Average annual temperature has increased approximately 2°F since the early 20th century, with warming concentrated during the winter and spring and nighttime minimum temperatures increasing about twice as much as daytime maximums. Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century.
Higher temperatures will increase evapotranspiration rates and increase the rate of soil soil moisture loss during dry spells, leading to an increase in the intensity of naturally-occurring future droughts.
Winter and spring precipitation is projected to increase, with associated increases in total seasonal snowfall. Heavy precipitation events are also projected to increase, raising the risk of springtime flooding.
South Dakota lies in the northern Great Plains, straddling the transition from the moist eastern United States to the semi-arid western United States. Due to its location in the center of the North American continent, far from the moderating effects of the oceans, the state experiences a wide range of temperature extremes. Average January temperatures range from less than 12°F in the northeast to more than 24°F in the southwest, while average July temperatures range from less than 64°F in Black Hills National Forest to more than 75°F in the south-central part of the state. Temperatures of 100° F or more occur nearly every year. The warmest year on record was 2012, with a statewide average annual temperature of 49.3°F, 4.7°F above the long-term average. The lack of mountain ranges to the north allows arctic air masses to enter the state frequently during the winter, bringing bitter cold spells.
Since the beginning of the 20th century, temperatures in South Dakota have risen approximately 2°F (Figure 1). Temperatures in the 2000s have been warmer than any other historical period, with the exception of the early 1930s Dust Bowl era, when poor land management likely exacerbated hot summer temperatures. This warming has been concentrated in the winter and spring, while summers have not warmed much in the state, a feature characteristic of much of the Great Plains and Midwest (Figure 2). This is reflected in a below average occurrence of extremely hot days (days with maximum temperature above 100°F) (Figure 3a) and no overall trend in very warm nights (days with minimum temperature above 75°F) (Figure 3b). In addition, nighttime minimum temperatures have risen at about twice the rate of daytime maximum temperatures. The winter warming trend is reflected in a below average number of very cold nights (days with minimum temperature below 0°F) since 2000 (Figure 4). There has been an increase in absolute humidity, which may be contributing to the increasing nighttime maximum temperatures.
Average annual total precipitation ranges from around 15 inches in the northwest to about 28 inches in the southeast. Statewide average annual precipitation has varied widely from year to year, ranging from a low of 10.90 inches in 1936 to a high of 27.97 inches in 1915. The driest multi-year period occurred in the 1930s, and the wettest in the late 1990s and from 2008 onward (Figure 3c). Annual precipitation has ranged from 15.47 inches during the driest 5-year period on record (1933–1937) to 23.20 inches during the wettest 5-yr period on record (2007-2011) . Most of the state’s precipitation falls during April to September when thunderstorm activity is highest (Figure 3d). The most severe of these storms can produce hail and tornadoes. While most of the state averages at least 30 inches of snow annually, portions of the Black Hills National Forest can receive upwards of 70 inches annually and South Dakota has generally experienced an increase in snowfall.
Like other states in the Great Plains, South Dakota experiences periodic episodes of severe drought, which can last for several years. One of the worst droughts in the state’s history was the 1930s drought of the Dust Bowl era, when dry conditions were exacerbated by extreme heat. Not only was 1936 the driest summer on record, with only 3.54 inches of precipitation (more than 4.5 inches below the long-term average), but it was also the hottest summer on record, with an average temperature of 76.4°F, 6.8°F above the long-term average. During the recent drought of 2012, South Dakota experienced its driest July–September, with only 2.86 inches of precipitation during the three-month period. Extreme heat waves alone can cause problems. In 2011, unusually warm and humid conditions in South Dakota took their toll on livestock and at least 1700 head of cattle perished.
Snowfall is highly variable from year to year. For example, the annual snowfall totals at Menno have varied from around 10 inches (in the winters of 1986–87 and 1999–2000) to near 70 inches (winters of 1959–60 and 1983–84) (Figure 5) and in the 2000s, from under 20 inches to near 50 inches (Figure 5). South Dakota’s northern location and proximity to the typical U.S. winter storm track makes it highly susceptible to the impacts of winter storm systems, including heavy snows, high winds, and low wind chill temperatures. In any given year, the probability of a blizzard occurring somewhere in the state is greater than 50%. On October 3–5, 2013, western South Dakota was hit by an early season blizzard. With reported wind gusts as high as 70 mph and widespread snowfall amounts of more than 20 inches, the storm was devastating. Among long-term weather observation stations, Lead reported one of the highest snowfall amounts with 55 inches over the 3-day period, 42 of which fell on October 4th. Rapid City reported 23.1 inches of snow, the second heaviest snowstorm on record for the city. It is estimated that more than 45,000 livestock died from the event, with some herds losing greater than 90% of their total populations.
With several large rivers running through the state, including the Missouri River, flooding is a great hazard for South Dakota. The frequency of heavy rain events has increased. Since 1990, South Dakota has averaged 14% more 1-inch rain events compared to the long-term average. (Figure 6). Some historic rain events have occurred in recent years. The state daily rainfall record (at official reporting sites) was set at Groton on May 6, 2007 with 8.74 inches. A near record amount of 8.43 inches occurred on June 16, 2014 at Canton. A devastating event occurred on June 9–10, 1972, when torrential rainfall (unofficially as much as 15 inches) fell overnight in the Black Hills area causing the Canyon Lake Dam to fail. The resulting flash flooding in Rapid City killed more than 200 people, injured more than 3,000, and destroyed 1,300 structures. Snowmelt can also cause severe flooding. In June 2011, runoff from a record winter heavy plains snowpack in the Rocky Mountains, along with heavy May rains in Montana, caused major flooding along the entire length of the Missouri River, causing several towns (including Pierre) to be evacuated and requiring rapid flood control measures. The extreme volume of water caused a long duration of flooding; below the Oahe Dam, the Missouri River at Pierre was above flood stage from May 24 to September 7.
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 heat wave intensity are projected, but the intensity of cold waves is projected to decrease.
Annual precipitation is projected to increase, with the largest increases occurring during spring and winter (Figure 7). Increased winter and spring precipitation can have both positive and negative impacts on South Dakota’s agricultural economy, increasing available soil moisture but causing loss of nutrients and potentially delaying and preventing planting and resulting in loss of yield. Heavy precipitation events are also projected to increase, leading to increased runoff and flooding which can reduce water quality and erode soils. Increased winter snowfall, rapid spring warming, and intense rainfall can combine to produce devastating floods.
The intensity of droughts is projected to increase. Droughts are a natural part of the climate system and because the projected precipitation increases are expected to occur during the cooler months, South Dakota will remain vulnerable to periodic drought. Higher temperatures will increase the rate of loss of soil moisture during dry spells, leading to an increase in the intensity of naturally-occurring future droughts.