Methodology to obtain isochrones from large wildfires

F. Manzano-AgugliaroA,B,D, J. Perez-ArandaA and J. L. De La CruzC

ADepartment of Engineering, University of Almeria, Escuela Superior de Ingenierıa,

Universidad de Almerıa, La Canada de San Urbano, E-04120 Almerıa, Spain.BBITAL (Research Center on Agricultural and Food Biotechnology), University of Almeria,

La Canada de San Urbano, E-04120 Almerıa, Spain.CDepartment of Applied Physics, University of Cordoba, Campus de Rabanales,

Edificio Albert Einstein (C2), Carretera de Madrid, Km 396, E-14071 Cordoba, Spain.DCorresponding author. Email: fmanzano@ual.es

Abstract. In Mediterranean countries, a change in traditional uses of land has caused an increase in both the number offires and the land area affected by fires. This situation creates a need to improve the efficiency and effectiveness of wildfire

extinguishing devices. This improvement should be based on knowledge of the fire behaviour of various fires affectingsimilar areas. To study these fires, we considered a methodology to obtain isochrones at different stages of a wildfirethrough temporal georeferencing of aerial fire photographs. This methodology was applied to two large wildfires (1098

and 4609 ha) that occurred in 2009 in the south of Spain. A total of 463 and 611 photographs were considered torespectively obtain seven and nine isochrones. These isochrones are representative of the development of the fires. Inperiods of greater intensity, this study exhibits a rate of propagation much higher than expected, reaching 7.8 hamin�1 of

burned surface and 160.0mmin�1 of perimeter growth in one example, whereas if we considered only the final perimeterof the fire, the speed of burned perimeter generation would be 28.2mmin�1 and of burned surface, 2.4 hamin�1.

Additional keywords: aerial photography, georeferencing, isochrone, rate of spread, wildfire.

Received 2 March 2013, accepted 12 December 2013, published online 8 April 2014

Introduction

Wildfires have existed since combustible vegetation first

appeared on Earth’s surface. Fire plays a vital role in thestructure and dynamics of Mediterranean ecosystems (Gill et al.1981; Trabaud 1987). Fire is one of the primary ecological

factors giving rise to the mosaic that characterises the landscape(Nunez et al. 2008); in short, fire is the manager of the Medi-terranean landscape (Grillo et al. 2008).

Controlled fires have often been used as a tool for landmanagement, and small problems occasionally have beencaused by agricultural burning accidents or lightning. In recentyears this has become a significant issue for human safety, as the

frequency and intensity of these events has increased dramati-cally (Moreno et al. 1998; Pausas and Vallejo 1999). Fires thatbehave differently from historical norms have become major

environmental problems for many regions. This increased levelof hazard is primarily due to two factors: an accumulation ofbiomass in areas that were previously cultivated or grazed but

are now unmanaged (Gardner et al. 1987; Turner et al. 1989)and fire suppression as a land management tool (Platt andSchoennagel 2009). In this sense, changes in land cover in

recent decades have been identified as amajor driver of fires andarea burned in Mediterranean countries, and a primary cause offorest disturbance (Trabaud 1981; Le Houerou 1987; Rego1991; Moreno et al. 1998). Large wildfires (LWF) – those

exceeding 500 ha – may affect urban areas, as well as forest land.The wildfire problem therefore becomes more than purely

environmental; it becomes a matter of civil protection.Thus, it is necessary to analyse the behaviour of fires by

integrating different variables that affect the development of the

fire – such as the amount of fuel (Rothermel 1972, 1983; Albini1976), the topography (Rothermel 1983; Kushla and Ripple1997) or weather conditions (Pereira et al. 2005) – using spatial

analysis tools such as Geographic Information Systems (GIS).This information will help us to predict the behaviour of futurefires (Catry et al. 2009). For fire managers, knowledge of firebehaviour in a given area under similar weather and vegetation

conditions is an important tool for predicting the development offuture fires (Albini 1976). Forest fire managers are aware thatfire growth typically occurs on a small number of days when the

burning conditions are conducive to fire spread (Podur andWotton 2011). However, because the same fire managermay not face a similar fire in a similar area more than once in

his working life, it is important to analyse and record firebehaviour such that future fire managers may capitalise uponthe experience.

To date, analyses of fires have extrapolated fire behaviourfrom their final signatures, as defined by the shape of theperimeter and the damage caused by the fire (Grillo et al.

