Reconciliation of Review Comments on:
Fire potential rating for wildland fuelbeds using the Fuel Characteristic
Classification System
David V. Sandberg, Cynthia L. Riccardi, and Mark D. Schaaf:
June 15, 2006
Reviewers
Matt Dickinson – USDA Forest Service, Northeastern Research Station
Mark Finney – USDA Forest Service, Rocky Mountain Research Station
Ruddy Mell – National Institute of Standards and Technology
Elizabeth Reinhardt – USDA Forest Service, Rocky Mountain Research Station
Scott Stephens – University of California Berkeley
Brian Stocks – Great Lakes Forestry Centre, Sault Ste. Marie, Ontario
Jan van Wagtendonk – USGS Western Ecological Research Center
David Weise – USDA Forest Service, Pacific Southwest Research Station
Matt Dickinson
1. The fire potentials are going to be really valuable, particularly in their integration with the
national fuel beds, their focus on fuel effects, and in allowing managers to readily get an idea of
what effect fuels management will have. As well, it is nice to finally see an effort to build on
Wilson and otherwise revise Rothermel’s model. The task of putting all this in a single paper is
huge, but my feeling is that what you’ve written shows it’s possible. Readers will need to be
familiar with Rothermel, though more descriptions of the concepts behind Behave would be
helpful. Certainly, you can’t provide a lot of background given space constraints.
I appreciate these supportive comments. Yes, readers will need to be familiar with Rothermel,
but I have taken your (and others’) suggestion to review his paper in a little more detail. As you
suggest, I don’t want to overburden the paper with background that is available elsewhere.
A. Order of materials. My sense in reading manuscript 4 was that Part I should follow
Parts II and III. This is for two reasons. First, space would be saved (e.g., Equation 3.1
is the same as Equation 1.5). Second, reorganized, the manuscript would flow more
easily and not end as abruptly. With Part I coming before the materials that describe
Part I, I didn’t really understand what was going on, and felt like a lot of background
was missing, until I had read the rest of the manuscript because the equations are like
Rothermel’s but with some important differences. As well, it’s been a while since I went
through Rothermel with a fine-tooth comb. The way the manuscript is organized will be
particularly problematic, I think, for readers who aren’t familiar with Rothermel (1972).
Thank you, we have made those changes in organization. We have divided the original
manuscript into three discrete manuscripts at the suggestion of several reviewers. This
Reconciliation of FCCS Potentials Manuscript -- 1
now articulates the individual components of the original manuscript much better. We
have emphasized the conceptual underpinnings of the potentials and related topics, and
have specifically addressed how new physical and modeling principles have been
developed in the context of Rothermel (1972).
B. Page 11, lines 5 and 6. It is a little confusing having both FBPS and FBP acronyms. By
FBPS, do you mean the Canadian FBPS or the system of Behave fuel models?
FPBS refers to the U.S. Fire Behavior Prediction System, and FBP refers to the Fire
Behavior Potential. We have clarified these terms and acronyms in the revision
C. Page 11, sentence beginning on line 22. Papers have compared Rothermel model
predictions to field data and published regression equations of predicted vs observed fire
spread rate and flame lengths that adjust for bias. When FCCS fire potentials are
confronted with field data, adjustments for bias will also be necessary since most of the
same basic equations are being used. I would be amazed if bias weren’t generally
present whether the fuels were described well (FCCS) or were tweaked/stylized (Behave).
It won’t be clear that the way FCCS treats fuel categories is better than Rothermel’s fuelclass averaging technique until FCCS fire potentials are compared with data. See also
page 42, lines 10-11.
I agree. The final proof will be in how much less or how much more consistently users
will find it necessary to correct for bias in order to achieve predictions that match their
observations of fires. We cannot prove with observational data that the new formulation
is more accurate, and most likely never will be able to except through user acceptance
and experience. However, we are confident that the logic of the new formulation is an
improvement. The current papers present the conceptual foundations of the
reformulation, and empirical data can be used to test the logic of this new approach.
In addition, McKenzie et al. (submitted manuscript) have illustrated an on-the-ground
application of FCCS for fuels mapping. This paper was developed in response to several
review comments.
D. Page 21, sentence beginning on line 13. Some amplification of this sentence would be
helpful.
Issues related to surface-to-volume ratios and surface area are now discussed in multiple
places in the revised manuscripts.
E. Page 21, line 22. It will only be known if FCCS fire potentials are more accurate than
Rothermel’s model when they are compared with data. I don’t think more accuracy can
be claimed before then.
As noted above, the final proof will be in how much less or how much more consistently
users will find it necessary to correct for bias in order to achieve predictions that match
their observations of fires. We cannot prove with observational data that the new
Reconciliation of FCCS Potentials Manuscript -- 2
formulation is more accurate, and most likely never will be able to except through user
acceptance and experience. However, we are confident that the logic of the new
formulation is an improvement. The current papers present the conceptual foundations of
the reformulation, and empirical data can be used to test the logic of this new approach.
F. Page 24, equation 2.2. Having a single equation here is confusing. Two are needed, one
for when d<=0.0028 ft and one for when d>0.0028 ft. See Equation 3.6b.
We now to use a single form of the equation for this particular application of the effective
heating number ε.
G. Page 26, sentence beginning on line 16, and equation 2.4. Why are all shrub fuels
assumed to be thermally thin? This is clearly not the case for many shrub species. For
shrub biomass, are only foliage and 1-hr fuels used?
Yes, we made this assumption in order to facilitate modeling of shrubs at this early stage
of development. As noted, this is not realistic for all shrub fuels, and we intend to
improve how shrubs are quantified and modeled using new empirical data from ongoing
studies.
H. Page 26, line 23. Not clear to me the significance of a 45:1 air:fuel ratio within a fuel
stratum. Assumption that all air involved in combustion is coming from the fuel bed?
See also page 34, line 12.
We are confident that some oxygen is supplied from outside the fuelbed. We also believe
that an optimal air:fuel ratio exists within the fuelbed, and have explained this concept in
much greater detail in the revised manuscript. Even if the exact ratio is slightly
inaccurate, it should not affect the calculations very much.
I. Equation 2.12, page 35. Shouldn’t this be in manuscript 3?
It is actually not part of the FCCS calculator output in the manuscript by Riccardi et al.
and is used only within the potentials as discussed in this manuscript.
J. Page 46, paragraph starting line 9. I am lost about how FP, RP, and FA values work in
Figures 13a and 13b.
Because the original manuscript has now been divided into three manuscripts, these
values are now addressed more clearly with respect to crown fire. There is now more
detail on the meaning and derivation of these values.
K. Page 49, equation 3.5. I am lost by equation 3.5, particularly what “tengap” is and the
overall rationale for the equation (sentence beginning on line 15).
Because the original manuscript has now been divided into three manuscripts, this term is
now addressed more clearly with respect to crown fire. There is now more detail on its
Reconciliation of FCCS Potentials Manuscript -- 3
meaning and derivation.
L. Page 50, line 9, not sure what is meant by “upper limit of the range of canopy abundance
affecting flammability”.
This term was incorrectly stated in the original manuscript and has been corrected in the
revision.
M. Page 50, line 19. Where do the threshold FAI value(s) come from?
In the original paper, these values came from a poll of expert users. TFAI has been
eliminated in the new set of papers.
N. Page 54, line 8, what is vertical stack velocity? Plume velocity?
Vertical stack velocity represents the momentum term in all plume rise models, all of
which were derived from observations of industrial smoke stacks. Plume velocity is the
vertical rise at any point, while vertical stack velocity is the initial plume velocity.
O. Figure 6. Not sure that independent crowning and dependent crowing potentials can be
compared since you have scaled them arbitrarily (TC/3, DC/1.5, IC), right?
We scaled the crowning such that torching only could yield a maximum of 3.3 for the
crowning potential. Dependent crowning only could yield a maximum of 7, and
independent is required to achieve an 8 or 10 rating.
In two of the Alaska fuelbeds, the differences between IC and DC are so large, especially
compared to other fuelbeds, that we feel the differences are real despite the scaling
problems. However, this is a good point that we have now mentioned in the revision.
P. Figure 19. Where did the crown closure threshold values come from?
These values are consistent with a poll of expert user opinion. No experimental evidence
exists, and no other crown models currently include crown closure as a variable – an
obvious weakness.
Q. Figures. Some of the vertical axis captions are incomplete or not as expected.
Figures have been revised to address this problem.
Mark Finney
In summary:
Reconciliation of FCCS Potentials Manuscript -- 4
•
The manuscript is not publishable as written and the content is not reviewable in a standard
scientific fashion since no data or tests are presented or even possible to conduct with indexbased outputs.
We have divided the original manuscript into three discrete manuscripts at the suggestion
of several reviewers. This now articulates the individual components of the original
manuscript much better. The Rothermel model formulation is entirely conceptual and
unsupported by data. We offer a new formulation that is equally conceptual but more
logical. At the suggestion of several reviewers, we have emphasized the conceptual
underpinnings of the potentials and related topics, and have specifically addressed new
physical and modeling principles.
It was agreed among the review panel that this would be an appropriate first stage in the
documentation and implementation of the FCCS, to be followed by validation and model
testing in subsequent documentation.
In addition, McKenzie et al. (submitted manuscript) have illustrated an on-the-ground
application of FCCS for fuels mapping. This paper was developed in response to several
review comments.
New conceptual and modeling information is valid even without extensive empirical
testing. The basic spread equations are supported by data, and we use the same data to
offer a slightly different form of 2 of the 12 basis equations where we believe the new
form more accurately represents the physics.
•
The concepts behind the fire potentials have some major assumptions that must be
substantiated and subjected to testing by the authors although no such effort was reported
(e.g. scalability of indices based on single set of impossible moisture conditions, use of real
fuel inventory data, national representation of fuelbeds given natural variability etc., see
below)
The concepts of scaling are comparable to those used in current applications of Rothermel’s
model. All published models use the concept of moisture damping that reduces the energy
release possible from dry fuels. We do not say that the fuelbeds are representative of
average national characteristics; only that they more accurately and completely represent real
world fuelbeds, in contrast to fuel models which represent homogeneous surface fuels only.
We use benchmark conditions for the current reformulation of Rothermel in order to
facilitate comparisons among different fuelbeds and their fire potentials.
The new conceptual approach within the FCCS demands different techniques for
quantification and display than those that have been traditionally used in fuel models and the
U.S. fire behavior prediction system. This does not preclude the value or applicability of fuel
models and FBPS; rather, these two approaches can be compared and perhaps used in
different applications.
Reconciliation of FCCS Potentials Manuscript -- 5
•
The impossibility of scientific review of fire potentials at this point means that they are not
acceptable for any kind of operational system.
We respectfully disagree with this comment. In fact, the FCCS and fire potentials have now
been reviewed by many scientists and resource managers, including beta testing of all aspects
of the FCCS. Furthermore, many of the original concepts were developed through workshops
held with managers across the United States. Feedback received from these workshops about
the fire potentials was generally very positive.
In general:
The paper aims to describe a technical basis of a system proposed for ordinating or ranking of
wildland fuels in terms of potential fire behaviors. From the description presented, it is clear
that the approach differs in most ways from traditional fire behavior modeling which requires
users to:
1) supply the topography, weather, and fuel moisture conditions necessary for the
estimating fire behavior,
2) select a standardized or user-customized set of fuel inputs (e.g. NEWMDL) to run the fire
behavior models, and
3) interpret fire behavior in physically measurable parametric units (flame length in meters,
spread rate in meters min-1 etc.) for the fuel complex as a whole (e.g. fireline intensity
might be produced by the combination of both surface and canopy fuels, not separated by
fuel stratum).
The notion of “potentials” put forth in the paper eliminates all of these by:
1) assuming a fixed set of artificial (and physically impossible) conditions for which
numerous assumptions are required to assess their validity, including:
a. that these have some general utility and equal probability across disparate
vegetation and climatic regions,
b. that the outputs scale across the range of environmental input variables,
c. that effects of non-linear and step-function fire behavior responses to alternative
inputs have minimal influence on comparisons among models,
d. that the ordination or relative ranking of fuel types remains the same as input
conditions change.
2) asserting that more complicated sets of fuel data are more useful, nationally applicable,
and statistically distinguishable from each other and from stylized fuel characterizations
as used traditionally, and
3) classifying the resulting behaviors into subjective categories for individual behaviors that
are not testable nor observable.
