Why, oh why, is it so wet?

This field north of Wolverton, Minn., sits under water in April 2011. - Michael Vosburg / Forum Photo Editor


John Wheeler – WDAY and WDAZ chief meteorologist

Ask a room full of people to explain why the rivers and lakes across our region have been flooding so much in recent years, and you will get myriad answers.

Some answers will have elements of truth. Some will be based on myths that need to be dispelled.

To begin with, the fact that the Red River flows northward is not why it floods the way it does.

Once the Red tops its banks, it spreads out across the flat terrain for miles.

Ice in the river channel cannot possibly be responsible for a 10- to 20-mile-wide river. Rather, it is the lack of slope downstream that causes flooding.

The average drop of the Red River from Wahpeton, N.D., to Halstad, Minn., is about 5 inches per mile. North of Grand Forks, the slope drops to 3 inches per mile. Between Drayton and Pembina, N.D., the slope is 1½ inches per mile. This is one flat river valley.

When waters gather due to snowmelt or heavy rain, the slope in the valley is just not able to move that water downstream as quickly as it gathers, causing the waters to rise out of the river channel and spread out over the land.

Second, urban sprawl is not a significant contributor to the increase in flooding.

It is true that rain falling on concrete does not soak into the soil but drains directly into the river. But the percentage of land covered in concrete remains small. Plus, there is no evidence of increased flooding immediately downstream from urban areas that cannot be otherwise accounted for.
What about changes in the way water drains from farm fields to the river systems?

Since the 1880s, farmers have been draining wetlands, building ditches and sculpting their land to allow fields to dry out more quickly in the spring and after heavy rains. Intuitively, this must have an effect because it means water gets to the river faster.

However, a comparison of annual stream flow totals to the five-year running average of precipitation shows that the ratio between these two has, over time, changed only a little.

Essentially, when it is dry, there is very little flooding, and when it is wet, flooding becomes a problem. And the effect is cumulative.

A run of dry years, as in the 1930s, reduces the water table to such low levels that the risk of flooding goes essentially to zero, and even a very snowy winter cannot create flooding. On the other hand, the current run of wet years has filled the lakes, the wetlands and the reservoirs to the point that now just slightly above-average precipitation causes serious flooding.

Devils Lake displays the same accumulative effect.

Its lowest modern-day level was not at the height of the 1930s drought, but in October 1940, when the lake was barely a mud puddle. During the past 19 years of wet weather, Devils Lake has risen and grown to new levels virtually every year. With the repetition of heavy winter snows and frequent summer downpours, the water just keeps coming.

Flash back to the room full of people.

Ask them why our weather is wetter than it used to be. Again there will be disagreement.

Some will lay blame on global climate change. Some will vehemently deny the very possibility of such a thing, saying it is merely natural climate cycles. Both responses are based in political dogma. Reality in weather is rarely so simple.

From intrusions of glacial ice to decades-long drought, natural cycles are certainly capable of tumultuous changes. However, it is foolish to categorically deny that human-caused changes in our atmosphere are incapable of changing climate.

The ongoing 19-year wet period likely has not one simple cause but many causes, layered on top of one another in a way that makes them difficult to identify. This means, of course, that there is no way of knowing what direction our climate will go next.
Will it remain wet? Will the flooding get even worse? Would it be possible for the climate to suddenly swing back into a multiyear drought that would leave us wanting for water?

A big-picture view of our climate makes it clear that all of these things can be expected. What we cannot tell is when to expect the changes because our climate, like today’s weather, is inherently unpredictable.

John Wheeler is the chief meteorologist at WDAY and WDAZ.

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