Wildfires are unplanned and uncontrolled fires that most frequently burn in natural areas such as grasslands, forests, and prairies. However, wildfires can occur anywhere and threaten the lives of humans and other animals as well as agriculture and infrastructure. Though dangerous, wildfires serve a crucial role in maintaining ecosystems by removing brush and debris from forest floors, exterminating unwanted pests, and redistributing nutrients throughout freshly uncovered soil.


How do wildfires start and spread?

Wildfires start for a variety of reasons (e.g., fireworks, faulty power lines, lightning, and lava), but all fires require three essential ingredients: oxygen, fuel, and heat

  • A heat source is responsible for initiating a fire by raising fuel temperatures to their ignition point. Heat allows a fire to spread with ease by warming surrounding air and drying out nearby potential sources of fuel.

  • Like wood in a campfire, fuel is any kind of combustible/flammable material that keeps a fire burning, such as trees, shrubs, grasses, and dead leaves. Wildfire fuel is primarily characterized by its moisture content. The drier the fuel, the more easily a fire can start and spread.

  • Oxygen starts and sustains combustion within the fire. When fuel burns, it reacts with oxygen to release heat, gases, smoke, and embers. This process is called oxidation.

Unfortunately, about 85 percent of wildfires over the past 20 years have been caused by humans. Some human-caused wildfires are set intentionally; however, many are accidentally sparked by unextinguished campfires, littered cigarettes, misuse of pyrotechnics (e.g., fireworks and smoke bombs), and equipment malfunction (e.g., outdoor grills and power lines). 

Wildfires can also start from natural ignition sources like lightning and lava. Most rural lightning fires in the American West are caused by dry thunderstorms. Dry thunderstorms are storms that occur in high elevation environments and produce little rainfall. In some cases, rainfall evaporates before hitting the ground, leaving only lightning to strike the hot and dry vegetation below.  


Types of Wildfire Incidents

Each fire event on this map layer features an incident name, a unique fire identifier that is defined by the National Wildfire Coordinating Group (NWCG), and one of three different “incident types” (Wildfire, Prescribed Fire, and Incident Complex) that describe the nature of the fire. Some fire events also display the cause of the event, a fire discovery date and time, daily acres burned (a measure of acres burned determined on-site), and calculated acres burned (a measure of acres burned determined from satellite images).

  • Wildfire (WF): An uncontrolled fire occurring on wildland that requires response and mitigation from firefighters.

  • Prescribed Fire (RX): Purposefully ignited wildland fires contained to a predetermined perimeter and managed by fire specialists and land managers. Prescribed burns are ignited to reduce the amount of fuel near developed areas in a controlled fashion, rather than waiting for the fuel to catch naturally. Prescribed fires are also used to minimize the spread of pests and diseases, maintain plant and animal species whose habitats depend on occasional wildfires, and recycle nutrients back into the soil to promote the growth of trees and other plants. 

To calculate the perimeter of a prescribed fire, firefighters or mapping specialists will add the lengths of the outer lines that enclose the black area of where the fire burned on-site or using infrared satellite imagery. For millennia, hundreds of indigenous people around the Great Plains and the western United States, such as the Yurok, Karuk, Hoopa, and Miwok tribes, practiced cultural burning. Cultural burning is traced back to the philosophy that fire is medicine and is used to renew local food, reduce wildfire risk, and clear thick foliage within forest canopies through controlled burns–much like prescribed burns that are implemented by land managers today.

  • Incident Complex (CX): Two or more human-caused or naturally occurring fires that burn in the same general area. These fires are frequently assigned to a single incident commander to manage.


Stay aware and be prepared!

The National Weather Service (NWS) issues wildfire warnings, watches, and mandatory action alerts to notify the public when there is a chance of a wildfire in their relative area. Each NWS office creates local criteria for fire weather watches and red flag warnings, as fires require different amounts of fuel, oxygen, and moisture to catch depending on their location. A red flag warning signifies that high temperatures, low humidity, and strong winds are occurring or expected within the next 24 hours—all ingredients to create extreme fires. A fire weather watch is similar to a red flag warning in that there is a watch for critical weather conditions; however, these alerts are issued 12-72 hours before weather conditions are expected. In the case of a red flag warning or a fire weather watch, always follow the instructions provided by your local fire department and be extremely cautious with open flames because a single spark can cause a major wildfire. To prepare for a wildfire, create an evacuation plan that includes several escape routes, assemble an emergency supply kit, know where personal, irreplaceable items are located, and have fire extinguishers on hand.


