Focus Article
Predicting climate change effects
on wildfires requires linking
processes across scales
Marc Macias Fauria,1† Sean T. Michaletz1† and Edward A. Johnson1∗
Accurate process-based prediction of climate change effects on wildfires requires
coupling processes across orders of magnitude of time and space scales, because
climate dynamic processes operate at relatively large scales (e.g., hemispherical
and centennial), but fire behavior processes operate at relatively small scales
(e.g., molecules and microseconds). In this review, we outline some of the current
understanding of the processes by which climate/meteorology controls wildfire
behavior by focusing on four critical stages of wildfire development: (1) fuel drying,
(2) ignition, (3) spread, and (4) extinction. We identify some key mechanisms that
are required for predicting climate change effects on fires, as well as gaps in
our understanding of the processes linking climate and fires. It is currently not
possible to make accurate predictions of climate change effects on wildfires due
to the limited understanding of the linkage between general circulation model
outputs and the local-scale meteorology to which fire behavior processes respond.
 2010 John Wiley & Sons, Ltd. WIREs Clim Change 2010 DOI: 10.1002/wcc.92
INTRODUCTION
I
ncreases in wildfire activity due to anthropogenic
global warming have been reported and/or
predicted for many regions of the world,1–6 although
trends in disturbance resulting from wildfires are still
a subject of controversy.1 These predictions stem
from the fact that wildfire incidence and size often
correlate with climate variables. However, accurately
predicting climate change effects on wildfires requires
an understanding of the causal mechanisms linking
climate/meteorology and fire behavior, which implies
linking processes across orders of magnitude of
spatial and temporal scales. Process-based models
have the potential to lead to better predictions than
strictly empirical models that may, at times, be
based on spurious correlations between arbitrarily
selected variables.7 Climate and wildfires are coupled
processes. Unfortunately, our current understanding
of these couplings is limited, and this hinders our
ability to predict climate change effects on wildfires.
† These
authors contributed equally to this work.
∗ Correspondence
to: [email protected]
1 Biogeoscience
Institute and Department of Biological Sciences,
University of Calgary, Calgary, Alberta, Canada
DOI: 10.1002/wcc.92
In this paper, we review the causal processes
through which climate/meteorology controls area
burned by wildfires at timescales relevant to the scopes
of current global warming research (i.e., from seconds
to decades/centuries). For example, fuel drying is the
result of coupled heat and water budgets driven
by surface weather conditions set by large-scale
ocean/atmosphere water and energy exchanges. We
do not intend to present an exhaustive geographical
review of wildfire activity and climate change, but
rather to define some of the key mechanisms required
for predicting fire behavior under climate change
scenarios, and to identify some of the gaps in current
knowledge. Although the examples and references
used are primarily from North America, the approach
adopted in this study is generalizable and should be
valid for most regions of interest.
Area burned is chosen here because it constitutes
an ecologically important effect of fire behavior8 and
has an unequivocal definition, unlike other variables
used in wildfire research which have meant different
things by different authors (e.g., severity7 ). This
does not mean that other relevant approaches could
not have been chosen. For example, wildfires affect
climate through shorter-term, fire-induced weather
and longer-term radiative forcing, associated with
large aerosol emissions and albedo and carbon
 2010 Jo h n Wiley & So n s, L td.
wires.wiley.com/climatechange
Focus Article
storage modifications due to soot deposition, post-fire
vegetation growth, and post-fire land-use changes.9–15
Likewise, land-use practices or vegetation shifts
related with changes in climate (e.g., long-term trend
toward moister conditions) may potentially change
the fuel distribution and type over a given area
(e.g., tree or shrub encroachment in a savannah),16,17
thus modifying the local/regional relationship between
climate and wildfire. Local or regional land cover
changes and their wildfire implications are not,
however, the focus of the present review.
The structure of the paper follows the
chronological sequence of events that characterize a
wildfire: (1) fuel drying, (2) ignition, (3) spread, and
(4) extinction.
FUEL DRYING
In forest fuels, water is a latent heat sink that affects
several aspects of combustion, including preheating,
pyrolysis, rate of spread, rate of energy release, and
time to extinction.18–20 Fuel water content is defined
as the mass of water per unit mass of oven-dry fuel,
and equals the balance of water transport to and from
the fuel surface, as well as transport and storage within
the fuel mass. Fuel dries as a result of coupled heat
and water budgets in which different processes (e.g.,
evapotranspiration, diffusion, adsorption, absorption,
conduction, convection, and radiation) operate in live
and dead fuels, with all of them being ultimately
controlled by the same meteorological factors (e.g.,
shortwave solar radiation, wind, and atmospheric
moisture). In this section, we first discuss the processes
controlling water content in forest fuels. Second, we
consider the different types of fuels in context of
their role in wildfire behavior. Finally, we discuss the
climatic patterns associated with the surface weather
conditions prone to rapid fuel drying, as well as their
interactions at synoptic to planetary (Rossby) scales
and their potential future dynamics in global warming
scenarios.
Water contents of dead fuels vary widely, from
below 2% to over 200% oven-dry mass.21 For dead
fuel, water content is controlled by various processes
depending on the fiber saturation level of the fuel.22–24
Below the fiber saturation point, water content
varies in response to molecular flow in cell walls
(bound water diffusion) or air spaces (water vapor
diffusion). Water exchange with the environment
occurs via adsorption of water molecules via hydrogen
bonding to hydroxyl groups of cell wall constituents
(cellulose, hemicellulose, and lignin22 ). Above the fiber
saturation point, water content varies in response
to flow through the capillary structure driven by
surface tension forces. Water exchange occurs via
absorption or evaporation of water molecules into the
bulk phase.
The water content of live fuels is less variable
than that of dead fuels, usually between 75 and
150% oven-dry mass.21 For live fuel, cell walls are
generally saturated because cell division occurs in
a water-saturated environment, maximizing bound
water content. In intra- and extra-cellular spaces,
water content is controlled by osmotic forces resulting
from intercellular differences in water content.24 In
xylem conduits (vessels and tracheids), water content
is controlled by capillary tension forces driven by
leaf transpiration. According to the Cohesion–Tension
theory,25 transpiration induces surface tension forces
at the stomata that are transmitted through a
continuous water column via cohesion and tension
forces (hydrogen bonding), effectively ‘pulling’ water
up from the soil, into the roots, and through the
xylem.26,27 Transpiration rates are controlled by the
stomata–air water potential gradient as well as the
stomata status (open or closed). A large soil–air water
potential gradient can water-stress live fuels, leading to
very high tension forces in xylem water and cavitation
via air seeding.28 When cavitation occurs, the conduit
contains water vapor in equilibrium with liquid
water at the conduit ends,29 leading to a decrease
in fuel water content. Another mechanism of water
absorption into xylem is foliar uptake of liquid water
or water vapor, perhaps via epidermal hydathodes,30
a cuticular pathway,31 or mucilage layers.32
Although water contents of dead and live fuel
are controlled by different processes, the processes
respond to the same meteorological controls.33 Water
loss results from evapotranspiration, which occurs
under a vapor pressure deficit (i.e., when water
vapor pressure of the fuel is higher than that of
the adjacent air). The vapor pressure deficit varies
with the atmospheric water vapor pressure, the fuel
and adjacent air temperature, and vertical mixing
of air. The fuel temperature is determined by an
energy budget comprising radiation and convection
terms.34 Incoming radiation is primarily from the
sun (shortwave) but also from the surrounding
environment (longwave). Convection varies with wind
velocity as well as with the fuel element size, shape,
and orientation. Water gain occurs from direct contact
with liquid water (e.g., precipitation or saturated
overland flow).
