control in rugged or inaccessible terrain.
4. Human Factors: Human activities, both accidental (such as unattended campfires, discarded cigarettes) and intentional (arson), are significant causes of wildfires. Additionally, the proximity of human settlements to forested areas (known as the wildland-urban interface) can increase the risk and potential damage of wildfires.
5. Changes in Land Use and Management: How land is used and managed can influence wildfire risk. For example, suppressing all fires can lead to an accumulation of vegetation, which might increase the intensity of future wildfires. Conversely, responsible land management practices, like controlled burns, can reduce the risk by removing excess fuel.
6. Climate Change: Climate change is leading to hotter, drier conditions in many regions, increasing the frequency and intensity of droughts and creating conditions more favorable to wildfires. This trend is expected to make wildfires more frequent and severe in many areas.

The Wildfire Risk Index we are preparing is based on Fire weather, an approach that focuses exclusively on climate and weather weather conditions and how it will evolve under climate change. It us used in a "Ceteris paribus" approach meaning all other drivers remaining constant, which can be considered valid for topography but not for human factors and land-use.

What is Fire weather?

Fire weather refers to specific meteorological conditions that are conducive to the ignition and rapid spread of wildfire risk. These conditions typically include a combination of dry, warm, and windy weather that can dry out vegetation and make it more flammable, thus increasing the likelihood and intensity of wildfires. Key components of fire weather include:

1. Low Humidity: Low relative humidity leads to drier air, which in turn dries out vegetation and makes it more susceptible to burning. Dry vegetation serves as fuel for fires and can allow them to ignite and spread more easily.
2. High Temperature: Higher temperatures can increase the likelihood of vegetation becoming dry and flammable. Hot weather can also enhance the intensity and spread of a fire once it starts.
3. Wind: Strong winds can rapidly spread wildfires by carrying hot embers and flames to new areas. Wind can also supply additional oxygen to the fire, increasing its intensity. Moreover, wind can change the direction and behavior of a fire, making it more unpredictable and difficult to control.
4. Drought Conditions: Prolonged periods of drought can significantly increase fire risk by drying out soil and vegetation. Drought-stressed vegetation becomes highly combustible and serves as ample fuel for wildfires.
5. Lack of Precipitation: A lack of recent rain or snow can lead to drier conditions and more readily available fuels for fires. Extended periods without significant precipitation contribute to the overall dryness of the landscape.
6. Meteorologists and fire agencies often use fire weather forecasts to assess the potential risk for wildfire development and spread. These forecasts help in making decisions about fire prevention measures, resource allocation, and issuing warnings to the public and firefighting crews. In many regions, fire weather is monitored using indices such as the Fire Weather Index, which considers several atmospheric conditions to estimate the fire potential. When the risk is particularly high, authorities might declare a fire weather watch or a red flag warning to alert communities and fire services of the potential for hazardous fire conditions.

What is the Fire Weather index ?

It is a weather variables based index used worldwide to estimate wildfire risk. It accounts for the effects of fuel moisture and wind on fire behavior and spread. The higher the index is, the more favorable the meteorological conditions to wildfire risk. The index used here is the Canadian Forest Fire Weather Index system. It is composed of several model components that account of the effects of the moisture content of the forest floor and weather conditions on fire behavior. It is calculated from five daily weather variables: temperature, relative humidity, wind speed, and 24-hour precipitation.

What climate data do you use to calculate the historical Wildfire risk?

Risk for present climate (1991-2020) are calculated using data from the ERA5-Land reanalysis. A reanalysis is produced by combining weather models with observations to provide a comprehensive description of recent global climate. The ERA5-Land dataset is provided by the Copernicus Climate Change Services (C3S) and is a world reference for historical climate analysis.

What climate data do you use to calculate future wildfire risk ?

Risk for future climate (2021-2100) are calculated using data from high-resolution climate projections. Those are obtained by statistical techniques called “downscaling” that combine reanalysis data and climate model simulations to increase the spatial resolution of the original climate model data (from hundreds of kilometers to tens of kilometers). We recently produced a high-resolution climate projections dataset, based on the recently published 6th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), that is coherent with the ERA5-Land reanalysis. This allows to have wildfire risk projections that are coherent with the historical series.

Figure. Future wildfire risk. 30 year average of the Fire Weather Index at the end of the century (2071-2100) for one climate model under Shared Socioeconomic Pathway 5-8.5 (SSP5-8.5).