Tuesday, 4 April 2017

The world's disappearing groundwater

Study finds 11 percent of disappearing groundwater used to grow internationally traded food
29 March, 2017

Wheat, rice, sugar, cotton and maize are among the essential internationally traded crops in the global economy. To produce these crops many countries rely on irrigated agriculture that accounts for about 70 percent of global freshwater withdrawals, according to the United Nations Water program. One freshwater source is underground aquifers, some of which replenish so slowly that they are essentially a non-renewable resource.

A new study by researchers at the University College London and NASA's Goddard Institute of Space Studies in New York City shows that 11 percent of the global non-renewable groundwater drawn up for irrigation goes to produce crops that are then traded on the international market. Additionally, two-thirds of the exported crops that depend on non-renewable groundwater are produced in Pakistan (29 percent), the United States (27 percent), and India (12 percent).

"It's not just individual countries that experience groundwater depletion, but also their trade partners," said lead author Carole Dalin of the University College London. "When people consume certain imported foods, they should be aware that they can have an impact on the environment elsewhere." The results were published March 30 in Nature.

Dalin and her colleagues used trade data on countries' agricultural commodities from the United Nations Food and Agriculture Organization. They then combined it with a global hydrologic model—validated with ground information and NASA satellite data—to trace the sources of water used to produce 26 specific crop classes from their country of origin to their final destination. Their analysis is the first to determine which specific crops come from groundwater reservoirs that won't renew on human time-scales and where they are consumed.

"Say I'm in Japan, and I'm importing corn from the United States," said co-author Michael Puma of NASA's Goddard Institute for Space Studies and Columbia University in New York City. "It's important from Japan's perspective to know whether that corn is being produced with a sustainable source of water, because you can imagine in the long term if groundwater declines too much, the United States will have difficulty producing that crop."

Globally, 18 percent of all crops grown are traded internationally. The remaining 82 percent stays in country for the domestic market. However, the amounts of various exported crops produced using unsustainable groundwater rose significantly between 2000 and 2010. India, for example, saw its exports of groundwater-depleting crops double in that period, while Pakistan's rose by 70 percent and the United States' rose by 57 percent.

Countries that export and import these crops may be at risk in the future of losing the crops, and their profits, produced with non-renewable groundwater. Importers may need to find alternative sources, possibly at a higher cost.

Major importers of crops raised with non-renewable groundwater include the United States, Iran, Mexico, Japan, Saudi Arabia, Canada, Bangladesh, the United Kingdom, Iraq, and China, which went from a net exporter in 2000 to a net importer in 2010. Countries on both lists often export different commodities than they import.

Aquifers form when water accumulates in the ground over time, sometimes over hundreds or thousands of years. Non-renewable aquifers are those that do not accumulate rainfall fast enough to replace what is drawn out to the surface, either naturally to lakes and rivers or in this case by people via pumping. Once that groundwater is depleted, it will effectively be gone for good on the scale of a human life-time, and will no longer be available for relief during crises such as droughts, Dalin explained.

Drawdowns in aquifers worldwide have been observed over the last fifteen years by NASA's Gravity Recovery and Climate Experiment (GRACE), a pair of satellites that detect changes in Earth's gravity field to see the movement of masses such as ice sheets and, in this case, underground water.

"What's innovative about this study is it connects groundwater depletion estimates with country level data," said hydrologist Matt Rodell at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who was not involved in the study. More research needs to be done which considers population growth, changing diets, climate change, the implementation of irrigation technology and policy changes to understand when these aquifers may begin to run dry, he said.

The absolute amount of water in many of these aquifers is difficult to quantify, though experts in many regions are already looking at better methods to determine how much water remains and how long it may last, Dalin said. Now and in the future, decision makers and local farmers will need to decide on a strategy for using this non-renewable water that balances the needs of short-term production versus long-term sustainability, she said.

Having grown up there this is UNBELIEVABLE – were it not for dairy.

Dam scheme proposed to solve Christchurch's dwindling water supply

3 April, 2017

A new dam scheme could help protect Christchurch's dwindling water supply - but charging residents for the water they use is still being considered.

Under the scheme, dams would be built on streams off the Waimakariri River, designed to store floodwater in winter and release it into the aquifers over summer.

It is one potential solution to Canterbury's water problems, as the water levels in the city's aquifers have dropped to record lows.

Water charges are also being looked at to try and reduce household water use, which takes the biggest portion of water drawn out of the aquifers.

A working group has been formed to look at potential solutions and report back to the Christchurch West Melton Water Zone Committee.

Working group chairman Chris Kelliher said there was a lot more work to do on the scheme before he could say if it was the best or most cost-effective option.

But he believed creating dams or water storage ponds was a good solution.

"The idea is to harvest water out of the river in the winter when there's a good flow and it's not being utilised, and then put it back in aquifers in the summer," he said.

Similar schemes have been successful in Australia, and one is being piloted in Hinds in South Canterbury.

He said the working group was initially focused on recharging the aquifers, but would also look at what could be done to reduce water use.

He said water charges were still "on the table" and likely to be considered in the future.

"We have to look at using water more wisely," he said.

Christchurch residents use an average of 357 litres of water per person per day, compared with 273 litres of water in Auckland where there are household water charges.

Environmental planner and groundwater expert, Bryan Jenkins, said he believed the plan would work.

He said Canterbury's aquifers usually only replenished over winter, because the soil dried up so much over summer that any rain would evaporate from the soil before it could trickle through to the aquifers.

If a pond or dam was built in the right place, water could be released steadily so the ground stayed moist and water could gradually soak through.

But even if dams were built, he believed water charges would still be needed.

"They should be doing both as quickly as possible," he said.

The scheme is set to be put to Environment Canterbury planners next month, who would investigate it in more detail.


Where water from Christchurch aquifers goes:

45 per cent residential and commercial
31 per cent industrial
22 per cent rural or irrigation
1 per cent recreational

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