A probabilistic model of fire ignition and spreading for the xingu headwaters
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A probabilistic model of fire ignition and spreading for the Xingu Headwaters. Rafaella Almeida Silvestrini – UFMG Britaldo Silveira Soares Filho – UFMG Ane Alencar – IPAM, UFL Hermann Oliveira Rodrigues - UFMG Daniel Curtis Nepstad – Moore Foundation/ IPAM Paulo Brando – IPAM, UFL.

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A probabilistic model of fire ignition and spreading for the xingu headwaters

A probabilistic model of fire ignition and spreading for the Xingu Headwaters

Rafaella Almeida Silvestrini – UFMG

Britaldo Silveira Soares Filho – UFMG

Ane Alencar – IPAM, UFL

Hermann Oliveira Rodrigues - UFMG

Daniel Curtis Nepstad– Moore Foundation/ IPAM

Paulo Brando – IPAM, UFL


Mauro Maciel

Motivation why study fire models
Motivation Xingu HeadwatersWhy study fire models?

  • The frequency of fire have been increasing dramatically (Cochrane et al., 1999; Alencar et al., 2006);

  • Forest Fires are a major Brazilian contribution to global warming. (FEARNSIDE, 2002);

  • Reduce forest ability to retain water, exacerbating flooding, erosion and seasonal water shortages. As a consequence, it increases forest flammability (Cochrane et al., 2003);

  • Lead the Forest remnants to a cycle of self-destruction (Nepstad et al., 1998)

  • Aerosols released by forest fires disrupt normal hydrological processes and reduce rainfall;

  • Affects human health.

  • So, fire modeling is important not only to understand fire drivers in the Amazon but also to check what may happen in the future.

Structure of the model
Structure of the Model Xingu Headwaters

  • Simulate the occurrence of hot pixels along the Amazon forest fringe;

    Hot pixels: pixels captured by NOOA-12 night.

  • Based on the hot pixels, simulate fire spreading at the Xingu Headwaters.

    Most of these fires are understory fires.

  • Feedback of fire in the quantity of fuel (biomass) and climate at the Xingu Headwaters.

    CARLUC (CARbon and Land-Use Change Model)

Step 1 modeling hot pixels
Step 1: Xingu HeadwatersModeling Hot Pixels

Part 1 modeling the hot pixels
Part 1: Modeling the hot pixels Xingu Headwaters

  • Spatial Modeling:

    anthropogenic and biophysical variables Spatial Probability

    Weights of evidence – Annual Maps

  • Space-time Modeling:

    climatic variable – VPD (vapor pressure deficit)

    Space-time Probability

    Logistic Regression – Monthly maps

  • Combining the two previous maps A space-time probability map

Only hot pixels within < 5 km from the forests were analyzed

Modeling the hot pixels

Combining the two probability maps
Combining the two probability maps Xingu Headwaters

Final Probability map


α (Anthropogenic Prob.) + (1- α) (Climatic Prob.)

where α is a constant that depends on the month of the year.

Given a high VPD value, hot pixels will concentrate in area of higher anthropogenic activity.

Modeling the hot pixels

Example: August, 2004 Xingu Headwaters

0.4 *

+0.6 *


Modeling the hot pixels

Simulating the hot pixels
Simulating the hot pixels Xingu Headwaters

The simulation is done using 10 steps, each one analyzing 10% of the cells, in each one:

1. There is a hot pixel if:

{Rand(dist)}- γ < Final Prob < {rand(dist)} + γ,


  • rand(dist) = random number from the “dist” probability;

  • γ = constant

    Furthermore, x% of the cells are allocated as null cells.

Control the number of hot pixels

Control the spatial distribution

2. The probabilty map is adjusted: Hot pixels neighboring cells have their probability increased by (1+ Moran Autocorrelation Index for month i)

Modeling the hot pixels

Observed hot pixels – August, 2004 Xingu Headwaters

Simulated hot pixels – August, 2004

Modeling the hot pixels

Validation 2002 2004 2005
Validation (2002, 2004, 2005) Xingu Headwaters

  • ROC Statistic:

    above 0.85 in all months of all years.

  • Fuzzy Similarity:

    Match of 60~70% within a 10 km x 10 km resolution for the dry months.

  • Time series of observed and simulated hot pixels:

    The number of simulated hot pixels was similar than the observed ones and the temporal distribution of the simulated events followed the seasonal tendency. Considering the whole year, the model predicted, in average, 15% more or less than the observed.

