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Organizer William Simpkins, a professor in the ISU Department of Geological and Atmospheric Sciences, said the café was a way to foster public discussion of science topics in a more casual environment.
"There are 65 to 70 monthly science cafés across the country in brew pubs, coffeehouses, museums and even a public TV station," Simpkins said.
Three of Simpkins' colleagues talked about their individual specialties and research projects, including professors Kristy Franz (100-year floods), William Gutowski (future extreme rainfall) and Michael Burkart (how landscape changes influences stream discharge).
Among the points they made:
* Franz said measurements of flooding in the Skunk River show that streamflow peaked at nearly 10,000 cubic feet per second on two occasions during floods last June. The river never reached that total in the "record" flood of 1993, although it surged above 6,000 CFS seven times that year compared to twice this year.
* Gutowski said persistent upper winds, combined with rising temperatures and humidity, could lead to more precipitation and bigger "spikes" in heavy rain/snow events by the end of the century.
* Burkart said "row crops," such as corn and soybeans, along with tiled farm fields and "channelized" (or straightened) waterways, tend to increase the amount of water going into the Raccoon River upstream of Des Moines.
Audience members posed questions on topics from measuring how much water can be held by farm field "potholes" to what Gutowski's climate predictions would mean for Mid-Iowa to how more data can improve the accuracy of 100-year flood data.
Other salient points from the panel included:
Franz -- 100-year floods.
* The term was developed to help define costs vs. benefits and acceptable risk (such as building in flood plains).
* Because we don't know what all the flood events look like, it's hard to estimate future events.
* Her class studied Skunk River flood events from 1921 to 2007. But because that is less than a century, data has to be extrapolated.
* The National Flood Frequency Tutorial indicates that there isn't enough data to make sure predictions. To see a multimedia presentation, visit: http://www.fema.gov/plan/prevent/fhm/ot_nffsr.shtm
* Three federal agencies use data to estimate 100- and 500-year events, including the Federal Emergency Management Agency (FEMA), the U.S. Geological Survey (USGS) and the U.S. Army Corps of Engineer. FEMA also keeps data showing the location of floodplains. because the agency controls the federal flood insurance program.
Gutowski - future extreme rainfall.
* We try to understand the behavior of the climate, not just run computer models.
* Researchers looked at data in 8-year increments because the computers were best equipped to look at that amount of material.
* In the study, researchers looked at regional events occurring every one to two years; they studied the contiguous United States, but, more specifically, the upper Mississippi valley. There were 476 observation sites and 316 "grid points" to plot results on a map.
* Although the cold half of the year was studied, data apply year round.
* Daily precipitation averaged .063 to .067 inch, but up to 4.7 inches for severe events, compared to the computer simulation of 1.7 inches.
* Upper wind patterns at 15,000 feet were examined. They show a big dip that begins along the west coast, parallels the Mexican border, then goes north roughly along the Mississippi Valley. The pattern draws a lot of moisture from the Gulf of Mexico, and a similar pattern was produced in future predictions.
* Future extremes depend on increasing humidity leading to a projection of 17 percent more future precipitation and 26 percent more in future "extreme events."
* There has been a 2.5-degree (Celsius) increase in temperatures since the mid-20th century.
* The study projects winter precipitation extremes of up to 7 inches and summer extreme of up to 8 inches by end of 21st century. Current extremes are 4.5 and 5.5 inches, respectively.
Michael Burkart - landscape changes on streamflow.
* Increased planted row crops correlate with higher stream discharges.
* Perennial plants intercept more water.
* The Raccoon River at Van Meter was near 6,000 CFS in 1993. Other high-water events were in 1932, 1951, 1973 and 1983. Except for a slight dip in 1983, records trend generally upward.
* An the study looked at the percentage of row crops in the Raccoon River watershed. It parallels the streamflow increase except for two slight dips in the 1980s.
* The debate is whether climate change or land use change is the main culprit.
* Studies of tiled farm fields showed that water pools where tiles are plugged or filled.
* As little as a 1-inch event showed sharp increases in discharge into the Raccoon River. Human drainage systems over a 1,000-acre study area discharged the water much quickly where -- if left in its normal state - would have retained the water longer.
* Only one-third of the Raccoon River watershed has natural wetlands and "hydric soils" that can retain water; and 99.4 percent of the wetlands have been drained, according to Calvin Wolter, of the Iowa Geological Survey.
* About 30 percent of the Raccoon River has been channelized - straightened and deepened with stream meanders removed and more stream ditches put in place.
Bob Zientara can be reached at 232-2161, Ext. 487, or rzientara@amestrib.com.
