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SPEAKER: Was 20 years ago this month, that record flooding of the Red River devastated Grand Forks and other cities along the Minnesota-North Dakota border. The flood damage was unprecedented, but climate researchers say some of the conditions that led up to it were not. In fact, as Elizabeth Dunbar reports now, the Red River in Grand Forks has seen four major floods since then.

ELIZABETH DUNBAR: The severity of a spring flood depends on many factors, and in 1997, those factors all came together. It started with a wetter than normal fall in the Red River basin, and then the ground froze pretty early, locking out additional moisture. North Dakota State climatologist Adnan Akyuz says the water typically gets stored like money in a savings account.

ADNAN AKYUZ: If you put your money in there and you don't touch it until you need it, this would be handy during the springtime planting when the precipitation is not there.

ELIZABETH DUNBAR: Except there was precipitation. Lots of it. All through the winter and in the spring too, capped by an April blizzard. And because the river runs North, Akyuz says it runs up against places where it's still winter. Frozen ground and big blocks of ice that get jammed, backing the river's flow onto the surrounding flat landscape.

ADNAN AKYUZ: These static conditions makes the Red River Valley very prone to spring flooding.

ELIZABETH DUNBAR: That geography also makes the region all the more sensitive to a changing climate. And in fact, floods have become more frequent. The Fargo-Moorhead area has had 16 major floods in its recorded history, with half of them occurring in the last 20 years. Akyuz says since 2006, it's been nearly back to back.

ADNAN AKYUZ: 2006, 2007, 2009, '10, '11, and '13 we have major floods.

ELIZABETH DUNBAR: North Dakota and Minnesota have become significantly warmer and both states are wetter overall. Precipitation in the fall has increased more than in any other season in the Red River basin. Why?

KAREN RYBERG: Right. And that is complicated.

ELIZABETH DUNBAR: Karen Ryberg is a research statistician with the US Geological Survey in Bismarck. Her studies of tree rings show how wet or dry it was all the way back to 1700, well before any formal record keeping took place.

KAREN RYBERG: There have been periods between now and the 1700s where it was drier than the 1930s Dust Bowl. The last couple decades in the Red River basin have been quite wet, but there have been some periods like that in the past as well.

ELIZABETH DUNBAR: So, Ryberg says, we can't just look at a few of these recent big floods and say, yep, that's climate change caused by humans burning fossil fuels and warming the planet. There is a direct relationship between rising temperatures and wetter conditions. The atmosphere holds more water vapor when it's warm. But predicting where and when that rain or snow will fall decades into the future--

KENNETH BLUMENFELD: It's not necessarily a trivial undertaking.

ELIZABETH DUNBAR: Kenny Blumenfeld is a climatologist for the Minnesota Department of Natural Resources. He says the wet period of the last few decades coincides with a major human-caused change in the atmosphere's composition, a composition that favors wetter conditions. But here, in the middle of the continent--

KENNETH BLUMENFELD: We're very sensitive to subtle shifts in the wind.

ELIZABETH DUNBAR: Air from the Gulf of Mexico tends to result in wet conditions, and air from the Southwest tends to result in dry ones.

KENNETH BLUMENFELD: As we move forward, no matter how the climate changes, we're always going to have that relationship with the Gulf of Mexico. And so we're going to have these boom years where it's really wet, sometimes too wet, and then we're going to have bust years where we can't buy rainfall.

ELIZABETH DUNBAR: Blumenfeld says all that uncertainty presents a challenge to farmers, engineers, architects, city planners.

KENNETH BLUMENFELD: If I'm building something for what's right now, the 100-year, 24-hour rainfall return, am I going to be off when I get to the middle of the century? Is it going to fail? And by how much? Well, that's not information that really anyone knows right now.

ELIZABETH DUNBAR: But if accurate, long-term forecasting remains a pipe dream, Steve Buan of the National Weather Service, says he and other hydrologists are in a much better position today to predict spring flooding in a given year than 20 years ago.

STEVE BUAN: In 1997, we were forecasting still on a system that was tied to a mainframe computer in Washington, DC. It was computer paper printouts, really only a decade or so after the invention of the PC.

ELIZABETH DUNBAR: Today, better river gauging systems and satellite data, plus new soil temperature data, will help the region know what kind of Red River to expect each spring. Reporting on the environment, Elizabeth Dunbar, Minnesota Public Radio news.