Urban

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. Warmer temperatures will result in fewer days with minimum temperatures below 32°F and a shorter freeze-free season by mid-century, increasing by 3-4 weeks in most areas, trending towards an earlier onset of spring.

With warmer temperatures and an increase of rain-on-snow events occurring in winter, the Northeast is expected to experience a reduced snowpack and earlier breakup of winter ice on lakes and rivers. The earlier snowmelt runoff will result in more frequent high-flow events in winter and spring. For parts of the northern Northeast region the probability of high-flow events may increase by as much as 80%.

A variety of models project that winters will become more mild across the Northeast as temperatures increase. Warmer temperatures will cause more winter precipitation to be delivered as rain. Snowfall, snow depth, and snow pack are all expected to be reduced.

There has been a 71% increase in the annual amount of precipitation falling in very heavy events for the Northeast region (defined as the heaviest 1% of all daily events) from 1958 to 2012. These trends are larger than natural variations for this region. The magnitude or even frequency of flooding could also potentially increase in the winter and spring due to increases in total runoff and peak stream flow during those times.

The Northeast is expected to see increased precipitation in winter, a change of 5 to 20%, by end of century for high emission scenarios. Models are in agreement that this change will be significant in comparison to the current average climate (1970 – 1999).

The Northeast region will potentially experience a decrease in the number of very cold days (below 10°F). The northern Northeast region is modeled to experience the greatest decreases with changes of 21 days or more. The smallest decreases are modeled to occur in coastal and southern areas where the number of occurrences in the present-day climate is small. These simulated decreases in cold days are in line with the recent observed changes in the Northeast region.

The frequency, intensity, and duration of heat waves is expected to increase for the Northeast. Much of the southern portion of the region, including the majority of Maryland and Delaware, and New Jersey and West Virginia, are projected by mid-century to experience more than 18 additional days per year above 95°F compared to the end of last century, under a high emissions scenario

Climate models under a high emissions scenario indicate temperatures will increase by 4.5F° to 10°F by the end of the century, whereas climate models under a low emissions scenario project temperature increases from about 3°F to 6°F by the end of the century.

Impact models agree that many temperate species will experience increasing suitable habitat and biomass across northern Wisconsin and western Upper Michigan, and that longer growing seasons and warmer temperatures will lead to productivity increases for temperate forest types. The list of species projected to increase includes shagbark hickory, black cherry, bur oak, white oak, and a variety of minor southern species. Models also indicate that deciduous forest types have the potential for large productivity increases across the Upper Midwest.

Impact models agree that boreal or northern species will experience reduced suitable habitat and biomass across the Upper Midwest, and that they may be less able to take advantage of longer growing seasons and warmer temperatures than temperate forest communities. Across northern latitudes, it is generally expected that warmer temperatures will be more favorable to species that are located at the northern extent of their range and less favorable to those at the southern extent.