Some experts are saying that irresponsible land use, and possibly human-induced climate change, are to blame for the severity of floods that have devastated the Upper Midwest this month.
Over the past century, farmers have drained wetlands, whose grasses have deep roots that help absorb water, and replaced them with profitable fields of corn and soybeans, plants with shallow root systems. Farms have also installed underground drainage systems, accelerating the amount of water that runs off into streams and rivers.
On top of that, previous rains had left the soil saturated, and much of the farmland was bare, as farmers had delayed their planting because of the unusually cold spring.
So when the skies opened up over the Midwest in late May and early June, the water had nowhere to go but into the streets, businesses, and homes.
Reuters quotes Kevin Baskins, a spokesman with Iowa's Department of Natural Resources, who says that the Hawkeye State – whose eastern regions have seen the worst of the flooding – was a very different place before settlers arrived:
"Pre-settlement, most of Iowa was under water, a shallow wetland type of system. That landscape has been altered for production purposes so the hydrology of the area has changed radically in the last century-and-a-half... With civilization, there come trade-offs. There are cases like this when you realize that the river is much more powerful than we humans are and there are some places that we have to give back to nature."
Kamyar Enshayan, the director of an environmental center at the University of Northern Iowa and a member of Cedar Falls's City Council, blames development on flood plains, as well as agricultural practices that have made the land unable to absorb rainfall. "Cities routinely build in the flood plain," he told the Washington Post last week. "That's not an act of God; that's an act of City Council."
By building along the riverbanks and forcing the Mississippi into a bed that is less than half the width of where it ran a century ago, residents are displacing water and forcing the river to run faster and higher. That, in turn, increases demand for taller, broader levees.
But as those levees make way for development that paves over wetlands, more runoff water is channeled into the river. Critics said the result is a self-perpetuating cycle: The rivers rise higher, new levees are built bigger, the rivers rise again.
Some even say that climate change is responsible for the 15 inches of rain that fell over the course of one week. Many are calling the flood a "500-year flood," which means that hyrologists believe that a flood of this magnatude has a 0.2 percent chance (1 in 500) of happening in a given year in a specific location.
The Midwest's last 500-year flood was in 1993.
"There has been in the last 30 years a tendency toward more heavy rainfall events in the central US. We have a past trend and our models, based on increased greenhouse gasses produced by humans, indicate that the trend will continue," Gene Takle, an agricultural meteorology professor at Iowa State University, told Reuters. He added that he could not prove that this particular flood is linked to global warming.
Not all experts see a human hand in these floods. Speaking to both Reuters and the Post, Iowa State meteorologist Elwynn Taylor said that the region has been experiencing a natural wet cycle for the past three decades, and that a drier climate will eventually return.
Others simply blame it on the rain. "With that volume of rain, you're going to have flooding. There's just no way around it," National Weather Service meteorologist Donna Dubberke told the Post. "This is not just because someone put in a parking lot."