2008), which are determined a posteriori by a GPS survey of

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International Journal of Wildland Fire 2014, 23, 338–349

http://dx.doi.org/10.1071/WF13166

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the burned area. This definition provides an overall idea of thefire’s behaviour; however, this impression could be misleading

if, during the spread of the fire, there were changes in its maindriving force, such as alterations in topography or wind speedand direction. The final perimeter of the fire allows us to

calculate the average values of the fire’s spread, but it tells usnothing regarding the parameters of its spread during periods ofhigher intensity, or the influence of fire control actions on the

final perimeter. Grillo et al. (2008) propose a classificationbased on the rate of spread (ROS) for wildland fires (Table 1).

To advance understanding of fire behaviour, which can vary

during the fire’s active period, it would be ideal to know everydevelopment stage from the time of ignition. This informationcannot be obtained with certainty but can be approximated byusing isochrones to delimit arbitrary periods throughout the fire

progression; such a task requires graphical documentation.The most important information is the position of the fire

front at various times (Alexander and Lanoville 1987). The

importance of documented case studies of wildfires has beenrepeatedly emphasised by both fire managers and fire resear-chers (Luke and McArthur 1978). Many case studies have

proven their value as training aids and as sources of researchdata (Chandler 1976). There are many examples in Canada, theUnited States and Australia where fire researchers haveobserved and documented the behaviour of wildfires with

various data collection methods and monitoring equipment(Alexander and Lanoville 1987).

There are examples in the literature of wildfire analyses based

on the location of the flame front at different time steps. In thecase of a wildfire near the town of Hay River, North-westTerritories (Canada) in July 1981 (Alexander and Lanoville

1987), repeated mapping from the air revealed a maximumaverage spread rate of 34.9mmin�1 over a 2-h period. In anotherCanadian wildfire near Brereton Lake, Manitoba (Hirsch 1989),

the position of the fire front was observed at intervals by firemanagers in helicopters. Front positions were recorded orally bythe helitac officer to calculate the ROS. In the first period, theROS was 23.3mmin�1 (high propagation) from the time of

detection of the fire (1540 hours) until 1753 hours. A finalexample (27–29 August 1985) is the Butte Fire on the SalmonNational Forest in Idaho, USA (Rothermel and Mutch 1986),

where isochrones were reconstructed from photographs andvisual observations, and there were moments when the ROS roseas high as 93.3mmin�1. These estimates were all based on visual

observations of workers at the time of the fire, but none of theminclude a technical methodology.

It is important to obtain vertical aerial photography of the firearea relatively soon after the fire starts, especially in areas

vegetated with shrubs or grasses. This is often a very useful toolto carry out case study research (Alexander and Thomas 2003).A spatially explicit fire model, FARSITE (Fire Area Simulator)

(Finney 1994; Finney 1998), has been widely calibrated in theUSA, efficiently producing spatial maps of fire growth andintensity (Finney and Ryan 1995). In some northern Mediterra-

nean regions, the local administration is using FARSITE as atool to improve wildland fire analysis and to predict conse-quences of fuel management options on fire growth (Molina and

Castellnou 2002). Further validation of the model in Mediterra-nean conditions and for real fires is needed (Arca et al. 2007).

In Mediterranean wildfires, studies are based on the final fireperimeter andonmodellingof thedevelopment of the fire through

simulators such as FARSITE. For example, Duguy et al. (2007)conducted a simulation of the Ayora Valencia fire in July 1979.Based on this, they modelled the effects of potential prevention

measures and evaluated the potential efficacy of these measuresin a real fire. Similarly, Arca et al. (2007) used FARSITE tosimulate fires in northernSardinia (Italy) between2004 and2006;

for the Budoni fire of 26 August 2004, they compared thesimulated with observed ROS at different times, but did notexplain how these real intermediate isochrones were obtained.

Havingdata fromdifferent periods of fire growthallowsa real andeffective adjustment of simulators such as FARSITE.

