Fire Risk Rating

Fire Weather Index for Earlscliffe over the last period (based on values taken at noon each day)

Current Fine Fuel Moisture Code for Earlscliffe Current Chandler Burning Index for Earlscliffe Fire Weather Index values for last two days at noon Yesterday Today FFMC 82.4 82.4 DMC 20 20 DC 195 202 ISI 1.9 2.1 BUI 31 33 FWI 4.0 4.6 Values last updated 02/06/23 at noon

Please note: Like all forms of forecasting, Fire Risk warnings are indicative, and conditions on the ground at a local level may differ significantly from those forecasted. Never base important decisions on this or any weather information obtained from the internet.

Importance of fire management and risk awareness

Uncontrolled wildfires have had devastating consequences in Ireland and around the world over the past number of years. Uncontrolled fires can pose a threat to habitats and species and to surrounding properties.

Forest fires are obviously a major concern for forest owners. February to May is a high risk period for forest fires as dead moorland vegetation can dry out very fast and it becomes highly flammable. However, when considering the overall risk of fire in Ireland, especially around Howth, the heathland, Gorse scrub and rank grassland are all at risk of wildfire.

The following chart shows the number of recorded forest and heathland fires in Ireland over the last ten years and the number of hectares of land destroyed in the process. The data is taken from the European Forest Fire Information System (EFFIS), specifically here.

A study carried out by Fingal County Council in 2019 entitled the 'Redrock Management Plan 2020-2030', showed that the Howth heathland is highly susceptible to fire due to the incendiary material shed by both Heather and Western Gorse. In terms of frequency, the residents at Earlscliffe have recorded major fires in the local heathland surrounding Earlscliffe approximately every 11 years over the last three decades (1995, 2006 and 2017). Some of the Howth heathland fires may have been started intentionally, while others may have been accidental as a result of a BBQ or thrown away cigarette.

Gorse fires are hard to control by the fire service due to the intense heat and the height of the flames. Even when they are seemingly extinguished they can smoulder and reignite again regularly over a period of weeks.

The tall Gorse also provides an important breeding habitat for birds such as Stonechat and Linnet. Therefore, management of heathland is important from both an ecological and environmental point of view.

For this reason, it is important to locally be aware of the factors that indicate a possible risk of fire, and to act accordingly.

At Earlscliffe, we are providing Fire Risk data to inform and advise the Howth community of the possible risks of local heathland and Gorse fires and to allow us to take any necessary precautions on the Earlscliffe land.

Fire Danger Rating Systems in Ireland

A number of Fire Danger Rating systems are publicly available at European and local levels, including the Met Éireann Fire Weather Index and the European Forest Fire Information System (EFFIS). These systems are based on the Canadian Fire Weather Index (FWI) model.

There is also another fire risk rating system called the Chandler Burning Index (CBI) that uses the air temperature and relative humidity to calculate a numerical index of fire danger. The CBI is used in some countries, but it is not used in Ireland and is included here for reference only. More details about the Chandler Burning Index can be found below.

Fire Weather Index (FWI)

A Fire Weather Index System provides numerical ratings of the relative fire potential in a standard fuel type (i.e., a mature pine forest) on a level terrain, based solely on weather observations measured daily at noon local standard time. This enables the fire danger to be rated at the mid afternoon peak from 2:00 - 4:00 pm. Weather observations/readings required are:

• Air temperature (in the shade)
• Relative Humidity (in the shade)
• Wind speed (at 10 metres above ground level for an average over 10 minutes)
• Rainfall (For the previous 24 hours)

The Fire Weather Index has six components; three fuel moisture codes and three fire behaviour indices. Each code and index is a numerical rating related to likely fire behaviour. The scales start at zero, and except for the Fine Fuel Moisture Code which has a maximum of 99, all are open-ended. Low ratings indicate high moisture content, and ratings rise as moisture content decreases, which in turn increases the risk of fire.

Three Fuel Moisture Codes

The FWI System evaluates fuel moisture content and relative fire behaviour using past and present weather effects on ground level fuels. The moisture codes reflect the net effects of daily moisture gains and losses and are broken into three levels based on surface depth as shown in the figure below.

