Bushfires in Australia

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Bushfires in Australia – Australia on fire

In southeast Australia in recent decades, bushfire has been the second biggest cause of insured property loss from natural hazards after severe thunderstorms. Victoria is the most exposed state, but the risk is also high in other regions like the suburbs of Sydney in New South Wales.

Bushfires are an intrinsic part of the natural ecology of the Australian landscape. The eucalyptus – the archetypal Australian plant – is particularly fire prone on account of its high oil content. In the southern part of the country, the dry months in summer are the most dangerous time, especially after rain has increased vegetation growth in the preceding winter. Unfortunately, the region most prone to major bushfires, southeast Australia, also has the highest concentration of people and insured values.

Natural and human influence on the bushfire hazard

The bushfire hazard in Australia results from the complex interaction of highly disparate anthropogenic and natural influencing factors. Natural variables include the type and amount of living or dead plant material and the weather situation that determines the condition and thus the flammability and combustibility of the vegetation. The spread of fire also depends on the topography and the wind conditions.

The natural fire potential is particularly great when warm, dry conditions prevailing in forests over a long period of time are combined with a strong wind, which can additionally whip up the fire once it has broken out, spread the fire quickly and carry embers over long distances. When abundant fuel is available and these conditions result in a major bushfire, fire fighters can basically do no more than try to contain the damage, as such fires are almost impossible to extinguish. A change in wind direction is especially dangerous because the side of a fire can suddenly become the new – and larger – fire front.

The majority of bushfires in southeast Australia are caused by human activity

Bushfire is the only natural hazard in which humans have a direct influence on the hazard situation. The majority of bushfires near populated areas are the consequence of human activity. Lightning causes the smaller portion naturally. Sometimes, a carelessly discarded cigarette or a glass shard, which can focus the sun's rays is all it takes to start a fire. Heat from motors or engines, or electric sparks from power lines and machines can ignite dry grass. Besides this accidental causes, a significant share of wildfires are started deliberately.

Humans also change the natural fire frequency and intensity. They decrease the natural fire frequency due to deliberate fire suppression near populated areas. If there is no fuel-reduction burning in forests for the purposes of fire prevention, large quantities of combustible material can accumulate at ground level.

Surface fires in these areas can become so intense due to the large amounts of fuel that they spread to the crowns of the trees and rapidly grow into a major fire. If humans had not intervened in the natural bushfire regime, more frequent low-intensity fires would have consumed the forest undergrowth and ensured that woodland grasses and scrubs do not proliferate excessively.

Viewed on a larger scale, climate is the most important factor influencing bushfire activity. It determines the vegetation at a given location and the natural fire regime (i.e. frequency, intensity, seasonality of fire occurrence). Australia encompasses different climate zones, so bushfire frequency ranges from zero or exceptionally infrequent occurrence in rainforests to very frequent fires in tropical savannah grasslands.

Mitigation measures, recent settlements and insurance aspects: Read on about the economic impacts of bushfires.

Dr. Astrid Zwick und Stefan Lämmle, Munich Re.

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