the future of fire in washington forests: risks and responses
TRANSCRIPT
The future of fire in Washington forests:Risks and responses
Dave PetersonUniversity of Washington
School of Environmental and Forest Sciences
What we’ll talk about today
• The science of wildfire
• Recent trends in forest fires
• Wildfire, weather, and climate
• Risk assessment and risk management
• How landowners can adapt to and
prepare for wildfire
THE SCIENCE OF WILDFIRE
• Combustible fuel
• An extended period of dry weather
• An ignition
Fire recipe
How a forest burns:
Fuel types
How a forest burns:
Fire types
How a forest burns:
Fire spread
1 – Surface fuel to canopy 3 – Understory tree to canopy
2 – Fallen tree to canopy 4 – Wind
Pre-ignition phase
• Fuels are heated
• Fuel moisture is driven off, water vapor is released
• Pyrolysis begins: thermal oxidation of cellulose to combustible vapors
Flaming phase
• Combustible vapors reach 600°F and mix with oxygen, causing rapid pyrolysis
• Emissions of carbon dioxide, water, and other gases
Smoldering phase
• Temperature and combustible vapor mixture too low to support flaming
• Temperature drops, gases condense
• Emissions are twice as high as in the flaming stage
Glowing phase (residual)
• All volatile gases driven off
• No visible smoke
• Carbon dioxide, carbon monoxide, and ash produced
Surface fuels
Fine fuels
(< 3 in. diameter)
contribute the
most energy to
active burning
Potential for intense fire?
Probably not
Consider
how you
build a
campfire
Ladder fuels
Remember last summer?
And 2017? And 2018?
IS THIS THE NEW NORMAL?
U.S. Washington
2020 10,200,000 713,000
2019 4,664,000 170,000
2018 8,767,000 439,000
2017 10,000,000 404,000
2016 5,510,000 294,000
2015 10,125,000 1,138,000
Total 49,266,000 3,158,000
Recent wildfire statistics (acres)
Washington wildfires — 2015
• 1,541 fires
• 1.1 million acres
burned
• $253 million fire
suppression cost
• Large economic
losses in rural
communities
Interacting disturbances
Wildfire
Insects &
disease
Map by R. Norheim
WESTSIDE WILDFIRE:A NEW CHALLENGE?
Historical westside fires were BIG
1701 fire event
• > 1 million acres on
the Olympic Peninsula
• > 3 million acres in
western Washington
Yacolt complex (1902)
• > I million acres
Tillamook burns
(1933, 1939, 1945, 1951)
• 350,000 acres
Forest fuels on
the west side of
the Cascades
Wildfire in western Washington?
Goodell Creek Fire, Newhalem, WA (August 2015)
Wildfire in western Washington?
Anacortes, WA (August 2016)
Recent fires near Mt. Adams
Map by R. Norheim
2020 fires in western Oregon
• Four large fires
burned 710,000
acres, mostly in
westside forests.
• East winds (high
windspeed, warm,
dry) were the key
factor in fire
spread.
Could fires similar to the 2020 Oregon fires happen in western Washington?
Yes, but the probability is low.
WILDFIRE AND THE ROLE OF WEATHER AND CLIMATE
Wildfire area burned in the U.S.
Average annual number of structures lost in U.S.
Fires starting in wildland vegetation and spreading into the built environment
220 405650
920
2633
7265
0
1000
2000
3000
4000
5000
6000
7000
8000
1960s 1970s 1980s 1990s 2000s 2010-2018
NU
MB
ER O
F ST
RU
CTU
RES
DES
TRO
YED
The wildland-urban interface is growing
Photo: FEMA- Andrea Booher
• WUI is the fastest
growing land-use type
in the U.S.
• Nearly half of the
population in the
western U.S. lives in
the WUI.
• Since 1990, 60% of
new homes in
California, Oregon,
and Washington have
been built in the WUI.
Fire suppression costs are soaringB
illio
ns
of
2017$
1990s
average $1
billion/year
2000s average $3.7 billion/year
USFS
DOI
Extremes matter
Agencies are very good at fighting fires
— 98% of fires are controlled within 24 hours.