In the current version of the FCCS, benchmark conditions are used in contrast to fuel models and
FBPS. This allows a user to hold conditions constant at some benchmark value so that fuelbeds
can be compared strictly on their different characteristics. This is necessary to document the
Reconciliation of FCCS Potentials Manuscript -- 6
major principles of the FCCS without considering additional options such as allowing weather
and fuel moisture to vary.
The FCCS is also capable of running the new fire behavior model formulation with midflame
windspeed and fuel moisture contents as inputs, in order to output fire behavior in real (not
indexed) terms. The user is cautioned that one thereby accepts the windspeed and moisture
damping coefficients in the Rothermel model, although many investigators have questioned their
value. But it does allow the user to use realistic benchmark or locally representative conditions
to make comparisons of potential fire behavior between fuelbeds.
In our conversations with users, there is no clear consensus as to whether they want to use the
idealized benchmark value (for simplicity and consistency) or use realistic environmental inputs
(for reality and for comparison with Behave outputs, for example). So we have documented the
foundation for either mode of usage, and will let each user to decide.
The other reason that we separate out environmental parameters is to allow for easy substitution
of other algorithms that express their influence, including existing algorithms from Wilson,
Gould, Catchpole, etc. as well as future alternatives. The current algorithms are weak (although
they are in common use in FARSITE and other models), and we want to make it easy to try other
approaches. That’s why we rearranged terms in the basic Rothermel equations.
Your observation “that (FCCS assumes that) the ordination or relative ranking of fuel types
remains the same as input conditions change” is an important point. As I know you are aware,
there are two mathematical reasons for the “crossover” in ordination as one changes the moisture
and windspeed. The first (and most logical) reason is that the relative tradeoff between the
effects of wind vs. moisture content is not the same for all fuelbed arrangements. Modeling that
tradeoff mathematically again requires that we accept the reality of algorithms. FCCS does no
more or no less than other Rothermel applications in providing this capability, except that we
offer the option of isolating the influence.
The second (and totally artificial) reason for the “crossover” is buried in the very questionable
distribution of moisture (as a heat sink) influence across non-uniform fuelbeds that is included in
current applications and the now-discredited “E” term in the Rothermel wind coefficient. We
believe that is an embarrassing misrepresentation of reality.
The improvement in the completeness and accuracy of fuelbed descriptions is a critical advance
made by the FCCS, compared to modeling only surface fuels. We also feel that the FCCS can be
reconciled with fuel models in the FBPS for some applications. In fact, we are currently
developing a crosswalk from FCCS fuelbeds to fuel models, although this is not discussed in the
current manuscripts.
FCCS fuelbeds are derived from empirical data and can be applied at any spatial scale without
loss of precision. There is no need to assert that they are statistically different from one another,
but only that we can quantify the effect of finite differences (however large or small is important
to the user) on fire behavior and fire effects.
Reconciliation of FCCS Potentials Manuscript -- 7
A user can set any boundaries and number of categories relevant to a specific application. There
is nothing subjective about the categories; rather, they are scaled numerical values of observable
and measurable fire behavior.
These main issues will be dealt with in detail below. In general, however, it is my opinion that
the scientific and technical justifications for these alternative approaches to fire behavior
calculation are not substantiated in the paper nor really presented explicitly as hypotheses that
then would need evidence of testing. For papers in the scientific literature, the standard scientific
methods require:
1. data (experimental or observational),
2. theoretically derived or statistical hypotheses of the behavior trends to test,
3. testing (with the possibility of independent repeatability of the testing) to accept or reject
the hypothetical explanation of the data trends.
Unfortunately, the first and third elements are completely absent in the paper and, therefore, it
falls short of the requirements of a scientific effort. Some derivation and physical reasoning are
presented in developing some of the revisions to surface fire spread equations, but the claims of
improvement are completely unverifiable without #1 and #3. Without this necessary scientific
framework it is not worthwhile to endeavor to review in detail the mathematics behind the
surface fire equations presented. I find absolutely no scientific merit in the crown fire concepts
that offer no data and only scanty derivation from established theory and no way to test indices
of potential. As conceptual work, the crown fire equations might be useful for informally
generating discussion of future approaches to research on crown fires, but it absolutely cannot
be considered the basis for any kind of operational system or published as science. Almost no
information was presented on the available fuel potentials and no review was even attempted for
this component. The paper contains many claims and assertions of system performance and
utility, as well as declarations of the equations adopted for this system, but presents no data on
which the reviewer can perform an independent comparison of the improvements claimed. It is
therefore impossible to review this manuscript from a standard scientific approach.
The primary objective of the FCCS is not to calculate fire behavior (although it does contain the
sole capability to predict fire behavior using native inputs), but rather to more accurately and
consistently quantify complex natural and managed fuelbeds. Fuel models and the FBPS have
been widely used even though they are often inaccurate and represent only surface fuels. The
concept of fire potentials offers an alternative for comparison of both absolute and relative fire
hazard. Our work with managers has shown that they value this approach, often in combination
with calculations of surface fire behavior with the FBPS. We view these different approaches as
complementary rather than mutually exclusive. We also feel that the FCCS is more useful at
large spatial scales where the coarse resolution of fuel models may be inadequate to describe fuel
characteristics and changes in those characteristics due to management activity.
Data are, in fact, a central element of the FCCS: all fuelbeds are based on empirical data,
sometimes supplemented with expert knowledge. We feel this is one of the strengths of the
FCCS, and fire managers are already building their own fuelbeds based on empirical data and
expert knowledge. It is true that, like most fire management tools, the FCCS will be improved as
Reconciliation of FCCS Potentials Manuscript -- 8
additional empirical data are collected, added to the system, and used to improve the calculation
of fire potentials.
We do not offer any new observational fire behavior data in these papers, although the
aggregation of data within each fuelbed is clearly a major contribution of the FCCS. We do test
the fire behavior formulation against the raw input data (i.e., fuelbeds) and observe outcomes
that are quantitatively realistic and comparable to outcomes calculated by other modeling
systems. We have demonstrated that we can get reasonable predictions using a wide range of
real world fuelbed characteristics as inputs. This is the first time that this has been accomplished.
The principles upon which the FCCS are based are both theoretically and empirically derived.
As noted above, empirical data are the foundation of fuelbeds. Fire potentials build on wellknown principles from fire physics, from Rothermel and related concepts, and from improved
logic and quantitative relationships derived from Rothermel. We recognize that there may be
some disagreements about which principles and quantitative approaches are most appropriate for
characterizing fuels and fire behavior. Indeed, there are already other existing systems for doing
this in Canada, Australia, and elsewhere. All these systems have theoretically and empirically
derived components, and all seek improvements through empirical testing, numerical simulation,
and additional thought.
One of the values of the current manuscripts is to allow scientists and managers to compare the
scientific foundation, conceptual approach, and potential applications of the FCCS to other
systems that quantify fuels and fire characteristics. This comparison is a normal step in the
development of a new scientific product without making value judgments about previouslydeveloped products. This can be done by comparing concepts without necessarily having
extensive quantitative validation, a process that has rarely been applied to any existing fire
management tools.
It was agreed among the review panel that this would be an appropriate first stage in the
documentation and implementation of the FCCS, to be followed by validation and model testing
in subsequent documentation. In addition, McKenzie et al. (submitted manuscript) have
illustrated an on-the-ground application of FCCS for fuels mapping. This paper was developed in
response to several review comments.
In detail:
Although the mathematical details of the various potentials are not ready for close scrutiny, the
concepts and assumptions of the FCC fire potential approach require some discussion since
they depart so dramatically from established approaches to fire behavior modeling and systems:
1. The idea of using a standard set of environmental conditions to compare and ordinate fuel
models is not supported in the paper.
First, the authors chose a physically impossible set of fuel moisture in the attempt to extract the
“intrinsic physical capacity of a wildland fuel bed to…” generate fire behavior. I
suggest that the notion itself of an “intrinsic physical capacity of fuel” is a very bold
hypothesis that must be tested. This hypothesis implies:
Reconciliation of FCCS Potentials Manuscript -- 9
1) that fuels don’t change their absolute or relative capacity with different moisture
conditions (this is provably wrong, since fuel types will switch positions on an ordinate in
terms of energy release rates and spread rates when moisture contents of the fuel
particles change) and that
2) there is actually information obtainable about some “intrinsic” nature of the fuel
relevant to fire behavior. In my reasoning there is no such “intrinsic capacity” because
it would be similar to claiming that the speed of a car can be predicted when provided
only with the properties of the fuel in the tank (quantity, octane). Clearly, this is not
possible because even a broken car on a hill could have some speed greater than zero!
The car’s velocity depends on the driver, the kind of car, the road, the weather etc. This
is also provably false from the basic elements of combustion that require fuel, oxygen,
and heat. In a wildland fire, the heat must be supplied from an external source of
ongoing combustion and transferred by convection and radiation which themselves
depend on the environmental factors of wind, slope, moisture content etc. Essentially
these are the same environmental influences on fire behavior. So, if combustion can’t be
explained without explication of the environment that determines heat transfer, neither
can fire behavior “potential”.
Second, embedded in the idea of using a fixed set of environmental conditions is the element of
“risk” – basically assuming an equal probability that the environmental conditions will
occur and are relevant to fire management activities. This is well known to be false
across areas as small as a few tens of miles, not to mention continents. High elevation
forests or bogs, or coastal forests do not have the same probability of experiencing dry
and windy conditions as low elevation montane forests or desert woodlands. It is simply
not valid to compare “potentials” (even if it existed) among these types without
identifying the likelihood of those conditions occurring. This idea of using a single fixed
set of environmental conditions almost presumes that the FCCS system “knows” more
about the relevant fire management problems of a particular area than the local
managers. For example, fuel treatments intended to minimize the probability of crown
fires must account for fire behavior when wind speeds are high (the most common factor
in crown fire occurrence) yet the FCCS benchmark conditions contain a midflame wind
of only 4 mph – which would not change if the canopy structure were modified by
treatment (and therefore effects on wind reduction as is well known from
micrometerology), and may or may not be “severe” as claimed in the manuscript (page
18, line 13) or high enough to represent crown fire conditions concerning managers in a
particular location.
Third, the notion of scaling and separating fire potentials (page 5, line 3) requires a number of
assumptions that have not been evaluated – the paper must offer a reader the ability to
assess if these ideas work or not. Specific issues include the nonlinear and threshold
responses of fire behaviors to the range of environmental drivers (which would prevent
linear scaling) and suggest independent scaling factors for each fuel type, switching the
relative position of fuel types rated in terms of their FCCS fire potential as a particular
environmental variable changes, and the idea that behaviors in each stratum can actually
be isolated. A case in point involves fires burning both the surface and canopy fuels and
produce a single spread rate and intensity from all of those fuels.
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2. Throughout the manuscript, the authors assert that using “real fuel data” are preferable to
traditional fuel models. I think this does reflect a legitimate desire by most fire and fuels people
(scientists and practitioners) to be able to use measured parameters as inputs to fire behavior
calculations. Nevertheless, there are several reasons why this is not supported by the
manuscript:
First, the variability of natural fuels is very high and in many surface fuel complexes is well
known to require sample sizes in the hundreds to obtain variances low enough to
statistically differentiate fuels in different locations (methods do exist for estimating the
sample sizes required). The FCCS data in the computer system does not reveal standard
deviations or confidence intervals around mean values (modal values are used for no
apparent reason) which would permit such tests of the claims that the inventory data on
fuel loadings and depths are significantly different from stylized values in fuel models or
that the proposed modifications of the Rothermel spread equation are required to
estimate the fire behaviors in these fuels. A ranking system is included in the software to
convey a subjective sense of confidence in the fuel data, but this does not help justify the
distinction of the fuel types. The manuscript does not address these issues at all – some
data must be presented to back-up any claim that these modifications improve the ability
to use “real fuels”. It is very likely that the so-called “real” fuels in the National fuel
beds can be lumped into just a handful of statistically different fuel types (and even
visually discernible fuel types), similar to the number of fuel models available
traditionally. In fact, Figures 2 and 3 tend to support this point in terms of the fire
behavior outputs-- these fire behavior outputs from the standard fuel models and FCCS
fuelbeds are all within the same range. Note also that the reaction intensity derived from
the litter layer is only a small fraction of the total reaction intensity, perhaps not
warranting the emphasis that this section takes in the manuscript.
Second, the authors provide no opportunity for a reviewer to assess the claim that more detailed
fuel data actually produce better fire modeling. The performance of the proposed model
cannot be evaluated because no data are shown depicting fire behaviors observed in
“real” fuels that are better approximated by the proposed models than by standard fuel
data or standard fire behavior fuel models without the proposed modifications. This is
absolutely essential to facilitate scientific review of this claim and to support one of the
main assertions for improved utility of FCCS for fuels and fire behavior!
