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4 Billion People Face Severe Water Shortages

Most of the people on Earth experience severe freshwater scarcity at least part of the year, reports a new study.

It's no secret that our planet is undergoing a serious water crisis, with population growth putting increasing stress upon the supply of fresh water. But the situation is even worse than we thought.

About 4 billion people across the world have serious difficulty getting enough water for at least one month of every year, according to a just-published study in the journal Science Advances.

NEWS: Global Water Supply–How Much is Left?

Co-authors Arjen Y. Hoekstra, a professor of water management at the University of Twente in the Netherlands, and post-doctoral researcher Mesfin Mekonnen used computer modeling to study a growing shortage that they say is being driven by population growth, improved living standards, changing consumption patterns and the expansion of irrigation in agriculture.

Unlike previous studies that looked at longer-term patterns of availability, which the researchers say underestimated the impact of water scarcity, they looked at how the supply of "blue" water -- that is, fresh surface water and groundwater -- fluctuates in the course of a year.

The result was that in addition to areas with year-round water scarcity -- such as Somalia and northern Mexico, for example -- the researchers identified places where water becomes scarce during certain seasons. In Africa, for example, the researchers identified a band roughly between 5 and 15 degrees northern latitude with low water scarcity from May or June to January but moderate to severe water scarcity from February to April. They found other spots -- such as India and northern China -- which experience water shortages during the spring and summer.

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Severe scarcity is defined as the demand being double the supply available in an area.

The researchers also found that about 66 percent of the world's population suffers from severe water scarcity for at least one month during the year. Of those 4 billion people, 1 billion live in India and another 900 million live in China. About 130 million live in the United States, mostly in western and southern states.

As Hoekstra told the New York Times, water scarcity isn't just a problem for those who don't have enough water. "Since the remaining people in the world receive part of their food from the affected areas, it involves us all," he said.

Most of the people on Earth experience severe freshwater scarcity at least one month out of the year, reports a new study. Pictured: An old dry well in Chennai, Tamil Nadu in India.

It might sound a bit cramped, but there's an entire world of organisms that can call a drop of water their home. And, up close, they look practically out-of-this-world. Each year, the Nikon Small World competition sets out to collect some of the best microphotography. Take a look at some of this year's most stunning images of creatures that live in water. This photo from Dr. Jan Michels of Christian-Albrechts-Universität zu Kiel in Kiel, Germany shows Temora longicornis, a marine copepod, from its ventral view at 10 times magnification.

SEE MORE PHOTOS: It's a Nikon Small World After All

This microphotograph shows the diatom Melosira moniliformis at 320 times its size.

This algae biofilm photographed up-close makes what's usually referred to as "pond scum" look like art.

This Philodina roseola rotifer was alive and well when this microphotograph was taken.

This microphoto shows a water flea flanked by green algae.

NEWS: Tiny Flea Has More Genes Than You

Warfare in a water droplet! This microphoto shows a Hydra capturing a water flea at 40-times magnification.

NEWS: Ocean's Most Abundant Food Source Disappearing

One of the ultimate human pests -- the mosquito -- begins life as larvae, here shown suspended in a single droplet of water.

Ever wonder what sex between two freshwater ciliates looks like magnified at 630 times its actual size? Now you know!

This freshwater water flea is shown at 100 times its actual size.

Closterium lunula, a kind of green alga, is shown here. This particular specimen came from a bog pond, according to the photographer.

While it may resemble a visitor from outer space, this is what a zebrafish embryo looks like under a microscope, three days after being fertilized.

This microscopic crustacean appears yellowish-orange because it is mounted in Canada Balsam with crystals and other artifacts.

A white-spotted bamboo shark's embryonic pectoral fin makes for a stunning image under a microscope.

SEE MORE PHOTOS: It's a Nikon Small World After All