The dramatic images resulting from this week's floods in the Midwest are, in a way, a welcome sight. Six months ago, the region was wracked by drought. While the sudden drought-to-flood transition may not be due to climate change, it's close to what some models predict.
High water has been pervasive throughout the upper Midwest, ranging from Michigan to Missouri. CNN reports that the worst isn't over: flooding is expected this weekend in North Dakota, into Illinois, down to St. Louis. Six months ago, much of the region was abnormally dry. The Washington Post's Capital Weather Gang describes how the pendulum has swung.
Since the fall, the most radical changes have occurred in the Middle and Upper Mississippi River Valley where the hydrological state of affairs has flipped. A large part of this area, which received almost no rain last summer, is under flood warnings due to recent heavy rains and snowmelt. …
“Over eight months, runoff in the Upper Mississippi River Basin has jumped from way below average to extremely high – including near record levels in some locations. In August 2012, drought had left runoff in the bottom 10 percent,” Climate Central writes. “... Now, water levels are in the top 95 percent. Obviously April numbers are not final yet, but many locations have already broken their record rainfall for the month.”
The Department of Agriculture's Drought Monitor offers week-by-week data on the level of drought in various regions. Last summer, levels of recorded drought spiked. In August, 38 percent of the Midwest was experiencing extreme levels of drought; in September, over 94 percent of the region was at least abnormally dry.
Compare that with drought conditions in the Northeast over the same time period: Less than 75 percent of the region has been drought-free only twice.
Jeff Masters of Weather Underground explains what's happening in the Midwest.
A warmer atmosphere is capable of bringing heavier downpours, since warmer air can hold more water vapor. … So how can you have worse droughts with more moisture in the air? Well, you still need a low pressure system to come along and wring that moisture out of the air to get rain. When natural fluctuations in jet stream patterns take storms away from a region, creating a drought, the extra water vapor in the air won't do you any good. ... The drought that ensues will be more intense, since temperatures will be hotter and the soil will dry out more.
In other words, a warmer atmosphere from climate change likely yields greater extremes in weather. This syncs with the draft report issued by the government's National Climate Assessment Development Advisory Committee last year. That report predicted the following for the Midwest: "longer growing seasons and rising carbon dioxide levels will increase yields of some crops, though those benefits will be increasingly offset by the occurrence of extreme events such as heat waves, droughts, and floods."
That prediction was meant to be borne out over the next several decades. What it predicted, though, has already been seen over the course of six months.