Forest [FAR1]

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).

The means of several climate models indicate that winter and spring precipitation may increase from 10 to 30% across the Midwest by the end of the century, with larger projected increases further north in the region. Fall precipitation may increase only slightly. Summer precipitation is projected to decrease by less than 10% across the Midwest by the end of the century, according to an average of multiple climate models.

The Midwest has already experienced a large increase in the frequency of heavy precipitation events. For example, storms in the 99th-percentile category increased by 42% from 1958 to 2016 across the region. Intense rainfall is expected to continue to occur more frequently, across different storm classes. For example, rain events that historically had an expected return of 5 years are expected to occur every 2-3 years by the end of the century. Large storms are also expected to deliver more rainfall as well.

Annual precipitation has generally increased by 5 to 10% across the Midwest compared to the early 20th century, although there have been greater increases as well as slight decreases. There is uncertainty between different climate scenarios for future precipitation projections in the Midwest. Generally, it is expected that annual precipitation will continue to increase slightly across the region, with an additional 2-4 inches of rain per year by the middle of the century across most of the region.

Daily low temperatures are projected to increase substantially across the Midwest, particularly under a higher climate scenario (RCP 8.5). For example, the coldest day of the year is expected to be about 9.4 degrees Fahrenheit warmer by the middle of the century (2036-2065), according to an average of 32 climate models under scenario RCP 8.5. The Midwest is also expected to experience 20 to 40 fewer days per year below 32 degrees Fahrenheit by the middle of the century.

Daily extreme temperatures are projected to increase substantially across the Midwest, particularly under a higher climate scenario (RCP 8.5). For example, the hottest day of the year is expected to be about 6.7 degrees Fahrenheit warmer by the middle of the century (2036-2065), according to an average of 32 climate models under scenario RCP 8.5. The Midwest is also expected to experience 5 to 40 more days above 90 degrees Fahrenheit by the middle of the century.

The Midwest has already warmed by about 1.3 degrees Fahrenheit since the first half of the 20th century. Climate models agree that temperatures are projected to increase over the 21st century across the Midwest. By mid-century (2036-2065), average annual temperature is expected to increase by 4.2 to 5.3 degrees, Fahrenheit. By the end of the century (2071-2100), temperatures in the Midwest are projected to increase by 5.6 to 9.5 degrees Fahrenheit.