The location of fuel in the forest strata plays an
important role in fuel moisture through its effects on
fuel element heat budgets and the vertical mixing
of air. Forest fuels can be categorized into three
types depending on their location: (1) surface fuels
 2010 Jo h n Wiley & So n s, L td.
WIREs Climate Change
Prediction of climate change effects on wildfires
comprising surface elements (litter) and small plants,
(2) ground fuels comprising organic soil horizons
(duff) and plant roots, and (3) crown fuels comprising
elements located within the forest canopy. Ground
fuel elements are part of a larger porous matrix,
which complicates heat and water transport from
individual elements; here, fuel bed properties become
important.35,36 Surface elements are more exposed to
the atmosphere and are coupled to ambient conditions
via their boundary layer, which varies with free stream
velocity as well as the shape and orientation of the
fuel element.34 For crown fuels, the shielding effect of
foliage on boundary layer development is important.37
Large fuel components play a lesser role in ignition,
rate of spread, and intensity of wildfires than fine dead
fuels.38–40 This, together with the very fast drying rates
of fine fuels (i.e., their strong coupling to weather
conditions) explains the great influence of weather
conditions on fire behavior.40
Abundant literature exists on the weather
conditions prior to and during wildfires, with fuel
drying being linked to persistent warm and dry
weather. In temperate and boreal regions, such
conditions have been related at a synoptic-scale
(over a variety of ecosystems such as savannas,
Mediterranean oak forests, temperate rainforest, and
boreal forests) to persistent positive mid-tropospheric
height anomalies that block zonal atmospheric
circulation, preclude precipitation due to atmospheric
subsidence, and enhance meridional flow of warm
air that rapidly dry fuel over large areas through
the processes explained above.41–51 At the surface,
these conditions are related to warm temperature
anomalies.52,53 In areas affected by the influence
of mountains or higher and over-heated adjacent
plateaus, such as the California chaparral, the
woodlands of Portugal, or the Eucalyptus forests of
south-east Australia, Föhn winds—warmed and dried
adiabatically as they move from the relatively warm
and dry high-elevation continental interior toward the
coastal lowlands—may also play an important role in
fuel drying and enhanced wildfire hazard.41,50,54,55
In ecosystems characterized by crown fires
(closed-canopy forests with a compact arrangement of
crown fuels), the coupling between wildfire occurrence
and weather tends to be relatively straightforward
(i.e., drought enhances fire hazard).56 For wildfires to
occur in these systems, fine fuels need to lose enough
moisture during the dry season (generally summer or
early autumn) through the processes explained above.
The time required for effective fine fuel drying has
been empirically found to range from 10 days to 3
weeks for some forest ecosystems (e.g., boreal forest,
chaparral).46,57 For understory fuels, it may vary
depending on the shielding effect of the forest canopy
(i.e., its ability to decouple the understory from free air
conditions). The frequency of occurrence of droughts
with these characteristics will partly set the overall
fire frequency in different ecosystems. Temperature
may potentially influence fuel drying by shortening
the time required for a given fuel component to
dry58 or by lengthening the fire season,59,60 the other
climatic variables remaining the same. In open canopy
savannas in which surface fires are more frequent
than crown fires, fuel continuity comes largely from
the herbaceous component of the vegetation. Here,
the coupling between wildfires and weather might be
more complex; wet seasons (up to several years) prior
to the fire season have been reported to be needed for
wildfire occurrence, as they allow for the herbaceous
vegetation to grow before the dry period and thus to
ensure fuel continuity.56,61–66
Overall, wildfire synchrony has been reported
in many regions of the planet at subcontinental to
continental scales.63,67–70 Oceans and atmosphere
interact creating modes of climate variability
(teleconnections) that affect vast areas and persist
from days to years.71,72 These modes are characterized
by persistent and preferred (i.e., occurring with
an elevated frequency) spatiotemporal patterns of
water (ocean) and air (atmosphere) masses, which
result in weather being correlated over large areas.
Because fire is largely controlled by weather,
teleconnections explain what causes wildfires to
occur in synchrony over vast areas. Wildfire
occurrence and area burned by wildfire have
been reported to be linked to El Niño-Southern
Oscillation (ENSO) in Tropical Asia and Amazon,
the North American boreal forest, Western USA,
Florida, Mississippi, and Northern Patagonia, and its
low-frequency extratropical counterpart, the Pacific
Decadal Oscillation (PDO), in the North American
boreal forest and Western USA46,49,51,63,65,68–70,73–88 ;
the Arctic Oscillation/North Atlantic Oscillation
(AO/NAO) in the North American and Eurasian
boreal forest69,82,84,86,89 ; or the Atlantic Multidecadal
Oscillation (AMO) in several ecosystem types in
North America.70,80,83,85 The temporal persistence
and quasi-periodic nature of these large-scale climatic
processes offer the potential to eventually produce
long-range forecasts for fire hazard that would
constitute an important tool to fire managers and
planners.56,83 However, the mechanisms driving the
dynamics of some of these patterns of large-scale
climatic variability are still largely unknown (e.g.,
PDO, AMO), and predicting their future behavior
and phase shifts remains elusive. Thus, despite being
useful to explain area burned/climate relationships
 2010 Jo h n Wiley & So n s, L td.
wires.wiley.com/climatechange
Focus Article
(they explain the preferential occurrence of air masses
directly linked to wildfire activity), their use and
interpretation need to be done with caution.
Interactions between major modes of climate
variability can change wildfire activity. For example,
increased area burned in eastern Canada during the
second half of the 20th century occurred under
synoptic-scale situations strongly correlated with
the positive mode of the AO; however, this only
occurred in coincidence with the warm phase of the
PDO.69 Likewise, in the Colorado Rocky Mountains,
‘the co-occurrence of the phase combination of La
Niña–negative PDO–positive AMO is more important
to fire occurrence than the individual influences of
the climate patterns’.80 Finally, Kitzberger et al.70
suggested a modulation of ENSO and PDO by the
AMO at multidecadal timescales when describing
climate/wildfire coupling in Western USA. Recent
empirical and theoretical studies offer plausible
mechanisms that would explain the nature of the
interactions between these major climate modes and
the resulting global climate shifts.90–92 These studies,
which use empirical analyses of the 20th century
major climate shifts and model simulations, attempt
to capture the essence of low-frequency variability
in the Northern Hemisphere92 as well as indicate
research lines that may eventually be able to explain
why a combination of modes often results in increased
wildfire activity.
Moreover, past changes in fire frequency
(based on area burned) have been found to be
synchronous at continental to subcontinental scales in
the montane and boreal forest of North America93–99
and globally.100 The mechanisms behind these changes
remain unexplained, but have been unanimously
attributed to climate. In North America, global
atmospheric circulation changes during and after
the Little Ice Age,95,101 and/or changes in the shape
and location of the jet stream and associated storm
tracks and pathways of cold and dry Arctic and
moist subtropical Atlantic air masses102,103 have been
suggested as possible explanations. Such changes have
in turn been linked to sea surface temperature changes
along the North Pacific coast104 and to the dynamics
of the PDO.105
The effects of climate change on the dynamics
of the teleconnections that control fuel drying remain
unknown. Although modeling studies pointed to a
trend toward positive AO situations due to increasing
greenhouse gases,106,107 they failed to predict the shift
of the AO to a neutral state since the late 1990s.108
Likewise, Collins109 reported contrasted forecasts on
the future response of ENSO to global warming (from
no response to increased amplitude and frequency
of ‘El Niño’ events110 to a higher ratio of central
Pacific El Niño/eastern Pacific El Niño events111 ),
depending on which global circulation model was
used. As for the PDO, too little is known so far about
its mechanisms to state whether its dynamics are being
affected by global warming.112 The overall picture is
thus one of a very dynamic and inter-related climatic
system organized in major modes of variability and
operating at timescales ranging from days to decades.
This controls the frequency, position, and physical
conditions of air masses that are responsible for drying
forest fuels on a local scale; thus, the climatic system
effectively synchronizes fire activity over large areas,
and will respond to global warming in yet unknown
ways.
IGNITION
Ignition is the sequence of processes linking the initial heating of a fuel by an external source of either
radiation or convection to self-sustaining combustion processes in the fuel where heat produced by
exothermic combustion reactions is sufficient to drive
endothermic pyrolysis processes. As discussed above,
water is a latent heat sink that can prevent or limit
combustion of forest fuels; consequently, fuel must
be sufficiently dry for ignition to occur. The degree to
which a fuel must be dried is determined by a heat budget that considers sensible heat input from the ignition
source, sensible heat accumulation in the fuel, latent
heat loss to water vaporization and fuel pyrolysis, and
sensible heat output to adjacent fuel elements and the
environment.34 Wildfire ignition can occur via anthropogenic or non-anthropogenic sources.50,59,113,114
Anthropogenic ignition (e.g., campfires) is dominant
in most Mediterranean and tropical ecosystems,
as well as in highly populated areas.50,54,89 Nonanthropogenic ignition (i.e., lightning8 ) is dominant
in other areas. Since both anthropogenic and nonanthropogenic sources require sufficiently dry fuel,
wildfire ignition is ultimately controlled by climate/meteorology. However, lightning is a weatherdriven phenomenon, and thus non-anthropogenic
ignitions are even further controlled by climate. In
this section, we first give an overview of the physical
mechanisms that generate lightning. Next, we discuss the mechanisms by which lightning ignites fuels,
resulting in a wildfire. We then consider the synoptic
weather situations associated with lightning activity
and briefly review current predictions about climate
change effects on lightning in the context of their
potential effects on wildfire ignition.