Try the Layer

acre
Noun

unit of measure equal to .4 hectares.

Noun

the art and science of cultivating land for growing crops (farming) or raising livestock (ranching).

alert
Verb

to warn and prepare to take action.

brush
Noun

dense growth of bushes, shrubs, and small trees.

calculate
Verb

to reach a conclusion by mathematical or logical methods.

canopy
Noun

one of the top layers of a forest, formed by the thick leaves of very tall trees.

combustible
Adjective

able to burn.

combustion
Noun

burning, or the process of a substance reacting with oxygen to produce heat and light.

controlled burn
Noun

planned fire to accomplish certain management goals for the land; also known as a prescribed burn.

criteria
Plural Noun

set of standards or rules.

crucial
Adjective

very important.

disease
Noun

harmful condition of a body part or organ.

Noun

community and interactions of living and nonliving things in an area.

Noun

height above or below sea level.

ember
Noun

small piece of wood, coal, or paper still slowly burning from a fire.

emergency
Noun

sudden, unplanned event that requires immediate action.

escape
Verb

to get away.

evacuation
Noun

removal of people, organisms, or objects from an endangered area.

evaporate
Verb

to change from a liquid to a gas or vapor.

exterminate
Verb

to completely destroy.

fire
Noun

a chemical process that releases heat and light due to burning.

fire department
Noun

professional or volunteer organization that works to prevent and put out fires, usually in a specific geographic area.

firefighter
Noun

person who works to control and put out fires.

fireworks
Plural Noun

controlled explosive devices that produce a striking display of light and loud noise, used for signaling or as part of a celebration.

flammable
Adjective

easily set on fire.

foliage
Noun

leaves of a plant, or the leaves and branches of a tree or shrub.

forest
Noun

ecosystem filled with trees and underbrush.

forest floor
Noun

ground-level layer of a forest.

fuel
Noun

material that provides power or energy.

gas
Noun

state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.

grassland
Noun

ecosystem with large, flat areas of grasses.

Noun

environment where an organism lives throughout the year or for shorter periods of time.

heat
Noun

energy that causes a rise in temperature.

ignite
Verb

to set on fire.

incident
Noun

event or happening.

Adjective

characteristic to or of a specific place.

indigenous people
Noun

ethnic group that has lived in the same region for all of their known history.

infrastructure
Noun

structures and facilities necessary for the functioning of a society, such as roads.

initiate
Verb

to begin.

intentional
Adjective

deliberate or on-purpose.

lava
Noun

molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.

Noun

sudden electrical discharge from clouds.

local
Adjective

having to do with the area around a specific place.

mitigation
Noun

process of becoming or making something milder and less severe.

moisture
Noun

wetness.

Noun

substance an organism needs for energy, growth, and life.

occasionally
Adverb

sometimes.

oxidation
Noun

chemical process of a substance combining with oxygen to change the substance's physical and molecular structure.

oxygen
Noun

chemical element with the symbol O, whose gas form is 21% of the Earth's atmosphere.

perimeter
Noun

outline or border.

pest
Noun

harmful or annoying person or thing.

philosophy
Noun

the study of the basic principles of knowledge.

Noun

large grassland; usually associated with the Mississippi River Valley in the United States.

prescribed burn
Noun

planned fire; it is also sometimes called a “controlled burn” or “prescribed fire,” and is used to meet management objectives.

public
Noun

people of a community.

rainfall
Noun

amount of precipitation that falls in a specific area during a specific time.

recycle
Verb

to clean or process in order to make suitable for reuse.

route
Noun

path or way.

rural
Adjective

having to do with country life, or areas with few residents.

satellite
Noun

object that orbits around something else. Satellites can be natural, like moons, or artificial.

smoke
Noun

gases given off by a burning substance.

soil
Noun

top layer of the Earth's surface where plants can grow.

species
Noun

group of similar organisms that can reproduce with each other.

Noun

degree of hotness or coldness measured by a thermometer with a numerical scale.

thunderstorm
Noun

cloud that produces thunder and lightning, often accompanied by heavy rains.

unique
Adjective

one of a kind.

vegetation
Noun

all the plant life of a specific place.

warning
Noun

notice or bulletin that alerts to a hazard.

watch
Noun

close guard of something in order to protect it.

Noun

uncontrolled fire that happens in a rural or sparsely populated area.