We are preparing a high-resolution (0.1° x 0.1°, about 10x10 km) Wildfire Risk Index dataset and 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 dataset will be available early 2022 to be used in forward looking physical risks assessments under climate change.
What is the Fire Weather index ?
The Fire Weather Index (FWI) is a weather variables based index used worldwide to estimate fire danger. It accounts for the effects of fuel moisture and wind on fire behaviour and spread. The higher the FWI is, the more favourable the meteorological conditions to trigger a wildfire are.
How is it calculated ?
The FWI 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 behaviour. It is calculated from five daily weather variables: temperature, relative humidity, wind speed, and 24-hour precipitation.
Why choose the Canadian Fire Model ?
There are three widely used fire risk weather based models developed in Canada (FWI), the USA (U.S. Forest Service National Fire-Danger Rating System), and Australia (McArthur Mk5 Forest Fire Danger Meter). The European Forest Fire Information System (EFFIS) network and the The Global Wildfire Information System (GWIS) adopted the Canadian Forest Fire Weather Index (FWI) as the reference for operational fire danger forecasts (they recently included the other two for comparison purposes). So did the Copernicus Emergency Management Service for the historical data. For the Future risk assessment, the Copernicus Climate Change Service also selected the Canadian Index as it is the reference for the EFFIS/GWIS. In short the Canadian, US and Australian national administrations use their own Fire Index while in Europe authoritative institutions adopted the Canadian model as reference. In the US, NASA also adopted the Canadian Index for global applications. The FWI used here can thus be directly compared to operational FWI products used elsewhere, especially the EFFIS system.
Which weather data do you use to calculate the historical values of the Index ?
FWI values 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.
Which weather data do you use to calculate future values of the index ?
FWI values 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).
The climate simulations that where downscaled are the ones supporting the recently published 6th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). We recently produced a high-resolution climate projections dataset that is coherent with the ERA5-Land reanalysis. This allows to have future values of FWI that are coherent with the historical FWI series. For more details on the dataset please see our preprint on eartharxive.org: A high-resolution downscaled CMIP6 projections dataset of essential surface climate variables over the globe coherent with the ERA5-Land reanalysis for climate change impact assessments.
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).