Climate studies project more Iowa flooding

Peak water flow in Iowa's rivers and creeks could increase 50 percent by midcentury, increasing the likelihood of flooding, a new review of scientific climate change studies reveals.

Iowans should be prepared for the possibility of more floods because of heavy rainfall in midsummer months when flooding has not ordinarily occurred, Iowa State University professor Eugene Takle.

While climate studies show that spring rainfall also will increase, Takle said it's not clear how much that will influence flooding, since warmer winters in Iowa also could cause more drainage and snow runoff before spring.

“I think we need to be watchful,” said Takle, who presented the Iowa Climate Change Advisory Council with a white paper last week after he reviewed scientific studies of climate change's projected impact on the state. The council is expected to release a fuller report in a year.

Takle cited one study showing precipitation increasing 21 percent across the Upper Mississippi River basin by the 2040s. That would increase stream flows by 50 percent, the study showed.

State Sen. Rob Hogg of Cedar Rapids, a non-voting member of the Climate Change Advisory Council, cited the report in a call for better flood-plain management. He said Iowa has sustained nearly $20 billion in flood damage, or $6,000 per Iowan, since 1984.

“This report shows that Iowa is at risk from even more flooding in the future due to climate change,” Hogg said.

Researchers expect stream flows to increase even more than precipitation for several reasons. One is the increased probability of “extreme rainfall events.” Another reason is the increased amount of development that speeds runoff, and a third is widespread use of drainage tile in agriculture.

Drainage tile speeds up the removal of water from fields to prevent ponding and saturation.

Study simulations for tile drainage show a range of results, depending on the climate model - from a 24 percent increase in precipitation by midcentury resulting in a 35 percent increase in drainage tile flow, to a 32 percent increase in precipitation and 80 percent increase in tile flow. Both show more water flow through field tiles in the spring months.

Hogg said the state needs better watershed management, better flood-plain management and recognition that any development should be designed to accommodate at least a 500-year flood.

Takle is director of the Iowa State University Climate Science Initiative, which conducted the precipitation and tile drainage studies, and was among the researchers. The precipitation study conducted in 2004 looked at the Upper Mississippi River basin. The tile study, projecting large precipitation increases, was conducted this year with the latest climate modeling from the Danish Meteorological Institute.