The Midwest Is Getting Drenched, And It’s Causin

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The Midwest Is Getting Drenched, And It’s Causing Big Problems

By Ella Koeze

Filed under Weather

Published May 17, 2018

https://fivethirtyeight.com/features/the-midw...cid=SigDig

Minnesota is getting wetter. Over the last 100 years, the state has seen more storms that produce heavy rainfall, and its strongest storms have grown more intense. One of the more dramatic changes is the increasing number of “mega-rain” events — rainstorms during which at least 6 inches of rain falls over at least 1,000 square miles and the center of the storm drops more than 8 inches of rain. Minnesota has had 11 mega-rains since 1973,1


and eight of them have come since 2000. Two mega-rains swept through in 2016, which is only the third time the state experienced more than one mega-rain in a year. (It also happened in 1975 and 2002.)

Experts suspect climate change is behind this and other shifts in precipitation patterns. But knowing what’s causing an increase in precipitation and knowing what to do about it are two different issues. Minnesota and states across the Midwest are confronting an uncertain, flood-prone future, one where changes in precipitation patterns could get even more dramatic.

The precipitation estimates that city planners have relied on in making preparations for flooding are based on historical weather trends, not predictions of future trends, and the estimates themselves were sometimes decades old. New estimates have been released for Minnesota, but they only show how much has already changed. They have nothing to say about what change is coming next.

Minnesota is not alone in its recent wetness. Though the Midwest is far from any hurricane-prone coasts, the region has seen an increase in both precipitation and, subsequently, flooding. “It’s a huge amount of water being added,” said Kenny Blumenfeld, a senior climatologist in the Minnesota Department of Natural Resources State Climatology Office, “and a huge water-management problem.”

This added water can be seen in the map below, which shows the nationwide changes in annual peak streamflows — that is, the highest yearly reading2 of how much water flowed past a gauge monitored by the U.S. Geological Survey.3

In the Upper Mississippi Valley, the peak ratings at nearly all the gauges show more water flowing through over the last century.

As the wet summer season approaches, no one knows whether 2018 will again bring historic levels of rain and flooding, but regardless, Minnesotans can be sure that those days aren’t far off.

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