- Since 1900, total annual precipitation has increased by 11% in the U.S. Great Lakes region.
- Total annual precipitation will likely continue to increase, but projections of future precipitation vary.
- Summer precipitation may decline or increase less than precipitation in other seasons.
- Warmer temperatures will lead to less precipitation falling as snow, and more falling as rain.
- Lake-effect precipitation may continue to increase in some areas.
Observed Changes in Precipitation
The frequency, amount, and form of precipitation falling in the Great Lakes region have changed. Overall, total precipitation has increased by 11% since 1900 in the 8 U.S. Great Lakes states, but trends vary by region. The Upper Peninsula of Michigan, northeastern Wisconsin, and parts of northern Minnesota have seen decreases, while the greatest increases have been seen in the southern Midwest. Changes in precipitation have also been variable by season. Changes in spring and summer precipitation have been highly variable in the center of the Great Lakes region. Fall precipitation has increased more uniformly, and is the only season in which the Upper Peninsula of Michigan has seen an increase. Winter precipitation has increased in the southern Midwest, roughly consistent with changes in the annual totals.
Projected Changes in Precipitation
Overall, total annual precipitation is anticipated to continue to increase, though models vary widely on the magnitude and seasonal distribution of future changes.1 2 3 4 5 6 Some models project that the amount of total annual precipitation will remain near current levels, but the seasonal distribution of the precipitation will change.7 Most models project increases during the winter and spring seasons, but models are more varied when looking at the summer and fall.1 8 9 10 7 One analysis indicates a potential 20-30 percent increase in winter and spring precipitation.9 By contrast, summer projections often diverge, with most models showing potential declines in total precipitation and the potential for more consecutive dry days during that period of the year, even as total annual precipitation is projected to increase. Other models project summer precipitation will increase as in other seasons.
Snowfall, Snow Cover, and Snow Depth
Snowfall has increased in northern lake-effect zones in the Great Lakes basin even as snowfall totals in Illinois, Indiana, and Ohio have declined with rising temperatures.11 Warmer Great Lakes surface water temperatures and declining Great Lakes ice cover have likely driven the observed increases in lake-effect snow. As global temperatures continue to rise and further warm the Great Lakes, areas in lake-effect zones may continue to see increasing lake-effect snowfall. Areas in more southern lake-effect zones may see lake-effect snow replaced by lake-effect rain, as winters shorten with warmer temperatures and become less suitable for snow.12 13 14
Snow cover and snow depth in the Great Lakes region are expected to continue to decrease, having already experienced some of the greatest declines in North America.15 Between 1975 and 2004, the number of days that had snow on the ground decreased five days per decade. The average snow depth across the region also decreased by 3 inches (5.1 cm) during this time period.16
Extreme precipitation events have become stronger and more frequent. In the Midwest and Northeast United States, the amount of precipitation falling in the heaviest 1% of precipitation days increased by 37% in the Midwest and by 71% in the Northeast from 1958 to 2012.17
The observed trends of greater frequency and intensity of extreme storm events is projected to continue or accelerate as the effects of climate change become more pronounced.18 19 20 21 22 While the frequency of severe storms such as thunderstorms, heavy rains, and snow may increase, the occurrence of other severe weather events such as hailstorms, tornadoes, and ice storms could decrease or remain unchanged.23 24
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