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Children collect drinking water from a well in Murkata, India.Credit: Biju Boro/AFP via Getty

The Earth has lost enough groundwater to thirsty humans to measurably tilt the planet’s axis of rotation1.The net water lost from underground reservoirs between 1993 and 2010 is estimated to be more than 2 trillion tons. That has caused the geographic North Pole to shift at a speed of 4.36 centimetres per year, researchers have calculated. The results appeared on 15 June in Geophysical Research Letters.A wobbling of the EarthThe tilt of the axis on which any celestial object spins tends to be stable. But small changes can occur when large masses shift location inside a planet and on its surface. “Every mass moving around on the surface of the Earth can change the rotation axis,” says Ki-Weon Seo, a geophysicist at Seoul National University.Astronomers can track such motions in the Earth’s axis by observing quasars, the bright centres of distant galaxies that constitute practically immobile points of reference. The largest axis change is seasonal and is triggered by the motion of atmospheric masses as the weather and seasons change. This effect causes the Earth’s geographic poles to wobble by up to several metres every year.
The world faces a water crisis — 4 powerful charts show how
Shifts in water masses can cause smaller but still measurable changes in the tilt of Earth’s axis. Until recently, researchers thought that these water-driven effects would be caused mainly by the melting of glaciers and ice caps. But when Seo and his collaborators tried to model the Earth’s water content to account for how much the axis has tilted, they could not fully explain the data. Adding the effects of changes in surface reservoirs did not help, says Seo, “so I just scratched my head and said, ‘probably one effect is groundwater’”.Gravitational surveys have measured the depletion of underground reservoirs, which is caused in large part by irrigation, especially in northwestern India and western North America. These surveys show that groundwater pumping shifted enough mass into the oceans to cause 6.24 millimetres of global sea-level rise between 1993 and 2010.By including these changes in their model, the authors calculated that they should have a substantial impact on the Earth’s rotation axis. They predicted that the displacement of groundwater alone causes a shift in the North Pole of 4.36 centimetres per year, roughly in the direction of Russia’s Novaya Zemlya islands. More

The Chilean government plans to nationalize 20 salt lakes in the unique Altiplano ecosystem and exploit them for lithium extraction. As well as creating a huge and long-lasting trail of environmental damage, intensive mining activity will disrupt the region’s delicate ecological and hydrological balance.
Competing Interests
The author declares no competing interests. More

CORRESPONDENCE
06 June 2023

Mohsen Maghrebi

University of Tehran, Tehran, Iran.

Roohollah Noori

University of Tehran, Tehran, Iran.

Amir AghaKouchak

University of California, Irvine, Irvine, California, USA.

To relieve Iran’s water crisis, the government invested about US$1.5 billion in modernizing the country’s irrigation systems, aiming to reduce agricultural water demand (Islamic Parliament Research Center 18724, https://rc.majlis.ir/fa/report/show/1756716; 2023). However, technology alone could not resolve the situation.

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Nature 618, 238 (2023)
doi: https://doi.org/10.1038/d41586-023-01851-y

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Visitors to Lake Mead, a reservoir in Nevada and Arizona that is fed by the Colorado River, see a bleached bathtub-like ring on its banks, indicating past water levels.Credit: Justin Sullivan/Getty

Seven US states this week finally agreed on a plan to cut their use of water from the Colorado River, an icon in the nation’s Southwest that supplies water to more than 40 million people, including in Mexico. The river, battered by overuse, drought and climate change, has been drying up. Although scientists welcome the plan, they say the agreement is only a temporary fix to a much thornier problem.
The world faces a water crisis — 4 powerful charts show how
“It does not change the fundamental problem of the overallocation of the Colorado River,” says Kathryn Sorensen, an economist at Arizona State University in Phoenix. “But it helps.” Combined with an unexpectedly wet winter in the western United States, which is now filling the river with snowmelt, the agreement buys time for officials to negotiate a more sustainable solution.From its headwaters in the Rocky Mountains to where it empties into the Gulf of California, the 2,300-kilometre-long river serves farmers, homeowners, businesses and many others, including people in 30 tribal nations and in cities including Los Angeles. The 22 May announcement is the latest in a decades-long dispute over who should cut back on their water use to preserve the river. The ‘lower basin’ states of California, Arizona and Nevada — the three that are farthest downstream as Colorado flows to the sea, with California the heaviest user of the river’s water — have agreed to conserve 3 million acre-feet (3.7 trillion litres) of water between now and 2026. That amount is enough to supply around 6 million households for a year.

