| Annual difference | Sometimes called anomaly, the annual difference shows us the difference between the climate that year and the average climate over many years. Rather than telling us exactly how hot (or wet or windy etc) a year is, it tells us how hot that year is compared to the long term average. |
| Area burnt | Literally, the space inside the final perimeter of a fire. Note that fires do not burn evenly, and so within the footprint of any fire will be vegetation burnt at a range of severities, from high severity to low severity and yes often sometimes unburnt. |
| Bioregion | A region with similarities in climate, geology, landform, native vegetation and species, used for organising environmental actions |
| Driver | A cause. Fire has many causes, and one useful way of thinking about them is what some (including us) call the 'drivers of fire': fuel, dryness, weather and ignition. |
| Dryness | A crucial ingredient if a plant is to burn. This is most obvious in a rainforest, which is generally too damp to burn, but it applies to forests, grasslands and other ecosystems too. Dryness is sometimes called fuel moisture, and broken up into dead (e.g. dropped leaves, twigs and bark) and live parts. |
| Everyday words | Cause a bit of confusion when talking about fire. Climate scientists, fire researchers and fire managers often have precise meanings in mind when they use words like severe, extreme, intense and even catastrophic. Unfortunately, these are exactly the words that media and general public often reach for when talking about serious fire weather, fire behaviour and fire impacts. |
| Fire | In Australia we call them bushfires, elsewhere they're called wildfires, but you may also hear forest fire, grass fire, wildland fire, and even biomass burning. |
| Fire agency | In Victoria this is the Department of Energy, Environment and Climate Action (DEECA) and the Country Fire Authority (CFA), but they have counterparts in every Australian state and territory. Vested with the statutory authority to fight fires and otherwise take actions to mitigate the risks posed by fire to people, property and the environment. |
| Fire district | A region, used for organising fire weather forecasts, total fire bans and other fire management actions. |
| Fire year | Runs from July to June, so that any given fire year contains a continuous, uninterrupted summer (when many of our fires occur). On this website, the 2020 fire year runs from July 2019 to June 2020. |
| Forest Fire Danger Index (FFDI) | Sometimes called the McArthur Forest Fire Danger Index, the FDI or the fire danger rating (FDR), this index aims to represent the influence of near-surface weather conditions on fire behaviour. It is calculated from temperature, rainfall, humidity and wind speed. FFDI has been replaced by a new Australian Fire Danger Rating System, but we have used FFDI because of its availability and familiarity to many. |
| Fuel | Something that can burn. In the case of wildfire, the main fuel is vegetation – trees, shrubs, grasses, herbs, forbs, you name it. Not all plants (and not all parts of a plant) are equally likely to burn or contribute to the spread of fire, which is one of the reasons fuel is arguably the most complicated driver of fire. |
| Fuel hazard | Fuel hazard is one way to represent the complex influence of fuel on fire behaviour. It refers to the amount and arrangement of fine fuels, which can be found in several layers: on the ground (surface), near the surface, higher up (elevated) and in bark. Each of these layers gets a score to indicate its potential contribution to fire behaviour, based on things like horizontal continuity, proportion of dead fuel, bark type and quantity, and litterbed depth. Individual layers can be added to give an overall fuel hazard. |
| Ignition | The chemical reaction that starts a fire. It can come from lightning or a range of human causes: power tools, power lines, cigarette butts, escaped campfires, arson and many more. Very hard to predict and very useful to detect. |
| Intensity | A measure of the energy output of a fire. Forests tend to burn at a much higher intensity than grasslands. |
| Likelihood | The chance of something happening, with zero meaning no chance and one meaning it is guaranteed to happen. Also called probability. |
| Satellite | Hi tech contraption floating through space, pointed at the earth and taking pictures of (i.e. remotely sensing) fire, vegetation greenness and many other things. |
| Seasonality | Refers to the time of year in which something (e.g. fire activity) is concentrated. In southern Australia, wildfires generally occur in late spring, summer and early autumn. |
| Severity | When it follows the word fire, this refers to the amount of vegetation consumed by a fire. It's not a bad shorthand for the immediate environmental impacts of a fire. In a forest, a low severity fire might only affect the litter and understorey, whereas a high severity fire can scorch or even consume the canopy, earning the label 'crown fire'. |
| Vapour pressure deficit (VPD) | Vapour pressure deficit (VPD) describes the difference (or deficit) between how much moisture is in the air, and how much moisture the air can hold when it's saturated. It is calculated from temperature and humidity. Once the air becomes saturated, water will condense to form clouds or dew on leaves. VPD is a measure of the atmosphere's thirst, influencing the dryness of forest and woodland fuels, and fire activity. |
| Weather | Weather is everything that happens between the earth and the stratosphere – heat, rain, wind, humidity and much, much more. Fire weather refers to the weather conditions that make fires more likely to start, more likely to spread and much harder to control. Hot, dry and windy conditions are a good example, but there's much more to fire weather than that. |