Modelagem dos focos de calor

Part 2 modeling fire spreading
Part 2: Xingu HeadwatersModeling fire spreading

Data Xingu Headwaters

  • Fire Scars in Xingu region, mapped by Ane Alencar.

  • Most of them are not detected by satellite – understory fires.

    Is there a relation between these scars and the Hot Pixels?

Relation between hot pixels and understory fire
Relation between hot pixels and understory fire Xingu Headwaters

  • Are the Hot Pixels and fire scars spatially dependent?

    Ripley’s K12 Function

  • Once the observed function is above the confidence envelope (dashed lines), there are evidences (with 99% of confidence) that hot pixels and forest fires are positively spatially dependent.

Probability of spreading
Probability of spreading Xingu Headwaters

  • Probability based on:

    • Distance to a hot Pixel

    • Altitude

    • Water bodies

    • Forest / non forest (<=4Km from the forest)

  • Probability based on the inner VPD For fires outside the forest this Probability is set to 1

Cost Map = fire effort to spread

Weihts of Evidence Probability Map

Fuzzy Function

Monthly Maps

Modeling the hot pixels

The spreading model
The Spreading Model Xingu Headwaters

For each month

Spreading (30)

Cost Prob. Map


Fuzzy Function

Inner VPD

Cellular Automata

Spread Map

Spread Map

Adjust the Probability

(initial map)

Hot Pixels

Calculate the number of neighbors in fire

Wind Map

(initial map)


June, July, August Xingu Headwaters

Validation Xingu Headwaters

Number of Simulated Scars = 1.023 Observed Scars

Considering the Fuzzy similarity we have achieved a match of 50% in a window of 9 km.

Part 3 coupling carluc and the fire model
Part 3: Xingu HeadwatersCoupling CARLUC and the Fire model

Foto: Antonio Ruano.

Carluc items
CARLUC Items Xingu Headwaters

  • Based on NPP, decomposition and mortality functions.

  • Disturbances: Deforestation, Logging and Fire.


Wood Debris


Wood Products





Fine Litter


Mortality rates
Mortality rates Xingu Headwaters

Conclusions Xingu Headwaters

  • Satisfactory validation results concerning the hot pixels model, considering both spatial and temporal distributions.

  • The probability map (hot pixels) is well fitted, so it can be useful on monitoring the occurrence of these events at the Amazon.

  • Anthropogenic variables, such as distance to town centers, roads, protected areas, etc – play an important role when talking about fire in the Amazon, where fire is not only a natural event.

  • Spreading model also showed good results once its spatial and temporal distribution were satisfactory.

  • Besides obtaining the extension of the areas that can be burned, the spreading model is important because given a hot pixel it is possible to be attentive to the areas that are more prone to the spreading of the hot pixels, mainly the understory fires, that the monitoring satellites can not easily capture.

  • Next step: finish CARLUC calibration so that the coupled model (fire, CARLUC) can give an estimative of the forest feedback on fire on the next 50 years.

Obrigada thank you


Obrigada/Thank you

Rafaella Almeida Silvestrini – UFMG

[email protected]

References Xingu Headwaters

  • Cochrane, M.A. 2003. Fire science for rainforests. Nature 42: 913-919.

  • Marengo, J. et al. The drought of Amazonia in 2005. Journal of Climate, 2006 (Submetido).

  • FEARNSIDE, Philip M.. Fogo e emissão de gases de efeito estufa dos ecossistemas florestais da Amazônia brasileira. Estud. av.,  São Paulo,  v. 16,  n. 44,  2002.  Disponível em: <http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-40142002000100007&lng=en&nrm=iso>. Acesso em: 08  June  2007.  Pré-publicação.

  • SISMANOGLU, R.A.; SETZER, A.W. Risco de fogo da vegetação na América do Sul: comparação de três versões na estiagem de 2004. Anais XII Simpósio Brasileiro de Sensoriamento Remoto [online], Goiânia, GO, p. 3349-3355, 16-21/Abr/2005. [acesso em 24 de maio de 2007]. Disponível em: http://www.cptec.inpe.br/queimadas/documentos/pub_queimadas.pdf

  • Soares Filho, B.S. 2006. Dinamica project. Disponível em <http://www.csr.ufmg.br/dinamica> Acesso em 3 set. 2006.

  • Bonham-Carter, G., 1994: Geographic information systems for geoscientists: modelling with GIS. Pergamon, 398 pp.