Source: US Bureau of Reclamation

Researchers say that the Colorado River is overtaxed by serving more people than it can handle, in a part of the country that doesn’t get a lot of rainfall. A drought that began in 2000 has caused the river’s water levels to drop steadily — culminating last year when the massive Lake Mead reservoir in Nevada and Arizona shrank (see ‘Drying up’) to the point that long-lost human bodies emerged on the shoreline. If the levels in Lake Mead and in Lake Powell in Arizona and Utah — both fed by the river — drop low enough, water will no longer pass through their dams to generate the thousands of megawatts of hydropower that are used by people across the west. Both reservoirs are currently only about 30% full, down from 95% full in 2000.The inevitability of climate changeOne bright spot in the Colorado River outlook is this winter’s heavy snows, which are now melting from the mountains and feeding the river. As a result, lakes Powell and Mead are starting to rise faster than they have in recent years. But scientists say that it is a rare event, and not something to be counted on in the future. “This one year doesn’t get us out of it,” says Jack Schmidt, a geomorphologist at Utah State University in Logan.
What the science says about California’s record–setting snow
Climate change, however, is plodding and relentless — and it’s expected to increase the frequency of droughts in the Colorado River basin. Every temperature increase of 1 ºC in the upper part of the river basin leads to a 9.3% drop in the river’s flow, the US Geological Survey has estimated1. Long-term strategies are needed to account for the inevitability of climate change, as well as the uncertainty of wet and dry seasons, says Kevin Wheeler, a water resource engineer at the University of Oxford, UK.Reducing water use is a linchpin to all such plans. In California and Arizona, for instance, water management officials are ramping up plans to recycle wastewater into drinking water. Some are experimenting with encouraging changes in residents’ behaviour by, for instance, charging more for water in the summer than in the winter. Other efforts focus on cutting back on agricultural uses of water — which is key, because farmers account for 75–80% of the water consumption from the Colorado River, much of which is used to grow hay and other fodder for livestock. Technologies such as drip irrigation, which delivers water directly to plants rather than flooding an entire field, can help — although their effectiveness is debated.A temporary fixThe four states that are upstream along the river — New Mexico, Utah, Colorado and Wyoming — have agreed with the lower-basin states. Together, they are asking the federal government, which oversees water releases from lakes Powell and Mead, to consider the new plan as a way forward between now and 2026. The US Department of the Interior has the power to modify, reject or accept the plan. The proposed cutback is only around half of what the department had been asking of the group of seven, but it still agreed to pay US$1.2 billion to support the proposal, for instance by paying farmers to let their fields lay fallow.
Mexico is seeding clouds to make rain — scientists aren’t sure it works
That’s a lot of money to support what is only a temporary fix, says Jennifer Gimbel, a water policy expert at Colorado State University in Fort Collins. “It concerns me that we’re spending that kind of money when we should be focused on a more permanent solution,” she says. Any permanent solution will involve a complex stew of government-backed incentives to conserve water across the entire river basin, all trying to balance the needs of many users.The agreement pushes off any further decision-making until 2026, when interim water-management guidelines are due to expire. Between now and then, the United States, Mexico and tribal nations must come up with an approach for how they will conserve the river’s limited resources in future.There’s no time to waste, Sorensen says. “Everyone understands that time is of the essence.” More

In their call for protection of the global water cycle, Johan Rockström and his colleagues propose putting an economic value on ‘green’ water, which is held in the air, biomass and soils (Nature 615, 794–797; 2023). In my view, it’s even more urgent to fix the underpricing of ‘blue’ water in rivers, lakes, reservoirs and aquifers if we are to reduce the risk of water-scarcity crises.
Competing Interests
The author declares no competing interests. More

