map shifting rainfall USA

With shifting rainfall patterns and amounts of water in the ground, the risk of flooding in the US is changing across the nation. Researcher says the north half of the country is at a greater risk of flooding, while the threat has declined in the West, South and Southwest regions.

With shifting rainfall patterns and ground water amounts, the risk of flooding in the US is changing across the nation.

Researcher are now warning the north half of the country is at a greater risk of flooding, while the threat has declined in the West, South and Southwest regions.

After analyzing data from streams and NASA satellites, the team discovered that the amount of ground water in the northern area of the US has increased.

The University of Iowa engineers Gabriele Villarini and Louise Slater made the discovery by comparing data from 2,042 streams with satellite information gathered over more than a dozen of years by NASA's Gravity Recovery and Climate Experiment (GRACE) mission showing 'basin wetness,' or the amount of water stored in the ground.

Uncovering the increased amount of ground water in the north means this area is at a higher risk of minor and moderate flooding.

On the other hand, the southern and western portions of the country experienced a drop in the amount of ground water.

However, both areas have been experiencing prolonged droughts, so this factor played a key role in decreasing their water table.

'It's almost like a separation where generally flood risk is increasing in the upper half of the U.S. and decreasing in the lower half,' says Villarini, associate professor in civil and environmental engineering and an author on the paper, published in the journal Geophysical Research Letters.

'It's not a uniform pattern, and we want to understand why we see this difference.'

Some of the regional variation can be attributed to changes in rainfall; a study led by Villarini published last year showed the Midwest and Plains states have experienced more frequent heavy rains in the past half-century.

More rainfall leads to more groundwater, a 'higher water base line,' Villarini explains.

'The river basins have a memory,' adds Slater, a post-doctoral researcher and the paper's corresponding author.

'So, if a river basin is getting wetter, in the Midwest for example, your flood risk is also probably increasing because there's more water in the system.'
groundwater saturation northern US, flooding hurricane sandy

The team compared data from streams and satellites showing the amount of ground water. They found the amount had increased in the north half putting areas at risk of flooding - similar to what happened to Hoboken, New Jersey during Sandy in 2012.


The team has not yet identified why some areas of the US are getting more, or less, rainfall than others.

But they believe it may be a result of rains being redistributed as regional climate changes.

The researchers hope that their findings could revise how changing flood patterns are communicated.

'The concept is simple,' says Villarini, whose primary appointment is in IIHR-Hydroscience, a branch of the College of Engineering.

'We're measuring what people really care about.'