Weather experts hope ’08 offers lesson
WATERLOO — Last month, the National Weather Service office in Des Moines released its assessment of the 2008 floods in Iowa. As weather experts expected, the report shows above-average precipitation totals leading up to the disaster, as well as heavy rains in early June.
What wows hydrologist Jeff Zogg, however, is the margin by which some long-standing records were broken. Iowa saw record rainfall totals and river crests in 2008.
“Normally when you break a record, you are only going to break it a little bit if you break it at all,” Zogg said.
The statewide precipitation average from January to June measured 24.47 inches, 8.13 inches above normal, the report stated, making it the wettest first six months of the year on record for Iowa since 1873.
As flood-affected communities look to ways to mitigate flooding, weather experts are working to improve the way flood situations are analyzed and reported. Ideas to perhaps improve disaster preparedness include possibly putting different rainfall scenarios online to show the range of possibilities, Zogg said.
Typical river forecasts use a 24-hour outlook because accuracy drops off after one day, he said. That system provides pretty good information under normal circumstances, he said, but June 2008 wasn’t typical. A 24-hour forecast doesn’t take into account the impact of future precipitation outside the prescribed window.
“In a lot of cases, we did chase the crest,” Zogg said.
The National Weather Service, in cooperation with the U.S. Geological Survey, also increased flood forecast services. For example, river forecasts are now available for the Cedar River at Waverly when high water is expected. This puts the city in a better position in the event of future flood events, Waverly’s City Engineer Mike Cherry said.
The National Weather Service also is working with the University of Iowa to propose funding for inundation maps for locations in Iowa. Such maps would show flooded areas corresponding to a specified river stage. The maps also would show the forecast depth of the water at different locations, Zogg said.
Those monitoring the weather always are looking for ways to do better, Iowa climatologist Harry Hillaker said. But it’s never an exact science, especially during a historic, record-breaking event like 2008.
“When you break new ground, it’s just hard to know how the river’s going to react,” Hillaker said.