Lightning is an energetic discharge of electricity
caused by the separation of positive and negative
 2010 Jo h n Wiley & So n s, L td.
WIREs Climate Change
Prediction of climate change effects on wildfires
charge in clouds.115,116 The process of charge
separation is thought to require water in mixed-phase
conditions (i.e., solid, liquid, and vapor phases).117
Although a variety of meteorological conditions
can generate lightning (e.g., isolated thunderstorms,
frontal storms, and snowstorms), the presence of
a mixed-phase region appears necessary. Charge
separation is thought to be caused by collisions
between smaller ice crystals and larger graupel
particles in the mixed-phase region117 ; positive charge
is selectively transferred to the ice crystals and
negative charge to the graupel particles. The more
massive and faster falling graupel particles carry
the negative charge to the bottom of the cloud,
resulting in a positive thundercloud dipole. This
positive dipole is responsible for causing the two most
common types of lightning: intra-cloud lightning and
cloud-to-ground lightning. Cloud-to-ground lightning
is relevant for wildfire ignition, and is thus our
focus here.
Cloud-to-ground lightning is generally initiated
within the lower negative charge reservoir of the
cloud.115,116 An ionized path called the stepped leader
forms in the air between the cloud and the earth,
carrying the large negative potential of the lower
cloud region toward the ground. This creates an
intense electrical field between the stepped leader
and the ground; once a connection is made, a highcurrent return stroke propagates back toward the
cloud at a velocity near that of light. The return stroke
occupies the majority of the duration of the strike
and is what the casual observer interprets as lightning.
For the majority of return strokes (about 70%), the
return stroke current peaks within one microsecond
and decays within a few hundred microseconds. It
has been shown through observation and simulation
that this short duration is insufficient to initiate
combustion of forest fuels.118,119 For about 30% of
return strokes, a low-level continuing current flows
after the current peak for a duration of up to hundreds
of milliseconds.116 Such ground flashes generally occur
in the latter part of storm development, and the
strongest continuing currents are observed underneath
the laterally broad precipitation regions of mesoscale
convective systems120 and winter storms. The duration
of the continuing current is important in the ignition
efficiency of lightning.121–123 Lightning flashes with
sufficiently long continuing currents account for a
small fraction of the total cloud-to-ground flashes,
and are most common during the dissipation of local
thunderstorms, in the extensive precipitation regions
of mesoscale convective systems, and in thunderstorms
entraining wildfire emissions.116
Since tree crowns are elevated, they constitute
a preferred path in the connection of lightning to
the soil, which can be considered as the ground
terminal.115,116,118 Although fine fuels in tree crowns
sometimes ignite, ignition of fine fuels in the litter
and duff layers is generally responsible for wildfire
initiation.118,122,123 Lightning ignition occurs via
spontaneous combustion; the ignition source (i.e.,
lightning arc) transports sufficient energy to adjacent
fuel to vaporize residual water, induce pyrolysis, and
ignite the vaporized fuel.20,115,124 At this moment, fuel
moisture must be less than the moisture of extinction,
i.e., the fuel moisture content at which the heat sink is
equivalent to the heat source.38,125,126 In order to be
successful, ignition must start a combustion process
in which volatized fuel supply rates are controlled by
positive feedback of heat from the combustion process
itself.20,127 This success will partly depend on electric
current duration, fuel bulk density, and fuel depth.115
Lightning is a requisite, but not a determinant,
of wildfire; fuel type and fuel state (particularly
water content) play a much larger role than lightning
density. Wildfire ignition largely depends on the
co-occurrence of summer lightning and low fuel
moisture. In the boreal forest, ignitions generally occur
during convective storms associated with persistent
summer high-pressure systems, resulting in large
numbers of lightning strikes and reduced and localized
precipitation.128 Lighting-fire ignitions have been
linked to summertime fronts in xeric locations in
the interior forests of northwest United States, due
to lightning storms that provide strong winds and
little precipitation.57 In some climates, peak lightning
activity does not coincide with low fuel moisture
conditions; in Southwestern United States (monsoon
climate) most area burned occurs in May or early
June, whereas most fires are ignited in late June or
early July when monsoon lightning storms break a
several month spring drought.56
Increases in frequency and intensity of lightning
have been predicted in global warming scenarios,
based on the short-term relationship between surface
temperatures and lightning activity.129 However,
it is still uncertain whether these relationships
hold on longer timescales.130,131 Predicting climate
change effects on lightning is difficult, since the
physical mechanisms underlying lightning are not
fully understood,116 and these operate at a much
finer resolution than the mechanisms of the general
circulation. Moreover, increased lightning density
alone would not necessarily imply a change in area
burned, as the coincidence in time of lightning activity
with dry fuel is an even more important determinant
of fire activity.
 2010 Jo h n Wiley & So n s, L td.
wires.wiley.com/climatechange
Focus Article
SPREAD
Wildfire spread can be considered as a series of piloted
ignitions of fine fuel elements adjacent to the flaming
fire front. Heat is released from combusting fuels
and transported to unburned fuel elements, which
are preheated to vaporize residual water and initiate
pyrolysis.20 Once pyrolysis produces volatiles at a rate
sufficient to sustain oxidation, combustion begins and
the fire front has effectively spread. This sequence of
processes determines rate of spread and, ultimately,
area burned. Larger fuels and thick layers of duff
generally combust after the passage of the fire front,
and thus do not play an important role in fire spread.
Wildfire spread relies on two heat transfer
mechanisms: radiation and convection. The relative
contributions of radiation and convection to fire
spread vary with the velocity and turbulence of the
ambient wind field, as well as the temperature, radiant
properties, and view factors (geometry, orientation,
and distance) of the flames and fuel.132–135 Tree
stem and forest canopy density can affect fire
spread via shielding effects on view factors.136,137
Convection is important for vertical spread into the
forest canopy138–140 and lateral spread by wind-tilted
plumes.134,141 Here, convection rates are determined
by the velocity of air flowing past forest fuels (function
of fire intensity and/or wind velocity) as well as by the
fuel structure and orientation.37,136,137 Convection is
also important for fire spread up hillslopes and in high
wind.142
Another important fire spread mechanism is
spotting, which can be envisioned as a sort of
advection process. Spotting is the mechanism by which
burning embers (firebrands) are lofted by the buoyant
plume and transported downwind, where they settle
out of the plume and initiate ignitions (spot fires)
ahead of the main fire front; these spot fires may
coalesce to start a new fire front, which eventually
burns into the main fire. Firebrands combust during
plume transport, which reduces their mass and makes
them more amenable to long-distance transport in
the buoyant plume. Firebrands can travel kilometers
ahead of the primary fire front,143 resulting in much
higher rates of spread than heating of adjacent fuel
by radiation and convection; indeed, spotting is the
dominant mechanism of fire spread in high-intensity
crown fires.143,144 Firebrand generation, path, and
distance traveled are determined by fuel properties
(size, form, type, species, and moisture content),
weather (local wind), and topography.
Wind is by far the single most important factor in
wildfire spread,132,145–147 regardless of the dominant
spread mechanism. Wind increases entrainment rates
of ambient air (oxygen) into the combustion zone,
which can increase fireline intensity and, consequently,
rates of radiation and convection heat transfer to
unburned fuel. Wind can also tilt buoyant fire plumes,
increasing convective heat transfer to adjacent fuels.