Third, despite the development of 216 “national” fuel beds, no evidence is presented that would
support the assertion that the variation in fuels corresponding to dominant vegetation
type is actually captured by these fuel beds. In fact, it is logical to question why 216
fuelbed could be adequate to even represent even a single forest vegetation type with
canopy and surface strata! Consider for example, that the various canopy themes can
vary independently (cover, height, crown base height, bulk density) and in combination
with surface fuel variations, probably produce 1000’s of unique combinations for each
vegetation type (e.g. 5 surface fuel types, 5 cover %, 5 bulk densities, 5 stand heights, 5
crown based heights = 55 =3125 different fuelbeds). The 216 existing fuelbeds cannot
possibly provide meaningful representation of those fuels within a single vegetation type,
Reconciliation of FCCS Potentials Manuscript -- 11
not to mention a national scale! The authors appear to be asking readers and users of
the FCCS system to accept the claimed national utility of the 216 fuelbeds on opinion and
faith alone.
3. The inability of the fire potential indices to be compared with observations. In contrast to all
fire behavior systems worldwide, the FCCS potentials offer no way to test against known or
observed fire behaviors. Although the stated intent of the indices is to facilitate communication,
in my experience, the few parametric descriptions of fire behavior (flame length, spread rate,
etc.) are well understood by all practitioners and scientists and are not one of the limitations to
either communication or to understanding that hinder fuel treatment planning or fire behavior
prediction. It is not possible from the manuscript for this reviewer to verify that the FCCS
potentials actually produce the stated benefits for surface fire behavior, crown fire behavior, or
fuel consumption because no comparisons are possible against alternative and currently used
fire behavior model formulations. For this to be considered as science, and reviewed as a
scientific paper, the authors must allow the possibility of testing and offer tests of their own in a
manuscript or most likely a series of manuscripts.
In the current version of the FCCS, benchmark conditions are used in contrast to fuel models and
FBPS. This is necessary to document the major principles of the FCCS prior to developing
additional options such as allowing weather and fuel moisture to vary. We understand that actual
weather and fuel moisture data are important inputs to traditional fire behavior modeling and
associated applications. The FCCS is also capable of directly emulating this traditional approach.
It also provides detailed fuels information for six fuel strata rather than only (homogeneous)
surface fuels. Weather and fuel moisture are clearly important in calculating fire behavior
outputs in the FBPS; however, they are not required (although the option is available) for
calculating potential fire hazard and fire effects. This is very different from how the FBPS is
used in operational fire management. The FCCS benchmark option may be more useful in fire
planning, especially at larger spatial scales where potential fire behavior and effects are relevant
to decision making (for example, fuel treatment planning).
We believe that comparing fire potentials — between fuelbeds and across landscapes —is a
useful concept in fire management planning. This has been verified through many discussions
with fire managers across the United States, most recently on the Okanogan-Wenatchee and
Deschutes National Forests, where articulation of differences in fuelbeds caused by diverse
factors such as fuel treatments, insects, and pathogens cannot be captured by traditional fuel
models. In addition, the FCCS can represent significant changes in fuelbeds due to the passage of
time. Finally, the effects of fire and fuel treatments on resource values at broad spatial scales (for
example, air quality and wildlife habitat) can be facilitated by comparing fire potentials. This
type of comparison is required in NEPA documents that address alternative management
scenarios.
We agree that modeling nonlinear fire phenomena and environmental thresholds is a major
challenge. This is true of all areas of natural resource science, not just fire. We also note that
existing fire modeling tools rarely address this issue in a robust manner. Several of the figures
included in the manuscripts display the range and resolution of outputs that can be derived from
the FCCS, including fire potentials. By capturing this range at a higher resolution than has been
Reconciliation of FCCS Potentials Manuscript -- 12
done through existing systems, the FCCS can express the diversity present in natural fuelbeds.
Although this does not address nonlinear issues, the entire field of fire science awaits the type of
data to accurately model nonlinearity.
We concur that the existing FCCS fuelbeds do not capture the entire range of possibilities of fuel
characteristics. (You may remember our first argumentative exchange several years ago when I
conjectured that there were at least 157,000 possible fuelbeds from these permutations. You
replied that their fire potential could be characterized by a dozen or fewer fuel models. I
believed then and believe now that we are both right. But relying on a dozen models means that
you can only measure 12 differences in fuelbeds). The current 216 fuelbeds were identified
because of their importance to fire managers (as determined from six regional workshops) and
availability of existing inventory data. In recent discussions with LANDFIRE scientists at the
Missoula Fire Lab, we have determined that the current 216 fuelbeds in the FCCS represent
approximately 70% of the land area of the contiguous 48 states. Development of fuelbeds that
will represent the other 30% of the land area is in process, in cooperation with LANDFIRE. We
also intend to add nearly 200 more fuelbeds from dry western forests to the system within the
next year. Clearly, some geographic locations are better represented than other in the current
version of the FCCS, but it is designed to continue to grow as more FCCS fuelbeds are
contributed by users. There are no constraints on the numbers of fuelbeds that can be used in the
FCCS; users can customize fuelbeds for a wide range of applications. This will expand both
geographical and ecological coverage.
As noted above, we do not feel that statistical discrimination is a relevant or appropriate means
of comparing entities designed a priori to characterize and classify a range of fuelbeds. It is up
to users to define meaningful biophysical differences, making statistical properties moot even if
they could be compared.
Our intention is to convey that the FCCS can lead to “better fire modeling,” in addition to our
primary purpose to produce higher resolution characterization and classification of fuel
properties. We have revised the wording of the manuscripts to indicate that we are building on
many of the traditional concepts developed by Rothermel, in addition to challenging a couple of
them. We indeed offer an alternative model formulation. We do want to convey that the FCCS
can characterize fire effects, and feel that this makes a significant contribution to ecological
analysis, outside the realm of fire science. In meetings with fire managers and planners
throughout the world, we consistently hear that they need to characterize fuels more accurately
and at higher resolution as a basis for other aspects of resource management. The FCCS is
designed to address this need, and complements traditional fire behavior modeling.
As noted above, our intention is not to focus on fire behavior exclusively or to emulate existing
fire behavior models. There are few published systematic comparisons of existing fire behavior
prediction systems with empirical data. Comparisons of which we are aware, both published and
unpublished, typically note large discrepancies between modeled and real fire behavior. This
does not reduce the utility of these systems, nor has it prevented these systems from being
institutionalized by federal agencies. Again, the FCCS is intended to complement existing fire
behavior prediction systems, not to compete with them in terms of the accuracy of specific fire
behavior parameters. The FCCS can be compared, validated, and improved with empirical
Reconciliation of FCCS Potentials Manuscript -- 13
data and experience – exclusive of traditional approaches to fire behavior. We feel that the
reviewer’s implication that the manuscripts cannot be “considered as science” is somewhat
disingenuous. As confirmed by participants on the review panel, publication of conceptual
advances is necessary and appropriate prior to rigorous numerical validation. We welcome
testing of FCCS concepts and algorithms by scientists and managers.
Ruddy Mell
This review focused on the surface fire potential since I’m much less familiar with crown fire
modeling. Overall, the new approach needs to be more thoroughly and clearly explained and
evaluated. In both the proposed approach and Rothermel’s approach spread rate and fire
intensity formulas for multicomponent fuels are presented. Both require some way of combining
the properties of distinct fuel categories to get a single spread rate or intensity that represents
the whole.
Thank you for these many helpful suggestions, most of which are incorporated in the revision.
We have singled out the multicomponent formulation from the basic spread equations to make
your point more clearly.
1. A fuller high-level discussion of the major differences, from both a fundamental derivation and
operational use point of view, between the three potentials (surface fire, crown fire, available
fuel) is needed. Are they all to be trusted equally for all scenarios? Why not just have one
potential instead of three?
2. A detailed description of the surface and crown fire potentials should not be in one
manuscript, especially since there is no effort to discuss the relative strengths and weaknesses
(as mentioned in 1 above). This is too much information and the approaches differ in their
formulation. The crown fire potential is empirical and rule based and is therefore much harder
to validate or assess.
The single long manuscript has now been divided into three discrete manuscripts. This allows us
to address each of the potentials in greater details both conceptually and quantitatively.
3. Editorial comment: The surface-fire-potential component would be better introduced first
without equations, only a general functional description (i.e., what they are meant to represent).
Then the equations can be developed in detail. In the current write-up the equations are
introduced twice which leads to confusion since not all the variable are defined each time.
Good idea. A general functional description has been written, and we have included greater
detail on the reformulation of the Rothermel model as you and other reviewers suggested.
4. The surface fire potentials are based on changes to Rothermel’s spread rate and reaction
intensity. The clarity of the presentation and the motivation would be VERY much improved if the
authors presented a derivation of Rothermel’s model (following Rothermel) and then introduced
their changes at the appropriate steps in the derivation. The motivation for the suggested change
Reconciliation of FCCS Potentials Manuscript -- 14
needs to be more fully described. Improvements to the model resulting from a proposed change,
needs to be shown to have occurred (i.e., the changes needs to be evaluated). For example
spread rates and reaction intensities for the same single component fuel bed from both
Rothermel and the new formulation should be compared across different parameter changes
(wind, moisture, slope, loadings, etc. with all other parameters held to the same value, as much
as possible, in both models). Comparisons to experimental results are also needed, when
available.
The primary objective of one of the manuscripts derived from the original manuscript is to
articulate how the Rothermel model was reformulated for the FCCS. Hopefully, this will provide
a better foundation for both understanding the fire potentials and for future development. As
suggested by the review panel, we confine our discussion at this point to concepts and principles,
and defer comparisons across parameter changes for a later date.
5. An example of a modification to the Rothermel model that needs clarification follows: A large
emphasis is placed on how the new approach “has the advantage of calculating the relative
contribution of each fuelbed component in the prediction of the reaction intensity” (line 10, p. 10
in original document). This shows up clearly in Eq. (2.10). However, Rothermel’s equation (58)
on Page 31 (Rothermel , 1972) also attempts to include contributions from different components
of a complex fuel bed. Why and how is the new formulation for composite fuel beds better than
the one used by Rothermel? This needs to be more fully discussed and evaluated for the same
multicomponent fuel bed. For example, the comparisons between the new approach and
Rothermel in Figs. 2,3 are not for an identical fuel bed.
This is a good suggestion, and we clarified in detail in the revised paper.
6. A discussion is needed that focuses on whether or not the suggested modifications to
Rothermel’s model apply to basic operational use or are the improvements mostly useful for the
FCCS potentials? Currently the only suggested use of the new approach is in FCCS. The reader
is left wondering why this is the case. If this approach is basically a physically motivated, but
none the less ad-hoc, modification of Rothermel’s equations to get to potentials that are believed
to be useful this needs to be clearly stated. I can’t imagine this was the case since so much
detailed work has been done.
The algorithms and reformulation can indeed be used independently of the FCCS, and we invite
further review and critique of the concepts presented here, as well as suggestions for specific
operational or planning applications. This manuscript focuses only on applications within the
FCCS, and complements several other companion manuscripts. However, we have
acknowledged in the manuscript that other applications are possible. We are working on a paper
to describe the application independently of the FCCS.
7. Sensitivity of FCCS potentials to variations in fuel properties are needed. These variations
need to be related to expected variations in fuel properties due to errors in fuel-data gathering
practices.
Reconciliation of FCCS Potentials Manuscript -- 15
The objective of current manuscripts is to describe concepts on which the FCCS, including fire
potentials, is based. We agree that sensitivity of potentials to variations in fuel properties is an
important issue, and are currently addressing this in a separate study. This will inform the
collection of data used to develop additional fuelbeds.
p2 line 5: after “equations” he added “based on the Rothermel model for fire spread,”
p2 line 6-10: after “release energy” added “(reviewer comment: This wording regarding
‘potential’ suggests that some information is used regarding the ignition process and subsequent
ramp up to established flame spread or ramp down to extinguishment. But this type of can not be
obtained from a reworking of the Rothermel model which assumed quasisteady flame spread. To
me, a better wording would be ‘the potential energy release of a fuelbed’,”
p2 line 13-18: after “dry conditions” added “(reviewer comment: Again, since the Rothermel
model from which the potentials are derived only provides information on well established fires
with quasi-steady rates of spread, it seems overreaching and implies too much to say that the
approach here ‘rates the intrinsic physical capability …’. There should be qualifiers here such
as ‘within the confines of the model equations’ and ‘assuming the fuel is dry,’”
p4 line 19-20: after sentence end he added “(reviewer comment: I did not see this in the Riccardi
et al. papers).”
p5 line 3: after “conditions” he added “and zero slope and wind?”
