Transcript Document

Term Papers due on Tuesday
Please turn in a hard copy plus your
draft paper with my comments
Tuesday: Review for Final
Fire Management
in the
Wildland-Urban Interface
(WUI)
Key Topics
• What is the WUI?
– Trends in WUI fire disasters
– Fire policies affecting the WUI
• Three approaches to protecting homes in the
WUI:
– Fire suppression
– Fuel treatments
– Creating defensable space (home ignition zone)
• Exercise: preventing fire in the home
ignition zone
Wildland-Urban Interface
Definition?
• Wildland:
– Area in which development is essentially nonexistent, except for roads, railroads, pwerlines,
etc., and any structures are widely scattered.
• WUI
– Zone where structures and other human
development meet or intermingle with
undeveloped wildland or vegetative fuels
(NWFCG 2006)
– An area where a wildland fire can potentially
ignite homes
Since 1970:
>15,000 homes lost to wildfires
Suppression costs >$25 billion
Insurance costs >$10 billion
Broad scale national assessment
of wildland fire risk
Trends in WUI fire disasters
• 1870-1920: massive wildfires across millions of
acres destroyed towns and caused thousands of
fatalities (WI, MI, MN, ID, MT) – greater
destruction of lives and property than past 50 yr.
• Since 1985 – wildfires in the WUI recognized as a
major problem
– Policies: National Fire Plan (2000), Federal Wildland
Fire management Policy (2001), Healthy forests
Restoration Act (2003), Firewise program
– Focus on increasing suppression efforts in WUI
– Vast amounts of money spent (funds often exhausted)
Trends in WUI fire disasters
• Despite recent emphasis on “fire use”, many
more wildland fires are suppressed compared to
those allowed to burn:
– 1998-2007: ~80,000 wildland fires suppressed, vs.
327 designated as desirable prescribed fires
• Suggests that the “fire exclusion paradigm” still
continues.
• In many ecosystems, resulted in changes in
vegetation fuel structures and fuel accumulation,
leading to more high intensity fires.
What is a “WUI fire Disaster”?
• Only occurs when homes ignite during wildfire,
otherwise problem doesn’t exist
• Wildland fire suppression operations successfully
control 97-99% of wildfires at initial attack.
• Structure firefighters usually limit a fire to a single
structure and prevent spreading.
• Only during extreme wildfire conditions do
numerous houses ignite and burn simultaneously –
overwhelm efforts
• Extreme fire behavior conditions account for 1-3%
of wildfires that escape initial attack.
WUI fire disaster conditions
Can more suppression efforts
prevent WUI fire disasters?
• Under extreme weather conditions and fire
behavior, suppression efforts are usually
overwhelmed.
• This is especially the case when multiple
houses burn simultaneously under extreme
fire conditions.
Can fuel treatments prevent WUI
fire disasters?
• Objective 1: Make wildlands “fire-proof”
– Not possible for fire-dependent ecosystems
• Objective 2: Facilitate suppression
– = “The wildland fire paradox”
– Fire suppression more effective, but the problem
becomes worse
– Less area burned in the short run, but more area
burned under extreme conditions, when
suppression is ineffective.
Can fuel treatments prevent WUI
fire disasters?
• Objective 3: Create conditions in which fire can
occur without devastating consequences
– Allow fires to burn without need for suppression
– Will usually need to include the “home ignition zone”
• Objective 4: Ecosystem restoration
– Some ecosystem restoration treatments reduce fuel
hazard, but not all fuel treatments restore ecosystems
– Depends on to what extent they emulate historical
conditions: what forests should we prioritize & why?