2% of all fires account for 95% of area burned
and fire suppression costs.
This is not a “fire control problem”!
Another way to look at fire risk
Based on weather and fuel
moisture measurements…
Fire Danger Level = VERY HIGH
• Fires can start easily from most causes.
• Fires will spread rapidly and increase in intensity following
ignition.
• Small fires can quickly become large fires and exhibit extreme
fire intensity, such as long-distance spotting and fire whirls.
• Fires can be difficult to control and will often become much
larger and longer-lasting fires.
More “very high” fire
danger days
Near future
Source: Northwest Climate Toolbox
More “very high” fire
danger days
Mid 21st century
Source: Northwest Climate Toolbox
OPTIONS FOR FOREST LANDOWNERS
Keep forests healthy:
Manage stand density and fuels
Thin dense stands to reduce
competition (“too many
straws in the glass”)
Consider removing surface
and understory fuels to
reduce fire intensity
Manage forest density and
fuels across landscapes
– Collaborate with neighbors
Thinning helps capture the capability of
a site and allocate it to selected trees
Hopefully when the trees
are this size…
…and continuing
through their life time
Variable density thinning
Target:
20% open stands
20% dense stands
60% standard thin
This can vary –
there are no rules.
75
TPA
100
TPA
75
PA
10
TPA
150
TPA
150
TPA
75
TPA
Skip
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Various spatial patterns of different tree densities
Increase landscape diversity
Diversify spatial
distribution of
species, ages, and
structures.
Orient the location
of treatments in
large blocks to
increase resilience
to disturbance.
LIVING WITH FIRE AND REDUCING RISK
https://www.nfpa.org/Public-Education/By-topic/Wildfire/Firewise-USA
Fuel treatment example
Before After
What does Firewise do?
• Reduces the potential for
structural ignition through
fuel reduction (mostly for
lower density housing).
• Firewise guidelines help
raise homeowner
awareness and reduce
ignition potential.
Houses and other structures are also fuels
Home Ignition Zone
Immediate zone (0-5 feet)
Home Ignition Zone
Intermediate zone (5-30 feet)
Home Ignition Zone
Extended zone (30-100 feet)
Immediate zone (0-5 feet)
• Remove dead leaves, needles, and twigs from roofs and
gutters.
• Replace or repair loose or missing shingles to prevent
ember penetration.
• Install 1/8-inch metal mesh to reduce embers that could
pass through vents in the eaves. Clean debris from all
vents.
• Screen areas below patios and decks with wire mesh to
prevent debris and combustible materials from
accumulating.
• Move flammable material away from wall exteriors and
from underneath decks and porches (vegetation,
firewood, etc.).
Intermediate zone (5-30 feet)
• Clear vegetation from under propane tanks.
• Create fuel breaks with driveways, walkways, etc.
• Keep grassy areas mowed to a height of 4 inches.
• Remove vegetation under trees, so a surface fire cannot
reach the crowns. Prune trees to 6-10 feet from the
ground, but do not exceed 1/3 of overall tree height.
• Space trees to a minimum of 20 feet between crowns.
• Plan tree placement to ensure the mature canopy is no
closer than 10 feet to the edge of the structure.
• Limit trees and shrubs to small clusters of a few each to
break up continuity of the vegetation.
Extended zone (30-100 feet)
• Dispose of heavy accumulations of ground litter and debris.
• Remove dead plant and tree material.
• Remove small conifers growing between mature trees.
• Remove vegetation adjacent to storage sheds and other
outbuildings.
• Ensure that trees 30 to 60 feet from the home have at least
12 feet between canopy tops.
• Ensure that trees 60 to 100 feet from the home have at
least 6 feet between the canopy tops.
Tree spacing in the different zones
Don’t let this happen to you!
Or we may show up at your house
In conclusion…
• The climate will continue to warm for the foreseeable
future.
• Fire season will be longer, fire frequency will
increase, and area burned will increase.
• More WUI fires will continue to occur during droughts
and extreme weather.
• There are options for adapting to climate change and
increased fire occurrence.
• There will be surprises.
