Warmer temperatures & extreme heat

The United States Environmental Protection Agency (EPA) estimates that over the past century, average annual temperatures have increased by 1-2°F across the Mid-Atlantic region. Consequently, warmer temperatures extend the shoulder seasons with spring seasons arriving earlier and fall lasting later in the year. The growing season is projected to be at least 3 weeks longer by the end of the century. Rising temperatures also lead to shorter, milder winters with less snow but an increase in rain. NOAA’s Mid-Atlantic Regional Integrated Sciences and Assessments (MARISA) Team compared winter 2022-2023’s temperature with average winter temperatures from 1991-2020 and found that most areas in the Mid-Atlantic experienced temperature increase of 4-6°F.

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Heat waves in the Mid-Atlantic have become more frequent between 1961 and 2021.

Environmental Protection Agency

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Heat waves in the Mid-Atlantic have become longer in number of days between 1961 and 2021.

Environmental Protection Agency

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Heat waves have become more intense and hotter in the Mid-Atlantic between 1961 and 2021. 

Environmental Protection Agency

Heat Waves

Not only are the average temperatures rising, heat waves or extreme heat days are becoming longer, as well as more frequent and intense. Heat waves refer to prolonged periods of excessive heat, typically lasting for more than two days. Across the U.S., extreme heat is the leading cause of weather-related deaths. Those living in heavily urbanized areas are particularly vulnerable to the urban heat island effect. In July 2022, five people in Philadelphia lost their lives from extreme heat, and in 2011, 35 people died from heat-related causes.

In general, national parks and surrounding areas have cooler temperatures compared to less forested areas in Washington, D.C. Data source: Open Data DC

What does this mean for national parks?

Temperatures will continue to rise as the Earth warms, and the role of national parks to cool it down has become more critical. Parks are essential to mitigate heat waves, especially in parts of urban areas that have vast areas of darker asphalt surfaces. D.C. Policy Center’s study of temperatures in different D.C. neighborhoods shows how tree canopies, green spaces, and – most importantly – parks can make a big difference in cooling down a city. The Center found that in August 2015, when the record temperature was 93°F, Ivy City and Trinidad with little tree canopy reached temperatures of 102 degrees while Rock Creek Park only reached 76. Similarly, in Philadelphia, neighborhoods with less tree canopies were found to be 22°F hotter than better shaded neighborhoods.

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Days that the Cherry Blossoms in DC bloomed early in response to warming local temperatures

Warming temperatures and shorter winters have also been altering the ecosystems in the Mid-Atlantic. For example, the cherry blossoms at the National Mall are blossoming earlier than usual. Today, D.C.’s final freeze of winter is at the end of March compared to the second week of April weeks in 1900. A thirty-year study in the D.C. area found that 89 out of 100 flowering plants, including Cherry Blossoms, bloomed 4.5 days earlier in response to warming local temperatures.