Nangarin Vineyard Estate

Nangarin Vineyard Estate
Picton, NSW, Australia

Use of the Nangarin Fire Weather Index

Most Nangarin residents should be aware that a local weather station has been installed and the data from that are available through the Nangarin website – see Local Links, Estate Related Links. The link gives local information relating to temperature, humidity and wind, and tides at Sydney Harbour. A second link associated with this weather station shows the daily Fire Weather Index (FWI) for Nangarin.

While the FWI cannot predict whether an attempt at ignition will occur, it can give residents substantial information on how a fire might operate should it do so. The index that comes with the weather station software is the same local weather system used in Canada and New Zealand. The Bureau of Meteorology (BoM) in Australia uses a slightly different system.

The BoM data comes from nearby weather stations, the closest of which is Camden Airport. Based on this information, local fire authorities make decisions relating to fires that might occur at Nangarin.

The weather at Camden Airport can be quite different to that at Nangarin at any particular time. So, one can assume that the Nangarin data are more relevant and of greater value. To quote from a BoM letter received recently:

“While the [BoM] calculates . . . [fire] index values daily for selected locations for agencies, . . . local variations in rainfall can have a significant effect on spot values of these indices. The nature of rainfall with thunderstorms can result in spot values being unrepresentative of the dryness of a surrounding area. . . . Consequently the value might vary significantly according to the start date and local rainfall [characteristics] . . .

Given [these issues], the [BoM] is not able to provide [fire] values [for Nangarin] since the caveats of uncertainty might not be understood. It is probably best that the calculations are built into the software you are using.”

The weather station does undertake its own calculations to calculate the FWI based on local weather conditions. However, final calibration for Nangarin will not occur until after an arbitrary date – typically, a wet period in early winter. The longer it runs, the more accurate it becomes.

The Nangarin FWI data are calculated once each day at 1:00 pm. It shows a simple dial that indicates whether the overall danger a fire might be low, moderate, high, very high or extreme. However, it also shows a series of graphs that give additional useful information to those who care to study and understand them. These are described in links to the New Zealand Rural Fire Service and Canadian Wildland Fire Information System and include:

1. Moisture Codes – indicate what fuels are likely to be involved and their ease of ignition:

(a) Fine Fuel Moisture Code – indicates the relative ease of ignition and flammability of fine surface fuel (litter layer), i.e. the materials that are relatively easy to ignite:

· Whether no fire ignitions are likely to be successful
· Whether many (~50%) fire ignitions are likely to be successful
· Whether all (~100%) fire ignitions are likely to be successful
· Whether all fire ignitions are likely to be successful and an extreme fire behaviour result.

(b) Duff Moisture Code – is similar, but relates to the upper layers of decomposed organic materials found below the litter layer, and to the medium-sized woody materials.

(c) Drought Code – is similar again, but relates to the lower layers of decomposed organic materials below the litter layer, and to large logs, i.e. the materials that are hardest to ignite. It also shows:

· Whether mop up is likely to be easy
· Whether prolonged mop up is likely.

2. Initial Spread Index – a numeric rating of the expected rate of fire spread ignoring the influence of variable quantities of fuel.

3. Build-up Index – a numeric rating of the expected likely total amount of fuel available for combustion. Note, though, that this is based only on weather station information. Amounts of fuel are not measured in the field.

4. Fire Weather Index Code – shows how extreme fire the intensity is likely to be and whether control will be difficult.

Not withstanding the above comments, decisions should not be made based solely on the Nangarin FWI that might jeopardise lives, safety or property. Whatever path you choose to follow, neither the Nangarin Executive Committee nor the owner of the weather station guarantee the accuracy or the usefulness of the data. The safest option is to take the advice of the local fire authorities.

See www.morseweather.com/fwi.htm for more information

Nangarin Weather