There is great potential for the use of satellite images instudying wildfires. Some high-resolution satellite images that

could be useful for this type of study are Quickbird (0.61m),Ikonos (1m), Spot (2.5m) and Landsat (15m). However, noneof these offer an appropriate temporal resolution for the study of

fire isochrones. In contrast, satellite platforms with an appropri-ate temporal resolution, such as Meteosat (30min), do not offera spatial resolution suitable for this type of analysis. In short, due

to temporal or spatial resolution, or simply economic limita-tions, available satellite imagery is not suitable for these types ofstudies. The objective of this study is to consider a methodologyto obtain wildfire isochrones based on the use of conventional

photographs taken from fire control aircraft.Currently in Spain, designated airborne personnel are

required to take photographs of the fire throughout the time

they are overhead. In this study, the Fire Prevention andSuppression Plan of Andalusia (INFOCA), implemented bythe INFOCA Provincial Operation Centre (COP) was applied

in the cases of two large fires in the province of Almeria in 2009.The territory of Andalusia has 4 658 105 ha of forested land,

covering 53% of the total region. Andalusia provides environ-

mental protection for 24 natural parks and 2 national parks. TheINFOCA plan protects 2.8� 106 ha from fire. In the province ofAlmeria in 2009, a total of 123 fires, 4 of which were LWFs,burned 9605 ha (see Fig. 1). All fires occurred under extreme

weather conditions and behaved in a manner that exacerbatedthe fire’s rate of spread, occasionally reaching extreme rates inexcess of 33mmin�1 (Grillo et al. 2008) and outpacing the

capacity of extinguishing efforts.Fires behave similarly in areas with similar vegetation, topo-

graphical characteristics, and meteorological conditions. The

LWFs that occurred in south-east Spain (Fig. 1) in 2009 exhibitedsimilar behaviour during days in which the extreme weatherconditions were similar. Furthermore, these fires re-burned areasdevastated by LWFs in 1994 and 1999, again under similar

Table 1. Classification based on the rate

of spread (ROS) (Grillo et al. 2008)

ROS (mmin�1)

Low ,0.5

Medium 0.5–2

High 2–33

Extreme .33

Obtaining isochrones from large wildfires Int. J. Wildland Fire 339

weather conditions. Therefore, episodes with similar character-istics are likely to be repeated in the future and as such, we mustdevise effective plans of attack based on past experience.

Materials and methods

Aerial methods

In Andalusia, INFOCA has an aircraft system covering the entirearea of the region at risk of wildfire. Types of aircraft included in

the INFOCA plan are described in Table 2. Some are devotedexclusively to suppression, including extinguishing helicopters(HEs), amphibious aircraft (AA) and land-based cargo planes

(ACTs); some, such as transport and extinguishing helicopters(HTEs), are devoted to both personnel transportation and sup-pression; and others, such as coordination aircraft (AC), arededicated to logisticalmanagement.Ondayswhen there aremore

than four aircraft at a time on awildfire, aACmust organise them.In 2010 inAndalusia, INFOCAhad at its disposal 38 aircraft: twoAA, seven ACTs, three AC, 22 HTEs and four HEs. When a

forest fire of any size occurs, a helicopter with a wildfiremanager

and seven wildfire firefighters attends automatically. The firstmanager to arrive evaluates the fire’s severity and requests the

requisite aerial methods and other resources. For example, in theNijar fire (fire 2009040044), a total of six HTEs, two HEs, twoAA, three ACTs and two AC were employed.

Photographic methods

Operations Technicians (TOPs) carried by HTEs or AC areresponsible for photographic reports of the fire’s development.

A priori photographs taken by the TOPs in a AC are particu-larly useful because of the flight altitude (600–900m) of theseaircraft (Sociedad Aeronautica Peninsular 2007) and the

unhampered ground visibility they provide due to their wingsbeing embedded at the top of their cabin (Consejerıa de MedioAmbiente 2003). Moreover, the AC TOPs remain in the aircraft

and thus have the ability to take photographs at every giveninterval of time, covering most or all of the fire, if it is not large.In contrast, the TOPs in the HTEs disembark with the SpecialistGroup when arriving at the fire to conduct operational tasks, and

are therefore only able to take photographs for a limited time.A 5-megapixel digital camera taking photographs of the

ground at an altitude of 900m can obtain a spatial resolution of

less than 1m; the temporal resolution is unlimited, given that thephotographer’s task is to take as many images as possibleprovided that the conditions for the flight are appropriate. If so,

the circumstances and methods used to take photographs takenfrom INFOCA aircraft determine their suitability for developingisochrones. To facilitate image classification for georeferencing

in this stud, the internal clocks of the cameras were synchronised.

555109846092642

28-Jun-200929-Jun-200914-Jul-200928-Jul-2009

Date Area (ha) Map colourSorbas

NijarTurre

Mojacar

Municipality

Fig. 1. Large wildfires in the province of Almeria (Spain) in 2009.

