Forest [FAR1]

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. The largest increases are projected for the high country of Wyoming and Montana.

The largest decrease (10-15%) in summer precipitation is expected in western Wyoming. The means of several climate models indicate that spring precipitation may increase around 3% across much of the Northern Great Plains by the middle of the century. Winter precipitation is expected to increase 6-12%, with larger increases expected in parts of the Dakotas. Under mild climate scenarios, changes are generally smaller than in more extreme climate scenarios.

Most of the region is projected to experience 0 to 45% more days each year with more than an inch of precipitation by the middle of the century. An increase in heavy precipitation events is expected for much of the region, other than high mountain areas in the southwestern area. By 2050, the frequency of two-day heavy rainfall events is expected to increase by 50%. The amount of rain falling in heavy, one-day events is expected to increase by 8-10% by mid-century. Days with more than 2 inches, 3 inches, and 4 inches of precipitation are also expected to occur more regularly.

There is uncertainty between different climate scenarios for future precipitation projections in the Great Plains. Generally, there is a south-to-north gradient in annual precipitation projections, with increases projected north of the Nebraska-South Dakota border. However, annual precipitation and streamflow projections show only modest changes. The region already experiences considerable variability in precipitation each year, which contributes to a higher degree of uncertainity about future potential for flooding and drought.

Different modeling approaches generally conclude that future climate conditions will increase the risk of wildfire across the Great Plains. Annual fire probability, calculated solely with climate data and physical principles, is projected to increase by 20% to 1200% across the region by the end of the century, with the largest increases occuring in Wyoming and western Montana.

The largest decreases in number of cool days are expected in western areas of Montana and Wyoming, with much of this area expecting 35-50 fewer days with a minimum temperature below 28 degrees by the middle of the century. Nebraska and the Dakotas are expected to experience 20-30 fewer cool days.

For an average of seven days per year, maximum temperatures reach about 95 degrees F in the Northern Plains. By mid-century, much of the region is expected to experience 20-40 more hot days (above 90 degrees F) each year. The southern parts of this region, particularly Nebraska and South Dakota, will experience the largest increase in number of days above 90 degrees F, while mountainous portions of Wyoming and Montana will experience the least.

All climate models agree that temperatures are projected to increase over the 21st century across the Northern Great Plains, with almost uniform temperature increases across the entire region. In winter, the greatest warming is expected in the northeastern part of this region, mainly in the Dakotas. Springtime warming is generally smaller than that of other seasons. Summer shows a large amount of warming, with the greatest increases in the southern part of the region, particularly in Nebraska and Wyoming.

All climate models agree that temperatures are projected to increase over the 21st century across the Northern Great Plains, with almost uniform temperature increases across the entire region. In winter, the greatest warming is expected in the northeastern part of this region, mainly in the Dakotas. Springtime warming is generally smaller than that of other seasons. Summer shows a large amount of warming, with the greatest increases in the southern part of the region, particularly in Nebraska and Wyoming.