Urban

The uncertainty of future precipitation patterns makes it difficult to determine whether conditions may become dry enough to increase moisture stress for plants in the Northeast. Forests that are affected by moisture deficits and drought are more likely to experience reduced tree vigor or increased mortality, both of which can affect forest composition and structure. Further, warmer temperatures can drive or enhance drought-induced mortality by disrupting plant physiology . This “hotter drought” can also interact with other forest stressors to cause tree death and forest die-off .

The loss of a traditionally cold climate and short growing season in the region may allow some insect pests and pathogens to expand their ranges northward such as hemlock woolly adelgid and southern pine beetle. Forest impacts from insect pests and pathogens are generally more severe in ecosystems that are stressed by drought and other stressors. Basic information is often lacking on the climatic thresholds that trigger increased populations of many forest pests, and our ability to predict the mechanisms of infection, dispersal, and transmission for disease agents remains low.

The uncertainty of future precipitation patterns makes it difficult to determine whether conditions may become dry enough to increase moisture stress for plants in the Northeast. Forests that are affected by moisture deficits and drought are more likely to experience reduced tree vigor or increased mortality, both of which can affect forest composition and structure. Further, warmer temperatures can drive or enhance drought-induced mortality by disrupting plant physiology . This “hotter drought” can also interact with other forest stressors to cause tree death and forest die-off.

Across the central U.S., very heavy (greater than three inches per day) and extreme (greater than six inches per day) precipitation events increased in the period from 1979 to 2009 compared to the 1948 to 1978 period. Model projections for the central U.S. suggest a potential increase in these events, especially during winter months. Other future climate projections indicate that the Midwest may experience two to four more days of extreme precipitation by the end of the century.

Mean annual precipitation is projected to only increase by 0.7 inches under the GFDL A1FI scenario for the final 30 years of the 21st century compared to the 1971 to 2000 baseline. By contrast, annual precipitation is projected to increase under the PCM B1 scenario by an average of 3.8 inches. Changes in precipitation are projected to vary greatly by season. Both models project an increase in precipitation in winter and spring. They differ in projections for summer and fall. PCM projects an increase of 1.8 inches, while GFDL projects a decrease of 5.8 inches in summer.

Mean annual daily temperature across the region is projected to increase by 8.2 °F (4.5 °C) under the GFDL A1FI (high emissions) scenario and 2.3 °F (1.2 °C) under PCM B1 (low emissions) for the final 30 years of the 21st Century compared to the 1971 to 2000 baseline. The most dramatic increase in temperature is projected to be in winter for the PCM B1 scenario and summer for the GFDL A1FI scenario. No spatial variation in temperature changes across the Chicago Wilderness region is discernable.