Finally, wind increases the lateral transport distance
of firebrands, causing spot fire ignition at further
distances and increasing the rate of spread. Thus,
fire spread is highly dependent upon the strength,
direction, structure, and fluctuations of wind.147
Wind properties are primarily controlled by
two factors: (1) the coupling of the fire with the
fire-induced flow and (2) the coupling of the fire
with the ambient flow in the atmospheric boundary
layer.147–149 The coupling of fire and fire-induced
flow is important because hot gases and water vapor
in the convective plume can directly influence local
atmospheric conditions and rates of spread by creating
fire-induced weather. For example, in a monitored
high-intensity fire in the boreal forest of Canada,9 fireinduced winds reached 12 m/second. Coupling of the
fire with ambient flow is also important, because fire
spread is largely controlled by exogenous (i.e., non-fire
caused) wind intensity in the atmospheric boundary
layer. In order for winds to enhance fire spread rates,
and hence cause large area burned, they should occur
after a period of fair weather in which forest fuels dry
out. Such conditions have been reported during the
breakdown of an upper ridge of high pressure43,150 or
during fast-moving surface lows,151 which also tend
to increase lightning activity, and hence are prone to
both ignition and spread. Without wind, wildfires can
burn with low rates of spread for periods of days.151
Finally, as mentioned before, Föhn winds will largely
increase spread rates and spotting regionally.41,50,54,55
Given the specific sequence of events required
for wind velocity to affect area burned by wildfire,
the spatial and temporal resolutions considered by
general circulation models (GCMs) are still too coarse
to predict future wind activity relevant to wildfire
spread, even when parameterized in order to infer
future average seasonal surface wind intensities.152
EXTINCTION
Fire extinction is once again an effect of heat budget
processes that balance heat source and heat sink terms.
Extinction has traditionally been considered in terms
of the fuel water content at which fire ceases to
spread (i.e., the moisture of extinction38 ), although
this approach has not been especially successful
because it neglects several fundamental processes that
govern combustion and spread.153 Using a heat budget
approach, Wilson153 defined a surface-fire extinction
index as the ratio of forest fuel heat source and sink
 2010 Jo h n Wiley & So n s, L td.
WIREs Climate Change
Prediction of climate change effects on wildfires
terms. The source term characterizes the potential
total heat output of the fuel while the sink term
characterizes the heat required to vaporize residual
moisture and increase temperature to ignition. It can
thus be seen that extinction can occur when heat
output is very low, fuel moisture is very high (via
precipitation or contact with surface water), or heat
transfer to adjacent unburned fuel is very low (e.g.,
in backing fires or discontinuous fuels). In this latter
aspect, changes in wind direction (i.e., blowing toward
the fire front) can play an important role by reducing
rates of convection to adjacent unburned fuel.
However, more recent laboratory burning
experiments suggest that the index fails to capture
all of the processes pertinent to extinction.154 For
example, the index does not adequately characterize
processes of radiation and convection heat transport
through fuel beds. Surprisingly, given the fact that
a great part of firefighting effort is directed toward
extinguishing fire, wildfire extinction is not completely
understood and clearly requires further research.
As with fire spread, the scales and/or the required
sequence of events needed in order to study fire
extinction largely hinder our current ability to
accurately forecast future extinction dynamics.
Increased atmospheric greenhouse gas concentrations associated with global warming imply an
increased magnitude of evaporation, which is predicted to enhance atmospheric moisture content and
accelerate the global hydrological cycle.155–157 Thus,
one might expect higher chances of precipitationdriven fire extinctions under global warming scenarios. This is a very general scenario, however, and a
great deal of regional variation is expected; whereas
precipitation (both average values and extreme events)
is projected to increase in high and tropical latitudes
(e.g., boreal and tropical forests), it would generally
decrease in the subtropics and mid-latitudes (e.g.,
Mediterranean ecosystems157,158 ). However, given
the need to forecast precipitation following a strict
sequence of events (i.e., after a dry period followed
by lightning and wind), the chances of being able
to accurately predict precipitation events (as well as
wind-direction shift events) relevant to wildfire extinction are presently very small.
CONCLUSION
Wildfire behavior is governed by small-scale processes
that respond to local meteorological conditions
including evaporation, convection, radiation, and
advection; all of these are the outcome of coupled
water and energy budgets, which in turn respond
to large-scale coupled ocean–atmosphere interactions.
Consequently, predicting climate change effects on
wildfires requires unification of climate and fire
behavior processes across scales. Unfortunately,
this endeavor is beyond our current abilities, and
many gaps exist between our understanding of
climate patterns and processes and the fine-scale
meteorological variation relevant to wildfire behavior.
Here, we briefly outline the key mechanisms necessary
for predicting climate change effects on wildfire
behavior, and identify areas where more work is
required for linking processes.
The sequence of wildfire behavior presented
here, i.e., fuel drying, ignition, spread, and extinction,
implies a directional series of events in which only
the first one (fuel drying) is not dependent of any of
the others. In this sense, fuel drying sets the area over
which wildfires will potentially occur, and this can be
described at a synoptic and even hemispheric scales.
Once ignition occurs over a location characterized by
dry fuel, the scale at which events take place is localto-regional and, thus, GCMs are not able to capture
or forecast them. Although we can describe situations
prone to lightning (e.g., convective storms associated
to persistent summer high-pressure systems) or fire
spread (e.g., breakdown of high-pressure systems
or fast-moving surface lows), our current ability to
explicitly forecast such a chain of events in global
warming scenarios is extremely limited.
Major research gaps involve bridging smallscale fire behavior processes (ranging from millimeters
to kilometers) with synoptic-scale climatic models.
Addressing them requires a movement toward highresolution climate system predictions, with a blurring
of the distinction between shorter term predictions
and longer term climate projections,159–161 perhaps
involving a coordinated hierarchical approach with a
suite of different models.161 To our understanding,
and by the reasons mentioned above, currently the
most pragmatic way of forecasting future wildland
area burned under a warmer world should focus on
fuel drying, and involve forecasting future changes in
the drying rates of fine fuels as well as modeling
future dynamics of upper air ridging, as already
suggested in Macias Fauria and Johnson.69,82 In the
case of surface-fire ecosystems requiring a season of
fuel buildup followed by a season of fuel drying,
research should focus on the future occurrence of
a wet period followed by a dry period. In this
respect, fully understanding the mechanisms driving
the dynamics of the planet’s major modes of climatic
variability (and thus their future performance under
global change scenarios) would provide a powerful
tool to forecast future wildfire activity. Advances in
downscaling climatic models to the adequate spatial
 2010 Jo h n Wiley & So n s, L td.
wires.wiley.com/climatechange
Focus Article
and temporal scales will imply increased potential for
wildfire forecasts.
Nevertheless, increases in area burned have been
forecasted in response to a warmer world based on
the positive correlation between temperature and area
burned during the last four decades; this suggests that
recent regional increases in area burned are already
the result of anthropogenic greenhouse gas-induced
global warming.2,6,162 However, such increases have
also been explained through the decadal influence of
large-scale modes of climatic variability on the frequency of occurrence of mid-tropospheric blocking
events conductive to large area burned.69,82,83 Forecasts of future area burned under global warming
scenarios are based on a diversity of modeled variables, from monthly temperature outputs to daily
modeled weather parameters known to be correlated
with fire activity. Although many predict increased
area burned,163–170 including an earlier start to the fire
season,171 some forecast insignificant changes due to
increased precipitation offsetting the effects of warmer
temperatures.103,172
Holocene fire reconstructions offer enough evidence that warmer periods are not necessarily linked
to increased fire activity. For example, the Little Ice Age was characterized by a much shorter
fire cycle in the boreal and montane forests of
North America.101,172,173 These seemingly contradictory results will eventually be resolved as the
field moves from correlation-based predictions toward
those based on the causal mechanisms linking climate
change and wildfire behavior.
ACKNOWLEDGEMENTS
The authors thank two anonymous referees for comments which improved the manuscript. This work was
supported by grants from NSERC-Discovery, GEOIDE (GEOmatics for Informed Decisions) and Alberta
Ingenuity, and a scholarship from the International Association of Wildland Fire (STM).
REFERENCES
1. IPCC. Climate Change 2007—Impacts, Adaptation
and Vulnerability. Contribution of Working Group II
to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, United
Kingdom & New York, NY, USA: Cambridge University Press; 2007.
2. Gillett NP, Weaver AJ, Zwiers FW, Flannigan MD.
Detecting the effect of climate change on Canadian
forest fires. Geophys Res Lett 2004, 31.
3. Williams AAJ, Karoly DJ, Tapper N. The sensitivity of
Australian fire danger to climate change. Clim Change
2001, 49:171–191.
4. Pausas JG. Changes in fire and climate in the eastern
Iberian Peninsula (Mediterranean basin). Clim Change
2004, 63:337–350.
5. Cary GJ. Importance of a changing climate for fire
regimes in Australia. In: Gill AM, Bradstock RA,
Williams J, eds. Flammable Australia : the Fire
Regimes and Biodiverstiy of a Continent. Cambridge,
United Kingdom: Cambridge University Press; 2002,
26–49.
