The bushfire outlook for many parts of Australia has changed dramatically over the past decade. Environmental conditions have changed, causing larger and more destructive wildfires.
The frequency of wildfires changing the atmospheric conditions around them has also increased. Nowhere was this more apparent than during the Black Summer wildfires of 2019-2020.
As we continue to experience the effects of climate change, these environmental changes and devastating fire events will only become more common.
Satellite imagery data collected over the last 20 years allows us to map and quantify the impact of climate change by region, and how it has affected the prevalence of fires in different parts of Australia. With more accurate wildfire models, we can help firefighters and land managers determine where to refocus their efforts as we adapt to the long-term climate change adaptation.
To that end, the maps in this article show where fires have occurred in two consecutive decades, and show the changes between them. They also show regions where those changes exceed a threshold, indicating a significant increase in fire activity. This enables more targeted fire risk management.
Read more: 200 experts dissected the Black Summer wildfires in unprecedented detail. Here are 6 lessons to watch out for
Two decades of satellite fire surveillance
More than 20 years ago, NASA launched two satellites, (Terra in 1999 and beyond aqua in 2002), to monitor the Earth’s surface with specialized sensors. One sensor, MODIS (MODerate resolution Imaging Spectroradiometer), was able to see both plumes of smoke and the infrared signature of fires. An algorithm has been developed to classify image pixels with fire, yielding a set of “hotspots”.
Both satellites have outlasted their planned mission duration. This is important for brand managers, who now have two decades of continuous hot spot data.
Mapping Australia’s hotbeds
For many years I have been analyzing MODIS data from the perspective of seasonality. I looked at when there was a fire and whether that reflected expectations. The goal is validation seasonal wildfire outlook.
The annual seasonal ratings for the past 20 years are now available online. Each year, the data from the previous 12 months was compared to that of a particular time period or control period. This was a ten-year period covering a mix of El Niño and La Niña years, indicating “average” conditions.
We recently passed the end of the second decade of MODIS data. This opened up the prospect of comparing two decades (starting in July 2002 and ending in July 2012) and looking for differences.
In a year of fire, Australia creates more than 450,000 hotspots. This makes the 20 years of MODIS data an irreplaceable resource for seamless, quantitative assessments of fire dynamics across Australia. The datasets are freely available online and have been used to make useful products to help firefighters.
Several caveats apply to hotspot datasets. Low-intensity fires (especially well-planned burns to mitigate risk), fires under heavy cloud cover, and fires that burn out quickly may not produce a hot spot. The latter was the case in many of the worst fire events during the Black Summer Fires.
There is also no way to separate wildfire from planned fire. This should be a goal, as both contribute to the fire regime, but the balance varies greatly between regions. Future fire planning can become a major challenge as large wildfires such as Black Summer bring much of the landscape into one fire era. This makes burning difficult until the forest recovers.
Read more: Australia’s firefighting has reached a crossroads and ‘business as usual’ won’t make it
To determine how fire activity had changed between the first and second decades of data, hotspots were aggregated into grid cells. Each spanned half a degree of both latitude and longitude.
By comparing the number and ratio of hotspots in the number of grid cells from decade one to that of decade two, we were able to determine where the firing frequency changed the most.
Some areas, such as eastern New South Wales, have a very high rate of change between the first and second decades, reflecting Black Summer. Some areas, such as Arnhem Land, have a very high number of hotspots and a slight increase from the first decade to the second, which could pose a significant challenge in the future.
Read more: We are professional fire watchers and we are amazed at the magnitude of the fires in remote Australia right now
To encompass the effects of both high numbers and high ratios, a threshold was established and each region that exceeded it was an area that needed the most attention.
This produced a series of geographic regions with consistent patterns.
The impacts described in the interactive map below (click on the dots for details) should be viewed as longer term management issues for the highlighted regions.
Year-over-year fire patterns have shown extreme swings in recent years, which can overwhelm long-term trends. However, these trends have picked up on many of the major operational challenges, including fire thunderstormsof recent years.
These challenges are evident in the forests of southeastern and southwestern Australia, southeastern Queensland, central Tasmania and the tropics.
Read more: Firestorms and flaming tornadoes: How wildfires create their own raging weather systems
Hotspot mapping in the future
Challenges as we move forward include developing ways to merge the MODIS data with next-generation satellite data, as well as separate wildfire and prescribed burn data.
This and other work will enable us to better anticipate what the next decade will bring.