Weather conditions

Bushfire weather conditions are largely determined by:

• Temperature
• Humidity
• Wind and atmospheric conditions
• Drought conditions or the amount of rain.

Hot, dry and windy days provide ideal conditions for a bushfire. A string of hot days dries out vegetation, making it easier to burn. In summer, these are common weather conditions that increase the flammability of vegetation. The drier the vegetation, the easier it will burn.

Low humidity and high temperatures, which are fuelled by hot winds, also dry out vegetation, allowing it to readily ignite.

A simple measure of weather conditions is the Forest Fire Danger Index (FFDI) and the Grassland Fire Danger Index (GFDI). These are used to help determine the fire danger rating.

Key consideration for planning decision making:

Planning schemes use weather conditions to inform an understanding of likely bushfire behaviour. Weather conditions are used in several ways.

When determining defendable space, approved measures in Clause 53.02 Bushfire Planning use weather conditions derived from the Australian Standard AS 3959:2018 Construction of buildings in bushfire-prone areas (Standards Australia).

Sometimes, planning decisions need to be based on a worst case or most likely weather scenario. This is especially so when considering the bushfire risk in the broader landscape and applying the clause 13.02-1S policies. For example, when siting buildings in high-risk locations or in places that may be too dangerous to develop.

A planning decision may require locally specific weather conditions to be analysed before approval is granted. This information will be provided in a bushfire hazard landscape assessment and bushfire hazard site assessment.