Bushfires and Lightning

Thunderstorms and Lightning

Thunderstorms increase the threat of fires starting because they cause lightning that can ignite fires. If little or no rain occurs with thunderstorms, as sometimes happens on hot days, there isn't enough rain to put out any lightning fires that start.

How does lighting start fires?

Lightning occurs across the Earth's surface. At least 100 flashes of lightning strike the Earth every second - this is more than 8.6 million strikes a day! A single stroke of lightning can carry 100 million volts of electricity. During its brief life span, a single lightning strike can carry enough energy to power a 100 watt light bulb for up to three months.

A single stroke of lightning can reach a temperature of 30,500^oC, or five times hotter than the Sun’s surface. If lightning strikes dry vegetation, this heat energy can start bushfires. Locating new fires

Major bushfire events in Victoria caused by lightning

Many fires were started by lightning during the 2002-2003 fire season. On one day alone, January 8 2003, eighty-seven fires were started by lightning strikes in eastern Victoria.

Other major bushfires have also been caused by lightning in Victoria.

How is lightning created?

Thunderstorms develop when dense cold air overlies dense, warm, moist air, converting the warm air's heat energy into electrical discharges and wind.

Lightning strikes that reach the ground begin with concentrated negative electrical charges, perhaps created by the collisions of rising ice crystals and falling hailstones that collect in the lower part of storm clouds. The strong negative pull of the lower part of the storm cloud provokes a reaction of positive charges on the ground below.

Eventually the electrical force between the charge of the cloud and the ground beneath it becomes too great and sparks known as 'stepped leaders' overcome the insulating ability of the air and shoot earthwards. As these leaders approach the ground, the positive charge below sends up sparks of its own called "upward streamers". These are generally shot up from the tallest objects, such as treetops, buildings and summit spires. Where the upward streamer and downward leader meet the circuit is closed and the flash of lightning can be seen.

Because the air around a lightning strike is suddenly superheated, it expands explosively. This creates shock waves that travel through the air - we call these shock waves thunder.