Study Tracks Climate Change in Prairie Pothole Region

Newswise — Climate change in the North American heartland could mean a smaller “duck factory” for producing the continent’s waterfowl.

That’s one implication in a South Dakota State University study that took the first comprehensive look at climate change in the Prairie Pothole Region that produces more than half of North America’s migratory duck population. The study found that some areas of the region became warmer and drier while others became cooler and wetter between 1906 and 2000.

The study of earlier this year is not only of interest to hunters and wildlife enthusiasts throughout North America, but also to the world’s scientists. SDSU geographer Bruce Millett said some of the scientists attending the climate change talks this week in Copenhagen asked for copies of it as background information on regional climate change with international ramifications.

“Our results showed that average daily air temperature rose by about 1 degree Celsius over 95 years, slightly above the global average of 0.6 degrees Celsius since the late nineteenth century,” Millett said.

But the east-west moisture gradient that characterizes the region steepened during the 20th century as weather stations in the west became drier and stations in the east became wetter — a possible concern for waterfowl and other wetland-dependent wildlife if the trend continues.

“If the moisture gradient continues to steepen, the area of productive wetland ecosystems will shrink,” SDSU wetland ecologist W. Carter Johnson said. “Consequences for wetlands would be especially severe if the future climate does not provide enough supplemental moisture to offset higher evaporative demand.” SDSU scientists looked at 20th century weather records across the region, an area of about 750,000 square kilometers, or nearly 300,000 square miles, that is home to millions of glacially-formed wetlands. The Prairie Pothole Region includes parts of western Iowa and Minnesota, the central and eastern Dakotas, and parts of Manitoba, Saskatchewan and Alberta.

Assistant Professor Bruce Millett in SDSU’s Geography Department and Distinguished Professor Johnson in SDSU’s Department of Horticulture, Forestry, Landscape and Parks published their study, “Climate trends of the North American Prairie Pothole Region 1906–2000,” in February 2009 in the prominent international journal Climatic Change. Their co-author on the study was Glenn Guntenspergen of the U. S. Geological Survey’s Patuxent Wildlife Research Center in Laurel, Md.

The researchers examined 20th century weather records starting in 1906 for 18 Prairie Pothole Region weather stations. They chose the stations because of the completeness of records and because of their locations within six smaller ecoregions of the Prairie Pothole Region, or areas with similar phenomena.

The researchers also calculated the Palmer Drought Severity Index values — a widely used drought assessment measure — for the 18 weather stations. They found that the decade of the 1930s was the driest decade of the 20th century for the Prairie Pothole Region, affecting 17 of the 18 stations in the study and hitting the Dakotas and western Minnesota the hardest. The 1920s were dry for 13 of the 18 stations.

The wettest decade was the incomplete period from 1906 to 1910, followed by the 1990s, a wet decade for 16 of the 18 stations, and then by the 1970s — a wet decade for 10 stations. The Palmer Drought Severity values for the 1960s were near normal for the Prairie Pothole Region. For the region as a whole, average annual precipitation increased by 49 millimeters during the 20th century, or 1.93 inches — an increase of 9 percent. “Our analysis determined that precipitation averaged across the Prairie Pothole Region increased during the past century, despite a precipitation decrease in the western Canadian prairies,” Millett said. The research showed a widespread trend toward warmer minimum temperatures, especially in the Canadian prairies, where some stations showed increases of nearly 3.5 degrees Celsius, or more than 6 degrees Fahrenheit. In contrast, the few stations in the study that showed significantly cooler minimum temperatures were in the southeastern part of the PPR, and they cooled only slightly. The study adds supporting data to what is known about climate change.

In a 2005 study using model simulations, Johnson showed that climate changes of the magnitude predicted by global circulation models could shift climatic conditions favorable for wetlands toward the eastern end of the Prairie Pothole Region. The problem with that scenario, Johnson said, is that most wetlands in that eastern area have already been drained for agriculture.

Draining of wetlands began with settlement in the eastern portions of the Prairie Pothole Region in about the 1870s. Iowa lost 89 percent of its prairie wetlands during the 20th century, while western Minnesota lost more than 90 percent. Wetland losses were 49 percent in North Dakota, 35 percent in South Dakota, and 27 percent in Montana.

“Climate change poses a conservation challenge because the highest densities of intact wetland basins and best upland nesting cover occur in the drier parts of the Prairie Pothole Region, where the effects of climate change are projected to be the most severe,” Johnson said.

Restoration of drained wetlands in the eastern part of the Prairie Pothole Region could help diminish the effects of increased droughts in the climatically drier west, Johnson and Millett said, though it’s likely to be expensive. Meanwhile, the researchers say, scientists and government agencies should watch the region’s climate closely in the future to look for signs of higher evaporative demand and to prepare for the possibility of a Prairie Pothole Region with less productive wetlands and fewer waterfowl.

The U.S. Geological Survey and the U.S. Environmental Protection Agency funded the research.