Table 2. Types of aircraft attached to the INFOCA plan

Type of aircraft Abbreviation TOP on board

Transport and extinguishing helicopter HTE Yes

Extinguishing helicopter HE No

Coordination aircraft AC Yes

Cargo plane on land ACT Yes

Amphibious aircraft AA No

340 Int. J. Wildland Fire F. Manzano-Agugliaro et al.

Approach

The base information consists of conventional aerial photo-graphs that have not been georeferenced nor have undergoneany sort of geometric correction. A series of steps are necessary

to use them to define isochrones.

Procurement of photographic fire reports

In the days following fire in Almeria, photographs taken during

wildfire suppression efforts are submitted from bases with air-craft to the COP,mainly those with HTEs andAC equippedwithTOPs; although any photograph taken from an aircraft by its

pilot, co-pilot, or technician, or even any INFOCA employee onthe ground, can contribute to determination of the fire status at agiven time. Large numbers of photographs are taken by

INFOCAduring large fires, but the percentage that are useful forthe development of isochrones is small (Table 3). Initially, anyphotographs whose time of creation is uncertain are discarded.After this, we select those photos that will be useful for our

purposes.

Selection and classification of photographs

Once the photographs are received by COP of Almeria, the

potentially useful photographs are selected to define the peri-meter of the fire at its various phases. A large number are notsuitable as they were taken in emergency situations in which the

TOP was under a high degree of stress and was occupied withseveral tasks at once. As an example, Fig. 2 shows two photo-graphs taken in the same minute from a AC: one is useful for

determining the fire perimeter, whereas the other is not due to

heavy smoke obstruction. A northern aspect greatly facilitatesgeoreferencing, especially for images obtained from the AC.Photographs taken facing north match up well with the orienta-

tion of the planimetry and avoid backlighting that might ruin theimage.

In fires with high ROS, even a 2-min time difference can be

too great to consider photos to be simultaneous. The selectionprocess is therefore highly specialised and depends on both thetype of fire being analysed andwhether there is a large change in

fire perimeter from one image to the next; this differencedetermines whether two photographs will be included in thesame period. Correct classification and selection of appropriatephotographs is integral to determination of the isochrones of

the fire. A similar proportion of photographs was selected forisochrone determination from two fires (Nijar fire 2009040044:42 of 463 photographs; Turre fire 2009040055 in: 61 of 611

photographs) (Table 3).Once the photographs are selected, temporal classification is

conducted by hour. As a general rule, as the fire increases in size,

more photographs are needed to define the perimeter at a givenmoment (Tables 4, 5). However, this requirement is not absolute

Table 3. Numbers of photographs taken and selected from the fires

that are the objects of this study

Fire Municipality Photographs taken Photographs selected

2009040044 Nijar 463 42

2009050055 Turre 611 61

(a) (b)

Fig. 2. Photographs taken from the coordination aircraft in the Nijar fire at 1455 hours: (a) selected photograph, (b) discarded photograph.

Table 4. Selected photographs and area covered by the isochrone for

fire 2009040044 in Nijar

Time of

isochrone

Total number

of photographs used

in the determination

of the isochrone

Type

of aircraft

Area covered

by the isochrone

(ha)

1350 – Beginning

1410 1 AC 9.79

1438 9 HTE 24.35

1455 7 AC 33.05

1630 10 AC(9)/HTE(1) 206.58

1730 9 AC 377.28

1900 6 AC 523.13

Final

perimeter

Measurement

with GPS

1098.26

Obtaining isochrones from large wildfires Int. J. Wildland Fire 341

because a photograph taken from a AC covers a much greatersurface area than one taken from an HTE. Moreover, as isevident in Table 5, it was impossible to complete the Turre fire

isochrones at certain times from aerial photographs alone, due tothe great cloud of smoke covering the fire; information from theground (photographs, observations) was therefore necessary.

For the times 1520, 1715 and particularly 2115 hours, thegeoreferenced photographs only allow partial determination of

the isochrone, as there were no aircraft in the area at that timeand only two photographs from the AC were appropriate.

