Temperature has risen in Minnesota about 2°F since the early 20th century. Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century. While warmer temperatures will reduce the heating energy demand and lengthen the growing season, it will also increase the intensity of naturally occurring droughts.
Precipitation has increased during the last century. Spring precipitation is projected to increase by about 15–20% by mid-century.
Intense rainfall events are projected to increase in intensity, resulting in increased flooding and associated impacts, such as increased erosion, infrastructure damage, and agricultural losses.
Photo by TumblingRun
Minnesota is located in the interior of North America, resulting in large temperature variations across the state, where winters are cold in the south and frigid in the north and summers are mild to occasionally hot in the south and pleasantly cool in the north. The lack of mountains to the north or south allows for incursions of bitterly cold air masses from the Arctic as well as warm, humid air masses from the Gulf of Mexico, further increasing the range of conditions that can affect the state. The summer is characterized by frequent warm air masses, either hot and dry continental air masses from the arid west and southwest or warm and moist air that pushes northward from the Gulf of Mexico. The summer is also punctuated by periodic intrusions of cooler air from Canada, providing breaks from summer heat. Temperature extremes have ranged from as low as -60°F (Feb. 2, 1996, Tower) to as high as 115°F (July 29, 1917, Beardsley). Minnesota’s wide range between highest and lowest temperatures is the third largest of non-mountainous states. Also, Minnesota is located on the eastern edge of the transition zone between the humid climate of the eastern United States and the semi-arid Great Plains, exemplified by large differences in average precipitation across the state. Snowstorms are a normal part of the winter and early spring climate, with average annual snowfall ranging from 40 to 60 inches over most of the state.
Temperatures in Minnesota have increased more than 2°F since the beginning of the 20th century (Figure 1). Since the year 2000, Minnesota has experienced 7 out of its 10 warmest years on record. This warming has been concentrated in the winter while summers have not warmed as much. The summer warming has been mostly an increase in nighttime temperatures, with the coolest nights of summer becoming warmer. By contrast, summer daytime high temperatures have increased very little. This is reflected in a below average occurrence of hot days (maximum temperature above 90°F; Figure 2a). There is no overall trend in warm nights (minimum temperature above 70°F) (Figure 2b). The winter warming trend is reflected in a decline in the number of very cold days (maximum temperature below 0°F) over the past two decades, with a historic low occurring during the 5-year period of 2000 to 2004 (Figure 2c). The date of lake ice-out has also been getting earlier in the last few decades (Figure 3).
Average annual precipitation has been above the long-term average for the past 25 years (Figure 4). Likewise, the number of extreme precipitation events (precipitation greater than 3 inches) has been above the long-term average over the past 30 years, with the record 5-year number occurring during the period of 1990 to 1994 (Figure 2d). Average annual precipitation, including rainfall and the water equivalent found in snowfall, ranges from 18 inches in the far northwest to more than 32 inches in the southeast. Nearly two thirds of the average annual precipitation occurs during the growing season (May through September). However, occasional drought is a natural feature of the climate, occurring when anomalous circulation patterns bring in dry air from the interior of North America.
Between 2000 and 2012, extreme weather events (including extreme drought, summer heat waves, severe storms, heavy rain and flooding, and tornadoes) caused an estimated $4.3 billion in damages to property. In general, thunderstorms cause more property damage than any other extreme weather type in Minnesota. The annual frequency of thunderstorm days is roughly 45 days in the southern part and 30 days along the northern border. Due to Minnesota's northern location, heat waves are infrequent, but they can have severe consequences as the population is less acclimatized to these events. Since 1995, excessive heat events have occurred most frequently in the central and southern counties (Figure 5). Since 2000, the number of very heavy rains (6 inches or more in a day) have been 2-3 times more frequent than in the 20th century.
Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century (Figure 1). Even under a pathway of lower greenhouse gas emissions, average annual temperatures are projected to most likely exceed historical record levels by the middle of the 21st century. However, there is a large range of temperature increases under both pathways, and under the lower pathway, a few projections are only slightly warmer than historical records. Increases in the number of extremely hot days and decreases in the number of extremely cold days are projected to accompany the overall warming.
Annual average precipitation is projected to increase, with increases most likely occurring in the winter and spring (Figure 6). This is part of a large area of the Northern Hemisphere in the higher middle latitudes projected to see increases. Increases in intense rainfall are also expected. Despite these increases in precipitation, it is possible that future droughts will be more intense because of higher temperatures, which will increase the rate of loss of soil moisture. In 2007, 24 counties in Minnesota received federal drought designations, while 7 counties were declared flood disasters. Again in 2012, 55 counties received drought designations at the same time that 11 counties declared flood emergencies. Recent events demonstrate the likelihood of simultaneous increases in both flooding and drought severity within the state.