Introduction
Geographical processes
Maps of seriously affected
Impacts of the hazard
Responses of society

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The causes of bushfires can be split into two categories - natural and human influence. Almost all natural bushfires are the result of lightning strikes. A stroke of lightnight carries more than 100 million volts, which can reach a temperature of up to 30500°C. Of course, a lightning strike this hot would definitely be enough to start a bushfire!

However, most bushfires are caused by human influence. Campfires are left unattended (or not distinguished properly) which quickly spread the fire.

Machinery used during suitable conditions causes a spark. This spark ignites vegetation and causes a bushfire. This includes chainsaws, wielders, slashers and vehicle exhaust.

Accounting for 7% of bushfires, just throwing a cigarette on the ground causes a bushfire too.

The deliberate lighting of a bushfire is known as arson. This is an actual crime - a criminal offence. Unfortunately, it accounts for a quarter of all bushfires.

Some farmers burn their land to control weeds. These kinds of fires are known as agricultural burns (or burning-off). However, they can go out of control, and therefore lead to a bushfire.




Most bushfires occur when temperatures are at their highest. The climate is usually very dry and hot. It is impossible, even on the hottest summer day, for the sun to raise grass and fuel to their ignition points. However, it does pre-heat to the stage where it will be easier to ignite with another source as a catalyst.

Relative humidity affects fires. A RH of 100% means that air has absorbed moisture to the point where it can't absorb anymore. Fuels contain a high level of moisture, which means the fire will not spread. However, on a day with low humidity (around a RH of 30%), the moisture will be released to the air which results in fires spreading rapidly.

A cloudless day is best for bushfires. Clouds 'shield' the fuel from the sun, letting it dry out more slowly.

As mentioned before, a dry, hot climate is best for bushfires. Droughts occur in Australia, which is why during the drought season there tends to be bushfires. Rain affects relative humidity - when it rains, there's a higher amount of moisture in the air.

Finally, wind speed and wind direction heavily affect the result of bushfires. In NSW, winds from N, NW and SW are dry and hot. All the other directions carry moisture and are cooler.

The fast wind speed can lift the fire and part of the fire may land in front. This is known as spotting - which leads to the spreading of more fires. The wind can push flames closer to the ground, allowing the surface to reach temperatures close to its ignition point. The speed of wind on the ground affects the height of the fire. Wind carries oxygen - oxygen is an important element which keeps combustion going.

All these processes combined will cause a deadly fire. A day with all these weather conditions are known as 'blow-up-days'. There are roughly 4 to 6 blow-up-days in bushfire season.



* Spot fire - fire embers carried by the wind which land in front of the actual fire and cause another smaller fire.

* Crown fire - fire that spreads quickly and burns the canopy of trees, which usually occur in forests.

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Labels: Geographical Processes

The causes of bushfires can be split into two categories - natural and human influence. Almost all natural bushfires are the result of lightning strikes. A stroke of lightnight carries more than 100 million volts, which can reach a temperature of up to 30500°C. Of course, a lightning strike this hot would definitely be enough to start a bushfire!

However, most bushfires are caused by human influence. Campfires are left unattended (or not distinguished properly) which quickly spread the fire.

Machinery used during suitable conditions causes a spark. This spark ignites vegetation and causes a bushfire. This includes chainsaws, wielders, slashers and vehicle exhaust.

Accounting for 7% of bushfires, just throwing a cigarette on the ground causes a bushfire too.

The deliberate lighting of a bushfire is known as arson. This is an actual crime - a criminal offence. Unfortunately, it accounts for a quarter of all bushfires.

Some farmers burn their land to control weeds. These kinds of fires are known as agricultural burns (or burning-off). However, they can go out of control, and therefore lead to a bushfire.




Most bushfires occur when temperatures are at their highest. The climate is usually very dry and hot. It is impossible, even on the hottest summer day, for the sun to raise grass and fuel to their ignition points. However, it does pre-heat to the stage where it will be easier to ignite with another source as a catalyst.

Relative humidity affects fires. A RH of 100% means that air has absorbed moisture to the point where it can't absorb anymore. Fuels contain a high level of moisture, which means the fire will not spread. However, on a day with low humidity (around a RH of 30%), the moisture will be released to the air which results in fires spreading rapidly.

A cloudless day is best for bushfires. Clouds 'shield' the fuel from the sun, letting it dry out more slowly.

As mentioned before, a dry, hot climate is best for bushfires. Droughts occur in Australia, which is why during the drought season there tends to be bushfires. Rain affects relative humidity - when it rains, there's a higher amount of moisture in the air.

Finally, wind speed and wind direction heavily affect the result of bushfires. In NSW, winds from N, NW and SW are dry and hot. All the other directions carry moisture and are cooler.

The fast wind speed can lift the fire and part of the fire may land in front. This is known as spotting - which leads to the spreading of more fires. The wind can push flames closer to the ground, allowing the surface to reach temperatures close to its ignition point. The speed of wind on the ground affects the height of the fire. Wind carries oxygen - oxygen is an important element which keeps combustion going.

All these processes combined will cause a deadly fire. A day with all these weather conditions are known as 'blow-up-days'. There are roughly 4 to 6 blow-up-days in bushfire season.



* Spot fire - fire embers carried by the wind which land in front of the actual fire and cause another smaller fire.

* Crown fire - fire that spreads quickly and burns the canopy of trees, which usually occur in forests.

←Back                                                                                                Next→

Labels: Geographical Processes