Wildfires in Florida

David T. ButryUS Forest Service

Marcia L. GumpertzNorth Carolina State University

Marc G. GentonTexas A&M University

Funding provided by USDA Forest Service

Study Site:SJRWMD

From 1996-2001:

•7249 small wildfires

•Arson—25%

•Accidents—43%

•Lightning—32%

•53 large wildfires

•Arson—17%

•Accidents—28%

•Lightning—55%

Size Distribution of Fires in SJRWMD 1981-2001

Large Wildfires Small Wildfires

Wildfire Models• Wildfire modeled as a function of:

• Fuel type, fire cause, time, location • Climate and weather at time of ignition• Prescribed burning, time to respond to fire• Landscape attributes, previous fire

• Three models estimated:• Area burned. Fires 1000 acres or less• Area burned. Fires >1000 acres• Probability that a fire becomes larger than 1000

acres.

• Fire Characteristics (XF): • Start time• Start year • Cause

• Climate/Weather (XC):• Niño3 • KBDI • Spread Index• Buildup Index• Humidity • Wind speed • Wind direction

• Management (XM): • Response time • Limited action fires • Prescribed fire

• Includes current and lagged values, as well as neighboring current and lagged values

• Landscape Characteristics (XS): • Population density • Income • Percent of population who

have attended college • Amount of road in section• Distance to nearest fire

department • Landscape landcover/landuse• Latitude & longitude • Fire district • Previous wildfire

• Includes current and lagged values, as well as neighboring current and lagged values

• GIS “hole”

KBDI Max Temp

24 h Precip

Annual rainfall

0-800

Buildup Index

Temp

Humidity

24 h Precipitation

Herbaceous stage

0 – 15 (low)       

16 -- 40 (moderate)  

41 – 80 (high)           

81 – 200 (very high) 

201 – 250 (extreme)

Spread

Index

Fuel moisture

Wind Speed

Precipitation

Lesser vegetation

0 – 4 (low)   

5 – 9 (moderate)

10 – 19 (high)

20 – 39 (very high) 40 – 100 (extreme)

Spatial and Temporal Scales of Data

• Individual fire

• Location: centroid of section

• Time of ignition

Spatial and Temporal Variables in Models

• Latitude and longitude (Albers projection)• Year• Time of day (morning, afternoon, evening, overnight)

Lagged Variables

• Previous wildfire• Section: same or neighboring• Year: earlier in same year; or in previous

12 years

• Prescribed burning prior to the fire • For hazard reduction:

• Section: same or neighboring• Year: earlier in same year; or in previous 3

years

• For silvicultural or other purposes• Section: same or neighboring• Any time in this year or previous 3 years

Model Specification

Area burned:

Ln(Wildfire Size) = X + ,

X may include lagged variables

Probability of Large Fire:

Xpe

AreapX

)(logit1

1)acres1000Pr(

Results—Small Wildfires, n=7249, R2=.19Factors related to greater area burnedResponse time up to 16 hoursLimited-action fires (let burn)Spread indexPalmetto-Gallberry, Grass, and Pine fuel typesArson ignitions (as opposed to lightning)Afternoon ignitions (as opposed to overnight)Area burned by wildfire in neighboring sections in the previous 1-12 years Previous non-hazard mitigating prescribed fire lagged up to 3 years

Factors related to smaller area burnedLa NiñaHumidityHazard-mitigating prescribed burning in the current yearPopulation density, up to about 70 persons per square kilometer (which is the median)Fire districts 10, 14, & 16Smaller fires in 1999, 2000, 2001% of water and wetlands in section% of grasslands and upland forests in neighboring sections

InteractionsSeveral with KBDI

Some Factors Related to Area Burned (Fires 1000 Acres)

Effects of KBDI

Results—Large Wildfires , n=53, R2=.73Factors Related to Greater Area BurnedSpread indexWildfire in previous 12 yearsPercent of wetland in the sectionPopulation densityIncome1998

Factors Related to Smaller Area BurnedFuel type grassArson and accidental ignitions, as opposed to lightningFire District 12

InteractionsIn GIS hole areas, percent of water in the section is positively related to large fire size

Some Factors Associated with Area of Fire, Fires > 1000 Acres

Results—Probability that Area Burned will Exceed 1000 Acres

n=7302, max rescaled R2=.32

Positive RelationLa NiñaIncomeBuild-upLimited-action fires (let burn)Wind speed1998Neighboring upland forest

Negative RelationEl NiñoUpland forestNeighboring Urban areas

InteractionsLog odds increases with KBDI in upland forest sections but not in other types of land cover.

Log odds decreases with hazard-reducing prescribed burning if response time is short, but not if response time is longer.

If the response time is long, the log odds decreases as hazard-reducing prescribed burning increases in neighboring sections.

Summary•Lagged variables in space and time capture much of the spatial/temporal information, but not quite all of it.

•Models don’t fit or predict nearly as wellas I’d like. There’s more to be done.

•Some encouraging results regarding ability to detect effects of managementpractices in section and neighbors.

•Continuing work on estimating magnitude of effect of prescribed burning -- using “propensity scores”.