6. Flannigan M, Stocks B, Turetsky M, Wotton M.
Impacts of climate change on fire activity and fire
management in the circumboreal forest. Glob Change
Biol 2009, 15:549–560.
7. Johnson EA, Morin H, Miyanishi K, Gagnon R,
Greene DF. A process approach to understanding disturbance and forest dynamics for sustainable forestry.
In: Adamowicz V, Burton P, Messier C, Smith D, eds.
Towards Sustainable Management of the Boreal Forest. Ottawa, ON: Ch. 8. NRC Press; 2003, 261–306.
8. Johnson EA. Fire and Vegetation Dynamics: Studies
from the North American boreal forest. 1st ed, vol. 1.
Cambridge University Press; 1992.
9. Quintiere JG. Canadian mass fire experiment, 1989.
J Fire Prot Eng 1993, 5:67–78. doi:10. 1177/1042391
59300500203.
10. Kurz WA, Apps MJ. A 70-year retrospective analysis
of carbon fluxes in the Canadian forest sector. Ecol
Appl 1999, 9:526–547.
11. Bowman D, Balch JK, Artaxo P, Bond WJ, Carlson
JM, Cochrane MA, D’Antonio CM, DeFries RS, Doyle
JC, Harrison SP, et al. Fire in the Earth System. Science
2009, 324:481–484.
12. Ramanathan V, Carmichael G. Global and regional
climate changes due to black carbon. Nature Geoscience 2008, 1:221–227.
13. Warren SG, Wiscombe WJ. A model for the spectral
albedo of snow. II: Snow containing atmospheric aerosols. J Atmos Sci 1980, doi:10.1175/1520-0469(1980)
037<2734:AMFTSA>2.0.CO;2.37:2734–2745.
14. Harden JW, Trumbore SE, Stocks BJ, Hirsch A, Gower
ST, O’Neill KP, Kasischke ES. The role of fire in
the boreal carbon budget. Glob Change Biol 2000,
6:174–184.
 2010 Jo h n Wiley & So n s, L td.
WIREs Climate Change
Prediction of climate change effects on wildfires
15. Randerson JT, Liu H, Flanner MG, Chambers SD, Jin
Y, Hess PG, Pfister G, Mack MC, Treseder KK, Welp
LR, et al. The impact of boreal forest fire on climate
warming. Science 2006, 314:1130–1132.
16. Archer S, Schimel DS, Holland EA. Mechanisms of
shrubland expansion—Land-use, climate or CO2.
Clim Change 1995, 29:91–99.
17. Roques KG, O’Connor TG, Watkinson AR. Dynamics of shrub encroachment in an African savanna:
relative influences of fire, herbivory, rainfall and density dependence. J Appl Ecol 2001, 38:268–280.
18. Cox G. Combustion Fundamentals of Fire. London,
United Kingdom: Academic Press; 1995.
19. Drysdale D. An Introduction to Fire Dynamics. 2nd
ed. New York, NY, USA: John Wiley & Sons; 1999.
20. Quintiere JG. Fundamentals of Fire Phenomena. vol. 1
New York, NY, USA: John Wiley & Sons; 2006.
21. Brown AA, Davis KP. Forest Fire Control and Use.
2nd ed. New York, NY, USA: McGraw-Hill; 1973.
22. Siau JF. Transport Processes in Wood. New York,
NY, USA: Springer-Verlag; 1984.
23. Skaar C. Wood Water Relations. New York, NY,
USA: Springer-Verlag; 1988.
24. Nelson RM Jr. Water relations of forest fuels. In: Johnson EA, Miyanishi K, eds. Forest Fires: Behavior and
Ecological Effects. New York, NY, USA: Academic
Press; 2001, 79–149.
25. Dixon HH, Joly J. On the ascent of sap. Ann Bot
1894, 8:468–470.
26. Tyree MT, Zimmermann MH. Xylem Structure and
the Ascent of Sap. 2nd ed. New York, NY, USA:
Springer; 2003.
27. Nobel PS. Physicochemical and Environmental Plant
Physiology. 3rd ed. Burlington, MA, USA: Academic
Press; 2005.
28. Zimmermann MH. Xylem Structure and the Ascent of
Sap. 1st ed. New York, NY, USA: Springer; 1983.
on pressure bomb measurements. Protoplasma 2007,
232:10–34.
33. Kunkel KE. In: Johnson EA, Miyanishi K, eds. Forest
Fires: Behavior and Ecological Effects. New York,
NY, USA: Academic Press; 2001, 303–350.
34. Incropera FP, De Witt DP, Bergman TL, Lavine AS.
Fundamentals of Heat and Mass Transfer. 6th ed.
New York, NY, USA: John Wiley & Sons, 2006.
35. Fosberg MA. Heat and Water Vapor Flux in Conifer
Forest Litter and Duff: A Theoretical Model. vol. 1.
Fort Collins, CO: USDA Forest Service, U.S. Dept. of
Agriculture; 1975.
36. Keith DM, Johnson EA, Valeo C. A hillslope forest
floor (duff) water budget and the transition to local
control. Hydrol Process 2010, 24:2738–2751.
37. Michaletz ST, Johnson EA. Foliage influences forced
convection heat transfer in conifer branches and buds.
New Phytol 2006, 170:87–98.
38. Rothermel RC. A Mathematical Mocel for Predicting Fire Spread in Wildland Fuels. vol. 40. Ogden, UT:
USDA Forest Service, Intermountain Forest and Range
Experiment Station; 1972.
39. Brown JK. The unnatural fuel buildup issue. Symposium and Workshop on Wilderness Fire, Missoula,
Montana, USA: U.S. Forest Service; 1983.
40. Bessie WC, Johnson EA. The relative importance of
fuels and weather on fire behavior in Sub-Alpine
Forests. Ecology 1995, 76:747–762.
41. Schroeder MJ, Glovinsky M, Hendricks V, Hood F,
Hull M, Jacobson H, Kirkpatrick R, Krueger D,
Mallory L, Oertel A, et al. Synoptic Weather Types
Associated with Critical Fire Weather. vol. 492. Berkeley, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Forest and Range Experiment
Station; 1964.
42. Finklin AI. Meteorological factors in the Sundance
fire run. USDA Forest Service general technical report
PNW INT 6. USDA Forest Service. 1973.
29. Grace JB. In: Borghetti M, Grace JB, eds. Water Transport in Plants Under Climate Change. Cambridge,
United Kingdom: Cambridge University Press; 1993,
51–62.
43. Janz B, Nimchuk N. The 500 mb chart - a useful
fire management tool. In: 8th Conference on Fire
and Forest Meteorology, Detroit, Michigan, Society of American Foresters, Washington, D.C.: 1985,
233–238.
30. Martin CE, von Willert DJ. Leaf epidermal hydathodes and the ecophysiological consequences of foliar
water uptake in species of Crassula from the
Namib Desert in southern Africa. Plant Biol 2000,
2:229–242.
44. Street RB. Drought and synoptic fire climatology of the
boreal forest region of the Canadian prairie provinces.
In: 8th Conference on Fire and Forest Meteorology, Detroit, Michigan Society of American Foresters,
Washington, D.C.: 1985, 108–112.
31. Yates DJ, Hutley LB. Foliar uptake of water by wet
leaves of Sloanea-Woollsii, an Australian subtropical
rain-forest tree. Aust J Bot 1995, 43:157–167.
45. Flannigan MD, Harrington lB. Synoptic weather conditions during the Porter Lake experimental fire
project. Climatol Bull 1986, 20:19–40.
32. Zimmermann D, Westhoff M, Zimmermann G, Gessner P, Gessner A, Wegner LH, Rokitta M, Ache P,
Schneider H, Vasquez JA, et al. Foliar water supply
of tall trees: evidence for mucilage-facilitated moisture uptake from the atmosphere and the impact
46. Johnson EA, Wowchuk DR. Wildfires in the southern Canadian rocky-mountains and their relationship to midtropospheric anomalies. Can J For
Res-Revue Canadienne De Recherche Forestiere 1993,
23:1213–1222.
 2010 Jo h n Wiley & So n s, L td.
wires.wiley.com/climatechange
Focus Article
47. Skinner WR, Stocks BJ, Martell DL, Bonsal B, Shabbar A. The association between circulation anomalies
in the mid-troposphere and area burned by wildland fire in Canada. Theor Appl Climatol 1999, 63:
89–105.
