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A wave of change is coming to our planet’s water resources

Thanks to climate change, Earth’s freshwater supplies will never be the same again, Science News for Students, BETH GEIGER, DEC 6, 2018 This is the fourth in a 10-part series about the ongoing global impacts of climate change. These stories will look at the current effects of a changing planet, what the emerging science suggests is behind those changes and what we all can do to adapt to them.

It’s January 2018 in Cape Town, South Africa. After three years of record low rainfall, reservoirs that supply this city’s water are dangerously low. The city is running out of water, and fast………..
Water world   Our cool blue planet is covered in water. Just 2.5 percent of that water, however, is fresh. Of that, only about one third is liquid. The rest is locked up as ice.That isn’t much freshwater. Yet we depend on it for everything. In the United States, each person uses an average of 340 liters (90 gallons) per day at home. And that doesn’t include the water needed to grow our food or manufacture everything from clothes to cars to cell phones. It takes 3,400 liters (900 gallons) just to make one pair of jeans.

As climate changes, though, so does how much water is available. Water, climate and weather are connected in a never-ending loop called the water cycle. And like any natural system, change one part of it — whether it’s temperature, soil moisture or even how many trees are in a region — and everything else changes, too.

Scientists use powerful supercomputers to explore the complex ways that climate change is altering the water cycle. They have found that as climate warms, the atmosphere holds more water: about 4 percent more for every 1.8 degrees Celsius (1 degree Fahrenheit). That affects everything from rainfall to how soggy soils might be……..

Data from computers, satellites and “boots on the ground” agree. Climate change is altering the availability of water around the world. In South Africa and many regions, droughts are becoming more common. In other areas, like California and Europe, shifting precipitation patterns have caused river flows to peak earlier each year, followed by water shortages. Meanwhile, the average rainfall in the United States has actually increased by 5 centimeters (2 inches) since 1895……

an international group of scientists analyzed Cape Town’s drought and water shortage. They studied computer models and rainfall records. Finally, they came to a conclusion: Climate change hadn’t caused the drought. But it had tripled the chance that a drought would occur.

Friederike Otto is a climate scientist at Oxford University in England and lead author of that study. The risk of drought could triple again by the end of the 21st century, she says. That’s when global temperatures are projected to rise another 1 degree Celsius (1.8 degrees Fahrenheit). She and her colleagues published their findings in Environmental Research Letters in fall 2018.

…….. double whammy for California. First, the rain triggers a deluge of winter floods. Second, there’s less snow to melt and fill water-storage reservoirs over the hot summer, when water is needed most. “It’s very tricky for water-resource managers,” says Rizzardo.

California is far from the only place where dwindling mountain snow and ice are causing problems. The Pacific Northwest, the Himalayas and other regions also are seeing snowpack and glaciers do a disappearing act.

That causes a serious trickle-down effect. Some rivers in this state, for example, get 25 percent less water from melting snow and ice than they did just a few decades ago, says Riedel. This leaves less water to irrigate farms. Warmer water in rivers, and less of it, has also caused some aquatic ecosystems to nosedive.        ………

Beneath the surface

Water flowing over or pooled atop the earth is not our only supply of freshwater. Groundwater is a secret stash. Deep below the surface, where it is silent and dark and cool, groundwater fills tiny gaps in the rock and soil, like water in a sponge. Groundwater can be hidden a few meters, or a few hundred meters, below the surface.

“Groundwater doesn’t get as much attention because we don’t see it,” says Laura Condon. “It’s so much harder to get your head around than surface water,” notes this hydrogeologist, or groundwater expert. She works at the University of Arizona in Tucson. Even though we can’t see it, an astounding 1.7 percent of all water on Earth is trapped underground. It sits in reservoirs called aquifers. That’s about 60 times more water than is held in all lakes and rivers combined.

Groundwater comes from water that seeps down from the surface, a process called recharge. We depend on groundwater and on the recharge that sustains it. But that recharge happens slowly. For instance, scientists estimate that it took hundreds of thousands of years for Arizona’s stash of groundwater to accumulate.

Half of U.S. drinking water comes from groundwater. But we may need to stop gulping, and start sipping. In 2017, scientists compared aquifer levels since 1948 to more recent measurements taken by the GRACE satellite mission. They determined that of Earth’s 37 biggest aquifers, 21 are now dropping faster than they are being recharged………

Future file

Could you live with just 50 liters (13 gallons) of water per day, like the residents of Cape Town? Or instead of water shortages, perhaps extreme floods, warm winter storms or dusty dry summers will be your new normal. Maybe your hometown will get more rain than you could ever use. These are all ways that climate change is altering water around the globe. No wonder the United Nations says that of all the impacts of climate change, shifting water availability is the impact people will feel most.

The good news is that around the world, people are paying attention. They are using science, imagination and even music to help adapt our watery ways to climate change.

In China, for example, engineers are creating “sponge cities.” As climate change brings more intense rainstorms and epic floods, sponge cities will soak up excess water. The “sponges” range from rooftop gardens to pavement that lets water sink in instead of running off. After a storm, as much as 70 percent of the stored water can later be re-used………

As Earth’s climate evolves, and the water cycle with it, we can’t predict exactly what will happen or where. But after living with Cape Town’s extreme water shortage, Reinders is sure of at least one thing: “No one here thinks about water like they used to,” she says. “It’s like gold now.”

December 11, 2018 - Posted by | 2 WORLD, climate change, water

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