- The fires started all over again in the south-east of Australia. 5.4 million hectares have already gone up in smoke and the worst could be yet to come. "Summer in Australia does not end until February," recalls researcher Dominique Morvan
- The heat wave and the wind help to propagate these gigantic fires. Dominique Morvan also points out, among the factors, that of the drought that hit Australia last winter, causing the water content of plants to drop very low
- Result: "the bush fire season started in September, instead of generally December, and 5.4 million hectares have already gone up in smoke," points out the researcher. And we are only at the beginning of January… a particularly hot month in Australia
A hundred active households in the state of New South Wales [whose capital is Sydney], fifty in the neighboring one of Victoria [Melbourne], and still others in Western Australia and Tasmania… L 'Australia is still ravaged by deadly forest fires, especially in the south-east of the mainland. Since September and the start of the bush fire season, these fires have engulfed 5.4 million hectares, destroyed 1,300 homes, killed 17 people ... and 480 million animals.
And there is no lull in sight. The flames have gone up again in recent days. To the point that, this Thursday, New South Wales, the most populous state in Australia, passed again in a state of emergency. Forced evacuations will be allowed starting this Friday and for seven days. It is the third time that this region has gone into a state of emergency since the beginning of September.
The worst would even come. Australian authorities are indeed expecting a dark Saturday on the fire front, anticipating sustained gusts of wind and temperatures above 40 ° C. As for the Australian Prime Minister, Scott Morisson, he spoke, also this Thursday, of the possibility that this situation could last for "months".
Possible? "This is one of the fears," replies Dominique Morvan, teacher-researcher at Aix-Marseille University, specialist in fire physics. He answers questions from 20 Minutes .
Wind gusts and high temperatures… How do the weather conditions expected on Saturday in Australia make the worst on the fire front fear?
These are indeed two factors that are conducive to the progression of these fires. They cause a very strong updraft of hot air. Vertical gas speeds sometimes exceed 250 km / h. These winds will carry incandescent particles - leaves, small pieces of bark, small flaming debris - to transport them to very high altitudes and sometimes very far. By falling, these particles can create new fires. We talk about brandon propagation. So much for the wind. As for the extreme heat - and by extreme heat, it is necessary to hear more than 40 ° C at this time in Australia -, it will further decrease by one notch the water content of the plants, which greatly increases their flammability.
Australia experiences bush fires every year… Why are they so devastating this year?
To understand this, we have to go back to the drought period that preceded the first fires in September. More than gusts of wind or hot weather, this is the first factor that explains the dramatic situation that Australia is currently going through. There was very little rain last winter [ie between June and August, note] and the water content of the plants recorded at the end of this season was very low. Experts then expected the bush fire season to start early and be very intense. It did not miss. Usually in Australia the fire season really starts in December, rarely in September like this year. Above all, the area already ravaged by flames is substantial. On average in Europe, wildfires devastate 500,000 hectares each year. There, we are already talking about 5.4 million hectares burned. For comparison, Corsica and the Provence-Alpes-Côtes-d'Azur region combined make up "only" 4 million hectares.
And we are that very early January. In other words, summer is far from over. It runs until the end of February in Australia, and January is a month marked by temperature peaks. Indeed, as Scott Morisson fears, these fires can last several weeks or even several months.
Should we see in these gigantic fires a consequence of climate change?
Australia is regularly affected by violent fires. There is one every year and has always been. The environment is favorable. A dry and hot climate and a biomass [quantity of vegetation] which can be important on the ground in certain regions. One of the most striking episodes in recent years has been the Victoria wildfires between February 7 and February 14, 2009. We even remember February 7 as "Black Saturday", the main damage having occurred on this single day [the various foci made more than 231 dead, burned 365,000 hectares and 1,000 houses]. What is striking, this year, as we have said, is the level of drought recorded at the end of winter, a drought which plays on the current intensity of the fires.
However, we already know that the average temperature of the atmosphere has increased. It is a certainty and no longer a hypothesis. Projections then vary from region to region, but this global warming should translate into more frequent and more frequent droughts. By extension, it could expose to more intense fires, especially in Australia. It's a bit like cyclones. Global warming will not make them more numerous, but potentially more intense [a high water temperature is one of the main “fuels” for a cyclone].
What can be done to control these fires? Is the situation literally out of control?
The behavior of a forest fire is controlled by three main factors. We speak of the "fire triangle". The first side is the weather. Temperatures, winds, last rains. The second side is the relief, a fire spreading much faster and powerfully on sloping ground. On these first two points, there is little man can do. The third side, finally, is the biomass, that is to say the amount of vegetation, from zero level (the soil) to the treetops.
In this area, preventive measures can be taken. By reducing biomass. The main challenge is to reduce the vegetation on the ground. Shrubs, undergrowth… Because it is always on the ground that a fire starts and it is often at this level that it spreads, and not from crown to crown.
The only technique, therefore, to control fires is brush clearing. On a large scale, the only tool at your disposal is the preventive fire. Of course, it is done according to a strict protocol and only during the rainy season. This solution can also only be envisaged in regions where the ecosystems [fauna and flora] are used to fires. But even this solution has its limits in Australia. One of the areas that had been the subject of a preventive fire in the Sydney area in 2016, burned again this year. And we see it now in New South Wales: faced with the violence of the fires, the authorities sometimes have no choice but to evacuate the area.
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