Georeferencing photographs

The next step for the establishment of isochrones is geor-eferencing the photographs. For this purpose, the software

ArcGIS 9.3 was used with two reference layers: orthophotosof Andalusia and 1 : 10 000 topographic maps. Given that thecoordinates of the fire starting point are known, it is easy to

locate the cartographic sheets corresponding to the area. Subse-quently, the photograph to be georeferenced is introduced andthe ground control points (GCPs) for the georeferencing areselected. TheGCPs are physical pointswith appearances that are

unchanged between the dates of creation of the orthophoto andthe fire photo – in this case, between 2007 and July 2009 – andare easily identifiable (Biasion et al. 2006). The GCPs can be

crossroads, paths, buildings, well-identified trees and so on.(Alasalmi et al. 1998). Once they have been recognised in thefire photograph, their equivalent points in the orthophoto are

located. Fig. 3 shows an example of the selection of these points.Fig. 4 shows the photograph once it has been georeferenced tothe orthophoto being used as a cartographic base. Table 6 shows

an example of the quality of the georeferencing using a 1st orderpolynomial transformation with an average root mean square(RMS) of 5.6m. If a GCP with a high error ratio was detected, itwas eliminated to avoid distortion of the image and damage to

the final georeferencing result.Depending on the number of control points obtained from the

georeferencing table, a 1st, 2nd or 3rd order transformation can

Table 5. Selected photographs and area covered by the isochrone for

fire 2009040055 in Turre

Time of

isochrone

Total number

of photographs used

in determination

of the isochrone

Type

of aircraft

Area covered

by the isochrone (ha)

(proportion performed

with georeferenced

photographs)

1147 – Beginning

1230 1 HTE 0.2414 (all)

1340 2 HTE 0.5818 (all)

1400 1 AC 7.84 (all)

1520 1 AC 159.25 (1/3)

1715 4 AC 997.91 (1/3)

2115 2 AC 2819.49 (1/10)

Final

perimeter

50

(FINAL

PERIMETER

FLIGHT)

HTE 4609.21 (all)

Fig. 3. Example of possible ground elements to be used as control points. Photograph taken by the AC in fire

200904044 in Nijar at 1455 hours on 28 June 2009.

342 Int. J. Wildland Fire F. Manzano-Agugliaro et al.

be conducted. Due to the fact that photographs have no coordi-nates, they are translated and scaled into a map using two least-square equations. Depending on the number of GCPs, different

polynomial transformations can be conducted (Fallas 1999;Hughes et al. 2006; Xu and Gao 2008):

1) Linear (1st order): minimumof three points but, optimally, atleast six to achieve a good adjustment. This is the recom-mended transformation. In this study, a maximum RMS of

10mwas established as an acceptable fit, although it was notthe only indicator used to make a decision.

2) Quadratic (2nd order): minimum of six points but, optimally,

at least 12 to achieve a good adjustment. This equationmagnifies the error in the control points and, therefore,should only be used when the 1st order equation gives an

unacceptable adjustment.3) Cubic (3rd order): minimum of 10 points but, optimally, at

least 20 to achieve a good adjustment. This equation mag-nifies the error in the control points and, therefore, should

only be used when the 1st or 2nd order equations give anunacceptable fit.

Once the transformation is chosen, the reliability of thegeoreferencing, expressed by the RMS error, should beobserved. In the methodology, a minimum RMS has been

established. However, sometimes with a high RMS, georeferen-cing has been useful to create at least one sector of the isochrone.Therefore, the analyst should decide whether georeferencing is

acceptable on the basis of both the RMS and the aspect of thegeoreferenced image with respect to the reference orthophoto.

A 1st order transformation shifts the image up, down, right or

left, stretches or compresses the image, or rotates the image.Finally, once georeferencing of the image is accepted, theperimeter is digitised for the moment in which the image wastaken (Fig. 5). This process is repeated with all of the photo-

graphs selected for that time period, and it is repeated for thedifferent periods of the fire.

Results

The results obtained after the process described above are the

isochrones at different periods of the fire. This methodology hasbeen applied to two LWFs in the province of Almeria: Nijar and

Fig. 4. Photograph georeferenced in ArcMap over the orthophoto.

