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article imageGlobal warming is creating a groundwater 'time bomb'

By Karen Graham     Jan 23, 2019 in Science
Over two billion people worldwide are dependent on groundwater for their source of fresh water. A new study shows we could be facing a groundwater "time bomb" because of climate change.
Groundwater is the water present beneath the Earth's surface in porous soil spaces and in the fractures of rock formations. These spaces are called aquifers. When the aquifers are saturated with water - the surface of the saturation reaches a point where the water pressure head is equal to the atmospheric pressure. This is called the water table.
Groundwater in aquifers is recharged through rainfall, of course, and this process is known as recharge. Groundwater doesn't just sit under the surface - instead, it is discharged into brooks, streams, rivers and the ocean - a never-ending cycle that ensures an overall balance between water in and water out.
Not only is our groundwater used to quench the thirst of billions of people, but it is also used in agriculture. As we already know, the global population is exploding and crop production is increasing just to feed everyone. Groundwater makes up about 20 percent of all the Earth's fresh water supply. This amounts to about 0.61 percent of the entire world's water, including oceans and permanent ice.
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UCI/NASA
An environmental "time bomb"
Extreme weather events, including drought and heavy rainfall, brought on by global warming, could easily have a long-lasting impact on how quickly aquifers are replenished, according to a study published Monday in the journal Nature Climate Change.
According to the study, over the next 100 years, climate-related rainfall changes could disrupt the recharge process in about 44 percent of the aquifers on the planet, reports Motherboard.
The international team of researchers used groundwater modeling, along with hydrologic data sets to create a timescale on how groundwater assets may respond to climate change.
In addition to suffering from a long drought  Central California is depleting its underground aquife...
In addition to suffering from a long drought, Central California is depleting its underground aquifers.
Columbia University
"Groundwater is out of sight and out of mind, this massive hidden resource that people don't think about much yet it underpins global food production," said Mark Cuthbert, from Cardiff University's School of Earth and Ocean Sciences, according to Phys.org.
"The effect we are having now is going to have this really long lag-time in terms of climate change. There's a memory in the system—and the memory is very large in some places," he told AFP.
Findings on groundwater depletion
The researchers found that almost half of the world's aquifers are expected to be depleted in the next 100 years, a sobering statement. Global warming will also interfere with the remaining aquifers on timescales longer than a century, said the authors. "The effect we are having now is going to have this really long lag-time in terms of climate change,” Cuthbert told AFP.
"This could be described as an environmental time bomb because any climate change impacts on recharge occurring now, will only fully impact the baseflow to rivers and wetlands a long time later,” he said.
One-third of the world's groundwater basins are in distress
This latest study is truly troubling. A study published in 2015 discovered that one-third of the planet's aquifers were already in distress. The world's most over-stressed aquifer is the Arabian Aquifer System, an important water source for more than 60 million people.
The second-most overstressed location is the Indus Basin aquifer of northwestern India and Pakistan. The third-most stressed groundwater basin is the Murzuk-Djado Basin in northern Africa. California's Central Valley, heavily used for agriculture, and rapidly being depleted, is labeled "highly stressed."
Another study, published in 2016 described a water crisis of monumental proportions in southern Asia, affecting over 750 million people in Pakistan, India, Nepal, and Bangladesh. At least 60 percent of their groundwater is contaminated with salt and deadly levels of arsenic.
Groundwater quality in the IGB aquifer system. a  Salinity measured as total dissolved solids  (TDS)...
Groundwater quality in the IGB aquifer system. a, Salinity measured as total dissolved solids (TDS) in the groundwater and areas where arsenic is known to be widespread. b, Volume of the water in the top 200 m of the aquifer.
Nature Geoscience
The Indo-Gangetic Basin accounts for a quarter of the Earth's groundwater reserves. There has been an arsenic poisoning crisis going on in southern Asia since at least the mid-1970s when water sources changed from surface to groundwater. As more and more wells were dug, the arsenic began accumulating in the deeper confines of the aquifers.
The research team said their research showed one of the "hidden" impacts of climate change and called for immediate action to ensure future generations aren't left high and dry.
More about Climate change, Groundwater, Time bomb, Science, water tables
 
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