Forested watershed

Simulated changes in summer precipitation by the end of the century range from a 37-percent decrease to a 12-percent increase, with a mean around an 10-percent decrease. The strongest agreement for drier summers occurs in Oklahoma and west Texas. The means of several climate models indicate that winter and spring precipitation may increase around 3 percent by the end of the century, with larger increases expected in 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 30% more days each year with more than an inch of precipitation by the middle of the century. The largest increases (up to 45% increases) in extreme precipitation are expected in North Dakota and Montana. Days with more than 2 inches, 3 inches, and 4 inches of precipitation are also expected to occur more regularly by the middle of the century.

There is uncertainty between different climate scenarios for future precipitiation projections in the Great Plains. Generally, there is a south-to-north gradient in annual precipitation projections, with increases projected north of the Nebraska-North Dakota border and decreases projected from Kansas to Texas.

The largest decreases are expected in the northern half of the region. The smallest decrease in cold days is expected in Oklahoma and Texas, where these kinds of cold days rarely occur. Similarly, the region is expected to have up to 32 fewer days with a minimum temperature below 32 degrees by the middle of the century, particularly in western Montana, Wyoming, and the western edges of Nebraska, Kansas, Oklahoma, and Texas.

All climate models agree that temperatures are projected to increase over the 21st century across the Great Plains, with almost uniform temperature increases across the entire region. The greatest warming is expected in the northern Plains, especially the Dakotas. In winter, the greatest warming is expected in northern states. Springtime warming is generally smaller than winter warming, with the largest increases occuring in southwest Texas. Summer shows a large amount of warming, with a localized maximum in southwest Kansas.

When considering the potential for ecosystem conversions, species migration is a critical issue. It is not necessarily communities that move, but instead species that move and then form new communities. Species distribution models have also indicated that species may respond individually to future climate change, with suitable habitat expanding for some species and declining for others.

Forest ecosystems throughout the Midwest Region are exposed to a range of natural, introduced, and anthropogenic stressors. Stressors such as 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.

Different modeling approaches generally conclude that future climate conditions will increase the risk of wildfire across the Midwest. Annual fire probability, calculated solely with climate data and physical principles, is projected to increase by 20% to 80% across the Midwest by the end of the century. The incidence of atmospheric conditions that contribute to large and erratic fire behavior, measured by the Haines Index, is also projected to occur more frequently by the end of the century.

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 frost-free season is projected to increase 10 days by early this century (2016–2045), 20 days by mid-century (2036–2065), and possibly a month by late century (2070–2099) compared to the period 1976–2005 according to a higher climate scenario (RCP8.5).