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”.