In our view, assessing the “social cost of water” is unrealistic (see J. Rockström et al. Nature 615, 794–797; 2023) because it risks oversimplifying a range of complex water issues. The social value of water varies across space, time and cultures, so it is not “akin to” the social cost of carbon, the global economic costs resulting from emitting one extra tonne of carbon dioxide, which is consistent across different contexts and countries. Such a flawed, catch-all concept could result in policies and investments that target the wrong challenges.
Competing Interests
The authors declare no competing interests. More

A storm dumps snow on California’s Mammoth Lakes on 28 March.Credit: Mario Tama/Getty

Not again! Earlier this week, California was battered by heavy rain, strong winds and thick snow — the latest in a seemingly unending procession of strong storms. Wild weather has afflicted the previously drought-stricken state for three months, resulting in devastating floods, paralysing blizzards and dozens of deaths. Data released Thursday show that the snowpack is the biggest on record. Nature spoke to atmospheric and climate scientists about what’s driving the surge in wet weather and what the state could look like in a warmer future.

A rare snowstorm in southern California frosted the mountains on the edge of Los Angeles on 1 March.Credit: Ringo Chiu./ZUMA Press Inc/Alamy

Why are so many storms hitting California?California’s recent parade of storms is driven by atmospheric rivers — long, narrow plumes of moist air that travel from the tropics to higher latitudes. When these ‘rivers in the sky’ sweep over mountainous regions they condense into clouds that produce heavy rain and snow, says Allison Michaelis, an atmospheric scientist at Northern Illinois University in DeKalb.An atmospheric river can ferry enormous amounts of water vapour; some discharge more than twice as much water as the Amazon River1. In the western United States, atmospheric rivers contribute up to half of the region’s annual rain and snow. Since last November, 31 atmospheric rivers have hit California, more than half of which ranged from moderate to extreme, according to data from the Scripps Institution of Oceanography in La Jolla, California.Although back-to-back atmospheric rivers are not unheard of, they make a significant impact, says Michaelis. “What might have typically been a more beneficial event could turn potentially hazardous if it comes on the heels of another system.”

Cars dot floodwaters from the Tule River on 21 March, after days of heavy rain in Corcoran, California.Credit: David Swanson/Reuters

How much snow is there?In the Sierra Nevada mountain range in eastern California, the season is the snowiest since 1952, says Andrew Schwartz, an atmospheric scientist who leads the University of California, Berkeley’s Central Sierra Snow Lab in Donner Pass. “It’s just dumping snow,” he says. A total of 18 metres of snow has fallen at the lab this season, nearly double the yearly average. And statewide, the snow’s water content — the amount of water that would result if the snow were melted — is roughly double the average, says Schwartz.The conditions have brought welcome relief after the three driest years on record in California, allowing the rollback of ‘exceptional’ and ‘extreme’ drought designations for the first time since 2020, according to the US National Oceanic and Atmospheric Administration’s US spring outlook. But capturing and storing water released as the thick snowpack begins to melt can be a race against time, says Tom Corringham, a research economist at Scripps. If the snow melts too quickly, the excess water ends up in the ocean instead of being stored and distributed to where it’s needed most, he says. “That’s not ideal for water management.”

People remove snow from a residential complex in Mammoth Lakes, California, on 29 March.Credit: Mario Tama/Getty

Is climate change playing a part?As the atmosphere warms, atmospheric rivers are likely to become more frequent and hold more moisture, and that will result in heavy downpours of rain and snow, says Schwartz. He notes that California is swinging between wet and dry periods that are more extreme than in the past. “While this variability has always existed, it’s becoming amplified due to climate change,” he says.Kim Reid, a climate scientist at Monash University in Melbourne, Australia, says that more work needs to be done to understand how climate change will affect jet streams and other systems that influence the direction of atmospheric rivers. If atmospheric rivers shift by a few degrees latitude, they could become more common in some regions and rarer in others, she says. More

Baghdad on the Tigris: this week Iraq became the first country in the Middle East to join the UN water convention.Credit: Getty

