"Severe bushfires often occur after long dry spells and when high temperatures, low humidity and strong winds combine to produce ideal conditions for the rapid spread of fire. Some of the most dangerous fires have been a result of a sudden change in wind direction that has altered the fire's behaviour."
Weather systems can produce a combination of conditions that increase the severity of the bushfire risk:
- High Temperature: In Australia, high temperatures are common due to our position in or near the tropics. Summer temperatures can reach in the high 30s and low 40s on a regular basis. When excessive heat occurs for several days, it is known as a heatwave. In these conditions the risk of a fire starting and quickly becoming an inferno, increases dramatically.
- Low Humidity: A lack of moisture in the air is called a moisture deficit and is often used as an indicator of extreme bushfire weather. It is important to note the time that has passed since rain last fell in a particular area because prolonged dry periods lower the humidity in the air.
- Strong Winds: Develop with weather systems such as lows and cold fronts moving across southern Australia. Low-pressure systems cause strong winds that can drastically increase the intensity and spread of fires.
Complete the following questions in your work book:
- What are the main conditions that lead to extreme fire danger days?
- Describe the summer temperatures experienced in Australia
- How do winds influence fire behaviour?
- Complete the Interactive Activity on page 113 of Pearson.