Table 6. Georeferencing table with list of GCPs and the chosen transformation

This georeferencing is performed to produce the isochrone at 1455 hours for fire 2009040044 in Nijar. Every link has a point in the photograph and its related

point in the map

Link X Source Y Source X Map Y Map Residual

1 660.278836 �754387269 573109.557731 4093361.067008 5.91889

2 2030.875042 �1115.305275 573751.846842 4093176.503701 5.46290

3 1414.639260 �1067.692647 573457.889323 4093198.578484 4.79700

4 1855.626017 �871.399696 573693.086348 4093321.391271 7.30799

5 1324.710516 �927.477697 573422.522887 4093283.076183 5.55163

6 1403.220737 �527.758515 573486.136758 4093527.667189 4.11599

Transformation: 1st order polynomial Total RMS Error: 5.61332

Obtaining isochrones from large wildfires Int. J. Wildland Fire 343

Turre. Figs 6 and 7 present the isochrones for the fires, in which

the starting point has also been marked, and they have beensuperimposed on to 1 : 25 000 cartography. These results,combined with a previous climatic study of the same fires and

vegetation and topographical surveys of the respective areas,present enormous potential for analysis. The stages involved inthe analysis are as follows.

Analysis of fire spread

1) Direction of fire spread according to its main driving force.For example, the main driving force of the Turre fire duringdaytime on 14 July was the south-westerly wind; on 15 July,it was the topography in the early morning and the easterly

wind during the day.2) Calculation of spread parameters by time period. Knowing

the exact location of the fire in each period, we can calculate

its ROS (the values reported represent the maximum ROS,i.e. the ROS of the fastest moving point of the fire front) andgenerate its perimeter, for example, both from the beginning

of the fire and between periods, as seen in Tables 7 and 8 . Forthe Turre fire (Table 8), if we only consider the final fire, theperimeter growth rate would be 28.2mmin�1, the speed of

burned surface area would be 2.4 hamin�1 and the ROSwould be 4.36mmin�1. However, spread in the periods ofgreater intensity reached far higher values, such as a perime-ter growth rate of 160.0mmin�1 and,7.8 hamin�1 surface

area burned between 1900 and 2115 hours, and a29.77mmin�1 ROS between 1520 and 1715 hours. For theNijar fire (Table 7), if we only consider the final perimeter of

the fire, the perimeter growth rate would be 35.47mmin�1,the burned area growth rate would be 0.95 hamin�1 and the

ROSwould be 6.40mmin�1, but the spread in the periods of

greater intensity reached higher values: 97.28mmin�1

perimeter growth rate between 1630 and 1730 hours,2.87 hamin�1 surface area burned in the same period and

20.95mmin�1 ROS between 1455 and 1630 hours.3) Once we know the weather conditions at each time, we can

use GIS to determine the ranges of slopes and fuels that were

affected and thereby estimate the linear intensity of the flamefront. We are thus able to determine the percentage by whichthe expansion of the fire exceeded the capacity of the firecontrol efforts. We use the concept ‘exceeding the capacity

of the fire control efforts’ when a fire is spreading with suchhighROS, intensity, flame length or crown fire activity that itis not possible to extinguish them. The threshold values at

which fire exceeds the capacity of the fire control efforts arenormally established by the Fire Prevention and SuppressionService, but we use (as established by Grillo et al. 2008)

flame length.3m, ROS.2 kmh�1 (0.55m s�1) and crownfire area. passive crown fire area.

The subdivision of the final surface area into intermediatesections enables us to adjust the simulation models of firebehaviour to the real data. BEHAVE software (Andrews 1986)

was used for calculating the different parameters (intensity andflame length).

If we relate the variables shown in Table 7 and 8 tometeorological, topographic and vegetation variables in each

period, we obtain important information about the spread andbehaviour of the fire in that period. This information can beintegrated into various wildfire simulation software programs,

such as BEHAVE, FARSITE and FLAMMAP (Finney 2006),to calculate such factors as rates of spread and flame lengths.

Fig. 5. Isochrone at 1455 hours of fire 2009040044 in Nijar, digitised over photograph taken by AC.

344 Int. J. Wildland Fire F. Manzano-Agugliaro et al.

This approach makes it possible to assess the operationalperformance of the fire control efforts for each fire and thus todesign more effective action plans for future situations.

Analysis of spot fires

Spot fires are one of the more worrying and important aspects of

fighting wildfires: first, for security reasons, as they are a maincause of entrapment accidents; second, because the occurrenceof spot fires is an important factor contributing to increased fire

spread rates (Lee et al. 2004). Using this method, it is possible tomeasure spotting distance depending on the type of fire and todemonstrate the generation of spot fires for those fires in which

the phenomenon was observed, which was previously difficultto quantify. This demonstration is achieved because spot firescan be observed in aerial photographs from the moment of

ignition, which requires photos to be taken continuously and athigh frequency. This is made possible by the continued presenceof AC in the area as specified in the INFOCA plan. In our study,this phenomenon occurred during the Turre wildfire (Fig. 7) for

the 1715 hours isochrone: three spot fires were observed on thenorth side at distances of 170–210m ahead of themain fire front.

