Wildfires and Weather

Germann Rad Fire

Germann Road Fire, Douglas County Wisconsin May 2013

A wildfire is an uncontrolled fire in an area of combustible vegetation that occurs in the countryside or a wilderness area. Other names such as brush fire, bush fire, forest fire, desert fire, grass fire, hill fire, peat fire, vegetation fire, and veldfire may be used to describe the same phenomenon depending on the type of vegetation being burned. A wildfire differs from other fires by its extensive size, the speed at which it can spread out from its original source, its potential to change direction unexpectedly, and its ability to jump gaps such as roads, rivers and fire breaks. Wildfires are characterized in terms of the cause of ignition, their physical properties such as speed of propagation, the combustible material present, and the effect of weather on the fire. An average of 5 million acres burns every year in the United States, causing millions of dollars in damage­. Once a fire begins, it can spread at a rate of up to 14.29 miles per hour (23 kph), consuming everything in its path.

 Wildfires in Wisconsin

Causes of Wildfires in Wisconsin, 2000 -2010

Causes of Wildfires in Wisconsin, 2000 -2010

Wisconsin has its share of wildfires. As of August 8, 2014, the Wisconsin Department of Natural Resources (DNR) indicated that for calendar year 2014 there had been 522 wildfires which had consumed over 2,700 acres. (Check http://dnr.wi.gov/topic/ForestFire/report.asp for updated information). In Wisconsin, people cause 98 percent of all wildfires. Most ignitions are accidental and caused by debris burning, equipment use, improper ash disposal and warming fires.

Wisconsin’s forests and grasslands are vulnerable to wildfires that arise when the ground is no longer snow-covered. Wildfires are primarily caused by human action, but can also be attributed to lightning strikes. Major weather factors that affect the status of wildfires are temperature, precipitation, humidity, and wind speed. These disasters are capable of property and infrastructure destruction, air and water pollution, and human harm; therefore, wildfires have a major impact on Wisconsin’s economy. In 2013, the Germann Road fire in Douglas and Bayfield counties destroyed 47 structures, including 17 homes and 15 garages.1 This fire consumed a total of 7,442 acres and displaced many families in the area. Based on these data, preparing for wildfires is a priority for Wisconsin governmental units, citizens, and businesses.

The Great Peshtigo Fire of 1871

The Great Peshtigo Fire of 1871

Historically, wildfires have been of great concern in Wisconsin. The single worst wild fire in U.S. history, in both size and fatalities, is known as the Great Peshtigo Fire which burned 3.8 million acres (5,938 square miles) and killed at least 1,500 in northern Wisconsin and the Upper Peninsula of Michigan during the week of October 8-14, 1871. Many sources put the size of the fire at 1.2-1.5 million acres but that included only the area that was completely burned and not the additional 2.3 million acres in surrounding counties that also suffered burn damage. The Wisconsin DNR maintains a list of Major Fires in Wisconsin History (http://dnr.wi.gov/topic/ForestFire/WisconsinFires.html)

All of Wisconsin at some level of risk for wildfires. This includes forest areas as well as suburban and urban areas. In Milwaukee County and the surrounding areas of Southeastern Wisconsin there are regular reports of grass fires. Wildfires in can cause extensive destruction of homes and other property located in the wildland-urban interface: a zone of transition between developed areas and undeveloped wilderness.

 Wildfires and Weather

Weather plays a major role in the birth, growth and death of a wildfire. Temperature, humidity, and winds influence fire development.

Cold fronts and other regional features bring moist air that slows fires down with cooler temperatures and raised humidity. But the strong winds of a passing front can feed fresh oxygen to stir up a fire that has died down, steer a fire in new directions, or accelerate its progress, making cold fronts a mixed blessing.

Dry thunderstorms with lightning and winds are major culprits in starting and spreading wildfires.

A wet thunderstorm can offer relief if it brings sufficient rain.

Lightning is the ignition source for most wildfires in remote areas of the western United States. But wherever they live close to forests, people now cause the majority of wildland fires.

Besides the weather brought in by regional cold fronts or local thunderstorms, wildland fires create their own weather.

The heated air in a raging wildfire rises, sending water vapor released during combustion into the atmosphere. This buoyancy also produces intense updrafts and horizontal winds that shape and drive the fire line itself, possibly triggering sudden changes in direction and intensity that can threaten firefighters’ lives.

Pyrocumulus Cloud forming as a result of a wildfire in

Pyrocumulus Cloud forming as a result of a wildfire in Northern Dodge County Wisconsin April 2005

Water vapor released by the heat of a fire is sometimes lifted high enough to form pyrocumulus clouds (Latin, pyro = fire). Cumulus clouds form when rising warm air encounters cooler air aloft. When conditions are right, pyrocumulus clouds may rise above the smoke from a major wildfire.

GreendaleWeather provides a report on fire danger.

Haines Index

The Haines Index (HI) is a numerical value that indicates the potential for large wildfires to experience extreme fire behavior. The HI combines both the instability and dryness of the air by examining the lapse rate between two pressure levels in the atmosphere and the dryness of one of the pressure levels.

 Wildfires and Climate Trends in Wisconsin and Beyond

Long-term trend analysis of Wisconsin’s climate indicates the state is becoming warmer. After analyzing historical climate data from 1950 to 2006 and developing downscaled local climate models, University of Wisconsin climate scientists created potential climate projections based on the historical trends and scientifically validated models. According to these models, over the past 50 years, Wisconsin has warmed an average of 1°F; and average precipitation has decreased in northern Wisconsin, enhancing the dryness of the region. Over the next 50 years, models suggest increasing temperatures and more heavy rainfall events are likely. Since total summertime rainfall is not predicted to change, there may be more dry days during Wisconsin’s summer. Increasing temperatures and an increasing number of dry days could strengthen wildfire conditions in Wisconsin.

Health Effects of Wildfires: Where There’s Wildfire There Is Harmful Smoke That Can Travel Far Downwind

Exposure to wildfire smoke can cause serious health problems, such as asthma attacks and pneumonia, and can worsen chronic heart and lung diseases. People with respiratory problems like asthma or with heart disease are particularly vulnerable, as are people living in areas with high levels of particulate pollution from roadways and industrial sources. Even otherwise healthy people may experience minor symptoms, such as sore throats and itchy eyes.

Smoke from Wildfires in 2011

Smoke from Wildfires in 2011 Affected Many Parts of the United States. Source: NRDC

According to a report by the Natural Resources Defense Council (NRDC), wildfire smoke can pose serious health risks to people even hundreds of miles away from a blaze. That means residents of cities and suburbs far from forests or grasslands may still be vulnerable to the asthma attacks, pneumonia, and more serious chronic lung diseases brought on by smoke.

Real time wildfire and smoke reports are available from Weather Underground.

More Information

More Information about wildfires and weather is available from the National Weather Service.

Click on the image above for an informative brochure about Wisconsin Wildfire Preparedness.


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