Urban

The freeze-free season is defined as the period of time between the last spring frost (daily minimum temperature below 32 degrees F) and the first fall frost. The length of the annual freeze-free season has been increasing since the 1980s, and all climate models agree that it will continue to increase in the future across the Southeast. The largest increases of 25-30 days are mainly expected in Louisiana, Tennessee, Kentucky, Virginia, and North Carolina.

Simulated changes in summer precipitation by the end of the century range from a 0-10% decrease, with the largest decreases occurring in southern Florida and Arkansas and Tennessee. The means of several climate models indicate that winter and spring precipitation may increase around 15% by the end of the century, particularly in the northern part of the region. Daily precipitation totals in the Southeast have increased substantially in the fall season; this trend is expected to continue, with the greatest expected increases along the Gulf Coast.

Extreme rainfall events have increased in frequency and intensity in the Southeast, and will continue to increase in the future. Most of the region is projected to experience 6% to 25% more days each year with more than an inch of precipitation by the middle of the century. The largest increases (up to 25% increases) in extreme precipitation are expected across the Appalachian Mountains. The smallest increases (less than 10%) are expected across Arkansas, Louisiana and Mississippi.

There is uncertainty between different climate scenarios for future precipitation projections in the Southeast. Generally, there is a southwest-to-northeast gradient in annual precipitation projections. The greatest increases are projected in North Carolina and Virginia (3-9% increase by the end of the century), and the greatest decreases are projected in Louisiana and Arkansas (3-12% decrease by the end of the century). Overall changes in precipitation for the Southeast are projected to be slight and comparable to current year-to-year variations.

The largest decreases are expected in Kentucky, Virginia, Tennessee, North Carolina and the northern part of Arkansas. The smallest decreases in cold days are expected along the coastal and southern areas, where these kinds of cold days rarely occur. Similarly, the Southeast region is expected to have more than 20 fewer days with a minimum temperature below 32 degrees by the middle of the century.

The smallest increase of 4 days per year is expected in areas with a currently low number of 95-degree days, including the highest elevation areas along the spine of the Appalachians where historically days above 95-degrees occur fewer than 10 days out of the year. The largest increase in the number of 95-degree days per year (35 days) is expected in south-central Florida, where these kinds of hot days are already common. The western portion of the region is expected to experience the largest number of consecutive 95-degree days, with as many as 16-20 additional days by mid-century.

All climate models agree that temperatures are projected to increase over the 21st century across the Southeast. The spatial variations are projected to be relatively small across the region, with the largest temperature changes occurring in the northwest part of the region (Arkansas, Kentucky, Mississippi, and Tennessee), the smallest variations occurring in southern Florida. Temperature increases will be the greatest in summer. The greatest warming during summer is expected in the northwest portion of the region.

Forest ecosystems throughout the Great Plains are exposed to a range of natural, introduced, and anthropogenic stressors. High-elevation forests and semiarid riparian forests are faced with their own distinct kinds of stressors. Invasive plants, forest pests, diseases, droughts, and floods are expected to become more damaging under climate change, and these factors may interact in unpredictable ways.