Minor comments above were revised as suggested. Some of these points are now more clearly
addressed because of the new organization of the manuscripts including more detailed analysis
of the reformulation of the Rothermel model.
p5 line 21- 22 and p6 line 1 - 8: After “consumption” he added “(Reviewer comment: It would
be more complete to discuss the presence or absence of any validation work regarding the
potentials. These appear to be relative ratings with meaning that is confined to model results, not
related to any experiments in which the physical equivalent of the potentials are measured)”
and “Reviewer comment: The paper would, I think, read better if the formulas for the potentials
were not included here, only in the appendix. What could be here is the use of the potentials in
the FCCS system. This would help with the many notation lapses that occur in this paper since
all the variables would be introduced in one place. Most of my comments regarding the formulas
are in Part II)”.
We believe that comparing fire potentials — between fuelbeds and across landscapes — is a
useful concept in fire management planning. This has been verified through discussions with fire
managers, most recently on the Okanogan-Wenatchee and Deschutes National Forests, where
articulation of differences in fuelbeds caused by diverse factors such as fuel treatments, insects,
and pathogens cannot be captured by traditional fuel models. In addition, the FCCS can represent
significant changes in fuelbeds due to the passage of time. Finally, the effects of fire and fuel
treatments on resource values at broad spatial scales (for example, air quality and wildlife
Reconciliation of FCCS Potentials Manuscript -- 16
habitat) can be facilitated by comparing fire potentials. Hopefully, the structure of the new
manuscripts formulas makes them more readable.
p6 line 14-15: deleted “physical” and replaced with “semi-empirical”.
We agree, and have made the change.
p7 line 3: added “area?” after “ground surface”.
We agree, and have made the change.
p7 line 12: (reviewer comment: how is this determined?)
This has been addressed in the revised papers.
p8 line 14-15: after “fuelbed depth” he wrote “(reviewer comment: What is meant by sensitive?
Is it the spread rate sensitive? This requires fuller discussion).”
“Sensitive” means that the heat sink is directly proportional to the fuelbed depth, and the spread
rate is inversely porporational to the heat sink.
p11 line 2-3: wrote “(reviewer comment: While term groupings are different, this can also be
done in the Rothermel formulation (see his Eq. 58))”.
This is why we offer an alternative formulation, because we believe Rothermel has some basic
logical errors. We have clarified this further in the revised papers.
p11 line 14-16: “(reviewer comment: It seems this could also be done within the Rothermel
formulation. A discussion as to why and how the current formulation is superior to Rothermel’s
would be very helpful.)”
Thank you for the comment. It led to a substantial revision to highlight this strongly in the
beginning of the revised paper.
p12 line 5-6: after “fuelbed mixtures” (reviewer comment: Defining what is meant by
heterogeneous is needed)”
“Heterogeneous” is now defined as a mixture of size classes and fuelbed components. .
p12 line 23 – p13 line 2: after “approach” (reviewer comment: No such energy balance
equation has been presented here. Is this referring to the Rothermel derivation? If so, this needs
to be stated and should be described as a semi-empirical approach),”
Both Rothermel and FCCS are by definintion one-dimensional heat balance equations.
Reconciliation of FCCS Potentials Manuscript -- 17
p13 line 18- p14 line 2: (reviewer comment: This comment addresses the previous three
paragraphs. These paragraphs describe the proposed modification to Rothermels formulation.
More needs to be done to explain the approach proposed here after a review of the Rothermel
formulation. This would give a reader the required familiarity of the Rothermel to understand
just what the suggested modifications mean. A step by step discussion/explanation of each
modification and illustrations of the resulting measured model improvements is needed. For
example more realistic spread rates or fire intensities. See general comments for this paper.
This is also expanded in the organizational revision of the papers in response to your comment.
p21 line 5: after “fuels” he added “on flat, level, surfaces.”
We disagree.
p21 line 13: deleted “bases” and replaced it with “basis”.
This is no longer in the revised manuscripts.
p23 line 20-21: after “(BTU lb-1)“ he added “specific heat, and assumed temperature of
ignition”
We think this is a good addition, and have made the change.
p25 line 15-21: Reviewer comment: It is not clear how Eq. (2.2) was derived. Is it assumed that
ε = 1 for diameters below a certain value and the fit to Frandsen’s data occurs for diameters
greater than the is value? What is meant by best fit? How is the fit used here any better than the
one used by Frandsen except in a limiting sense? What impact did it have on spread rate
predictions over a range of surface-area-to-volume ratios? This really only affect the woody
fuels, since ε is assumed to be unity for the others, and is still based on only two experimental
points, so why is this important?
This has been clarified in the revised in the manuscripts.
p26 line 10-14: (reviewer comment: please define IR, ξ, φs and φw and state that they will be
discussed below. Also more discussion is needed on the motivation and rational for expressing
the spread rate in a multi-component fuel bed in this way. Comparisons to Rothermel’s spread
rate in multicomponent fuels [Eqs. (75), (58), (77) in Rothermel (1972)] would help clarify the
difference.
This has been clarified in the reorganized manuscripts.
p27 line 3: after “surface area” added “equivalent to Rothermel’s Aij (his Eq. 53)”
You are correct. However, we do not want to so completely present Rothermel’s original
formulation.
Reconciliation of FCCS Potentials Manuscript -- 18
p28 line 1-2: (Reviewer comment: How are woody fuels that are thermally thin handled?)
Currently we state the assumption that all woody fuels are thick. If that is not true, it would be
easy to add a category of thermally-thin woody fuels as an additional and identical term in the
equation.
p28 line 5-6: (Reviewer comment: An explanation of how one gets FAI ςI ρP / δ from θ ρb
εFCCS for woody fuels is needed)
This was eliminated for brevity because this seems obvious to us.
p28 line 13: after “ratio” he added “by mass?”
No, the air-fuel ratio is by volume. In reviewing Rothermel and Frandsen’s experimental design,
it is actually impossible to tell whether they measured a volume or a mass ratio in fact, but our
best guess is that it was a volume measurement.
p29 line 1: after “flux” he added “ratio”.
Thank you. This has been added.
p29 line 8-9: after “βε and β” he added “(what’s the difference?)”
Adding the subscript ε represents the effective packing ratio. This is defined in the paper.
p30 line 9-10: (reviewer comment:From what I can tell R ϒ was defined way back on page 7!
What is this variable and how is it’s value determined?).
Presentation is now reordered.
p31 line 2: (Reviewer comment: The derivation of this equation is not clear).
It is simply a reorganization of terms.
p32 line 9-10: he wrote “(should be 1.1),”
Presentation is now reordered.
p32 line 14: added “of” after “effect”.
p33 line 4: added “(what equation is referred to here?)”
p33 line 7: (Reviewer comment: Eq. (2.9) is not Rothermel’s equation for a multicomponent
fuelbed. How is the potential reaction velocity, Γ'max, determined?
p34 line 20-21: (reviewer comment: where did these functional forms come from?)
Reconciliation of FCCS Potentials Manuscript -- 19
Minor comments above were revised as suggested. Equations and definitions have been clarified
throughout.
p35 line 18-19: (reviewer comment: how can the heat of combustion lead to a heat sink?)
When the specific heat, including that of the moisture, is greater than the heat of combustion, the
net result of adding the fuel is a heat sink. No current applications of the spread model allow any
fuel component to be a net heat sink. This reformulation will allow that in future developments.
p36 line 7-8: (reviewer comment: how much did this affect calculations of spread rates and
intensities?).
We have greatly expanded on this in the revised manuscripts.
p36 line 9-10: (reviewer comment: Why? βop is a bulk property while ε is a particle property)
You are correct in your statement that βop is a bulk property while ε is a particle property.
p36 line 17-19: (Reviewer comment: the units in this equation don’t work. Right-hand-side is
dimensionless; left-hand-side has a term defined in the next sentence which is either a length or
length squared??)
Thank you. This has been corrected.
p37 line 9-10: (Reviewer comment: I did not see this quantity defined in the Riccardi paper)
p37 line 20: (Reviwer comment: where did this equation come from?)
Minor comments above were revised as suggested. Equations and definitions have been clarified
throughout.
Figure 4. Review comment: vertical axis labels are incomplete
Figure 5. Reviewer comment: These are confusing figures. What are the units for spread rate
and flame length? What do the different colors in the vertical bars denote?
Figure 8. Reviewer comment: incorrect units for surface-area-to-volume ratio.
Figure 9. Reviewer comment: Please refer to the equation in the text (2.11?) from which the
FCCS results were derived. What are RT and IT? Likewise for Fig. 10.
Figure 10. See comments for Figure 9.
Reconciliation of FCCS Potentials Manuscript -- 20
Figures were revised and reorganized in response to the reviewer’s comments. Labeling and
figure captions were corrected as needed. Numbers and organization of figures are now much
different due to the new manuscript structures.
Elizabeth Reinhardt
General comments: I am skeptical that the equations presented here contribute to better
understanding of wildfire behavior or effects. Perhaps time may prove them to be very useful.
This paper doesn’t show that however. In order to demonstrate the usefulness of the “new fire
behavior prediction system” (page 2, line 12) presented here, it would be imperative to see the
performance of the system over a range of conditions. Until this behavior is demonstrated, I
wouldn’t be willing to use it.
The manuscript at times seems to be about documenting FCCS and at other times a separate
paper containing musings about fire behavior. Perhaps these should be pulled apart into two
papers, and the one about FCCS could cite the other and be more readable, while the second
could be more abstract, contain more supporting information, and be more persuasive.
We appreciate these comments and have taken them to heart by reorganizing the initial
manuscript into three discrete manuscripts with the primary objective of describing
reformulation of the Rothermel model, comparing logic between Rothermel and the FCCS, and
suggesting appropriate applications. Hopefully the manuscripts are now more readable, as
requested by the reviewer. As recommended by the review panel, we feel it is necessary and
sufficient to document the conceptual basis of the FCCS. The FCCS is designed to complement
existing fire modeling systems. As the reviewer notes, certain aspects of the FCCS remain to be
tested and compared with existing fire tools.
I prefer predicted values with units to the index values reported throughout this ms. If in fact the
indices correspond to some real aspect of fire behavior, report that directly and give us a chance
to evaluate it (possibly by comparing to sample data).
Comparing fire potentials — between fuelbeds and across landscapes —is a useful concept in
fire management planning exclusive of traditional fire behavior parameters. This has been
verified through many discussions with fire managers across the United States, most recently on
the Okanogan-Wenatchee and Deschutes National Forests, where articulation of differences in
fuelbeds caused by diverse factors such as fuel treatments, insects, and pathogens cannot be
captured by traditional fuel models. In addition, the FCCS can represent significant changes in
fuelbeds due to the passage of time. Finally, the effects of fire and fuel treatments on resource
values at broad spatial scales (for example, air quality and wildlife habitat) can be facilitated by
comparing fire potentials. This type of comparison is required in NEPA documents that address
alternative management scenarios.
The concept of evaluating the fire behavior potential at “benchmark environmental conditions”
(conditions (0% woody fuel moisture) that could never be expected to occur), and then assuming
that ranking these values is indicative of fire behavior potential seems deeply flawed by an
implicit assumption that all fuelbeds respond linearly in terms of fire behavior as moisture
Reconciliation of FCCS Potentials Manuscript -- 21
conditions change. Won’t fuelbeds with the most biomass always yield the largest index values
for index 3, and the fuelbeds with the highest FAI always give the highest potentials for index 1?
So why bother to go through all these calculations instead of just reporting loading and FAI as
indicators? This would be more straightforward and easier to interpret.
In the current version of the FCCS, benchmark conditions are used in contrast to fuel models and
FBPS. This is necessary to document the major principles of the FCCS prior to developing
additional options such as allowing weather and fuel moisture to vary. We understand that actual
weather and fuel moisture data are important inputs to traditional fire behavior modeling and
associated applications. The FCCS is not intended to directly emulate this traditional approach
when the benchmark conditions are used.
It does, however, provide detailed fuels information for six fuel strata rather than only
(homogeneous) surface fuels. Weather and fuel moisture are clearly important in calculating fire
behavior outputs in the FBPS; however, they are not required for calculating potential fire
hazard and fire effects. We also provide the option to enter moisture and wind to obtain real fire
behavior predictions. In this case, all of these calculations are necessary.
This is very different from how the FBPS is used in operational fire management. The FCCS
may be more useful in fire planning, especially at larger spatial scales where potential fire
behavior and effects are relevant to decision making (for example, fuel treatment planning).
Fuel loading, FAI, and many other fuelbed characteristics are included in the FCCS fuelbeds
reports, and are readily accessed by users of the FCCS software. These data can be used in
combination with the potentials for a variety of applications.
Part 2. I haven’t reviewed part 2, pages 20-42. I will comment that it is difficult to review in its
current form. No data is presented. No behavior analysis is presented. If this is intended as a
science paper, comments on page 40 and 41 about what future versions of FCCS will do are
completely irrelevant.
The original manuscript has been completely reorganized and divided into three separate
manuscripts. This should eliminate the coarseness of the original presentation. As noted above,
the objective of these manuscripts is to describe concepts underlying the FCCS. There is, of
course, a huge database that underlies all of the FCCS fuelbeds, including a wide range of fuel
properties for six fuel strata. Analysis of fire behavior is not within the scope of this work.
This is a conceptual paper, just as the original Rothermel model formulation was conceptual.
Part 3. I suggest that the entire crown fire potential method be reconsidered. Currently two
useful methods exist for assessing crown fire hazard or potential. One is to look directly at
canopy fuel characteristics – canopy bulk density, canopy fuel load, and canopy fuel load. All
these can be altered directly by management, and are readily understood by managers. The
other is to look at expected fire behavior – the conditions under which the fuelbed might be
expected to burn with surface fire, torching, or active crown fire, following methods developed
by Joe Scott and me, implemented in Nexus and FFE-FVS, and certainly amenable to adaptation
Reconciliation of FCCS Potentials Manuscript -- 22
to any other fire behavior prediction system. These methods enjoy wide acceptance by managers
and scientists, and could be expanded to include independent crown fire if the FCCS developers
deem this necessary.
At a minimum, the behavior of the method needs to be documented to merit publication.
The approach used to calculate crown fire potential has indeed been reconsidered as suggested.
One of the three manuscripts derived from the original manuscript now focuses specifically on
this topic. We agree that canopy fuel characteristics are important, and several are included in the
FCCS fuelbed reports. We have taken your suggestion and reconsidered the entire method. Our
revision much more carefully relates to Reinhardt and Scott as suggested.
Specific Comments:
Page 2, line 16 “comparable to components in Scott and Reinhardt and Van Wagner” – not very
closely comparable.
Revised as suggested.
Page 6, line 17. Why choose a benchmark condition that might never occur?
I hope I made that more clear. It is to avoid locking into one of the multiple and questionable
alternatives to including wind, slope and moisture that are in the literature and in current use. In
the current version of the FCCS, benchmark conditions are used in contrast to fuel models and
FBPS. This is necessary to document the major principles of the FCCS prior to developing
additional options such as allowing weather and fuel moisture to vary. We understand that actual
weather and fuel moisture data are important inputs to traditional fire behavior modeling and
associated applications. The FCCS is not intended to directly emulate this traditional approach. It
does, however, provide detailed fuels information for six fuel strata rather than only
(homogeneous) surface fuels. Weather and fuel moisture are clearly important in calculating fire
behavior outputs in the FBPS; however, they are not required for calculating potential fire
hazard and fire effects. This is very different from how the FBPS is used in operational fire
management. The FCCS may be more useful in fire planning, especially at larger spatial scales
where potential fire behavior and effects are relevant to decision making (for example, fuel
treatment planning).
Page 8, line 1. A figure might illustrate this.
We appreciate this comment but have chosen not to use a figure to illustrate this point.
Page 8, line 3-4. Can this be done in FCCS? If not should you bother discussing it in this
paper? It seems to imply the FCCS has capabilities that it does not.
This has been deleted as suggested.
Page 9, line 23. “Currently the units do not work out” Why?
Reconciliation of FCCS Potentials Manuscript -- 23
This equation comes from Byram, and we were just pointing out that there was an implied
constant of proportionality.
Page 10, line 17-18. “The FCCS also displays the ability to vary conditions to predict fire
behavior across a range of fuel moisture conditions.” Is this true? I thought I learned at the
workshop that FCCS does not yet have this capability, in which case I feel it is unacceptable to
say it does.
This has been corrected.
Page 13, line 13. “Torching potential is the probability for individual crown ignition.”
TC does not seem to me to be a probability at all, but rather maybe an “indicator of the relative
likelihood”
Revised as suggested.
Page 14. The index values here are the result of so many unitless indicators multiplied together
that I cannot assess how useful they would be in comparing crown fire potential from one stand
to another, and I frankly doubt they will be useful. Can’t tell though, since no behavior analysis
or examples are included. A good example might help. Why not just use more conventional and
easily interpreted indicators of crown fire potential? For example, an indicator of torching
potential might be canopy base height. An index of independent crown fire potential might be
canopy closure.
We have taken your suggestion and reconsidered the entire method. Our revision much more
carefully relates to Reinhardt and Scott as suggested.
Page 17, lines 11-15. Is this statement honest? I believe FCCS version 1.0 does NOT allow the
modeling of surface fire behavior in any meaningful way, only the calculation of index values at
some rather un-useful benchmark conditions.
This was revised and corrected. On the contrary, the FCCS allows either a calculation of indices,
or realistic modeling of surface fire behavior at any environmental conditions.
Page 17, line 19-20. An example illustrating this would greatly enhance this paper.
A new manuscript by McKenzie et al. that focuses on fuelbed mapping illustrates this point in
greater detail.
Page 20, pg 22. Fofem does not use Rothermel’s fire behavior model.
This has been corrected.
Page 54, line 6 – where did this equation come from.
This is much more developed in the revision.
Reconciliation of FCCS Potentials Manuscript -- 24
Scott Stephens
Reviews the “Development of the FCCS crown fire potential model’ section of this manuscript. I
also wrote comments on the other sections of this manuscript for you to consider as well.
One general comment is the use of the term fuel loading throughout this and the other
manuscripts. I would recommend using fuel load to describe the quantity of biomass that has the
potential to burn. The addition of ing to the end of this word is not justified. You are simply
interested in the fuel loads, not fuel loading.
I do agree with the authors that modeling crown fire behavior or the potential for a particular
system to be support crown fire is very challenging and our existing systems are not rigorous
enough. That said I cannot support the development of this new system that attempts to calculate
crown fire potential. You have essentially created 7 new variables and then multiplied them
together to produce a new crown fire potential. While many of your 7 variables are related to
crown fire potential they have all been developed subjectively. There is no lab or quantitative
analysis to back this up. I know that you actually write this in the manuscript but without a
strong quantitative analysis linked to crown fire behavior, I cannot support this new system.
The new manuscript on crown fire potentials has been extracted from the larger original
manuscript. The manuscript is completely revised, including new equations, different logic, and
a new senior author. We are hopeful that the conceptual framework for crown fire potentials is
now clearer and more logical.
I would recommend using Scott and Reinhardt’s Crowning Index and Torching Index. It is true
that both of these are indices but they are directly linked to our existing crown fire equations.
Both of these have been peer-reviewed and are in the literature. You could possibly modify these
equations but again this must be directly linked to our quantitative understanding of crown fires.
Crowning Index and Torching Index are quite useful indices for some applications, although they
have considerable quantitative limitations at higher values where they become meaningless. It is
our understanding that they have been subjected only to friendly review within the Forest Service
publication process, not to outside anonymous review. In any case, those indices are tied to the
traditional fuel model system that has low resolution capability for fuel characteristics, and
addresses only surface fuels, not all fuels strata.
Until the modifications to the Rothermel surface fire equation proposed in this work have been
tested in a laboratory or field setting, I believe it would be best to use the existing surface fire
model in this work. It is true that this model (Rothermel’s) is not perfect but it does have
standing in the fire research and management communities in the USA and abroad. As you work
to improve the surface fire model you can update this system. To include these modifications
without testing is not an appropriate and I believe would not pass peer review at a journ
al. A separate paper that focuses on possible modifications to the surface fire model would be
interesting.
Reconciliation of FCCS Potentials Manuscript -- 25
We appreciate these comments and have taken them to heart by reorganizing the initial
manuscript into three discrete manuscripts with the primary objective of describing
reformulation of the Rothermel model, comparing logic between Rothermel and the FCCS, and
suggesting appropriate applications. As recommended by the review panel, we feel it is
necessary and sufficient to document the conceptual basis of the FCCS. The FCCS is designed to
complement existing fire modeling systems. As the reviewer notes, certain aspects of the FCCS,
including the reformulation of the Rothermel model, remain to be tested and compared with
existing fire tools.
[Notes on ‘Fire potential rating for wildland fuelbeds using the fuel characteristic classification
system’]
The items listed below were transcribed from comments and edits made directly on the
manuscript. Although we have tried to interpret them accurately, the intention of some of the
comments is unclear.
p.2 line 5: circled ‘the potential of a fuelbed to release energy’.
p.2 line 7: circled ‘a set of relative values’ and ‘intrinsic physical capacity’.
p.2 line 9: circled ‘nine’ and wrote ‘9 potentials’.
p.2 line 12: circled ‘using a new fire behavior prediction system’ and wrote ‘new fire behavior
prediction system’.
p.2 line 14: underlined ‘rule-based ranking’.
p.2 line 15: underlined ‘on admittedly limited scientific’ and wrote ‘yes’.
p.2 line 18: Crossed out ‘ing’ in ‘loading’.
p.3 line 3: wrote ‘crown fire indexes. not physically linked. use Rein. & Scott here first’.
p.4 line 9: underlined ‘assigning a’.
p.4 line 10: circled ‘potential’ and ‘hazard assignment’.
p.4 line 12: underlined “we derive key algorithms that describe fire potential’.
p.4 line 15: underlined ‘derivation of the surface fire spread model’ and ‘derivation of the
crown fire potential model’.
p.4 line 22: circled ‘relative values’ and underlined ‘intrinsic physical capacity of a’.
p.5 line 1: wrote ‘just dry? What about moderate conditions?’.
Reconciliation of FCCS Potentials Manuscript -- 26
p.5 line 14: underlined ‘three-digit number’.
p.5 line 16 & 17: underlined ‘surface’, ‘crowning potential’, and ‘available fuel’.
p.5 line 18: wrote ‘surface, crown, consumption’.
p.5 line 19: wrote ‘Best to actually report the values here, not index values. Very hard to
understand in index form’.
Minor revisions were made in the manuscript as appropriate. Index values are used here as an
inherently distinctive part of the FCCS. Index values are more useful at larger spatial scales for
planning and can complement values from fire behavior prediction calculations. It is anticipated
that actual fire parameter values will be incorporated in future versions of the FCCS.
p.6 line 7: underlined ‘0 to 10’.
p.6 line 12: wrote ‘surface fire behavior potential’ after ‘FBP’, and wrote ‘flaming combustion’
after ‘(energy release’.
p.6 line 17 & 18: underlined ‘no-slope’, ‘(4 mi h-1)’, ‘midflame wind speed’, ‘moisture contents
of 0’, and ‘60%’.
p.6 line 20: wrote ‘how different than Roth.?’.
p.7 line 5: wrote ‘broken fuelbed into 4 layers for surface fire estimation. Interesting idea, but
need validation. No validation in paper.’.
Minor revisions were made in the manuscript as appropriate. The logic used for surface fire
estimation is described in some detail and reflects our understanding of physical properties of
fuels and fire. As with many concepts in existing fire science and modeling, it is difficult to
validate some of these concepts with conventional quantitative approaches.
p.7 line 21: underlined ‘Spread potential’ and ‘proportional to the rate of spread (ft min -1)’.
p.8 line 1: circled ‘The heat sink term is quite sensitive to fuelbed depth.’ and wrote ‘why?’.
p.8 line 2: circled ‘a scaling factor’ and wrote ‘???’. Underlined ‘0.25’ and ‘1/4 is the rate’.
p.9 line 7: underlined ‘Flame length potential’ and ‘length (ft)’.
p.9 line 8: underlined ‘benchmark environmental conditions’.
p.9 line 9: circled ‘0.5’.
p.9 line 10: underlined ‘1/2 the flame length’ and wrote ‘why 0.5?’.