48. Skinner WR, Flannigan MD, Stocks BJ, Martell DL,
Wotton BM, Todd JB, Mason JA, Logan KA, Bosch
EM. A 500 hPa synoptic wildland fire climatology
for large Canadian forest fires. Theor Appl Climatol
2002, 71:1959–1996.
49. Hessl AE, McKenzie D, Schellhaas R. Drought and
Pacific Decadal Oscillation linked to fire occurrence
in the inland Pacific Northwest. Ecol Appl 2004,
14:425–442.
50. Pereira MG, Trigo RM, da Camara CC, Pereira JMC,
Leite SM. Synoptic patterns associated with large summer forest fires in Portugal. Agric For Meteorol 2005,
129:11–25.
51. Trouet V, Taylor AH, Carleton AM, Skinner CN.
Fire-climate interactions in forests of the American
Pacific coast. Geophys Res Lett 2006, 33.
52. Trigo RM, Pereira JMC, Pereira MG, Mota B, Calado
TJ, Dacamara CC, Santo FE. Atmospheric conditions
associated with the exceptional fire season of 2003 in
Portugal. Int J Climatol 2006, 26:1741–1757.
53. Kharuk VI, Ranson KJ, Dvinskaya ML. Wildfires
dynamic in the larch dominance zone. Geophys Res
Lett 2008, 35.
54. Keeley JE, Fotheringham CJ. Historic fire regime in
Southern California shrublands. Conserv Biol 2001,
15:1536–1548.
55. Bryant E. Natural Hazards. 2nd ed. New York, NY,
USA: Cambridge University Press; 2005.
56. Keeley JE, Aplet GH, Christensen NL, Conard SG,
Johnson EA, Omi PN, Peterson DL, Swetnam TW.
Ecological foundations for fire management in North
American forest and shrubland ecosystems. U S Forest
Service Pacific Northwest Research Station General
Technical Report PNW-GTR; 2009, 1–92.
57. Gedalof Z, Peterson DL, Mantua NJ. Atmospheric,
climatic, and ecological controls on extreme wildfire years in the northwestern United States. Ecol Appl
2005, 15:154–174.
Forest, central Colorado. Can J For Res-Revue Canadienne De Recherche Forestiere 2001, 31:1526–1539.
63. Kitzberger T, Swetnam TW, Veblen TT. Interhemispheric synchrony of forest fires and the El
Nino-Southern Oscillation. Glob Ecol Biogeogr 2001,
10:315–326.
64. Van Wilgen BW, Govender N, Biggs HC, Ntsala D,
Funda XN. Response of Savanna fire regimes to
changing fire-management policies in a large African
National Park. Conserv Biol 2004, 18:1533–1540.
65. Taylor AH, Beaty RM. Climatic influences on fire
regimes in the northern Sierra Nevada Mountains,
Lake Tahoe Basin, Nevada, USA. J Biogeogr 2005,
32:425–438.
66. Littell JS, McKenzie D, Peterson DL, Westerling AL.
Climate and wildfire area burned in western
U. S. ecoprovinces, 1916–2003. Ecol Appl 2009,
19:1003–1021.
67. Swetnam TW. Fire history and climate-change in
Giant Sequoia Groves. Science 1993, 262:885–889.
68. Swetnam TW, Betancourt JL. Fire—Southern Oscillation Relations in the Southwestern United-States.
Science 1990, 249:1017–1020.
69. Macias Fauria M, Johnson EA. Large-scale climatic
patterns control large lightning fire occurrence in
Canada and Alaska forest regions. J Geophys 2006,
111.
70. Kitzberger T, Brown PM, Heyerdahl EK, Swetnam
TW, Veblen TT. Contingent Pacific-Atlantic Ocean
influence on multicentury wildfire synchrony over
western North America. Proc Natl Acad Sci USA
2007, 104:543–548.
71. Wallace JM, Gutzler DS. Teleconnections in the
geopotential height field during the Northern Hemisphere winter. Mon Weather Rev 1981, 109:784–812.
72. Trenberth KE, Branstator GW, Karoly D, Kumar A,
Lau NC, Ropelewski C. Progress during TOGA in
understanding and modeling global teleconnections
associated with tropical sea surface temperatures.
J Geophys Res 1998, 103:14291–14324.
58. Westerling AL, Bryant BP. Climate change and wildfire in California. Clim Change 2008, 87:S231–S249.
73. Simard AJ, Haines DA, Main WA. Relations between
El-Nino Southern Oscillation anomalies and wildland
fire activity in the United-States. Agric For Meteorol
1985, 36:93–104.
59. Westerling AL, Hidalgo HG, Cayan DR, Swetnam
TW. Warming and earlier spring increase western US
forest wildfire activity. Science 2006, 313:940–943.
doi:10.1126/science.1128834.
74. Veblen TT, Kitzberger T, Donnegan J. Climatic and
human influences on fire regimes in ponderosa pine
forests in the Colorado Front Range. Ecol Appl 2000,
10:1178–1195.
60. Wotton BM, Flannigan MD. Length of the fire season
in a changing climate. For Chron 1993, 69:187–192.
75. Heyerdahl EK, Brubaker LB, Agee JK. Annual and
decadal climate forcing of historical fire regimes in
the interior Pacific Northwest, USA. Holocene 2002,
12:597–604.
61. Grissino-Mayer HD, Swetnam TW. Century-scale climate forcing of fire regimes in the American Southwest.
Holocene 2000, 10:213–220.
62. Donnegan JA, Veblen TT, Sibold JS. Climatic and
human influences on fire history in Pike National
76. Beckage B, Platt WJ, Slocum MG, Pank B. Influence
of the El Nino Southern Oscillation on fire regimes in
the Florida everglades. Ecology 2003, 84:3124–3130.
 2010 Jo h n Wiley & So n s, L td.
WIREs Climate Change
Prediction of climate change effects on wildfires
77. van der Werf GR, Randerson JT, Collatz GJ, Giglio L,
Kasibhatla PS, Arellano AF, Olsen SC, Kasischke ES.
Continental-scale partitioning of fire emissions during
the 1997 to 2001 El Nino/La Nina period. Science
2004, 303:73–76.
78. Schoennagel T, Veblen TT, Romme WH, Sibold JS,
Cook ER. ENSO and PDO variability affect droughtinduced fire occurrence in Rocky Mountain subalpine
forests. Ecol Appl 2005, 15:2000–2014.
79. Trouet V, Taylor A, Carleton A, Skinner C. Interannual variations in fire weather, fire extent, and
synoptic-scale circulation patterns in northern California and Oregon. Theor Appl Climatol 2009,
95:349–360.
80. Sibold JS, Veblen TT. Relationships of subalpine forest fires in the Colorado Front Range with interannual
and multidecadal-scale climatic variation. J Biogeogr
2006, 33:833–842.
81. Collins BM, Omi PN, Chapman PL. Regional relationships between climate and wildfire-burned area
in the Interior West, USA. Can J For Res-Revue Canadienne De Recherche Forestiere 2006, 36:699–709.
82. Macias Fauria M, Johnson EA. Climate and wildfires
in the North American boreal forest. Philos Trans R
Soc B-Biol Sci 2008, 363:2317–2329.
83. Skinner WR, Shabbar A, Flannigan MD, Logan K.
Large forest fires in Canada and the relationship to
global sea surface temperatures. J Geophys Res 2006,
111.
84. Le Goff H, Flannigan MD, Bergeron Y, Girardin MP.
Historical fire regime shifts related to climate teleconnections in the Waswanipi area, central Quebec,
Canada. Int J Wildland Fire 2007, 16:607–618.
85. Schoennagel T, Veblen TT, Kulakowski D, Holz A.
Multidecadal climate variability and climate interactions affect subalpine fire occurrence, Western Colorado (USA). Ecology 2007, 88:2891–2902.
86. Dixon PG, Goodrich GB, Cooke WH. Using teleconnections to predict wildfires in Mississippi. Mon
Weather Rev 2008, 136:2804–2811.
87. Heyerdahl EK, McKenzie D, Daniels LD, Hessl AE,
Littell JS, Mantua NJ. Climate drivers of regionally synchronous fires in the inland Northwest
(1651–1900). Int J Wildland Fire 2008, 17:40–49.
88. Goodrick SL, Hanley DE. Florida wildfire activity and
atmospheric teleconnections. Int J Wildland Fire 2009,
18:476–482.
