Why Wildfire Risks Are Increasing

A changing environment means higher temperatures and a drier atmosphere, creating conditions which are prime for wildfires to spread.

Changes in the environment have already increased wildfire risk across the United States, doubling the number of acres burned and increasing the duration of wildfire season by over 3 months.

Temperatures are increasing.

Over the last 30 years, the average temperature in the contiguous US has increased by 1.2°F compared to the previous half-century, with the largest increases seen in the western US, where the average increase has been over 1.5°F. As the atmosphere warms, surface temperatures increase in kind. This increases the rate of evaporation in dense wilderness areas, causing soil and vegetation to dry more quickly and more completely than in past seasons. In the next few decades, this warming trend will continue, with temperatures expected to rise over 2.5°F compared to current averages.

    Rising average temperatures increase the rate of evaporation in dense wilderness areas, causing soil and vegetation to dry more quickly and become flammable.

    Change in temperature (°F) in 30 years
    1°F
    2°F
    3°F
    4°F
    Source: Eagle Rock Analytics, based on the NOAA Real-Time Mesoscale Analysis (RTMA) 2011-2020 hourly time series and adjusted to future conditions using the RCP 4.5 emissions scenario.

    The impact of increasing temperatures

    Dried ground and vegetation acts as fuels for wildfires, causing fires that start by natural sources such as lightning to ignite more easily, and causing wildfires with human sources such as campfires and poorly disposed charcoal to get out of control more rapidly. This leads to fires that spread faster and threaten a greater number of homes, especially those in areas designated as part of the Wilderness Urban Interface.

    Changing precipitation trends are drying already vulnerable areas.

    A warming planet and increased evaporation also means changing weather patterns. As a result of changes in weather patterns across the US, many areas already prone to wildfires will see changes in precipitation that will result in more severe storms with longer dry spells between them during hot summer months. These weather pattern shifts can also result in changes in wind direction, blowing wildfires into areas, or allowing them to spread to areas, where they may not have done before.

      Changing precipitation patterns are exacerbating dry seasons in areas prone to wildfires, causing burns to become more frequent and severe.

      LIGHTERHEAVIER
      <-15%
      -10%
      -5%
      0%
      5%
      10%
      15%+
      Source: Eagle Rock Analytics, based on the NOAA Real-Time Mesoscale Analysis (RTMA) 2011-2020 hourly time series and adjusted to future conditions using the RCP 4.5 emissions scenario.

      The impact of changing precipitation

      Because the time between rainstorms will only increase as climate change intensifies, long dry spells will contribute to the drying of fuel layers brought on by excessive heat, leading to easier wildfire ignitions and harder to control wildfire spread. The growing time between rainfall events also removes a natural check on the spread of wildfires, resulting in longer burns that will require more resources and human intervention in order to stop.

      Changing humidity patterns are drying out plant life.

      Another consequence of changing precipitation patterns is lower air humidity. As the humidity decreases in already arid and vulnerable areas, the resultant dry air creates what is known as a vapor pressure deficit between the ambient atmosphere and the local plant life, causing plants to release their stored moisture into the air to balance the environment and causing vegetation to dry out in the process.

        Lower humidity in the air causes plants to release their moisture to balance the environment, resulting in dried vegetation that is more susceptible to wildfire.

        Change in relative humidity in 30 years
        -2%
        -1%
        0%
        1%
        2%
        Source: Eagle Rock Analytics, based on the NOAA Real-Time Mesoscale Analysis (RTMA) 2011-2020 hourly time series and adjusted to future conditions using the RCP 4.5 emissions scenario.

        The impact of reduced humidity

        Dried plants act as highly combustible fuels for wildfires, causing fires to start more easily, spread more readily, and burn hotter than they might if plants were able to retain more of their moisture. This makes more homes, especially those in the WUI, vulnerable to wildfire as the environment continues to change.

        Additional factors increasing risk

        Another side effect of a changing environment is the rapid growth of vegetation that acts as fuel for wildfires. While precipitation decreases are expected during warm months, increasing precipitation during the winter months acts as an accelerant to plant growth.

        Non-environmental factors like development patterns and short-term fire suppression are also exacerbating fire risks. Expanded development in wildlife urban interface areas simultaneously puts more people and community assets at risk, while short-term fire suppression creates excessive amounts of unburned fuels that allow fires to burn more intensely.

        How does Fire Factor® incorporate changing wildfire risks?

        The data on Risk Factor™ considers how changing temperature and fire weather patterns will affect the available fuel layers and how that may cause wildfires to spread into populated areas.

        What can be done to stop wildfires?

        Although wildfire risk can never be completely eliminated, there are a wide range of protection measures that reduce risk.

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