Reconciliation of FCCS Potentials Manuscript -- 27
p.9 line 23: circled ‘currently the units do not work out.’.
p.10 line 1: underlined ‘216 FCCS’ and wrote ‘216 National fuelbeds’.
p.10 line 3: circled ‘thousands of’ and wrote ‘really? tested?’.
p.10 line 8 & 9: underlined ‘No scaling factors were used to force the agreement between the
two outputs’.
p.10 line 12: underlined ‘surface fire intensity in certain’.
p.10 line 13: underlined ‘nonwoody fuels; in other’.
p.10 line 16: wrote ‘why is this?’ after ‘Rothermel’s’.
p.10 line 20: underlined ‘evaluate both the heat sink and heat source’.
p.10 line 22: underlined ‘The ability to segregate the heat sink and heat source’.
p.10 line 23: underlined ‘about the spread-no spread conditions’ and wrote ‘chaparral?
Maybe’.
p.11 line 3: circled ‘Fig. 5 arrays’.
p.11 line 4 & 5: underlined ‘using FBPS fuel model #8, and the other half against FBPS fuel
model #10’ and wrote ‘interesting, any verification?’.
Minor revisions were made and additional clarification included in the manuscript as
appropriate. It is unclear in this case that kind of verification is requested. Some of these notes
are similar to those indicated by other reviewers for which responses are indicated above.
p.11 line 13: underlined ‘that Frandsen (1973) used the wrong equation form to fit his
laboratory data, and the error propagates through the calculation of effective heating number’
and wrote ‘errors’ and wrote ‘this is a key issue’.
p.11 line 16: underlined ‘all empirical coefficients’.
p.11 line 18 & 19: underlined ‘(and ignoring litter)’ and wrote ‘?’.
p.12 line 4: wrote ‘still homogeneous fuel beds at some scale’.
p.12 line 6: underlined ‘alternate method to evaluate the effective heating number’.
p.12 line 7: underlined ‘Frandsen’s data’.
p.12 line 8: underlined ‘from ε’.
Reconciliation of FCCS Potentials Manuscript -- 28
p.12 line 9: Crossed out ‘ing’ in ‘loading’.
p.12 line 12: circled ‘the ghosts of’ and wrote ‘??’.
p.12 line 14 – 17: underlined ‘ratio’, ‘wind and slope’, and ‘advancements’. Wrote ‘is there
any testing? Lab results?’.
p.12 line 21: underlined ‘rule-based’.
p.13 line 1: underlined ‘spreading line fire under a’.
p.13 line 3: underlined ‘dependent’.
p.13 line 9 – 11: underlined ‘torching’, dependent crown’, independent crown’, and ‘multiplied
together’. Circled ‘0 to 10’. Wrote ‘Multiplied together, max = 10 index’.
p.14 line 8: underlined ‘be expressed as flame length’.
p.14 line 13: circled ‘(LAI)’ and wrote ‘does this work for different heights?’.
Minor revisions were made in the manuscript as appropriate. LAI and the related concept of FAI
should work for any height in terms of their physical meaning, although LAI is conventionally
measured near the ground surface using a specific calibration process.
p.14 line 22: wrote ‘many factors, is this all theory?’.
p.15 line 1: circled ‘as a response curve on a scale of zero-to-one’.
p.15 line 3 & 4: underlined ‘is based on expert judgment’.
p.15 line 11: wrote ‘need to’.
p.15 line 14: Crossed out ‘ing’ in ‘loading’.
p.15 line 18: underlined ‘apply a consumption factor based on fuel moisture’ and wrote ‘why
not include?’.
We use benchmark conditions for the current reformulation of Rothermel in order to facilitate
comparisons among different fuelbeds and their fire potentials. In the current version of the
FCCS, benchmark conditions are used in contrast to fuel models and FBPS to document the
major principles of the FCCS prior to developing additional options such as allowing weather
and fuel moisture to vary. It is anticipated that user inputs will be added to the software in future
versions.
p.16 line 2: underlined ‘in of the surface’ and wrote ‘1/2”? 1-10hr idea?’.
Reconciliation of FCCS Potentials Manuscript -- 29
p.17 line 14 – 18: underlined all and wrote ‘is this better?’.
p.18 line 1: circled ‘physical fuelbed characteristics separately’.
p.18 line 13: circled ‘Specific fire behavior or effects can be scaled downward by substituting
specific conditions’ and wrote ‘how?’.
p.18 line 16 – 17: bracketed both lines and wrote ‘yes’.
p.19 line 1: underlined ‘Fire potentials are a set of relative values that rate the’.
p.19 line 3 & 4: underlined ‘new algorithms’, ‘express surface fire’, ‘for realistically
heterogeneous’, and ‘inventoried fuelbeds’.
p.19 line 10: wrote ‘still no testing or lab work’.
p.20 line 4: underlined ‘a quasi steady-state condition’.
p.20 line 8: underlined ‘unrealistic fuelbed depth’ and crossed out ‘ing’ in ‘loading’.
p.20 line 13: circled ‘expand and correct the physical bases for’.
p.21 line 5: underlined ‘only surface fuelbeds’ and wrote ‘yes’.
p.21 line 7: underlined ‘basis of laboratory burning of excelsior and wooden cribs’ and wrote
‘yes’.
p.22 line 8: underlined ‘no-wind, no-slope condition’.
p.23 line 9: crossed out ‘ing’ in ‘loading’.
p.23 line 16: underlined entire sentence beginning with ‘We feel that...’.
p.24 line 4: circled ‘best fit to Frandsen’s data’ and wrote ‘did you get a copy of this? What
does Frandsen say?’.
p.27 line 19: circled ‘capability to input the percentage slope in the’ and wrote ‘no slope in new
system’.
p.27 line 21: circled ‘”effective wind speed”’.
p.28 line 19: circled ‘we do not include it here given its modest importance’.
p.28 line 21: circled ‘of 4 mi h-1’.
Reconciliation of FCCS Potentials Manuscript -- 30
p.29 line 3 & 4: underlined ‘We are confident about predicting spread rate at 4 mi h-1’, and ‘is
our benchmark wind speed’.
p.30 line 15: circled ‘primary heat-source term’, and underlined ‘is reaction intensity’.
p.33 line 9 & 10: underlined ‘attempt to include litter in stylized fuel models by including them
as a virtual 1-hour fuel loading through expert judgment’ and wrote ‘not really’.
p.34 line 12: circled ‘we conjecture that’.
p.34 line 14: underlined ‘calculate’.
p.34 line 15: underlined ‘data’.
p.35 line 2: underlined ‘1,050 to 3,500 ft -1’.
p.35 line 5: underlined ‘fuelbed depth more than 5 times deeper than the FCCS calculation’ and
wrote ‘wow’.
p.35 line 22: crossed out ‘ing’ in ‘loading’.
p.38 line 18: circled ‘moisture damping from fire extinction’.
p.39 line 18 – 21: underlined most of these four lines.
p.40 line 14: underlined ‘calculate surface-fire behavior at any moisture’.
p.41 line 18: circled ‘we have not tested the effect of applying’.
p.42 line 10: circled ‘No adjustment to or stylization of inventoried’, and wrote ‘would be
improvement’.
p.43 line 13 – 15: underlined most of these three lines and wrote ‘true’.
p.43 line 18: circled ‘non-mechanistic’ and wrote ‘not useful. Must be tied quantitatively’.
Minor revisions were made as appropriate, although some points were difficult to interpret from
comments on the hard copy. As noted above – and as recommended by the review panel – the
objective of these manuscripts is to provide the conceptual foundation of the FCCS prior to
further quantitative analysis, a process that has rarely been rigorously applied to existing fire
tools and models. Also as noted above, we use benchmark conditions for the current
reformulation of Rothermel in order to facilitate comparisons among different fuelbeds and their
fire potentials.
p.44 at bottom margin: wrote ‘I cannot support the use of these 7 variables to compute crown
fire hazards’.
Reconciliation of FCCS Potentials Manuscript -- 31
p.45 after line 5: wrote ‘This is hard to justify, why is this an improvement over Scott and
Reinhardt? Torching Index, Crowning Index’.
As noted above, the new manuscript on crown fire potentials is completely revised, including
new equations, different logic, and a new senior author. We are hopeful that the conceptual
framework for crown fire potentials is now clearer and more logical. The crown fire potentials
other fire potentials, and the FCCS in general are intended to complement existing fire behavior
prediction systems. Concepts like Torching Index and Crowning are useful at small spatial
scales, for example, calculations for forest stands as in the FFE-FVS modeling approach.
Scaling up to thousands of hectares leads to inaccuracies. Fire potentials in the FCCS are more
useful for planning at larger scales where spatial patterns of fire hazard can be compared
without loss of resolution.
p.45 line 21: crossed out ‘ing’ in ‘loading’.
p.46 line 7 & 8: circled ‘post-frontal flaming is hypothesized’ and ‘independent crown fires’ and
wrote ‘why?’.
p.46 line 18 – 22: underlined most of these five lines.
p.47 line 8 – 13: underlined most of these six lines.
p.47 line 19: underlined ‘non-uniformities that exist within a stand’.
p.47 line 22 & 23: underlined both lines.
p.48 line 7: circled ‘3/2 power of he vertical gap’ and wrote ‘why?’.
p.48 line 10: underlined entire line.
p.48 line 13 – 17: underlined most of these 5 lines.
p.55 line 8: wrote ‘yes’ after the word ‘planning’.
p.55 line 10 & 11: underlined ‘surface models, the surface fire behavior model by Rothermel
(1972)’ and wrote ‘good though’.
p.55 line 18: circled ‘provides no new experimental results or new physical theory’ and wrote
‘true – this is the biggest problem’.
Figure 1: wrote ‘nice figure’.
Figure 5: wrote ‘conifer’ in place of ‘confer’ on both charts. Also wrote ‘interesting, but has
there been any verification? Field testing?’.
Reconciliation of FCCS Potentials Manuscript -- 32
As noted above – and as recommended by the review panel – the objective of these manuscripts
is to provide the conceptual foundation of the FCCS prior to further quantitative analysis.
Brian Stocks
This paper is loaded with formulations and assumptions, but there is no actual data presented to
validate any of this. This was discussed in detail in Seattle, and one solution suggested was the
development of a “concept” paper, with a clear statement that the intent in doing so was to use
the approach outlined in the paper to gather “validation” data, which would then result in a
second paper showing just how well the new model works. It could then be compared to other
models, and this would make an interesting and valuable journal paper.
We very much appreciate this comment which corroborates the recommendation of the review
panel. We have divided the original manuscript into three discrete manuscripts that articulate the
individual components of the original manuscript much better. The Rothermel model formulation
is entirely conceptual and unsupported by data. We offer a new formulation that is equally
conceptual but more logical. At the suggestion of several reviewers, we have emphasized the
conceptual underpinnings of the potentials and related topics, and have specifically addressed
new physical and modeling principles. It is one step in a process and we would welcome the
opportunity for validation in the future, including comparison to Canadian data sets.
Some of the key equations (e.g. equations 1.5 and 3.2) lack a real physical justification of the
model form. In fact there are numerous assumptions made in terms of functional forms and
values of coefficients that do not have the physical reasoning explained. There are a lot of
processes being included in the models, making it very difficult to judge whether they are going
to have a strong effect or not.
The Rothermel formulation has obvious deficiencies (those that require stylized fuel models to
correct). It is our full intention here to propose new concepts and formulations that overcome
these deficiencies.
In the revised manuscripts, we have tried to provide better logic and definitions. Much of the
general logic – especially in the early part of the original manuscript and in the new manuscript
that describes reformulation of the Rothermel model – is derived from the published algorithms
in Rothermel (1972) and related literature. In some cases, it did not seem necessary to include
lots of detail where the concepts and equations were already available. However, we did try to
include sufficient justification for concepts and equations that are novel or revised.
The development of the 3-digit FPR does not really seem useful, and is open to much
misinterpretation (e.g. is 611 more dangerous than 161 or 116?). It is always more desirable to
try to predict fire behavior potential in absolute terms, rather than an index, but I understand the
data limitations. From a fire management standpoint it would be much more useful to focus on
the onset of crowning – trying to define for each fuel type the threshold when surface fires would
move into the crowns. Even in general terms, this is very useful from a fire control standpoint.
Reconciliation of FCCS Potentials Manuscript -- 33
We appreciate this comment and in the revised manuscripts, especially the one specifically on
fire potentials, we have reduced the emphasis on the fire potential rating. In our workshops we
find that some users prefer the indices and others find them less useful, so we have chosen to
retain the option. The value of the rating depends greatly on the particular application and local
management objectives. We very much agree with the reviewer that addressing thresholds of
crown fire is critical. Unfortunately those thresholds are poorly understood and difficult to
predict. It is also important to note that the available fuel potential is very important for
determining fire effects, especially biomass consumption and smoke production; smoke is often
the most important environmental and social impact of prescribed burning and wildfire.