89. Jupp TE, Taylor CM, Balzter H, George CT. A statistical model linking Siberian forest fire scars with
early summer rainfall anomalies. Geophys Res Lett
2006, 33.
90. Tsonis AA, Swanson K, Kravtsov S. A new dynamical
mechanism for major climate shifts. Geophys Res Lett
2007, 34.
91. Swanson KL, Tsonis AA. Has the climate recently
shifted? Geophys Res Lett 2009, 36.
92. Wang GL, Swanson KL, Tsonis AA. The pacemaker
of major climate shifts. Geophys Res Lett 2009, 36.
93. Masters AM. Changes in forest fire frequency
in Kootenay-National-Park, Canadian rockies. Can
J Bot-Revue Canadienne De Botanique 1990,
68:1763–1767.
94. Bergeron Y. The Influence Of Island And Mainland
Lakeshore Landscapes On Boreal Forest-Fire Regimes.
Ecology 1991, 72:1980–1992.
95. Johnson EA, Larsen CPS. Climatically induced change
in fire frequency in the Southern Canadian rockies.
Ecology 1991, 72:194–201.
96. Johnson EA, Miyanishi K. Fire and population
dynamics of lodgepole pine and Engelmann spruce
forests in the southern Canadian Rockies. In: Nakagoshi N, Golley FB, eds. Coniferous forest ecology
from an international perspective. The Hague, The
Netherlands: SPB Academic Publishing; 1991, 77–91.
97. Reed WJ. Reconstructing the history of forest fire frequency: identifying hazard rate change points using the
Bayes information criterion. Can J Stat-Revue Canadienne De Statistique 2000, 28:353–365.
98. Weir JMH, Johnson EA, Miyanishi K. Fire frequency
and the spatial age mosaic of the mixed-wood
boreal forest in western Canada. Ecol Appl 2000,
10:1162–1177.
99. Bergeron Y, Gauthier S, Flannigan M, Kafka V. Fire
regimes at the transition between mixedwood and
coniferous boreal forest in Northwestern Quebec.
Ecology 2004, 85:1916–1932.
100. Power MJ, Marlon J, Ortiz N, Bartlein PJ, Harrison
SP, Mayle FE, Ballouche A, Bradshaw RHW, Carcaillet C, Cordova C, et al. Changes in fire regimes since
the Last Glacial Maximum: an assessment based on a
global synthesis and analysis of charcoal data. Clim
Dyn 2008, 30:887–907.
101. Bergeron Y, Archambault S. Decreasing frequency of
forest fires in the southern boreal zone of Québec
and its relation to global warming since the end
of the ‘Little Ice Age’. Holocene 1993, 3:255–259.
doi:10.1177/095968369300300307.
102. Laird KR, Cumming BF, Wunsam S, Rusak JA,
Oglesby RJ, Fritz SC, Leavitt PR. Lake sediments
record large-scale shifts in moisture regimes across
the northern prairies of North America during the
past two millennia. Proc Natl Acad Sci USA 2003,
100:2483–2488.
103. Girardin MP, Tardif J, Flannigan MD, Wotton BM,
Bergeron Y. Trends and periodicities in the Canadian
Drought Code and their relationships with atmospheric circulation for the southern Canadian boreal
forest. Can J For Res-Revue Canadienne De Recherche
Forestiere 2004, 34:103–119.
104. Girardin MP, Tardif J, Flannigan MD, Bergeron Y.
Multicentury reconstruction of the Canadian Drought
Code from eastern Canada and its relationship with
 2010 Jo h n Wiley & So n s, L td.
wires.wiley.com/climatechange
Focus Article
paleoclimatic indices of atmospheric circulation. Clim
Dyn 2004, 23:99–115.
105. Tian J, Nelson DM, Hu FS. Possible linkages of lateHolocene drought in the North American midcontinent to Pacific Decadal Oscillation and solar activity.
Geophys Res Lett 2006, 33.
106. Shindell DT, Miller RL, Schmidt GA, Pandolfo L.
Simulation of recent northern winter climate trends by
greenhouse-gas forcing. Nature 1999, 399:452–455.
doi:10.1038/20905.
107. Hoerling MP, Hurrell JW, Xu T. Tropical origins for
recent North Atlantic climate change. Science 2001,
292:90–92. doi:10.1126/science.1058582.
108. Overland JE, Wang M. The Arctic climate paradox:
the recent decrease of the Arctic Oscillation. Geophys
Res Lett 2005, 32:doi:10.1029/2004GL021752.
109. Collins M. Understanding uncertainties in the
response of ENSO to greenhouse warming. Geophys
Res Lett 2000, 27:3509–3512.
110. Timmermann A, Oberhuber J, Bacher A, Esch M,
Latif M, Roeckner E. Increased El Nino frequency in a
climate model forced by future greenhouse warming.
Nature 1999, 398:694–697.
111. Yeh Sang-Wook, Kug Jong-Seong, Dewitte Boris,
Kwon Min-Ho, Kirtman Ben P, Jin Fei-Fei. El Nino
in a changing climate. Nature 2009, 461:511–514.
DOI:10.1038/nature08316.
120. Williams ER. The positive charge reservoir for spriteproducing lightning. J Atmos Solar Terrest Phys 1998,
60:689–692.
121. Fuquay DM. Lightning Damage and Lightning Modification Caused by Cloud Seeding. In: Hess WN, ed.
Weather and Climate Modification. New York, NY,
USA: John Wiley & Sons; 1974, 604–612.
122. Fuquay DM, Baughman RG, Taylor AR, Hawe
RG. Characteristics of seven lightning discharges
that caused forest fires. J Geophys Res 1967, 72:
6371–6373. doi:10.1029/JZ072i024p06371.
123. Fuquay DM, Taylor AR, Hawe RG, Schmid CW
Jr. Lightning discharges that caused forest fires.
J Geophys Res 1972, 77:2156–2158.
124. Latham DJ. Anode column behavior of long vertical
air arcs at atmospheric pressure. IEEE Trans Plasma
Sci 1986, 14: 220–227.
125. Wilson RA Jr. Observations of extinction and
marginal burning states in free burning porous fuel
beds. Combust Sci Technol 1985, 44:179–193.
126. Xavier Viegas D. Forest fire propagation. Philos Trans
R Soc Lond Ser A Math Phys Eng Sci 1998,
356:2907–2928. doi:10.1098/rsta.1998.0303.
127. Michaletz ST, Johnson EA. How forest fires kill trees:
a review of the fundamental biophysical processes.
Scand J For Res 2007, 22:500–515.
112. Mantua NJ, Hare SR. The Pacific Decadal Oscillation. J Oceanogr 2002, 58:35–44. doi:10.1023/A:10
15820616384.
128. Nash CH, Johnson EA. Synoptic climatology of
lightning-caused forest fires in subalpine and boreal
forests. Can J For Res-Revue Canadienne De
Recherche Forestiere 1996, 26:1859–1874.
113. van der Werf GR, Randerson JT, Giglio L, Gobron N,
Dolman AJ. Climate controls on the variability of fires
in the tropics and subtropics. Glob Biogeochem Cycles
2008, 22.
129. Price C, Rind D. Possible implications of global
climate-change on global lightning distributions and
frequencies. J Geophys Res 1994, 99:10823–10831.
114. McKenzie D, Gedalof Z, Peterson DL, Mote P. Climatic change, wildfire, and conservation. Conserv Biol
2004, 18:890–902.
115. Latham DJ, Williams ER. Lightning and Forest Fires.
In: Johnson EA, Miyanishi K, eds. Forest Fires: Behavior and Ecological Effects. San Diego, California, USA:
Academic Press; 2001, 375–418.
116. Rakov VA, Uman MA. Lightning: Physics and Effects.
Cambridge, United Kingdom: Cambridge University
Press; 2003.
117. Williams ER. The tripole structure of thunderstorms. J Geophys Res 1989, 94:13151–13167.
doi:10.1029/JD094iD11p13151.
118. Taylor AR. Lightning effects on the forest complex. In:
Proceedings of the Annual Tall Timbers Fire Ecology
Conference, Number 9; Macon, Riverside, Missoula:
1969, 127–150.
119. Darveniza M, Zhou Y. Lightning-initiated fires:
energy absorbed by fibrous materials from impulse
current arcs. J Geophys Res 1994, 99:10663–10670.
doi:10.1029/94jd00147.