Fine Fuel Moisture Code (FFMC)

A numeric rating of the moisture content of surface layer and litter (1-2 cm deep). This code is an indicator of the relative ease of ignition and the flammability of fine fuel. The moisture content of fine fuels is very sensitive to the weather. Even a day of rain, or of fine and windy weather, will significantly affect the FFMC rating. The system uses a time lag of two-thirds of a day to accurately measure the moisture content in fine fuels. The Fine Fuel Moisture Code Component FFMC of the FWI has been found by experience to have the strongest correlation with actual fire risk under Irish conditions. As FFMC and risk rating level increases, there is a corresponding increase in fuel ignition potential and consequent fire behaviour, intensity and spread rates. These basic fire risk conditions will be further compounded by presence of wind and local topographical factors. *

The FFMC rating is on a scale of 0 to 99. In Ireland, any figure above 70 is considered high, and above 80 is extreme. *

Duff Moisture Code (DMC)

A numeric rating of the average moisture content of loosely compacted organic layers of moderate depth (3-10cm deep). The code indicates the depth that fire will burn in moderate duff layers and medium size woody material. Duff layers take longer than surface fuels to dry out but weather conditions over the past couple of weeks will significantly affect the DMC. The system applies a time lag of 12 days to calculate the DMC.

A DMC rating of more than 30 is dry, and above 40 indicates that intensive burning will occur in the duff and medium fuels. Burning off operations should not be carried out when the DMC rating is above 40.

Drought Code (DC)

A numeric rating of the average moisture content of deep, compact organic layers (10-20cm deep). This code is a useful indicator of seasonal drought effects on forest fuels and the amount of smouldering in deep duff layers and large logs. A long period of dry weather (the system uses 52 days) is needed to dry out these fuels and affect the Drought Code.

A DC rating of 200 is high, and 300 or more is extreme indicating that fire will involve deep sub-surface and heavy fuels. Burning off should not be permitted when the DC rating is above 300.

Three Fire Behaviour Indices

The three behaviour indices are relative to the fuel moisture content. They indicate what a fire is likely to do. The lower the moisture content, the higher the Fuel Moisture Codes, and the higher the Fire Behaviour Indices, the more active the fire will be.

Initial Spread index (ISI)

A numeric rating of the expected rate of fire spread. It is based on wind speed and FFMC. Like the rest of the FWI system components, ISI does not take fuel type into account. Actual spread rates vary between fuel types at the same ISI.

The open-ended ISI scale starts at zero and a rating of 10 indicates high rate of spread shortly after ignition. A rating of 16 or more indicates extremely rapid rate of spread.

Build Up Index (BUI)

A numeric rating of the total amount of fuel available for combustion. It is based on the DMC and the DC. The BUI is generally less than twice the DMC value, and moisture in the DMC layer is expected to help prevent burning in material deeper down in the available fuel.

The BUI scale starts at zero and is open-ended. A rating above 40 is high, above 60 is extreme.

Fire Weather Index (FWI)

A numeric rating of fire intensity. It is based on the ISI and the BUI, and is used as a general index of fire danger.

Sources of Fire Risk Rating System information

Most of the information above on Fire Risk Rating systems in Ireland is based on the Canadian Forest Fire Weather Index (FWI) model except for * taken from the Irish Department of Agriculture, Food and the Marine document on the Forest Fire Risk Warning System (PDF).

Fire Weather Index Component Relationships and Calculations

The fire weather index calculation structure.

Fire warnings/fire danger notices

The following is courtesy of The Department of Agriculture, Food and the Marine and Met Éireann.

Met Éireann Fire Weather Index forecast

Met Éireann produces a Fire Weather Index, based on the Canadian Forest Fire Weather Index (FWI) model, which assesses the fire risk in an area taking into account current and past weather conditions. It also uses forecast weather information to produce a forecast fire weather index for five days ahead.

As this forecast is only generally available from February to October each year, check the dates on the following data before using.

Data courtesy of Forestry.ie and is based on European Centre for Medium-Range Weather Forecasts (ECMWF) forecast data.

Other Fire Risk Rating Systems

Chandler Burning Index (CBI) - not used in Ireland

The Chandler Burning Index (CBI) uses the air temperature and relative humidity to calculate a numerical index of fire danger. That number is then equated to the Fire Danger severity of either extreme, very high, high, moderate, or low. It is based solely on weather conditions, which is why it is often used by people with Personal Weather Stations (PWS) who can easily calculate it. However, CBI does not take into account fuel moisture or winds, which can override the index.

The monthly fire potential is represented by a modified version of the Chandler Burning Index (CBI) which provides a measure of the effects of average monthly temperature and humidity on fire intensity and rate of spread. Both the intensity and spread components of the Index are linearly related to temperature (an increase in temperature results in a proportionately higher Index), but are exponentially related to humidity (a small decrease in humidity results in a large increase in the Index).

The formula for the modified version of the CBI is as follows:

where:

• RH = Current relative humidity (percent)
• T = Current temperature (degrees Celsius)

Please note that the Chandler Burning Index is not used in Ireland and is included here for reference and comparative purposes only.

According to the Chandler Burning Index, the fire risk today at Earlscliffe is