The Mississippi River has continued to rise through the weekend, flooding thousands of acres in the region. Forecasters expect the river to crest in Memphis on Monday night, earlier than previously expected, and farther downstream, Louisiana officials are bracing for a potential flooding disaster. To lessen the chances of flooding in Baton Rouge, New Orleans, and other Louisiana cities, the Army Corps of Engineers is expected to open the Morganza Spillway later this week, after already opening the Bonnet Carre Spillway this morning. Is this larger flood part of a trend, and if so, what role has climate change played?
Two years ago, James Knox of the University of Wisconsin analyzed sediment deposits along the Upper Mississippi River to determine flood magnitudes over the last several millenia. (Greater magnitude floods leave a higher percentage of larger soil particles.) Knox found "striking similarities" between the post-1950 flood record of the Upper Mississippi, and two previous warm periods, one during the Medieval warm climate of about 600 to 1000 years ago, and the other a "warm climate episode between about 3300 and 5500 years ago." All three periods showed both more year-to-year variability in flood size, and a higher frequency of large floods, a pattern Knox expects to continue in the 21st century. In addition, the largest floods tended to occur, not surprisingly, after early spring rains on a "melting winter snowpack," a condition more common during warm weather.
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