Published: June 23, 2014.
California may be in the midst of a severe drought, but plump, juicy strawberries and raspberries continue to roll north by the truckload.
And they are still affordable despite predictions of price shocks for Canadian consumers who gobble up California fruits, veggies and nuts worth close to $2.4 billion a year.
The drought is severe — reservoirs are at record lows, wetlands are parched and rivers are so short of water that young salmon are being trucked hundreds of kilometres to help them out to sea.
But water is still flowing on many Californian fields’ thanks in large part to groundwater. Farmers are expected to make up about 75 per cent of this year’s shortfall by drilling ever deeper into the water sitting in aquifers beneath the state’s fertile Central Valley.
But there are ominous signs of overuse. Water levels are dropping. And the water withdrawals are so massive they are moving California’s mountains, according to a recent study that underscores how dependent farmers — and consumers — are on groundwater that is running low in many thirsty regions of the world.
“It’s just mind-blowing to think that we can have such an impact on the Earth’s crust,” says Pascal Audet, a geoscientist at the University of Ottawa, and co-author of the study in the journal Nature on the geological impacts of California’s groundwater depletion. Along with moving mountains, the study suggests the water withdrawals may also be increasing the number of small earthquakes along the San Andreas Fault.
Groundwater is the world’s largest freshwater resource. It slowly seeps through soil and rock fractures and collects in aquifers where much of it has been stored for thousands of years. Almost 40 per cent of global irrigation now comes from groundwater, which also supplies drinking water for close to two billion people.
But it is so over exploited that about 1.7 billion people live in regions where groundwater is “under threat,” according to research by hydrologist Tom Gleeson of McGill University, who has assessed almost 800 aquifers around the world.
Using groundwater “footprints” that compare how much water is flowing into aquifers to how much is sucked out, Gleeson and his colleagues have shown that several large aquifers, especially in Asia and North America, are being “unsustainably mined.”
It is not yet known if or when critical aquifers — like the two that help keep U.S. crops growing — could run dry.
But Gleeson says it is clear groundwater needs to be better managed in an increasingly thirsty world.
“Even though we may not know exactly how long it is before we run out of groundwater in certain areas, we know we are using it unsustainably,” he says.
This year’s searing drought, which has hit not just California but much of the U.S. southwest, is “exacerbating” depletion of both the High Plains and Central Valley aquifer systems as farmers and communities look for relief, Gleeson says. The impacts go beyond drinking water and irrigation, he says, as groundwater also provides “base flow” to rivers, streams and wetlands that helps keep ecosystems alive.
The High Plains Aquifer, also known as the Ogallala, is one of the world’s largest aquifers and contains mostly water that has been underground since the end of the last ice age, he says. Eight states – South Dakota, Nebraska, Wyoming, Colorado, Kansas, Oklahoma, New Mexico and Texas — dip into the aquifer to grow wheat, corn, cattle and cotton.
While the northern parts of the aquifer are replenished by rain and snowmelt, Gleeson says large swaths of the aquifer under Texas and Kansas are dropping faster than they are being recharged. One U.S. study estimates irrigation wells could run dry in 35 per cent of the southern high plains within 30 years.
Groundwater levels are also dropping under California’s Central Valley, which is one of richest and most productive agricultural areas on Earth. The state grows nearly half the fruits, nuts and vegetables consumed in the U.S. and also keeps Canada in fresh fruits and vegetables year round.
But California is pumping so much water out of the ground that the mountains near the agricultural belt in the Sierra Nevadas and California Coast Ranges rise a few millimeters each year, according to the study on the geological impacts.
Groundwater is heavy and its weight depresses the Earth’s upper crust, says Audet. Remove massive amounts from the ground and he says the crust “bounces up like a spring.”
He and his U.S. colleagues report that about 160 cubic kilometres of groundwater has been “lost” from the Central Valley over the past 150 years because of increasingly intensive agriculture. “That’s enough water to fill a lake 160-kilometres long, a kilometre wide and a kilometre deep,” says Audet.
An El Nino is expected to bring rain and relief to California later this year — the “great wet hope,” as it’s being called, that could end the drought that has prompted California Gov. Jerry Brown to declare a state of emergency. While it would top up the groundwater the scientists don’t see El Nino putting an end to California’s water woes.
“It’s a long-term problem that can’t be recovered by a single wet year or two,” says Gleeson, stressing that need for better monitoring and management of groundwater.
Along with assessing the world’s aquifers, he and his colleagues are calculating the groundwater footprints of different types of crops. In a recent study they show that corn, hay and cotton are putting the most stress on the U.S. aquifers.
Such “crop per drop” analysis is determining how much water it takes to produce everything from broccoli to burgers. Livestock production is by far the thirstiest and has the biggest water footprint– it takes about 15,000 litres of water for every kilogram of beef that makes it to the supermarket.
Researchers say optimizing groundwater use will become even more important in future, especially in dry regions like the U.S. southwest that is expected to see more droughts.
“Climate scenarios are forecasting even drier climates in the future for California, so there is no way this is sustainable,” Audet says of the current groundwater use.
As for the earthquakes, he says it is too early to tell if the extra water withdrawals this year are triggering more small tremors along the San Andreas Fault.
“We are keeping an eye on the situation,” says Audet, noting that it will require data for the entire year to be able to see if there is a significant increase.
By the numbers:
Canada has a big appetite for California’s bounty, importing about $3.8 billion a year in agricultural products from the golden state including:
– $1.4 billion in fruits and nuts (including $255 million in strawberries)
– $927 million in vegetables
– $397 million in wine and alcoholic drinks
Source: Agriculture and Agri-Food Canada
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