The word "bushfire" builds on the concept of "the bush", referring to sparsely-inhabited regions. Bushfires in Australia are generally defined as uncontrolled, non-structural fires burning in a grass, scrub, bush, or forested area. Australia, being a geographically and meteorogically diverse continent, experiences many types of bushfires. There are two main categories, depending on local topography.
- Hilly/mountainous fires – burn in hilly, mountainous or alpine areas which are usually densely forested. The land is less accessible and not conducive to agriculture, thus many of these densely forested areas have been saved from deforestation and are protected by national, state and other parks. The steep terrain increases the speed and intensity of a firestorm. Where settlements are located in hilly or mountainous areas, bushfires can pose a threat to both life and property.
- Flat/grassland fires – burn along flat plains or areas of small undulation, predominantly covered in grasses or scrubland. These fires can move quickly, fanned by high winds in flat topography, and they quickly consume the small amounts of fuel/vegetation available. These fires pose less of a threat to settlements as they rarely reach the same intensity seen in major firestorms as the land is flat, the fires are easier to map and predict, and the terrain is more accessible for firefighting personnel. Many regions of predominantly flat terrain in Australia have been almost completely deforested for agriculture, reducing the fuel loads which would otherwise facilitate fires in these areas.
Common causes of bushfires include lightning, arcing from overhead power lines, arson, accidental ignition in the course of agricultural clearing, grinding and welding activities, campfires, cigarettes and dropped matches, sparks from machinery, and controlled burn escapes.