Midwestern US states are getting soaked by rise in damaging floods

Maria Galluci in the International Business Times: The U.S. Midwest is getting soaked. Damaging floods are hounding the region with increasing frequency, leading to billions of dollars in agricultural losses and displacing thousands of people, a new study found. Scientists say the trend will likely get worse in coming decades as the effects of climate change accelerate.

Fourteen states in the Midwest and surrounding area saw “increasingly more frequent flood episodes” from 1961 to 2011, according to a University of Iowa study published Monday in the journal Nature Climate Change. Researchers pored over daily geological reports from 774 stream gauges, and found that about a third of stations experienced increasingly frequent flooding. Only 9 percent of stations showed a decrease in flood events.

“There was a feeling that these flood events have been increasing, but the question was, Is it just our perception of the recent past vs. present?” Gabriele Villarini, an engineering professor at Iowa and the report’s lead author, said. “So that’s when we decided to do this analysis.”

Five major floods have pummeled the Midwest region over the past two decades, including a record 2008 disaster in Cedar Rapids, Iowa, that caused up to $6 billion in flood-related damage and forced 25,000 people from their homes...Nationwide, many states have also seen a rise in “nuisance flooding,” the minor events that shut down roads down and clog storm drains but aren’t particularly dangerous, the U.S. National Oceanic and Atmospheric Administration reported last fall....

Villarini said the increased frequency of Midwest floods is largely the result of changes in regional temperatures and rainfall patterns. In the northern states, the spring season has become steadily warmer over the past few decades, while at the same time, snowmelt -- the watery surface runoff caused by melting snow -- has also increased. In other areas, heavy rainfall events are happening more often, leading to more frequent flooding.

...But he noted that the findings are consistent with how climate scientists generally believe global warming is affecting the hydrological cycle. As the atmosphere warms up, it can retain more moisture; all that added vapor, in turn, can lead to more intense and frequent precipitation. In the Midwest, that could lead to more “erosion declining water quality and negative impacts on transportation, agriculture, human health and infrastructure,” according to the National Climate Assessment, a sweeping 2014 report by the White House....

Cedar Rapids in a 2008 flood, shot by Matt Herzberger Matt Herzberger, Wikimedia Commons via Flickr, under the Creative Commons Attribution-Share Alike 2.0 Generic license

The water cycle amplifies abrupt climate change

A press release from the Helmholtz Center in Potsdam: The role of the hydrological cycle during abrupt temperature changes is of prime importance for the actual impact of climate change on the continents. In a new study published in Nature Geoscience online (January 19, 2014) scientists from the University of Potsdam, Germany and the GFZ German Research Centre for Geosciences show that during the abrupt cooling at the onset of the so-called Younger Dryas period 12680 years ago changes in the water cycle were the main drivers of widespread environmental change in western Europe. The team of scientists analyzed organic remains extracted from Meerfelder maar lake sediments from the Eifel region, western Germany, to reconstruct changes in precipitation patterns in unprecedented detail. They were able to show that the intrusion of dry polar air into western Europe lead to the collapse of local ecosystems and resulted in the observed widespread environmental changes at that time.

The exact sequence of events during abrupt climate changes occurring over only a few years is one of the great unknowns in paleoclimate research. The new results presented here were obtained by using a novel method, where molecular organic remains derived from plant fossils were extracted from precisely dated annually laminated lake sediments. The ratio of the heavy Deuterium to the light Hydrogen isotopes in these biomarkers can be used to reconstruct changes in precipitation regime and moisture sources with unprecedented detail.

... Dirk Sachse, the head of the workgroup at the Institute of Earth and Environmental Sciences of the Potsdam University explains: “In our new study we can show for the first time that this change in the pathway of westerly wind systems brought dry polar air into western Europe and this was the ultimate cause for the widespread disappearance of forests in the area.”

With these new results, the group also supports the hypothesis that this change in atmospheric circulation patterns over western Europe took place 170 years after the onset of cooling, as observed in the Greenland Icecores. The authors attribute this delay to the subsequent southward expansion of sea ice in the North Atlantic following the onset of cooling. This lead to a southward shift of the polar front channeling dry polar air into western Europe. “Our results also show that abrupt climate and environmental change may not be coeval on large regional scales, but can take place with substantial regional and temporal delays” explains Prof. Achim Brauer from the GFZ German Research Centre for the Geosciences.

The results of this study, which was funded by the German Research Foundation (DFG) through its Emmy-Noether Programme and the Helmholtz Climate Initiative REKLIM, do not only show unequivocally that temperature changes can have regionally different impacts, but also that the water cycle acts as amplifier of change with potentially severe effects on continental ecosystems. ...

A view of the Meerfelder Maar, shot by Bungert55 , Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license