Forest [FAR1]

The largest simulated increases occur in southern Idaho, with as many as 18 more days above 95 degrees F each year. The smallest increases in hot days occur in high-elevation areas of the Cascades and Rocky Mountains, because projected temperature increases are still not enough to increase the chance of such warm days.

All climate models agree that temperatures are projected to increase over the 21st century across the Northwest, with almost uniform temperature increases across the entire region. The greatest warming is expected in southern Idaho and along the coast. The greatest warming is expected during summer months, particularly in Idaho and Oregon. The warming trend is projected to be accentuated in certain mountain areas in late winter and spring.

Global sea level rise is projected to rise between 1 and 4 feet by the end of the century. Sea level rise and related increases in storm surges pulsing farther inland will continue to exacerbate ongoing land loss in low-lying coastal areas and may result in excessive saltwater inundation of coastal forests. The number of Category 4 and 5 hurricanes has increased since the 1980s, and this trend can be attributed both to natural variability and climate change.

Rising temperatures and increases in the duration and intensity of drought are expected to increase wildfire occurrence and also reduce the effectiveness of prescribed fire in the Southeast. While this region experiences the highest number of wildfires in the country, prescribed fire is currently more common than wildfire in Southeastern forests. However, as fire seasons lengthen in the future, the window for prescribed burning may decrease because of increased fuel flammability.

Forest ecosystems throughout the Southeast Region are exposed to a range of natural, introduced, and anthropogenic stressors. Stressors such as invasive plants, forest pests, and diseases are expected to become more damaging under climate change, and these factors may interact in unpredictable ways. The southern pine beetle is already the most destructive pest in the region's forests, and longer growing seasons could allow populations of the pest to expand more rapidly.

Red spruce and eastern hemlock are already declining in some areas, and these species are projected to be extirpated from the southeast by 2100 as a result of the combined stresses of warming, air pollution, and insects. If temperature continues to increase and precipitation becomes more variable, conditions for pine growth may begin to deteriorate. Even if regional forest productivity remains high for pine species, the center of forest productivity could shift northward into North Carolina and Virginia, causing significant economic and social impacts.

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.