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.