Evaluation of fire control efforts

Fire perimeter growth occurs in every direction at variousspeeds. From the lengths of these perimeters, worker perfor-mance can be easily calculated by knowing each worker’s timeand working area. These data are extremely valuable for effi-

cient management of fire suppression resources in future fires.Inactivity at parts of the perimeter between two consecutiveperiods may have little to do with worker performance, because

the back of the fire (facing into the wind) burns slowly or maynot move at all. In contrast, the degree of forward spread woulddepend not only on the worker but also on wind speed and

direction, slope, aspect and fuels. However, even where the fireis inactive, workers continue to check the perimeter.

This method can help evaluate the performance of fire

control efforts at an internal level, regarding both fire behaviourand the operations and movement of assets. This method istherefore useful in planning future improvements.

Simulation of alternative fire control plans

It is necessary to assess actions performed during the fire andcreate alternative plans a posteriori to improve the effectiveness

perimeter 1410

Legend(Isochrones)

perimeter 1438

perimeter 1455

perimeter 1630

perimeter 1730

perimeter 1900

final perimeter

FIREORIGIN

Fig. 6. Isochrones of fire 2009040044 (Nijar 29 June 2009).

Obtaining isochrones from large wildfires Int. J. Wildland Fire 345

perimeter 1400

Legend(Isochrones)

perimeter 1520

perimeter 1715

perimeter 1900

perimeter 2115

perimeter 0900

final perimeter

FIREORIGIN

Fig. 7. Isochrones of fire 2009040055 (Turre 14 July 2009).

Table 7. Variables describing the spread of the fire over time between isochrones studied for fire 2009040044 in Nijar

Date Time Surface

(m2)

Perimeter

(m)

Burned area growth rate

(m2min�1)

Perimeter growth rate

(mmin�1)

Rate of spread

(mmin�1)

28-Jun 1350 0 0 0 0 0

28-Jun 1410 97906 1522 4895.30 76.10 20.40

28-Jun 1438 248416 3643 5375.60 75.75 12.21

28-Jun 1455 322445 4615 4354.64 57.17 10.58

28-Jun 1630 2065806 12813 18351.17 86.29 20.95

28-Jun 1730 3792933 18650 28785.45 97.28 19.33

28-Jun 1900 5305762 20971 16809.21 25.78 14.44

29-Jun 0900 10982400 40789 6757.90 23.59 2.36

346 Int. J. Wildland Fire F. Manzano-Agugliaro et al.

and efficiency of fire control methods. This allows us to assessthe state of the fire when it was discovered and its characteristics

during each period. Through reports and meetings of the tech-nical team, we can propose alternative attack plans and thusdetermine whether other actions would have been more effec-tive. In this sense, fire simulators such as FARSITE can be used

to verify the different alternatives.As part of the constant effort to improve the methodology of

this type of analysis, which is integral to fire control systems,

INFOCA already uses a possible alternative solution to acommon problem with aerial photographs: smoke that preventsviewers from seeing the fire front line. A solution would be to

incorporate forward-looking infrared (FLIR) cameras that havebeen used in fire suppression for many years such that smoke atthe active fire front does not pose a problem for the subsequentestablishment of the isochrone. Although these technologies

already exist, including those that automate the georectification,mosaicing and digitising of images, they are much more expen-sive than those used in the present study.

Discussion

Alexander and Lanoville (1987) demonstrated the importance ofisochrone development by periodic observations of fire devel-opment. These researchers considered this observation an

essential step in the analysis of wildland fires, as it allows us toknow exactly how each fire develops. Alexander and Thomas(2003) noted the value in documenting not only a fire’s progressand behaviour but also fire suppression activities. Considering

only the final perimeters, according to Table 1 (Grillo et al.

2008), many fires with average speeds of propagation would beconsidered moderate, such as those analysed by Duguy et al.

(2007) in Valencia (Spain) with an average ROS of 1.8mmin�1;however, the FARSITE simulation results revealed high prop-agation situations (28.0mmin�1) in certain areas of the fire.

