Recent St Louis flooding made worse by human changes to landscape

Recalculating route... (credit: Missouri National Guard)

Humans put considerable effort into controlling river flood water. We build dams to hold the water back, levees to keep it in the river channel, and floodways to divert it from protected areas if the first two reach their limit. The great irony of levees, though, is that the more of them you build, the more dangerous the river becomes. Whatever volume of water comes down the river has to go somewhere. Wall off part of the river’s natural floodplain, and it will have to take up extra space somewhere else.

Climate change looks to be responsible for greater flooding risk in some places, as extreme rainfall becomes more common or weather patterns shift. But greenhouse gas emissions are not the only way we bring more flood damage on ourselves. We also manipulate river systems and construct new developments in risky places.

In late December, a weather system juiced by the El Niño conditions in the Pacific dragged rain across the central US. The Meramec River, which joins the Mississippi on the south side of St Louis, saw about 20 centimeters of rain fall around it over three days. Because a storm a few days earlier had already soaked the ground, most of that rain ran along the surface into the nearest stream. The Meramec River hit record flood stages in the St Louis suburbs, and at least twelve people died in Missouri despite evacuations.

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