– Examples: ponderosa pine, mixed conifer, drier
Douglas-fir forests
Arizona
Montana
Principles of restoring fire regimes to dry
forests with fire hazard reduction treatments
Principle
Reduce
surface
fuels
Increase
height to
live crown
Effect
Advantage
Reduces flame Control
length
easier, less
torching
Longer flame
Less torching
length needed
for torching
Concerns
Surface
disturbance
Decrease
crown
density
Reduces treeto-tree spread
of crown fire
Reduces
crown fire
potential
May increase
surface wind &
drying of
surface fuels
Keep big
trees of
resistant
species
Reduces tree
mortality from
fire
Restores
Less
historic forest economical;
structure
increase risk of
insect attack
May increase
surface wind
Fuelbreak in Wenatchee, WA
Fuel treatment area (removed surface
& ladder fuels) - Megram Fire, CA
Fuel treatment: thinning &
prescribed burning (Cone Fire, CA)
Home Ignitability & Survival: Can
creating defensible space in the ignition
zone prevent WUI fire disasters?
Preventing Disaster: Home Ignitability
in the WUI (Cohen 1998)
• 3 Approaches to determining ignitability
and the ignition zone:
1) Modeling
2) Fire experiments
3) Case studies
• TTYP – Explain for your case:
1) how the study was conducted?
2) what were the results?
3) what are the implications for preventing WUI fire
disasters?
Fire experiments –
wood ignition
Exterior plywood (not treated)
Heat flux sensors
Repeated burns:
10 m
20 m
30 m
10m: scorched, no ignition
20m: lightly scorched
30m: not affected
SIAM: Structure Ignition Assessment Model
Ignition time:
- Heat flux
-Distance
* Wildfire burn
Duration = 50-70 sec
Overestimates radiant heat flux - Extreme case scenario
- Black-body radiating flame front (maximum heat transfer)
- Wildfires = variable heat
20 homes destroyed
under tree canopy
Case Studies
• Bel Air fire (484 homes destroyed, 1973)
• Painted Cave fire (479 homes destroyed,
1994)
• Los Alamos (200 homes destroyed, 2000)
– 90% survival of homes with vegetation
clearance 10-20 m
– Homes with nonflammable roots: 70% survival
rate (vs. 19 % for flammable roofs)
Investigation of Cerro Grande
Fire: Los Alamos (2000)
• 200 homes totally destroyed or irreparably
damaged
• Fire suppression – saved some homes
• High ignitability of most homes
– Fires spread quickly
– Simultaneous house fires
– Overwhelmed suppression forces
Lake Arrowhead, CA – Oct. 22, 2007
(homes continued to ignite and burn after
wildfire intensity slowed)
Can creating defensible space in the
ignition zone prevent WUI fire disasters?
• The evidence: homes burn even when fire
behavior in nearby forests is not extreme
• A home’s ignition potential determined by:
– Characteristics of its exterior materials & design
– Response to burning objects within 100 feet
– Response to firebrands
• Combustion occurs by two principal ways:
– Flames (radiation & convection heating)
– Firebrand ignitions
Home can ignite
from 2 sources:
1) Directly from flames
2) Firebrands on house
*** Defensible space***
TTYP: Reducing fire risk in the WUI
• You just bought a new home in the
mountains of New Mexico, in the heart of
ponderosa pine country (see photo on the
wall). Make a list of all the actions that
you plan to take in order to reduce the risk
of fire to your new home. Separate your
list into those actions that will reduce
home ignitability, and those that will
increase the amount of defensible space.
Common home situation in Los Alamos residential areas
• The Firewise Communities/USA project provides citizens with the
knowledge necessary to maintain an acceptable level of fire readiness,
while ensuring firefighters that they can use equipment more efficiently
during a wildland fire emergency.
• The program draws on a community's spirit, its resolve, and its willingness
to take responsibility for its ignition potential.
• Enlist a wildland/urban interface specialist to complete a community
assessment and create a plan that identifies agreed-upon achievable
solutions to be implemented by the community.
• Sponsor a local Firewise Task Force Committee which maintains the
Firewise Community/USA program and tracks its progress or status.
FireWise Communities
• What are some actions that communities
can accomplish better than individual
homeowners to reduce the risk of fire in the
WUI?