What exactly causes forest fires? Why are they so devastating?

Forest fires have a maximum impact on moist forest areas (high humidity), which become excessively drier and hotter (than usual) in summer season. Dry grasslands are less prone to such fires, as a drier & hotter condition creates barren land, which does not create a continuous stretch of vegetation for the forest fire to continue (isolated fires). In the US alone, the forest fires cost the nation over $1 billion each year ^[1].

Scientific evidence suggests high ‘fuel aridity’ (fuel = vegetation, aridity = life-promoting moisture) to be a main cause of forest fires. Extreme heat and low humidity in generally high humidity forest areas are a result of global warming. Increased atmospheric CO2 and nitrogen pollution together help fertilize plants. These together contribute to an increase in the growth of flammable vegetation ^[2].

Under such conditions, even small sparks/splinters due to normal human activity (hammering concrete, tyre rim scraping asphalt) have led to devastating fires (Ranch and Carr fires, California). The spread of particulate matter (aerosols like carbon soot) from a forest fire onto snow helps darkening of snow, which raises local temperature and affects the water cycle. These aerosols also make it harder for clouds to form water droplets in tropics. Over the last two decades, such conditions have increased the frequency of forest fires and the area burnt down in each fire ^[3].

Human intervention like conversion of forest areas to plantations for economic growth in countries like Indonesia, Bolivia, Brazil, add to global warming, as burning of many trees releases huge amounts of carbon dioxide ^[4].

The Fort McMurray fire of 2016 in Canada led to evacuation of 90,000 people, destroyed 2,400 building, and costed the nation $10 billion in damage. Canada is expected to have a 50% to 200% in increase in the number of dry & windy days (per year), which are ideal conditions to start & spread such fires ^[5].

Forests can absorb up to 30% of human greenhouse gas emissions, but forest fires contribute 5% to 10% of annual global CO2 emissions per year ^[6].

To conclude, global warming alters the climate of moist forest area (drier & hotter, more CO2 & nitrogen pollution). This also affects the type of vegetation that adapts to this change (flammable vegetation). Such conditions allow forest fires to be ignited by minor sparks too. Forest fires have enabled the growth of more such fires and net increase in global temperatures due to the aftereffects (spread of aerosols, additional CO2 released). Australia in its peak summer faced a huge disaster due to multiple forest fires recently. The rest of us in the world should be prepared to handle such a disaster each summer, as this would be a constant global threat from now onwards.

© Sudhanshu Vuppuluri, 08-01-2020

References:

1. https://www.ucsusa.org/resources/global-warming-fueling-increased-wildfire-risks
2. https://www.carbonbrief.org/factcheck-how-global-warming-has-increased-us-wildfires
3. https://climate.nasa.gov/news/2912/satellite-data-record-shows-climate-changes-impact-on-fires/
4. https://www.france24.com/en/20190913-forest-fires-destroying-vital-buffer-against-climate-change
5. https://climateatlas.ca/forest-fires-and-climate-change
6. https://insideclimatenews.org/news/23082018/extreme-wildfires-climate-change-global-warming-air-pollution-fire-management-black-carbon-co2
7. Images: unsplash.com (Photo by Cata on Unsplash), pexels.com