With about half of the country still suffering from extreme drought, farmers and businesses in the Western United States are looking at another hot, dry summer.

And the country's water risk is a lot worse than most assessments suggest, according to a recent study from the Columbia University Water Center.

Taking into account past patterns of drought and water use, the Columbia study reveals that several major metro areas, including New York City, Washington, D.C., and Los Angeles, are at high risk for water scarcity, along with the Great Plains agricultural belt extending from North and South Dakota down to North Texas.

Here's a list of the top 10 areas with the highest risk for water scarcity:

Washington DC metro area

New York metro area

California area, from San Diego to Santa Barbara and inland

Agricultural belt: Dakotas

Agricultural belt: Nebraska

Illinois

Lower Mississippi belt: Arkansas area

Agricultural belt: North Texas

Agricultural regions in Ohio

Agricultural regions in Minnesota

"All cities and all businesses require water, yet in many regions, they need more water than is actually available — and that demand is growing," said Upmanu Lall, director, Columbia Water Center. "The new study reveals that certain areas face exposure to drought, which will magnify existing problems of water supply and demand."

The study notes that a 99% population increase since 1950 combined with a 127% increase in water use has further decreased water availability, making it increasingly difficult to replenish water supplies after a drought.

The report doesn't predict when or where the water scarcity will become an issue. In New York and Washington, D.C., for example, water is brought in from outside of the city from other sources, which are typically plentiful.

In other areas, however, the current drought — the worst since the Great Depression — is already bringing water availability issues to the fore.

According to the most recent federal forecast, about 48% of the contiguous U.S. is now experiencing moderate to exceptional drought, down from a high of 60% at the beginning of the year. The drought is expected to intensify in the West this summer, and while conditions should "ease" in the Plains states, the drought is not expected to end anytime soon and temperatures are expected to be above-normal for most of the lower 48 this summer.

"Even if you don't believe in climate change, the North American continent historically has had frequent and severe droughts," Lall said. "There are very significant droughts that have happened here historically — they are not that unusual."

The New York Times highlighted the growing water worries this week, with a story examining the depleting resources of the High Plains Aquifer, which provides irrigation for agricultural centers in the Midwest.

The Times reports:

Two years of extreme drought, during which farmers relied almost completely on groundwater, have brought the seriousness of the problem home. In 2011 and 2012, the Kansas Geological Survey reports, the average water level in the state’s portion of the aquifer dropped 4.25 feet — nearly a third of the total decline since 1996.

This map shows the decline in the aquifer:

As the Atlantic Wire's Philip Bump points out, the High Plains Aquifer has been a "hydrological savings account" for farmers in the Great Plains. But as the aquifer's resources dwindle, farmers are being forced to subsist on water from rainfall, at the same time that rainstorms are becoming less and less frequent.

The ramifications for agriculture and business are predictably devastating.

Bloomberg reports that an Ernst & Young corporate sustainability study recently found that 76% of corporate representatives think water is the top resource at risk.

According to the federal forecast, national pasture and rangeland conditions are at record lows, and 39% of the U.S. winter wheat crop was rated poor or very poor, up from 25% last year.

Lall points out that the water scarcity could also pose huge problems for the burgeoning domestic energy industry. A recent Ceres research paper found that a lot of hydraulic fracturing— a process that uses tons of water — is taking place in water-scarce regions, with nearly 47% of wells located in highly-stressed water basins, including 92% of wells in Colorado and 51% of wells in Texas.

The map below shows water competition in U.S. shale exploration:

According to Lall, there are two solutions to mitigating U.S. water risk. The first, he said, is raising awareness about the problem and managing water needs. The second, more problematic solution, is developing and improving the country's water storage capabilities — which would require significant investment in water infrastructure.

"If you add up all the water infrastructure in the country, almost $1.5 trillion needs to be spent on water infrastructure in the next 20 years," Lall said. "We have made almost no investments in water infrastructure since the Reagan administration. Something needs to be done about it."