Forty-six years. That’s how long it took the United Nations to organize a high-level conference on water. The 3-day event, held last week in New York, was brief compared with its 12-day predecessor, which took place in Mar del Plata, Argentina, in 1977. That meeting helped to catalyse the drafting of the UN’s 1992 water convention, an international agreement through which countries agree to cooperate on the use and protection of shared waterways. Delegates to this month’s conference did not make any binding commitments, but countries are converging on several ideas. One is to establish a panel of scientists to regularly advise on water issues. Another is for the UN to appoint a ‘water envoy’, a high-level diplomat representing secretary-general António Guterres. The conference also increased the visibility of the 1992 convention.Each of these is an important step. The appointment of a UN envoy would send a powerful signal that this is a hot topic, high on the agenda of world leaders, and that a boost to the science is overdue. For decades, there’s been much rhetoric around applying science to water resources at the intergovernmental level, but action has been piecemeal. The 1977 conference report (known as the Mar del Plata Action Plan) and the 1992 convention recognize the need for research and development. This need was most recently incorporated into the UN’s Sustainable Development Goals (SDGs) in 2015; SDG6 aims to achieve equitable access to safe water and sanitation by 2030. These agreements also mention the need for countries to share data — for example, on river flows, weather and climate, and water quality. But with some two billion people still lacking safe water in their homes, SDG6 is a long way from being achieved.
The world faces a water crisis — 4 powerful charts show how
The necessity of studying and sharing such data is underscored by a Comment in Nature written by climate scientist Johan Rockström, economist Mariana Mazzucato and their colleagues. Among other things, they describe how land-management practices in one country can impact atmospheric water flows in other countries. But to properly take advantage of such knowledge, countries need to both collect and share data.One option proposed by the UN’s science agency UNESCO is modelled on the Intergovernmental Panel for Climate Change, and would produce periodic global literature reviews to be signed off by governments. Such an idea needs rigorous analysis and testing. Separately, there is also a real need for input from independent scientists on water disputes between nations.At the start of the year, Mohammed Basheer, a water-resources economist at the Humboldt University of Berlin, and his colleagues published a modelling study addressing a protracted dispute over Africa’s largest hydroelectric dam on the Nile River. The work showed how Egypt, Ethiopia and Sudan, the three countries involved, could benefit if each was willing to compromise (M. Basheer et al. Nature Clim. Change 13, 48–57; 2023). However, it’s not clear whether these recommendations will find their way into negotiations. Relations between Egypt and Ethiopia are fraught, and there is no clear path for the provision of independent scientific advice on the dam.
Why we need a new economics of water as a common good
A study by Patience Mukuyu at the International Water Management Institute in Pretoria, South Africa, and her colleagues, published in early March, reaffirms that relatively few countries that share watercourses are cooperating, such as by sharing data (P. Mukuyu et al. Water Int. https://doi.org/j36p; 2023). Co-author Alistair Rieu-Clarke at Northumbria University, UK, who studies transboundary water issues, emphasizes that there are demonstrable benefits to data sharing. In September 2021, four African countries — Gambia, Guinea Bissau, Mauritania and Senegal — agreed to cooperate (including by sharing data) on a giant underground aquifer, which covers more than 300,000 square kilometres and supplies water to 80% of their combined populations.The list of transboundary water disputes is lengthening. The Indus Waters Treaty, a 63-year-old agreement between India and Pakistan on sharing the Indus River’s waters, is in trouble. The melting of glaciers as a result of climate change is affecting river flows; at the same time, both countries have plans in the works to build dams. In January, India announced that it wants to renegotiate the treaty to take account of a changed environmental and geopolitical situation, rather than work within what it sees as an outdated framework. However, Pakistan wants to continue to resolve disagreements using the treaty’s dispute-settlement procedures. Elsewhere, Iran, Iraq, Syria and Turkey have long been at odds over the shared Euphrates–Tigris river basin, where water availability will also be affected by climate change.The idea of a UN water envoy and science panel offer an opportunity to make a difference to such disputes. More countries that share water resources also need to sign and ratify the 1992 UN water convention. Last week, Iraq, Nigeria and Panama were among ten countries to either do so or announce that they intend to do as much.The UN and its member states have made a positive start. Increased visibility of the 1992 convention will pay dividends, as will boosting research to help policymakers to better understand and resolve water crises, although the devil will be in the detail. Science, as Basheer told Nature earlier in the year, can show countries how to “help each other, look after each other and look out for each other”, when water disputes are being discussed. Ultimately, countries need to accept that scientists must have a seat at the table during these discussions. More