130. Price C. Thunderstorms Lightning and Climate
Change. In: Betz HD, Schumann U, Laroche P, eds.
Lightning: Principles, Instruments and Applications:
Review of Modern Lightning Research. vol. 1. Dordrecht, The Netherlands:: Springer; 2009, 641.
131. Williams ER. Lightning and climate: A review. Atmospheric Research 2005, 76:272–287.
132. Cunningham P, Linn RR. Numerical simulations of
grass fires using a coupled atmosphere-fire model:
dynamics of fire spread. J Geophys Res 2007,
112:D05108, doi:10.1029/2006jd007638.
133. Albini FA. A model for fire spread in wildland fuels by
radiation. Combust Sci Technol 1985, 42:229–258.
134. Albini FA. A model for the wind-blown flame from a
line fire. Combust Flame 1981, 43:155–174.
135. Howell JR. A catalog of radiation heat transfer configuration factors. (McGraw-Hill Book Company). New
York 1982.
136. Tibbals EC, Carr EK, Gates DM, Kreith F. Radiation and convection in conifers. Am J Bot 1964,
51:529–538.
 2010 Jo h n Wiley & So n s, L td.
WIREs Climate Change
Prediction of climate change effects on wildfires
137. Gates DM, Tibbals EC, Kreith F. Radiation and convection for ponderosa pine. Am J Bot 1965, 52:66–71.
138. Michaletz ST, Johnson EA. A heat transfer model of
crown scorch in forest fires. Can J For Res 2006,
36:2839–2851.
139. Van Wagner CE. Conditions for the start and spread
of crown fire. Can J For Res 1977, 7:23–34.
140. Cruz MG, Butler BW, Alexander ME, Forthofer JM,
Wakimoto RH. Predicting the ignition of crown fuels
above a spreading surface fire. Part I: model idealization. Int J Wildland Fire 2006, 15:47–60.
141. Mercer GN, Weber RO. Plumes above line fires in a
cross wind. Int J Wildland Fire 1994, 4:201–207.
142. Viegas XD. Convective processes in forest fires. In:
Plate EJ, ed. Proceedings of the NATO Advanced
Study Institute on Buoyant Convection in Geophysical
Flows. Dordrecht, The Netherlands: Kluwer Academic
Publishers; 1998, 401–420.
143. Sardoy N, Consalvi J-L, Porterie B, FernandezPello AC. Modeling transport and combustion of
firebrands from burning trees. Combust Flame 2007,
150:151–169.
144. Tarifa CS, Del Notario PP, Moreno FG. On the flight
paths and lifetimes of burning particles of wood. Symp
(Int) Combust 1965, 10:1021–1037.
145. Viegas XD. Forest fire propagation. Philos Trans R Soc
Lond Ser A Math Phys Eng Sci 1998, 356:2907–2928.
doi:10.1098/rsta.1998.0303.
146. Fendell FE, Wolff MF. Wind-aided fire spread. In:
Johnson EA, Miyanishi K, eds. Forest Fires: Behavior and Ecological Effects. New York, NY, USA:
Academic Press; 2001, 171–223.
147. Sun R, Krueger SK, Jenkins MA, Zulauf MA, Charney JJ. The importance of fire-atmosphere coupling
and boundary-layer turbulence to wildfire spread. Int
J Wildland Fire 2009, 18:50–60.
148. Stull RB. An Introduction to Boundary Layer Meteorology. Dordrecht, The Netherlands: Kluwer Academic Publishers; 1988.
149. Clark TL, Jenkins MA, Coen J, Packham D. A coupled atmosphere-fire model: convective feedback
on fire-line dynamics. J Appl Meteorol 1996, 35:
875–901.
150. Nimchuk N. Wildfire behavior associated with
upper ridge breakdown. Alberta Energy and Natural Resources, Canadian Forest Service, Report T150.
1983.
151. Fryer GI, Johnson EA. Reconstructing fire behavior
and effects in a subalpine forest. J Appl Ecol 1988,
25:1063–1072.
152. Breslow PB, Sailor DJ. Vulnerability of wind power
resources to climate change in the Continental United
States. Renew Energy 2002, 27:585–598.
153. Wilson RA. Observations of extinction and marginal
burning states in free burning porous fuel beds. Combust Sci Technol 1985, 44:179–193.
154. Dickinson MB, Johnson EA. Surface Fire Extinction
in Mixedwood Boreal Forest Fuels. Sustainable Forest Management Network Project Reports 2003/2004.
2004.
155. Huntington TG. Evidence for intensification of the
global water cycle: review and synthesis. J Hydrol
2006, 319:83–95. doi. 10.1016/j.jhydrol.2005.07.
156. Held IM, Soden BJ. Robust responses of the hydrological cycle to global warming. J Clim 2006,
19:5686–5699. doi:10.1175/JCLI3990.1.
157. IPCC. Climate Change 2007—The Physical Science
Basis. Contribution of Working Group I to the Fourth
Assessment Report of the IPCC. Cambridge, United
Kingdom & New York, NY, USA: Cambridge University Press; 2007.
158. Houghton J. Global warming. Rep Prog Phys 2005,
68:1343–1403.
159. Hurrell JW. Decadel climate prediction: challenges
and opportunities—art. no. 012018. Scidac 2008: Sci
Discov Adv Comput 2008, 125:12018–12018.
160. Hurrell J, Meehl GA, Bader D, Delworth TL, Kirtman B, Wielicki B. A unified modeling approach to
climate system prediction. Bull Am Meteorol Soc 2009,
90:1819–1832. doi:10.1175/2009bams2752.1.
161. WCRP. The World Climate Research Programme
strategic framework 2005–2015: Coordinated Observation and Prediction of the Earth System (COPES).
2005, 65.
162. Soja AJ, Tchebakova NM, French NHF, Flannigan
MD, Shugart HH, Stocks BJ, Sukhinin AI, Varfenova EI, Chapin FS, Stackhouse PW. Climate-induced
boreal forest change: predictions versus current observations. Glob Planet Change 2007, 56:274–296.
163. Wotton BM, Martell DL, Logan KA. Climate change
and people-caused forest fire occurrence in Ontario.
Clim Change 2003, 60:275–295.
164. Flannigan MD, Logan KA, Amiro BD, Skinner WR,
Stocks BJ. Future area burned in Canada. Clim Change
2005, 72:1–16.
165. Tymstra C, Flannigan MD, Armitage OB, Logan K.
Impact of climate change on area burned in Alberta’s
boreal forest. Int J Wildland Fire 2007, 16:153–160.
166. Girardin MP, Mudelsee M. Past and future changes
in Canadian boreal wildfire activity. Ecol Appl 2008,
18:391–406.
167. Mudelsee M, Girardin MP. Risk prediction of Canadian wildfires. PAGES News 2008, 16:28–30.
168. Malevsky-Malevich SP, Molkentin EK, Nadyozhina
ED, Shklyarevich OB. An assessment of potential
change in wildfire activity in the Russian boreal forest
zone induced by climate warming during the twentyfirst century. Clim Change 2008, 86:463–474.
 2010 Jo h n Wiley & So n s, L td.
wires.wiley.com/climatechange
Focus Article
169. Balshi MS, McGuire AD, Duffy P, Flannigan M,
Kicklighter DW, Melillo J. Vulnerability of carbon
storage in North American boreal forests to wildfires during the 21st century. Glob Change Biol 2009,
15:1491–1510.
170. Krawchuk MA, Cumming SG, Flannigan MD. Predicted changes in fire weather suggest increases in lightning fire initiation and future area burned in the mixedwood boreal forest. Clim Change 2009, 92:83–97.
171. Stocks BJ, Fosberg MA, Lynham TJ, Mearns L, Wotton BM, Yang Q, Jin JZ, Lawrence K, Hartley GR,
Mason JA, et al. Climate change and forest fire potential in Russian and Canadian boreal forests. Clim
Change 1998, 38:1–13.
172. Flannigan MD, Bergeron Y, Engelmark O, Wotton
BM. Future wildfire in circumboreal forests in relation
to global warming. J Veg Sci 1998, 469–476.
173. Lesieur D, Gauthier S, Bergeron Y. Fire frequency and
vegetation dynamics for the south-central boreal forest
of Quebec, Canada. Can J For Res-Revue Canadienne
De Recherche Forestiere 2002, 32:1996–2009.
 2010 Jo h n Wiley & So n s, L td.