Forested watershed

Large variation exists for projected changes in precipitation for Michigan and the Upper Midwest. Although individual model projections may differ, there is general agreement that annual precipitation is expected to increase slightly (2 to 4 inches) during the 21st century. Models also tend to agree that precipitation patterns between seasons may shift substantially. Averages across multiple climate models indicate that winter and spring may experience 20-30% more precipitation by the end of the century, while summer precipitation is projected to decrease by less than 10%.

Heavy precipitation events have been increasing in number and severity in the upper Midwest in general and for Michigan in particular, and many models agree that this trend will continue over the next century. For example, storms in the 99th-percentile category incrased by 42% from 1958 to 2016 across the Midwest. Large storms are also expected to deliver more rainfall as well. In the Midwest, 20-year return storms are projected to deliver 11 to 20% more rainfall by the end of the century. Most heavy precipitation events occur during summer in the Upper Midwest.

Evidence at both global and local scales indicates that growing seasons have been getting longer, and this trend is projected to become even more pronounced over the next century. As seasons shift so that spring arrives earlier and fall extends later into the year, phenology may shift for plant species that rely on temperature as a cue for the timing of leaf-out, reproductive maturation, and other developmental processes. Longer growing seasons could also result in greater growth and productivity of trees and other vegetation, but only if balanced by available water and nutrients.

In the Upper Midwest, the duration of frozen ground conditions suitable for winter harvest operations has already shortened by 2 to 3 weeks in the past 70 years. Cold-season soil temperatures are projected to increase between 1.8 and 5.4 °F by the end of the century, and total frost depth is projected to deline by 40 to 80 percent across northern Michigan by the end of the century. These conditions could increase water infiltration into the soil and reduce runoff, but they may also lead to greater soil water losses through increased evapotranspiration.

A variety of models project that across the Upper Midwest, more winter precipitation will be delivered as rain, more snow will melt between snowfall events, and the snowpack will not be as deep or consistent. Lake-effect snowfall may increase in the short-term, but these events may convert to rain as temperatures increase.

Northern Wisconsin and the western Upper Peninsula have already warmed more than 1.5 degrees since the first half of the 20th century, which is one of the fastest rates of warming across the country. All global climate models project that temperatures will increase with continued increases in atmospheric greenhouse gas concentrations. More warming is projected under a high climate scenario (RCP 8.5) and more moderate warming is projected under a moderate climate scenario (RCP 4.5).

Northern Michigan has already warmed more than 1.5 degrees since the first half of the 20th century, which is one of the fastest rates of warming across the country. All global climate models project that temperatures will increase with continued increases in atmospheric greenhouse gas concentrations. More warming is projected under a high climate scenario (RCP 8.5) and more moderate warming is projected under a moderate climate scenario (RCP 4.5).