Flood forecasters can rely on more sophisticated tools | St. Louis Public Radio

Flood forecasters can rely on more sophisticated tools

Apr 27, 2011

This article first appeared in the St. Louis Beacon, April 27, 2011 - As rivers in Missouri and other parts of the Midwest begin their all-too-familiar spring rise, are forecasters better equipped to let people in flood-prone areas know how high and how wide the water will go?

Charles Graves of the Saint Louis University Department of Earth and Atmosphere Sciences says a lot of the tools that were in their infancy in earlier floods, like 1993, are now at the point where they can be a real help in determining what will actually occur.

"Then," he told the Beacon, "we were just learning what they were capable of providing. Now these tools have matured and we are much better at incorporating the data into our forecasting."

Current projections have the river at St. Louis at its highest point today -- 33.4 feet (flood stage is 30 feet). The Army Corps of Engineers said today it will wait until the weekend to decide  whether to punch a hole in the Birds Point levee in Mississippi County in southeast Missouri to relieve water pressure.

Missouri Attorney General Chris Koster went to court Tuesday to block the move, saying it would flood 130,000 acres of prime agriculture land. A corps spokesman told the Associated Press today that even if a judge gives the go-ahead, the agency cautiously will wait until it gets a better forecast of the river crests to see if the breach is necessary

Graves noted that flooding this spring was expected, according to an alert issued a few months ago by the National Weather Service. The prediction, he said, is based in part on tools that have come along in recent years.

In a spring flood outlook, the National Weather Service weather forecast office said it based its flood predictions on "streamflows and soil moisture over the area." It also looked at "upstream snowpack in the Mississippi, Missouri and Illinois river basins," as well expected rainfall over a period of three months.

"Two or three months out they realized the setup was there for the potential for flooding," Graves said. "That doesn't mean it is going to occur, but three months out they could see there was a strong potential; all the ingredients were there. The thing that was still unknown was how much additional rainfall was going to occur, and where.

"You're going to see a lot more of that, what the National Weather Service calls situational awareness, where you are aware that the potential for an event exists. Because of that, you can start to take action to minimize its effects. I think that's what you are going to see a lot more of in the next five to 10 years."

Mark Fuchs, a service center hydrologist with the weather service in St. Charles County, said that kind of data wasn't around back in the record flooding of 1993.

"We didn't have the integrated capability of radar and hourly rain gauges around the area to give us a blanket representation of how much rainfall we have been getting in a particular basin," Fuchs said. "That data have improved, and it's going directly into our river models.

"The river forecasting program that we're using is also being expanded and being improved because we have more to look at."

He noted that such forecasting for the Mississippi River is actually done at two centers -- one in Minnesota, for the river down to Chester, Ill., and the other in Louisiana, for everything south of Chester. Forecasts for the Missouri River basin are issued from a center in Pleasant Hill, Mo., near Kansas City.

"The guidance that we get from them essentially becomes our forecasts for crests, rises and falls," Fuchs said.

While levees come under the jurisdiction of the Corps, not the weather service, Fuchs said flood predictions do take into account when breaks occur, since water escaping through or over levees will result in a reduction of the amount in the river.

"Every river gauge has a rating curve," he said, "which says that at such and such height you have so many thousands of cubic feet of water going through this point, or in the case of the Mississippi River hundreds of thousands of cubic feet.

"When a levee breaks, that changes the equation. Such-and-such height may no longer mean that same amount of water, because it has escaped. Now that you have the flow traveling downstream or getting stuck behind a levee, those are complications that change the calculations."

What's in the long-range forecast for flood predicting tools? Fuchs said new computer modeling will help make it easier to tell what is going to happen at longer range.

"I'm not sure we're able to take advantage of it just yet," he said. "It's a long process trying to get newer models in place. But that will certainly be an enhancement to river forecasting."

He compared those tools with the ones used by meteorologists in trying to make better predictions of daily conditions.

"They may not make one specific forecast better," Fuchs said, "depending on which way a forecaster ends up going. But in the longer run, it will probably lead to better forecasting in a meteorological sense, and when you look at it from a hydrological sense, I think it would do the same."

Graves, at SLU, says forecasters are looking at another aspect, one that is less scientific and less predictable but one that is likely to have a bigger impact in the long run on families who depend on predictions but may not always react in the way that forecasters expect.

"There is an aspect of forecasting that deals with human reaction or lack of reaction," he said. "How do you word your forecasts to provide the information to individuals so they can understand what the potential is and how they should react to it? This is true not just with flooding but with severe weather: How can they issue those warnings so they can get people to act?

"It's an avenue that merges science with what you might call social studies, and an avenue that is currently growing. The National Weather Service is well aware of this area and has added things to their operations to enhance that. They are tasked with public safety, and it doesn't matter how good the science is if the public is not reacting to the information they are providing.

"Most scientists are not naturally drawn to that aspect of science. They want to do their science, and they don't want to have to worry about the perception of what they are doing. But in meteorology, especially in the forecasting arena, that is not an option."