There is a complete lack of discussion of the research effort on the Albini crown fire model
development, which has involved the use of Canadian experimental fire datasets, and was the
motivation behind the International Crown Fire modeling Experiment (ICFME) in Canada
between 1997 and 2000. The Bret Butler paper in the CJFR Special Issue devoted to ICFME is
quite relevant here, as are recent publications by Cruz et al. on crown fire model development.
All of thee papers show the Rothermel crown fire model performing very poorly in comparison to
other models (Canadian FBP System, Cruz et al.) in terms of predicting crown fire spread rates.
It seriously underpredicts by a large margin, making it operationally useless. If this paper is
trying to build a state-of-the-art model, not including some of the better work that has taken
place is a serious oversight. The statement about the Canadian FBP System being based on
Rothermel, while an oversight, is further indication that the Seattle group needs a better
understanding of what is going on elsewhere.
This point is well taken and was a shortcoming of the original manuscript. The new manuscript
on crown fire is completely rewritten, including special attention to the recent and landmark
literature on crown fire modeling. All the new manuscripts on the FCCS have made an effort to
provide broader coverage of important literature on fuels and fire modeling.
I still cannot understand the reason/rationale for including the prediction of independent crown
fire within this system. Despite the fact that it can occur for short periods, particularly where
steep slopes are involved (chaparral in CA, black spruce in Alaska), it is not possible in almost
all forest fuel types, where crown fire is dependent on, and linked to, the spreading surface fire.
Once again, it seems to me that the emphasis should be on predicting the surface-to crown fire
threshold. So, predicting crown fire alone should be good enough – and it, in and of itself, has
proven enough of a challenge.
The reviewer is correct that classic independent crown fire, in which fire spread through the
crown is unrelated to surface fire, is unusual in many forest ecosystems. However, we have
observed independent crown fire at several locations including riparian and boreal forests in
which crown fuels are dry and surface fuels are moist. This component is included primarily to
provide a more conceptually and analytically complete perspective on crown fire. Independent
crown fire is also included in traditional fire behavior prediction, so there is some comparability
there.
Reconciliation of FCCS Potentials Manuscript -- 34
In the revision, we have taken your suggestion that we overstated the importance of independent
crown fire and have reverted to the “passive/active” terminology. Now our concern is that we
have understated the importance of independent crowning.
As it stands, this paper still needs a better summary that ties everything together, in particular
talking about how fire potential values would be used and interpreted. Right now, you can’t take
this paper and say “OK, now I know how to calculate and use these new fire potentials”?
This is a good point, and hopefully the reorganization of the manuscripts will resolve this. The
manuscript that focuses on the fire potentials includes a section that summarizes appropriate
applications. In addition, the new manuscript by McKenzie et al. describes how FCCS fuelbeds
can be arrayed across a landscape as a means of assessing fire hazard at broad spatial scales.
As part of the required validation exercise, the Seattle group should look closely at the datasets
used to develop the Canadian FBP System. These include fuel consumption, spread rate and
intensity data for surface and crown fires in many fuel types, based on wildfire observations and
experimental fires. Most of this data is published or available from the Canadian Forest
Service. An in-review paper by Alexander and Cruz comparing crown fire spread rates using the
Cruz et al. and Rothermel models would be particularly useful, as it includes data from
American wildfires along with Canadian data.
This is an excellent idea, and would be a good next step in development of the FCCS. We are
familiar with the recent work by Alexander and Cruz, and integration of their empirical approach
with the FCCS could advance the state of crown fire modeling.
Jan van Wagtendonk
General Comments:
Sam is to be commended for tackling the difficult job of refining the Rothermel spread equation.
Both Rothermel and Albini recognized the limitations of the model and indicated where it could
be improved. There is a need for improving the accuracy of the model and for incorporating
more fuel characteristics.
My greatest concern is the lack of validation of the Fire Potential model. Before this module can
be implemented, the reformulation of the Rothermel spread model must undergo empirical
testing and comparison with the original model.
I would envision three articles published in the peer-reviewed scientific literature; the first a
conceptual treatment of the Rothermel model and the rationale for the reformulation, the second
presenting the results of the empirical testing and comparison, and the third the development of
the crown fire potential model. The International Journal of Wildland Fire would be appropriate
for all three of these articles. I also think an additional technical report that deals with the
“potential cube” (most of Part I) would be useful.
Reconciliation of FCCS Potentials Manuscript -- 35
We appreciate these helpful comments. We agree that Rothermel and Albini always recognized
weaknesses in their approach, but improvements have come very slowly. We have taken your
suggestion to develop three separate manuscripts; the first and third are exactly as you suggest,
although the other one focuses on discussion of the fire potentials. As recommended by the
review panel, we feel it is necessary and sufficient to document the conceptual basis of the
FCCS. As the reviewer notes, certain aspects of the FCCS remain to be tested and compared with
existing fire tools. Validation will be a worthwhile undertaking as the next step.
Specific Comments:
Page 4, line 7. Delete “innovative.” They are new, but we’ll let time tell us how innovative they
are.
Done.
Page 11, lines 12-17. There are many ways to fit an equation to data. Although you provide a
good case for a different fit on page 23, It does not necessarily mean that Frandsen’s equation
was “wrong.” With only two data points, it becomes an interpretation. I suggest rewording this
sentence. In addition, the magnitude of the ramifications of the “error” are never presented.
Without new laboratory, the real fit cannot be known. I strongly suggest that an effort be made
to conduct the experiments to gather those before the scientifically reviewed article is submitted
for publication.
In this case, we really do feel that Frandsen’s equation is wrong, a point that has not been
challenged by any other reviewers. It’s not a question of fitting a curve to 2 data points, but of
choosing the form of a function that can be calibrated at 2 data points. It is the form of
Frandsen’s equation that we contest, not the fit. As noted above, we look forward to numerical
testing following publication of the conceptual basis for the FCCS.
Page 11, lines 18-23. Again, it is not necessary to use words like “elegant,” “shortcomings,”
and “artfully.”
Done.
Page 11, line 18-19. Litter is not ignored in the stylized models but is included in the 1-hour
time-lag category. For example, models 8 through 13 all have surface to volume ratios three to
five times higher than the 500 ft-1 you would get if only woody particles were included (see Albini
1976). Also, Burgan and Rothermel (1984) include litter fuels in their field procedures for
building fuel models. In addition, Brown (1972) includes the litter layer in his fuel depth
calculations.
Good points. We have clarified this. The artificial combination of litter and woody fuels in
Rothermel’s formulation limits it to the assumption that both have the same combustion
environment. By separating the two, we allow for a different combustion efficiency and rate in
the two components.
Reconciliation of FCCS Potentials Manuscript -- 36
Page 20, line 6. Delete “artfully.”
Page 20, line 8. Delete “unrealistic.” Remember, it’s a model – a simplification of reality.
Page 20, lines 10-14. Until the testing of the new model is completed, it is not appropriate to use
words such as “deficiencies,” “correct,” or “realistic.”
Minor revisions made as appropriate.
Page 21, line 4. These are not so much technical problems, but rather model simplifications and
assumptions. The authors must show that there formulation, although physically representative,
produces more accurate fire behavior predictions. This has not been done through testing or
comparisons with the previous model.
The objective is to provide an alternative approach that complements traditional fire behavior
prediction systems, not necessarily to make more accurate predictions. An important issue
emphasized in the revised manuscripts is that the FCCS is capable of higher resolution, with
several fuelbeds (and associated ranges of potentials) between much coarser scale fuel models.
New conceptual approaches have scientific and management value regardless of how they
compare to traditional approaches.
We have also corrected errors in the original basic equations which should lead to improved
accuracy.
Page 21, line 11. I would use “represented by” rather than “effectively reduced.”
I believe our statement is accurate.
Page 21, line 14. The weighting by SV is done to appropriately give more influence to flashy fine
fuels than larger diameter fuels in their effect on flaming front spread. Whether this “somewhat
erroneous” assumption makes any difference in fire behavior predictions is unproved. Is there
really much difference between using the surface to volume ratio or a value based on multiplying
the surface area density by the particle density and the ignition shell thickness (0.0028 ft) for
those particles greater than 0.0056 ft in diameter plus the weight of particles smaller than
0.0056 ft, or am I missing something? Only the testing will tell for sure.
Yes, it makes a huge difference; a multiple of 5 difference for high sigma fuelbeds. We have
demonstrated this mathematically and graphically. It does not require an empirical test.
Page 21, line 16. The characteristic surface to volume ratios include leaves and needles as well
as small diameter woody particles.
Rothermel’s calculation of characteristic surface-to-volume ratio is the basis for his formulation
that we question. We agree that combining them accentuates the error; that is why we address
each component separately.
Reconciliation of FCCS Potentials Manuscript -- 37
Page 21, line 22. The claim that one can obtain more accurate fire behavior predictions is
unfounded at this time.
Only that we can reasonably assume that correcting obvious errors is likely to improve accuracy.
Page 24, line 22. and an “a” between “that” and “fuelbed.”
Minor revisions made as appropriate.
Page 25, equation 2.4. I like the idea of having separate variables for the heat sink. Sure would
like some validation data, though.
We would also like some validation data. Several investigators have tried and failed to do this
experimentally. Maybe it can be done numerically?
Page 26, line 20. It is important that we have empirical “evidence.”
It would be nice to have that in the future.
Page 28, line 11. There needs to be an “end quote” somewhere here.
Thank you.
Page 30, line 6. This, too, should be validated with additional experiments.
An abundance of experimental evidence has already been published by others.
Page 30, line 12. add an “s” to “allow.”
Thank you.
Page 30, line 22. Add an “of” between “effect’ and efficiency.”
Thank you.
Page 32, equation 2.10. I like the idea of calculating separate Gammas, but we need empirical
data.
It would be a difficult experiment to perform, but an impossible one unless someone first
advances a theory. We have now done that.
Page 32, line 9. Replace “with” with “from.” Do you mean equation 2.9?
Page 33, line 15-16. Delete “once again.”
Reconciliation of FCCS Potentials Manuscript -- 38
Minor revisions made as appropriate. The issue of testing has been addressed in previous
comments above.
Page 34, line 7. Although it might be easier for the field practitioner to visualize fuel bed than
packing ratio, I think we lose an important insight into fire behavior factor when we use the
former. If they measure fuel bed depth, they can calculate the packing ratio. In teaching fire
behavior at all levels, I never have any difficulty getting the students to understand the packing
ratio concept. All I have to ask them is how they build a campfire. Do they pack all of the
kindling into a small bundle and try to start it or do they arrange it in a “teepee” in order to get
it to ignite? None of them say, “But, gee, Jan, I always arrange the kindling to be at an optimum
depth!” The carburetor example also works well with students. What we are looking for is a
mixture of fuel and air that optimizes combustion, not too lean nor too rich.
This point is well taken. We feel that it comes down to a matter of personal preference or
perception, and have indicated this in the revision. Another approach is to instruct fire builders to
leave about 2.5 cm of airspace between each piece of firewood, in effect building the fuelbed to
an optimum depth.
Page 35, lines 6 and 7. This begs for some field measurements and testing.
Not necessarily. It is provable mathematically.
Page 37, line 15. There is a contradiction here. In the cases of reaction velocity and effective
heating number, you opt for the “realistic” rather than the simple. Here you opt for simplicity.
You need to make changes where there are data to support them and a rationale for doing so. If
I understand it correctly, the effective packing ratio is the amount of fule that actually burns per
unit of volume of air and fuel. But here you are using the effective heating number which you
discounted as “wrong.”
Thank you. The term ε must be identified as the FCCS version of the effective heating number.
Page 39, line 12. Delete “elegant.”
We feel they did an elegant job considering what was available in 1972.
Page 48, lines 13-15. Although in boreal forests independent crown fires might be initiated by a
torching tree, in most forest types independent crown fires are usually initiated from dependent
crown fires.
Independent crown fire is initiated in most cases from dependent crown fires as suggested by the
reviewer. However, we have observed independent crown fire at several locations including
riparian forests in which crown fuels are dry and surface fuels are moist. This component is
included primarily to provide a more conceptually and analytically complete perspective on
crown fire. Independent crown fire is also included in traditional fire behavior prediction, so
there is some comparability there.
