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CLIMATE-FIRES-CALIFORNIA
Ten ways climate change can make wildfires worse
PARIS, Nov 11, 2018 (BSS/AFP) – Deadly wildfires such as those raging in
northern and southern California have become more common across the state and
elsewhere in the world in recent years. AFP talked to scientists about the
ways in which climate change can make them worse.
Other factors have also fuelled an increase in the frequency and intensity
of major fires, including human encroachment on wooded areas, and
questionable forest management. “The patient was already sick,” in the words
of David Bowman, a professor of environmental change biology at the
University of Tasmania and a wildfire expert.
“But climate change is the accelerant.”
– Fine weather for a fire –
Any firefighter can tell you the recipe for “conducive fire weather”: hot,
dry and windy.
No surprise, then, that many of the tropical and temperate regions
devastated by a surge in forest fires are those predicted in climate models
to see higher temperatures and more droughts.
“Besides bringing more dry and hot air, climate change — by elevating
evaporation rates and drought prevalence — also creates more flammable
ecosystems,” noted Christopher Williams, director of environmental sciences
at Clark University in Massachusetts.
In the last 20 years, California and southern Europe have seen several
droughts of a magnitude that used to occur only once a century.
– More fuel –
Dry weather means more dead trees, shrubs and grass — and more fuel for
the fire.
“All those extremely dry years create an enormous amount of desiccated
biomass,” said Michel Vennetier, an engineer at France’s National Research of
Science and Technology for Environment and Agriculture (IRSTEA).
“That’s an ideal combustible.”
– Change of scenery –
To make matters worse, new species better adapted to semi-arid conditions
grow in their place.
“Plants that like humidity have disappeared, replaced by more flammable
plants that can withstand dry conditions, like rosemary, wild lavender and
thyme,” said Vennetier.
“The change happens quite quickly.”
– Thirsty plants –
With rising mercury and less rain, water-stressed trees and shrubs send
roots deeper into the soil, sucking up every drop of water they can to
nourish leaves and needles.
That means the moisture in the earth that might have helped to slow a fire
sweeping through a forest or garrigue is no longer there.
– Longer season –
In the northern hemisphere’s temperate zone, the fire season was
historically short — July and August, in most places.
“Today, the period susceptible to wildfires has extended from June to
October,” said IRSTEA scientist Thomas Curt, referring to the Mediterranean
basin.
In California, which only recently emerged from a five-year drought, some
experts say there’s no longer a season at all — fires can happen year-round.
– More lightning –
“The warmer it gets, the more lightning you have,” said Mike Flannigan, a
professor at the University of Alberta, Canada and director of the Western
Partnership for Wildland Fire Science.
“Especially in the northern areas, that translates into more fires.”
At the same time, he noted that 95 percent of wildfires worldwide are
started by humans.
– Weakened jet stream –
Normal weather patterns over North America and Eurasia depend heavily on
the powerful, high-altitude air currents — produced by the contrast between
polar and equatorial temperatures — known as the jet stream.
But global warming has raised temperatures in the Arctic twice as fast as
the global average, weakening those currents.
“We are seeing more extreme weather because of what we call blocked ridges,
which is a high-pressure system in which air is sinking, getting warmer and
drier along the way,” said Flannigan.
“Firefighters have known for decades that these are conducive to fire
activity.”
– Unmanageable intensity –
Climate change not only boosts the likelihood of wildfires, but their
intensity as well.
“If the fire gets too intense” as in California right now, and in Greece
last summer — “there is no direct measure you can take to stop it,” said
Flannigan.
“It’s like spitting on a campfire.”
– Beetle infestations –
With rising temperatures, beetles have moved northward into Canada’s boreal
forests, wreaking havoc — and killing trees — along the way.
“Bark beetle outbreaks temporarily increase forest flammability by
increasing the amount of dead material, such as needles,” said Williams.
– Positive feedback –
Globally, forests hold about 45 percent of Earth’s land-locked carbon and
soak up a quarter of human greenhouse gas emissions.
But as forests die and burn, some of the carbon is released back into the
atmosphere, contributing to climate change in a vicious loop that scientists
call “positive feedback.”
BSS/AFP/MRI/1555 HRS