This finding highlights the importance of the methodologyproposed in this paper. Arca et al. (2007), in their study of theBudoni fire (Italy) in August 2004, obtained similar resultswith an average propagation speed of 8.1mmin�1, whereas

the maximum simulated speeds (also by FARSITE) were10.3mmin�1 – both high values of ROS. However, these esti-mates are simulations without real data on intermediate stages

of fire propagation. This finding highlights the need for inter-mediate data on fire spread.

In our study, average ROS was ,4.4mmin�1 for the Turrefire and 6.4mmin�1 for the Nijar fire, whereas the maximum

observed ROSwas,29.8mmin�1 at Turre and,20.9mmin�1

at Nijar. Both fires had high ROS (according to Grillo et al.

2008) at certain times that could not be observed only byknowing the final perimeter of the fire. These intermediate fire

parameters are in line with other studies that analysed time stepsof fire spread: for example, a maximum ROS of 34.9, 23.3 and93.3mmin�1 was recorded by Alexander and Lanoville (1987),

Hirsch (1989) and Rothermel and Mutch (1986). All threestudies demonstrate the intermediate propagation speeds offires, but they are all based on the intervals set visually, rather

than with a measurement methodology.

Conclusions

Based on the selection, classification, georeferencing and digi-tisation of conventional aerial photographs taken during firesuppression efforts, the proposed method is effective in

obtaining the isochrones for narrow time intervals in largewildfires. At present, this method is the only technically andeconomically viable approach for determining the evolution of

wildfires and thus predicting behavioural patterns in the analysisof subsequent wildfires.

The importance of synchronisation of the cameras used in

these studies was highlighted. Georeferencing of aerial photo-graphs is a laborious process when a large wildfire is involved.Only ,10% of the photographs taken from aircraft were usedand the synchronisation in date and time of the various cameras

was important in studying the evolution of the fire. Photographstaken facing north were particularly useful, as they avoidbacklight effects.

Using thismethod, it is possible to calculate the realROSof thefire and demonstrate the generation of spot fires for fires in whichthey occur. This and other important aspects had previously been

difficult toquantify.This studyhighlights that in periods of greaterintensity, there have been spread ratesmuch higher than expected,reaching 29.8mmin�1 ROS, 7.8 hamin�1 burned surface and160.0mmin�1 perimeter growth rate in the Turre fire, for exam-

ple. If we considered only the final perimeter of the fire, the ROSwould be 4.4mmin�1, the perimeter growth rate, 28.2mmin�1,and that of the burned surface area would be 2.4 hamin�1.

Calculating the perimeter of the fire over time and adding adetailed weather, topographic and vegetation survey enables a

Table 8. Variables describing the spread of the fire over time between isochrones studied for fire 2009040055 in Turre

Date Time Surface

(m2)

Perimeter

(m)

Burned area growth rate

(m2min�1)

Perimeter growth rate

(mmin�1)

Rate of spread

(mmin�1)

14-Jul 1147 0 0 0.00 0 0

14-Jul 1230 2414 294 56.14 6.84 2.07

14-Jul 1340 5818 434 48.63 2.00 1.19

14-Jul 1400 78414 1498 3629.80 53.20 23.80

14-Jul 1520 1592586 6238 18927.15 59.25 21.36

14-Jul 1715 9979133 15007 72926.50 76.25 29.77

14-Jul 1900 18195013 22598 78246.48 72.29 20.47

14-Jul 2115 28194942 44249 74073.55 160.37 14.81

15-Jul 0900 44461528 52025 23073.17 11.03 4.54

15-Jul 1930 46092128 53658 2588.25 2.59 0.95

Obtaining isochrones from large wildfires Int. J. Wildland Fire 347

muchmore in-depth analysis of the behaviour of the fire at everymoment. Therefore, this approach also allows the analysis ofminute details, which offer valuable and necessary information

regarding both the behaviour of the fire and the fire controloperations, such as the movement of the flanks and fronts at agiven time. The evolution of the signature of the fire can be

analysed at different stages at a level far beyond final perimeter-based analyses, even allowing estimation of the percentage ofsurface area that exceed the capacity of fire control efforts in

each period.

Acknowledgements

We thank the Fire Prevention and Suppression Plan ofAndalusia (INFOCA),

specifically the INFOCAProvincial Operation Centre (COP) in the province

of Almeria for providing us the data for this manuscript.We are also grateful

to Beatriz Duguy (University of Barcelona) for her valuable information.

Finally, we are grateful for the support of BITAL – Centro de Investigacion

en Biotecnologıa Agroalimentaria (University of Almeria).

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