Farm Horizons, Feb. 2011
Ready for soggy soil this spring?
By Starrla Cray
After a long, cold winter, many area farmers look forward to warmer weather and the opportunity to get back in the fields.
That anticipation has been “watered-down,” however, by the strong possibility of flooding this spring.
“There are five factors that we look at when determining the likelihood of flooding, and the odds are already stacked heavily against us this year,” University of Minnesota climatologist Mark Seeley said.
Although no one can predict future weather events with 100 percent accuracy, the following conditions play a significant role in the probability and severity of spring flooding:
“In the fall of 2010, most of the state had above normal precipitation, which reduces the storage capacity in the soil for added moisture,” Seeley said.
In Carver County, 6.61 inches of rain was recorded in August 2010, and 5.33 inches was recorded in September, according to data from the State Climatology Office. Wright County had less rain in August (4.98 inches), but made up for it in September, with a total of 6.68 inches.
McLeod County also had high precipitation amounts during those two months, with 6.53 inches in August, and 6.01 inches in September. Meeker County had the highest observed precipitation in early fall, with 6.87 inches in August, and 6.99 in September.
According to the Minnesota Department of Natural Resources (DNR) website, the average annual precipitation in the state ranges from about 18 inches in the far northwest to more than 32 inches in the southeast.
“We’ve been having above-normal precipitation and below-normal temperatures,” said Bob Byrnes, regional director of the U of M extension service.
Persistence of snow cover
This winter, it’s been impossible to ignore the immense snow piles decorating the state, with near record-setting snowfalls.
“It’s been one of those years,” Seeley said.
According to the state climatology office, all-time high December precipitation totals were reported in Rochester (3.68 inches), Jordan (3.30 inches), and Hutchinson (3.12 inches), mostly in the form of snow.
Across southern and central Minnesota, numerous observers reported 3 or more feet if snow in December, roughly triple the historical average.
The sheer amount of snow isn’t the only factor involved when it comes to flood risk, however. Also important is the water content in the snow.
“The water content of that snow cover is rather high,” Seeley said, explaining that many areas have between 3 to 5 inches.
Compared to the record spring flooding of 1997 (with 5 to 7 inches of water content in the snow), it doesn’t seem too bad, but Seeley said it’s still a concern.
“The problem is, we still have a long way to go,” he explained.
Depth of frozen ground
The deeper the soil is frozen, the more likely flooding will occur, because frozen soil doesn’t allow water to infiltrate.
In 1997, frost depth was recorded at well over 3 feet.
This year, it’s not as bad, but it’s still something to watch.
“Frost depth is all over the place,” Seeley said, explaining that many areas are at between 20 and 30 inches.
If spring comes gradually, in “pulsed” freeze/thaw cycles, the chances for flooding are reduced.
“That would be ideal,” Seeley said, but added that he doesn’t expect this to be the case.
If instead, there is a rapid, compressed thaw, flooding is much more likely.
Wet weather continuing into March and April compound the risk of flooding, and it’s even worse if the precipitation is in liquid form.
“Rain actually helps the snow pack melt faster,” Seeley said. “We have gotten thunderstorms in the past that left 6 inches of rain in April. That would be kind of a ‘worst-case’ scenario.”
Meteorologists and climatologists evaluate all factors when assessing flood risk, and according to Seeley, many are a bit uneasy about what will happen this spring.
Because of the weather pattern La Niña, which is expected to linger through April, it’s likely that spring will be delayed this year, increasing the risk of flooding.
“This system is a player in the cold, snowy weather we’ve been having,” Seeley said.
Offsetting the flood risk is unlikely at this point, according to Seeley.
“The conditions we would need are exceptional,” he said. “We would need to have an exceptionally dry February and March, with a gradual spring thaw. There’s a low probability that we’ll have those types of conditions. More likely, it’ll be a normal to above-normal snowfall with a compressed warm up.”
Despite the possible flood risk ahead, it’s still too early to determine how the growing season will impact area farmers.
“Getting crops planted on time that’s going to be a challenge,” Seeley said.
However, there are also some benefits of damp weather.
“We do know that soil will be amply filled with moisture,” Seeley said. “That will act as a buffer to the root zone if we have a drought later on.”
The National Weather Service website (www.weather.gov) includes frequent flood outlook updates.
More information is also available at the U of M extension website, www.extension.umn.edu/flood.