Agriculture Reference
In-Depth Information
Urban Management
Factor
G
in
Equation (13.1)
, chance of fire propagating, is a function of urban
fuels that include home construction characteristics, landscaping and home
attachments. Often these are a more significant threat to urban environments
than wildland fuels (Spyratos
et al.
2007
). Predicting the impact of these factors
on fire risk is complicated by housing density, socio-economic status and age of
the development (Syphard
et al.
2007
; Luck
et al.
2009
). We know relatively little
about the potential trade-offs of different landscape planting palettes on fire
spread in the urban environment. Combustion studies have provided a basis
for selecting landscaping plantings (Weise
et al.
2003
; White & Zipperer
2010
).
However, the widespread use of palm trees and pine trees is of some concern as
these trees within the urban environment can act as ember catchers and relay
embers. Exacerbating the situation is the observation that landscape changes in
vegetation fuels over the past half century have in some regions been greater on
the urban side of the wildland-urban interface (
Fig. 13.5b
). Although some plants
appear to be more fire resistant than others, perhaps the primary factor determin-
ing impact on home ignition is the proximity of landscaping to structures
(Wilson & Ferguson
1986
) and the degree of litter accumulation on roofs
(C.J. Fotheringham & J.E. Keeley unpublished data).
Home construction characteristics should make a difference as to whether or not it
survives a wildfire, although most of the evidence for this is circumstantial, or based
on small-scale tests (Dietenberger
2010
). Shutters on windows and special attic vents
to prevent ember entry into homes are some of the recommended structural changes
that could lead to reduced building losses (Ramsay
et al.
1995
). InCalifornia, maps of
fire hazard severity are constantly updated for the purpose of informing decision
makers on the construction codes necessary to reduce losses from wildfires. It is
interesting that an Australian study of bushfire losses found that over the past
century the annual probability of building destruction has remained almost constant
(McAneney
et al.
2009
). These authors suggested that despite improvements on
several fronts, housing losses were the result of severe fire weather, and homes in
the path of these firestorms stood little chance of surviving. This suggests that
changes in construction materials may not provide the necessary level of protection
and perhaps more drastic changes in urban growth patterns designed to avoid
dangerous landscapes may hold the most promise for reducing wildfire losses.
Social and Political Constraints
Political and social factors (
Box 13.2
) are critical to minimizing
D
, risk of destruc-
tion (
Equation 13.1
). Preventing wildfires from reaching the urban environment is
generally the responsibility of state and federal governments, and community
planning is often predicated on the belief that these fire management agencies
can eliminate wildfire threats. However, there is abundant evidence that
D
will
never be reduced to zero by wildland management activities alone. Despite the
scientific evidence for this, differing agendas by stakeholders often diminish the
