The Forest fire weather index (FWI) (French: indice forêt météo, IFM) is an estimation of the risk of

wildfire A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of Combustibility and flammability, combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a ...

computed by Météo France and the Meteorological Service of Canada. It was introduced in France in 1992 but is based on a

Canadian Canadians () are people identified with the country of Canada. This connection may be residential, legal, historical or cultural. For most Canadians, many (or all) of these connections exist and are collectively the source of their being ''C ...

empirical model developed and widely used since 1976.

Description

The index is a whole

number A number is a mathematical object used to count, measure, and label. The most basic examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with number words. More universally, individual numbers can ...

that ranges between 0 and 20 in France and up to above 30 in Canada. It is computed from five components. The first three components are numeric ratings of the moisture content of

litter Litter consists of waste products that have been discarded incorrectly, without consent, at an unsuitable location. The waste is objects, often man-made, such as aluminum cans, paper cups, food wrappers, cardboard boxes or plastic bottles, but ...

and other fine fuels, the average moisture content of loosely compacted organic layers of moderate depth, and the average moisture content of deep, compact organic layers. The last two components are the rate of fire spread if fuel is available for combustion, and the frontal fire intensity. The essential information needed to calculate this index is: * the

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog t ...

of the

air An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

at the beginning of the afternoon (when it has its lowest value); * the

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

in the middle of the afternoon (when it has its highest value); * the 24-hour total

precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...

(from noon to noon); * the maximum

speed In kinematics, the speed (commonly referred to as ''v'') of an object is the magnitude of the change of its position over time or the magnitude of the change of its position per unit of time; it is thus a non-negative scalar quantity. Intro ...

of the average

wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...

Usages

Australia

The FWI was adapted for use in Australia, with large FWI values most commonly associated with high wind speeds, followed secondly by low relative humidities and then thirdly by high temperatures.

France

This index is computed for 40 zones of France, three are in the Landes (

département In the administrative divisions of France, the department (, ) is one of the three levels of government under the national level (" territorial collectivities"), between the administrative regions and the communes. There are a total of 101 ...

with the biggest

forest A forest is an ecosystem characterized by a dense ecological community, community of trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, ...

France France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...

). Météo France sends the IFM to civil defense authorities, which allows the prepositioning of men and vehicles, especially air units. The computed index is revised every year to take new data into account.

Canada

Each provincial forest fire prevention authority is calculating the FWI for the different regions under their jurisdiction. The ''Daily Severity Rating'' (DSR) is a numeric rating of the difficulty of controlling fires, based on the Fire Weather Index, that is calculated afterward. It reflects more accurately the expected efforts required for fire suppression.

New Caledonia

A daily fire weather outlook is issued twice a day to alert the fire authority and help local firefighters to get organized. Provided information is based on FWI values computed at 20 weather stations representative of the climatic diversity of the country.

Croatia

FWI has been adopted in 1980s at Meteorological and Hydrological Service of Croatia where it is computed daily and used as a predictor in forest fire risk assessment. Final product is calibrated and ranked in 5 risk classes, from very low to very high. Product is daily forwarded to civil defense authorities. Forest Fire Risk Index Croatia
, DHMZ (in Croatian)

References

Bibliography

*Stocks, B.J., B.D. Lawson, M.E. Alexander, M.E., C.E. Van Wagner, R.S. McAlpine, T.J. Lynham, D.E. Dube. 1989.
The Canadian Forest Fire Danger Rating System: An Overview
'' Forestry Chronicle Vol. 65 issue 6 : 450-457. {{Meteorological variables Wildfire suppression Firefighting Forestry and the environment Atmospheric dynamics Hazard scales Meteorological indices