Frequency of Iowa flooding and precipitation on the rise


fig10-3
Graph showing the average amount precipitation per year in Iowa. The average amount of has increased dramatically in the state. Since 1960, has seen 10 percent increase in the amount of annual precipitation. (Iowa State University)
Jake Slobe | October 26, 2016

Recent Iowa State University data shows that 100-year flood plain maps actually map 25-year flood plains.  The data also shows that an increasing frequency of large rainfall events throughout Iowa. In Cedar Rapids, the number of heavy rainfall events has increased by 57 percent over the last 100 years.

Kamyar Enshayan, director of the University of Northern Iowa Center for Energy and Environmental Education says that part of the reason for these increases in flooding is coming from changes in land use.

“Over the last 100 years, we have significantly altered the hydrology of our state. The part that we can do something about that would have fairly immediate results is land use change, meaning changing the way our cropping system works, and reestablishing some of the elements we’ve lost like wetlands and forests.”

Currently, the vast majority of Iowa’s agricultural land has, for a long time, been under cultivation in a two-year, corn-soybean rotation. Long-term studies at Iowa State University have demonstrated that moving to a three or four-year crop rotation would lead to a significantly different system that could naturally reduce flooding.

Researchers in Iowa are now analyzing the impact of upstream flood mitigation efforts — as well as determining the costs of potential efforts.

For example, the cost of funding watershed management projects, to help mitigate flood in the state is estimated to be around $5 billion, which is a bargain when put in the context of the cost of flood damage recovery. The damage from the 2008 flood alone was estimated at $10 billion across the state.

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