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Australian fires 2019/20

January 12th, 2020 Leave a comment Go to comments

Australia is a very flammable continent, and fires have been occurring there for millions of years. As a consequence, many plants and animals have developed adaptations and strategies to cope with recurrent fires. However, the current fire season in eastern Australia is really very severe, including not only very large fires but also high intensity firestorms. SE Australia has suffered other sever fire seasons in the past (an iconic example is the Black Friday bushfires in 1939). Why is this happening now? Here I’ve compiled key figures that help us to understand it.

In the last few years, Australia has been suffering an increase in temperature; on average, each year is hotter than the previous year (Fig. 1). In fact, 2019 was the warmest years, but also the driest year (with the lowest rainfall) ever recorded. December 2019, when most fires started, was climatically an extreme (Fig. 2). During the December heatwave (Fig. 3) some meteorological station (e.g., Penrith, near Sydney) recorded temperatures over 48oC, and the record of highest average maximum temperature for Australia was broken on two consecutive days (40.7 and 41.9oC  on 17 and 18 Dec, respectively). January 4 was Canberra’s hottest day since records began (44oC). In such extreme weather conditions, ignitions easily become a wildfire (in fact, several of the wildfires started from a dry lightning), and fires spread very quickly in a vegetation that has been in a drought for many months. This generates not only huge areas burned (Fig. 4), but also very hot fires and strong uplift air columns that reach the stratosphere (pyrocumulonimbus). These are called firestorms. Firestorms produce there own winds and spread embers and the fire very fast; they even produce lightnings that generate additional wildfires. Firestorms produce extreme fire behaviour that is beyond the capacity of firefighters. In those fires, as it happens in volcanoes, the smoke reaches the stratosphere and circulates at very long distances (e.g., currently smoke from these fires has already reached South America).

The fire season has not ended yet. The ecological effects of these fires will depend on many factors (spatial variability of fire intensity, previous fires, species, etc…). The size and intensity of these fires suggest that they can have some negative consequences, but it is too early for any quantitative evaluation. Many plants are starting to resprout just few days after the fire, even under those drought conditions; some animals are leaving their hiding places, exploring the burned area, and carcasses are locally abundant suggesting patches of high animal mortality. We’ll see when will the rain come, and how plants and animals will respond. For humans, the consequences are catastrophic (fatalities, destruction of many infrastructures, smoke problems, etc.).

Fig. 1. In Australia, each year is hotter than the previous year, on average. From Australian Bureau of Meteorology
Fig. 2. December 2019 was climatically an extreme, unprecedented in relation to rainfall and temperature. Elaborated with data from Australian Bureau of Meteorology
Fig. 3. Global temperature in December 18th, 2019, as shown by Windy. Note also that part of the differences in temperature are due to the different time zones; i.e., middle of the day in Australia, night time in South America, and early morning in Africa.
Fig. 4. Major fires in south-east Australia by January 10th, 2020 (5,634,000 ha). From @eforestal [update Jan 18th: 6 millions ha]

More information:

Australian Bureau of Meteorology  | @eforestal maphub  | NSW fire service | VIC emergency | Desinformation |

Update (4/2020): For a map of the time-since-fire and fire severity across NSW fires, see: Bradstock et al. 2020, Global Change Biol., doi:10.1111/gcb.15111 (spoiler: most fires burned at relatively low severity!)

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