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Atmospheric Rivers Deliver Vast Amounts of Moisture

Former IIHR postdoc David Lavers studies atmospheric rivers and their often staggering strength and vast amounts of moisture.

Former IIHR postdoc David Lavers studies atmospheric rivers and their often staggering strength and vast amounts of moisture.

Iowa City residents won’t soon forget the spring of 2008. Hundreds made heroic efforts to try to save University of Iowa landmarks and other structures, filling sandbags around the clock for weeks. Tragically, many of those efforts were in vain, as the relentless floodwaters rose and eventually overtopped some sandbag fortifications.

That 2008 brought floods to the state is not news, but the idea that a vast atmospheric river (AR) delivered the moisture might be a novel concept to most Iowans. The strength of ARs can be staggering, says IIHR Postdoctoral Scholar David Lavers. For instance, the atmospheric river that hit Iowa City in 2008 carried with it 110 times as much flow as the Mississippi River at St. Louis.

Lavers’s research focuses on atmospheric rivers, which are defined as regions of very high water transport in the lower atmosphere. ARs have been studied for about 20 years, making them a relatively new concept in hydrometeorology. Satellite observations, field campaigns, and large-gridded globally-observed datasets have made it possible for researchers to analyze what’s going on in the atmosphere, and thus to study ARs much more effectively.

In the northern hemisphere, ARs tend to flow northwards from the tropical regions toward the poles. They form within a storm, and the storm’s circulation causes the very narrow AR structure to develop. The AR that commonly flows over Iowa and the Midwest is known as the “Maya Express,” because it carries moisture northwards from Latin America.

The water that ARs delivers is critical for agriculture, public water supplies, and the environment, Lavers says. For instance, a handful of intense rain events triggered by ARs can deliver up to half of California’s water supply for the year.

But that same intensity can have tragic results as well, as extreme rainfall often leads to flooding. “It can be devastating,” Lavers says. Scientists have noted a high correlation between ARs and flood events. With improved monitoring of AR conditions, such as those in the western United States, researchers can better understand intense rain events and flooding, Lavers explains. This in turn creates a clearer picture of the characteristics of an incoming atmospheric river, providing a warning system that could save lives and improve flood readiness.

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Last modified on January 10th, 2017
Posted on January 10th, 2017

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