Reconciliation of FCCS Potentials Manuscript -- 39
Page 50, line 12 Pi is the assumed cross-sectional shape of foliage?
Yes.
Page 55, line 11. Add an “n” to “crow.”
Done.
David Weise
The items listed below were transcribed from comments and edits made directly on the
manuscript. Although we have tried to interpret them accurately, the intention of some of the
comments is unclear.
Your accurate and constructive comments are greatly appreciated. These comments have
contributed enormously to improving the manuscript..
p1 line 1: he wrote “Suggest title change to something like “Reformulation of Rothermel’s rate
of spread equation for real-world fuel beds”.
Excellent suggestion. The title of the new manuscript is very close to this.
p2 line 2: he wrote “There is too much detail in the abstract.”
This has been resolved by dividing the manuscript into three separate manuscripts.
p6 line 1: after “(1972)” he wrote “Albini (1976) modifications?”.
p6 line 4: after “(1973)” he wrote “Did Rothermel 1972 include earlier work from Project Fire
Model and the Rothermel/Anderson papers of the late 60s? Perhaps using those data (along
with Catchpole et al) and my work with UCRiverside for comparison with original Rothermel
formulation.”
Corrections have been made. Thank you. Yes, using the data from Catchpole and your work is a
very good idea.
p6 line 13: after “conditions” he wrote “What is the need for benchmark conditions in the
reformulation?”
The need is to set the conditions constant so that fuels can be compared to fuels.
p6 line 16: after “min -1” he wrote “Use metric for a journal article. System outputs are easily
converted between systems.”
Done.
Reconciliation of FCCS Potentials Manuscript -- 40
p6 line 23: after “(dimensionless)” he wrote “What is the purpose of scaling the values to 0 to
10?”.
This is somewhat arbitrary, but provides a reasonable range for evaluation.
p7 line 8: after the second “ δ ” he wrote “ s the ratio ’ ?”.
It is correct in the original manuscript.
p7 line 19: he wrote “How was this derived or is it a definition?”
It is simply a theory.
p8 line 2: he wrote “Perhaps the benchmark conditions and assumptions/simplifications for
application to FCCS should be in a separate manuscript.”
Minor revisions were made as appropriate. We feel it is important to state the benchmark
conditions here rather than separate them from relevant portions of the manuscript.
p8 line 18: he wrote “What is the basis for this value? Is ignition depth/particle radius a
function of surface area/volume ratio? Is ignition depth the depth at which a thermally-thick fuel
is assumed to be thermally thin? Is ignition depth a function of fuel density or thermal
diffusivity? Is this value based on wood? Is the value different for a fuel that is principally
unlignified cellulose?”.
Great question. Yes, I believe it is a variable dependent upon those and a few other properties, as
did Wilson. But the outcome is not very sensitive to a precise determination. Nonetheless, we
hope to tighten this up with future observational research.
p9 line 13: he wrote “While BEHAVE uses Byram’s flame length-fireline intensity, is this the
best flame length correlation to base FP on? Is there a mass loss – flame length or energy
release – flame length correlation that is better?”.
We feel that the Byram derivation is sufficient for now in the absence of a better quantitative
approach. There may indeed be a better way to do this, but we hesitate to tinker with it.
p10 line 18: he wrote: “How is this different from Rothermel? Is this an improvement? How
different are predictions based on mean fuel bed values (Rothermel approach) versus predictions
based on individual components?”
One of the primary differences between the FCCS and Rothermel is that the former includes six
fuel strata, while the latter includes only (homogeneous) surface fuels. The FCCS addresses
surface fire differently by including duff and the lichen-litter-moss strata, thereby leading to
different biophysical relationships. We feel that consideration of the greater complexity in real
fuels is more realistic.
Reconciliation of FCCS Potentials Manuscript -- 41
p10 line 23: he wrote “This is a hypothesis that I’d be happy to work with you to test using our
published dense chaparral fuel bed tests.”.
Thank you. This will be a great topic for future collaboration, especially with respect to Clint
Wright’s ongoing work in chaparral and other shrub systems.
p11 line 12: he wrote “Can you be more explicit? Do you mean the properties of the function
used to fit the data is not appropriate? Provide more explanation of this assertion.”.
In this case, we really do feel that Frandsen’s equation is wrong, a point that has not been
challenged by any other reviewers. It’s not a question of fitting a curve to 2 data points, but of
choosing the form of a function that can be calibrated at 2 data points. It is the form of
Frandsen’s equation that we contest, not the fit. As noted above, we look forward to numerical
testing following publication of the conceptual basis for the FCCS.
p12 line 5: he wrote “Is the FCCS a fire behavior model or is it a system to classify fuel
characteristics?” and “Suggest moving the modeling details in Section II into this paper.”
The FCCS characterizes fuel properties and classifies fuelbeds. It also includes a fire behavior
model. The reorganized manuscripts should reduce confusion.
p12 line 14: after “ηM” he wrote “What about Wilson’s formulation?”
FCCS calculates both formulations, Wilson and Rothermel. Either results in a moisture damping
coefficient. The user may choose either. This specifically follows from your recommendation
when we were together in Los Alamos last year. It was a lot of work to enable this, but you were
right on.
p13 line 9: he wrote “Much of the work on crown fires seems to be overlooked.”
This point is well taken and was a shortcoming of the original manuscript. The new manuscript
on crown fire is completely rewritten, including special attention to the recent and landmark
literature on crown fire modeling. All the new manuscripts on the FCCS have made an effort to
provide broader coverage of important literature on fuels and fire modeling.
p14 line 4: he wrote “See earlier comment re indices and needing to scale. I support the idea of
grouping like fuel beds – that should be done prior to indexing.”
Although there is some logic to grouping similar fuelbeds, we feel that one of the values of the
discrete fuelbeds is that they represent real fuel properties to resource managers.
We reject the ideas that classifications can only be made on inputs. We prefer to classify outputs,
but allow the users to decide the breadth of the classes useful to their applications.
p15 line 8: he wrote “Why a maximum and how were the divisors arrived at?”
Reconciliation of FCCS Potentials Manuscript -- 42
We normalized to an index value of 9 for approximately 95% of the 216 fuelbeds.
p16 line 2: he wrote “Why ½ inch? Shouldn’t the available fuel for flaming be determined by
the ignition depth previously defined?”
No. Available fuel consumption includes post-flaming. At your suggestion, we have added
another sub-potential called “reaction available fuel” that is consistent with your interpretation.
p20 line 1: after “model” he wrote “This part should stand as an individual manuscript – this is
where the greatest contribution is.”
Done.
p20 line 14: he wrote “Is it possible to measure the components of reaction intensity (when
summed by fuel classes? Is it simply additive or is there a feedback process so that the sum of
the parts is less than the total energy release rate? How do multiphase models handle various
fuel size classes?”
We can’t justify anything but additive. In reality, it must be slightly less than additive to satisfy
the second law of thermodynamics.
p20 line 18: after “1992” he wrote “I’m sure Charlie Van Wagner is rolling over in his easy
chair over this statement.”
This has been corrected.
p20 line 23: after the second “2003” he wrote “LANDSUM (Keane)”.
p21 line 15: he wrote “Is this assumption stated or was it done simply to strongly weight the fine
fuels. Recall that in fire danger, values are loading-weighted.”
Exactly so. It was stated by Rothermel, but it is our contention that it was a mistake to consider
flaming combustion strictly surface (mass-less) phenomenon. NFDRS recognized the error, but
no one attempted to fix it before now.
p23 line 3: he wrote “What is FBP FCS?”
This reference has been eliminated.
p23 line 9: after “depth” he wrote “Does this matter for thermally-thin fuels?”
Yes, it matters because the intensity still depends upon the pyrolyzing fuel mass.
p24 line 1: after “flash fuel” he wrote “Or “flash fuel””.
Reconciliation of FCCS Potentials Manuscript -- 43
Corrected.
p26 line 23: after “ratio” he wrote “Why this ratio as opposed to some other? Is this a lean
flammability limit?”
This has been clarified. Not as a lean limit, but as an optimal ratio consistent with Frandsen’s
published data. It is calculated from his original data.
p27 line 3: after “calculator” he wrote “Have these data been published? Can they be
presented here if not?”
No, they have not been published in this form yet – or even fully analyzed. We use an
approximate mean of our extensive data set to supply a preliminary estimate. This will be
published in another context later, but we cannot wait until every approximation is published
before we formulate a new spread model.
p27 line 5: he wrote “Is the assumption of fuel bed uniformity a function of flame depth?
Wilson and Zhou et al looked at M <= 2.5
as a criterion for spread in marginal fuel beds.”
No doubt you are correct. Given the assumption of a quasi-steady state fire spread in uniform
fuels, however, it is not relevant to this paper.
p27 line 21: he wrote “See R.M. Nelson’s papers in Int. J. Wildland Fire re effective windspeed
(for wind and slope). See also paper on reaction time for wind tunnel data in same journal.”
This is now included.
p28 line 16: he wrote “What is
?”
It is the fuel particle volume.
p30 line 8: after “1986” he wrote “Weise, D.R. and G.S. Biging. 1997. A qualitative
comparison of fire spread models that contain wind and slope. Forest Science 43(2): 170-180.
There have been several papers in the International Journal of Wildland Fire on wind effects
from work in EU– Dupuy I think.”
The Weise and Biging citation has been included – thank you for recommending it.
p31 line 6: he wrote “You may want to show how the heterogeneous fuel bed will affect Wilson’s
moisture formulation.”
Good idea for future work; it is beyond our scope in these papers.
p34 line 14: he deleted an “s” changing a word’s spelling to “Frandsen’s”.
Corrected.
Reconciliation of FCCS Potentials Manuscript -- 44
p34 line 15: after “45:1” he wrote “How was this calculated?”
It is the volumetric air:fuel ratio consistent with Frandsen’s 2 data points used to calculate
epsilon at optimum packing ratio.
p35 line 17: he wrote “I presume 45 is somehow related to the air:fuel mixture.”
Correct.
p36 line 20: after “33:1” he wrote “Calculations?”
Because of Frandsen’s experimental technique, it is not absolutely clear whether he observed a
volumetric or mass ratio at optimum packing. It is possible that 33:1 is correct. We chose the
most likely interpretation. It is included here only to provide a future reference when we
complete current ongoing experimental verification of which is correct.
p37 line 20: he wrote “Shouldn’t the intercept be forced through 0? If effective packing ratio =
0, then there is no fuel so LHS should be 0.”
If the function were truly linear, yes. But over the range of values actually possible, a linear
assumption of the (poorly conceived) function is adequate.
p40 line 6: after “0.30” he wrote “Is this too low for living grass?”
It is what Scott and Burgan, and others, use now in applying Rothermel.
p43 line 1: he wrote “Does this apply only to conifer forests?”
No, it applies to all flammable canopies.
p43 line 7: after “2001” he wrote “What about Grishin, Albini, Alexander 1998?”
*** address with Mark on Monday ***
p43 line 17: after “speed” he wrote “Where is wind speed determined – in canopy or above
canopy?”
In the canopy, but we do not consider the canopy to necessarily be continuous.
p43 line 23: he wrote “Where are these defined?”
We have completely revised the crown fire potential in a new manuscript that is based much
more faithfully on previous approaches. You and other reviewers have asked for this
evolutionary development. The result will be a less complete conceptual framework, and a more
incremental improvement on existing models.
Reconciliation of FCCS Potentials Manuscript -- 45
p45 line 9: he wrote “Does Cruz model work? If so, why not use?”
The recent publication by Cruz has been noted in the new revised manuscript on crown fire
potentials. This is interesting work based on empirical data from crown fires, although there are
clearly some inaccuracies and the extent to which empirical regression models can be applied to
a broad range of forest conditions is unclear. We expect that integration of our conceptual
approach with the Cruz regression approach could provide future advances in crown fire
modeling.
p46 line 4: he wrote “How does this approach compare to current approaches?”
We have completely revised the crown fire potential in a new manuscript that is based much
more faithfully on previous approaches. You and other reviewers have asked for this
evolutionary development. The result will be a less complete conceptual framework, and a more
incremental improvement on existing models.
p47 line 12: after “(RAC)” he wrote “Is RAC defined anywhere in terms of what it is
quantitatively?”
This is no longer in the revised formulation.
p48 line 22: he wrote “What is the source of the exponent?”
It is derived from Van Wagner’s original moisture at initiation.
Reconciliation of FCCS Potentials Manuscript -- 46