Why flooding? Valley's in wet cycle
FARGO -- As Fargo-Moorhead watches floodwaters subside after the crest of the third major flood in as many years, residents naturally wonder: When will the weather finally turn dry?...
FARGO -- As Fargo-Moorhead watches floodwaters subside after the crest of the third major flood in as many years, residents naturally wonder: When will the weather finally turn dry?
Even the experts don't know when the Red River Valley's relentless wet cycle will end.
Many believe the wet period began in 1993. Since then, six of the top 10 record crests have occurred in Fargo-Moorhead, and Devils Lake, a giant bathtub within the Red River basin, has more than tripled in size.
But the U.S. Geological Survey actually traces the beginning of the wet cycle to about 1980, interrupted by a drought in the late 1980s, suggesting it is now about 30 years old.
"It's been going on for about 30 years, but that means nothing," in terms of when the wet cycle might end, said Skip Vecchia, a researcher for the U.S. Geological Survey.
Wet periods tend to last, on average, 30 years in the Red River basin, alternating with dry or normal periods lasting 120 years on average. Thus, the area switches cycles roughly every 150 years.
"We probably haven't been this wet since the 1820s," Vecchia said. Fur traders' journals described epic floods at the time.
Still, those are averages. The current wet period could last another five or six years, or another six decades, Vecchia said.
In fact, the U.S. Geological Survey, in trying to predict whether Devils Lake will overflow in the years ahead, recently calculated that there is a 72-percent chance the wet conditions will last at least 10 more years; a 37-percent chance they will last at least 30 more years; and a 14-percent chance wet conditions will persist at least 60 years.
Once wet periods become established, they're difficult to break and tend to persist, sometimes for decades. In fact, the end might be so gradual that it won't be apparent until it is recognized a few years in retrospect.
Ultimately, though, the cycle reverses and normal or drier conditions prevail.
"Floods come in clusters," Vecchia said. "We're just starting to understand that."
Devils Lake has overflowed several times in the past 4,000 years, most recently 800 to 1,500 years ago, according to the U.S. Geological Survey. Thus, prolonged wet cycles clearly are part of the natural climate.
The National Oceanic and Atmospheric Administration, which oversees the National Weather Service, would like to study the prolonged wet pattern in the Red River Valley.
No determination can be made that climate change caused by the accumulation of greenhouse gases emitted from fossil fuels is to blame for the stubborn wet period, NOAA has said.
"While individual weather events cannot be attributed to climate change, the wet regime we have seen is consistent with what scientists have projected with a warming climate," a National Weather Service report said of this spring's flood. "A warmer atmosphere can hold more water and therefore precipitate more water."
Doug Kluck, NOAA's central region climate program director, said he has asked directors of two climate labs to study the wet cycle in the Red River Valley to try to determine whether climate change is at least partly to blame.
"From a climate point of view, we would like to get more information," he said. The goal would be to come up with information that would lead to more accurate forecasts, both short-term and long-term.
"It's very, very complex," said Kluck, who is based in Kansas City and oversees climate in 14 states. "This is within the realm of what we call climate variability. Apparently, we are in one of those cycles. There does appear to be a wet and dry cycle across the plains."
The U.S. Army Corps of Engineers, which is planning a diversion channel to protect Fargo-Moorhead from catastrophic flooding, also studied the area's climate.
A panel of experts was evenly divided about whether climate change was influencing the valley's wet cycle.
But the experts agreed that wet conditions are almost twice more likely to prevail than dry conditions over the 50-year lifespan of a diversion.
"We didn't address duration at all," Aaron Snyder, a corps project manager for the diversion, said of the relentless wet period. "All we know is it will transition to a dry period at some point."
The U.S. Geological Survey won't even try to predict when the wet cycle will end, Vecchia said.
"It's really totally random," he added. "It could go on another 10 years. It could go another 60 years. Not only can we not predict it, but we won't know it happened until well in the past."