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Many southeastern cities are particularly vulnerable to climate change compared to cities in other regions, with expected impacts to infrastructure and human health. The vibrancy and viability of these metropolitan areas, including the people and critical regional resources located in them, are increasingly at risk due to heat, flooding, and vector-borne disease brought about by a changing climate. Many of these urban areas are rapidly growing and offer opportunities to adopt effective adaptation efforts to prevent future negative impacts of climate change.

Rapid Population Shifts and Climate Impacts on Urban Areas

While the Southeast is historically known for having a rural nature, a drastic shift toward a more urbanized region is underway. The Southeast contains many of the fastest-growing urban areas in the country, including a dozen of the top 20 fastest-growing metropolitan areas (by percentage) in 2016.22 Metropolitan Atlanta has been swiftly growing, adding 69,200 residents in just one year.23 At the same time, many rural counties in the South are losing population.24 These trends towards a more urbanized and dense Southeast are expected to continue, creating new climate vulnerabilities but also opportunities to adapt as capacity and resources increase in cities (Ch. 17: Complex Systems). In particular, coastal cities in the Southeast face multiple climate risks, and many planning efforts are underway in these cities. Adaptation, mitigation, and planning efforts are emphasizing “co-benefits” (positive benefits related to the reduction of greenhouse gases or implementation of adaptation efforts) to help boost the economy while protecting people and infrastructure.

Increasing Heat

Figure 19.4: Historical Number of Warm Nights

Historical Number of Warm NightsA map of the Southeast region shows the annual number of warm nights (those with a minimum temperature greater than 75 degrees Fahrenheit) averaged over the period 1976 to 2005. Historically, most of the region has experienced 5 or fewer warm nights, on average, per year. Exceptions include coastal Louisiana and South Florida, which both average 30 to 100 warm nights per year.

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Cities across the Southeast are experiencing more and longer summer heat waves. Nationally, there are only five large cities that have increasing trends exceeding the national average for all aspects of heat waves (timing, frequency, intensity, and duration), and three of these cities are in the Southeast region—Birmingham, New Orleans, and Raleigh. Sixty-one percent of major Southeast cities are exhibiting some aspects of worsening heat waves, which is a higher percentage than any other region of the country.12 The urban heat island effect (cities that are warmer than surrounding rural areas, especially at night) adds to the impact of heat waves in cities (Ch. 5: Land Changes, KM 1). Southeastern cities including Memphis and Raleigh have a particularly high future heat risk.25

Figure 19.5: Projected Number of Warm Nights

Projected Number of Warm NightsFour maps of the Southeast region show the projected annual number of warm nights (those with a minimum temperature greater than 75 degrees Fahrenheit) by mid-century (2036 to 2065) and late century (2070 to 2099) under the higher RCP8.5 and lower RCP4.5 scenarios. Under the lower scenario, much of the region will experience 10 to 30 warm nights a year by mid-century, and by late century, 30 to 50 warm nights a year will by commonplace. Under the higher scenario, much of the Southeast is projected to experience 30 to 50 warm nights annually much earlier than that—as soon as 2036 to 2065. By late century, 50 to 100 annual warm nights are projected to be widespread across the entire region, with the exception of the southern Appalachians. In all scenarios, the areas surrounding the southern Appalachians are expected to see the fewest number of annual warm nights, no more than 10. The states of Florida and Louisiana are expected to see the greatest number of warm nights, ranging from 30 to 150 under the lower scenario, and 50 to more than 150 under the higher scenario.

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Explanation: