Climate Matters•August 25, 2021
Western Fire Weather Days Increasing
KEY CONCEPTS
Climate change is worsening wildfires across forested land and lengthening wildfire seasons in the western United States.
Heat, dryness, and wind—the main components of wildfire weather—affect fire behavior. A new analysis from Climate Central shows the frequency of fire weather days are increasing across most of the American West, driven by dryness and heat.
Fire weather conditions are causing problems even where fires aren't burning. When fire weather is in the forecast, utilities may shut off power to prevent equipment-related ignitions.
Smoke from the many wildfires harms people hundreds of miles downwind, especially those with asthma or other health conditions.
It’s already been a brutal year for wildfires, with at least 104 large fires burning across 12 states, including Oregon, Montana, Washington, California, and Idaho. Hot, dry, and windy conditions fueled the intensity of both the Dixie and the Bootleg fires, which have forced evacuations and devastated dozens of communities.
What is fire weather?
Fire weather generally refers to meteorological conditions that promote the spread of wildfires, although specific definitions of fire weather can vary. Climate Central’s analysis focuses on three meteorological elements fundamental to fire weather—relative humidity, temperature, and wind.
Relative humidity is a measure of how close the air is to being saturated by water vapor. When humidity levels are very low, the air feels dry and it sucks moisture from the land, leaving vegetation dry and prone to burning.
Hotter temperatures affect humidity of the air and the dryness of the ground. They also have a direct influence on fire behavior, heating the fuels and making them more likely to ignite.
Wind supplies oxygen to a fire, so it burns more rapidly. Wind increases evaporation, drying out the land and providing more fuel for the fire. Wind also carries embers, which help a fire spread. Changes in wind speed or direction can cause a fire to shift, altering the rate of spread and intensity of the fire.
Where are fire weather days increasing?
To explore changes in weather conditions that increase risk of wildfire, Climate Central analyzed data from weather stations in 225 locations across 17 states going back to 1973. The data from individual weather stations was then aggregated by climate division (you can find your climate division here).
Parts of New Mexico, Texas, and Southern California have experienced some of the largest increases in fire weather days each year. Areas of New Mexico are now seeing two more months of fire weather than was the case nearly a half century ago.
Some of the climate divisions in Texas, California, Oregon, and Washington are experiencing fire weather more than twice as often now as in the early 1970s.
Fire weather days increased more in interior regions than in coastal regions. Higher humidity levels along the coast mean these areas are less likely to reach the low relative humidity threshold used in the analysis.
By contrast, some parts of North Dakota, South Dakota, Kansas, and Nebraska experienced a decline in the frequency of fire weather days. This is part of a region where springs and summers have been cooling slightly—most likely from local agricultural practices.
Fire weather conditions are also causing problems even where fires don’t ignite.
On fire weather days, power companies are shutting off electricity to millions of people in an attempt to avoid equipment-related ignitions. These “public safety power shut offs” (PSPSs) reduce the risk of fire but create health risks, especially to those who depend on refrigeration or need air conditioning to stay cool during heat waves. Researchers found that the daily power needs for 12 million people were unavailable in Northern California in 2019 due to the PSPSs, causing estimated economic impacts of around $10 billion.
Communities near wildfires and those far downwind are also being affected. Smoke is a dangerous pollutant that contributes to a variety of health problems, increasing susceptibility to asthma and asthma attacks. It can also make one more vulnerable to influenza and other viruses like COVID-19. Smoke poses especially high risks to those with other health problems, particularly among seniors and others with weakened lung health.
POTENTIAL LOCAL STORY ANGLES
What are solutions to the increasing risk of wildfires?
A number of solutions to adapting to the risk of wildfire include increased use of land management techniques that eliminate excessive fuels, such as prescribed burns; forest thinning to remove young trees and bushes; and allowing small fires to burn themselves out when it’s safe to do so. There are also toolkits to prepare homes and create evacuation plans. But fire weather conditions will increase around the world as the planet warms. Reducing carbon pollution to net zero by 2050 by aggressively switching away from fossil fuels would limit global warming and stabilize climate conditions.
Is my area at risk of wildfires?
You can find daily reports of elevated fire weather conditions at NOAA’s Storm Prediction Center. The Incident Information System identifies where wildfires have been reported and provides detailed information on conditions. You can stay updated about risk of fire with the North American Seasonal Fire Assessment and Outlook, produced by the National Interagency Fire Center (NIFC) in Boise, Idaho at the beginning of each month. You can also search your locality on the Wildfire Risk to Communities website.
Are wildfires affecting air quality in your area?
AirNow, a partnership of multiple government agencies, has a number of publications on wildfire smoke and air quality, and a wildfire and smoke tracking map. California Air Resources Board (CARB) maintains a series of interviews with experts on wildfire smoke and air quality, that are available for attribution, as well as air quality data. PurpleAir also maps air quality indexes across the country.
LOCAL EXPERTS
The SciLine service, 500 Women Scientists or the press offices of local universities may be able to connect you with local scientists who have expertise on wildfires and climate change. The American Association of State Climatologists is a professional scientific organization composed of all 50 state climatologists.
NATIONAL EXPERTS
Climate and wildfires
John Abatzoglou, Ph.D., Associate Professor and Graduate Program Chair (MIST)
University of California, Merced
jabatzoglou@ucmerced.eduDaniel L. Swain, Ph.D., Climate Scientist, Institute of the Environment & Sustainability, UCLA
California Climate Fellow, The Nature Conservancy
dlswain@ucla.eduKaren Aline McKinnon, Ph.D., Assistant Professor, Institute of the Environment and Sustainability, Department of Statistics, UCLA
kmckinnon@ucla.edu
Wildfire smoke and health risks
Colleen Reid, Ph.D., Assistant Professor of Geography, University of Colorado, Boulder
colleen.reid@colorado.eduErin Landguth, Ph.D., Associate Professor, School of Public and Community Health Sciences, University of Montana
erin.landguth@mso.umt.edu
METHODOLOGY
See detailed methodology in the appendix of the report.