Tag Archives: water

New Research Casts Doubt on Doomsday Water Shortage Predictions

New Research Casts Doubt on Doomsday Water Shortage Predictions: Scientific American.

MELTDOWN: The melting of mountain glaciers around the world may not contribute as much to water supplies as thought, new research argues. Image: Abhishekjoshi/Flickr

From the Andes to the Himalayas, scientists are starting to question exactly how much glaciers contribute to river water used downstream for drinking and irrigation. The answers could turn the conventional wisdom about glacier melt on its head.

A growing number of studies based on satellite data and stream chemistry analyses have found that far less surface water comes from glacier melt than previously assumed. In Peru’s Rio Santa, which drains the Cordilleras Blanca mountain range, glacier contribution appears to be between 10 and 20 percent. In the eastern Himalayas, it is less than 5 percent.

“If anything, that’s probably fairly large,” said Richard Armstrong, a senior research scientist at the Boulder, Colo.-based Cooperative Institute for Research in Environmental Sciences (CIRES), who studies melt impact in the Himalayas.

“Most of the people downstream, they get the water from the monsoon,” Armstrong said. “It doesn’t take away from the importance [of glacier melt], but we need to get the science right for future planning and water resource assessments.”

The Himalayan glaciers feed into Asia’s biggest rivers: the Indus, the Ganges and the Brahmaputra in India, Pakistan and Bangladesh, and the Yellow and Yangtze rivers in China. Early studies pegged the amount of meltwater in these river basins as high as 60 or 70 percent. But reliable data on how much water the glaciers release or where that water goes have been difficult to develop. Satellite images can’t provide such regular hydrometeorological observations, and expeditions take significant time, money and physical exertion.

New methods, though, are refining the ability to study this and other remote glacial mountain ranges. Increasingly, scientists are finding that the numbers vary depending on the river, and even in different parts of the same river.

Creeping hyperbole
“There has been a lot of misinformation and confusion about it,” said Peter Gleick?, co-director of the California-based Pacific Institute for Studies in Development, Environment and Security. “About 1.3 billion people live in the watersheds that get some glacier runoff, but not all of those people depend only on the water from those watersheds, and not all the water in those watersheds comes from glaciers. Most of it comes from rainwater,” he said.

A key step forward came last year when scientists at Utrecht University in the Netherlands, using remote sensing equipment, found that snow and glacier melt is extremely important to the Indus and Brahmaputra basins, but less critical to others. In the Indus, they found, the meltwater contribution is 151 percent compared to the total runoff generated at low elevations. It makes up about 27 percent of the Brahmaputra — but only between 8 and 10 percent for the Ganges, Yangtze and Yellow rivers. Rainfall makes up the rest.

That in itself is significant, and could reduce food security for 4.5 percent of the population in an already-struggling region. Yet, scientists complain, data are often inaccurately incorporated in dire predictions of Himalayan glacial melt impacts.

“Hyperbole has a way of creeping in here,” said Bryan Mark, an assistant professor of geography at Ohio State University and a researcher at the Byrd Polar Research Center.

Mark, who focuses on the Andes region, developed a method of determining how much of a community’s water supply is glacier-fed by analyzing the hydrogen and oxygen isotopes in water samples. He recently took that experience to Nepal, where he collected water samples from the Himalayan glacier-fed Kosi River? as part of an expedition led by the Mountain Institute.

Based on his experience in the Rio Santa — where it was once assumed that 80 percent of water in the basin came from glacier melt — Mark said he expects to find that the impact of monsoon water is greatly underestimated in the Himalayas.

Jeff La Frenierre, a graduate student at Ohio State University, is studying Ecuador’s Chimborazo glacier, which forms the headwaters of three different watershed systems, serving as a water source for thousands of people. About 35 percent of the glacier coverage has disappeared since the 1970s.

La Frenierre first came to Ecuador as part of Engineers Without Borders to help build a water system, and soon started to ask what changes in the mountain’s glacier coverage would mean for the irrigation and drinking needs of the 200,000 people living downstream. Working with Mark and analyzing water streams, he said, is upending many of his assumptions.

Doomsday descriptions don’t fit
“The easy hypothesis is that it’s going to be a disaster here. I don’t know if that’s the case,” La Frenierre said. He agreed that overstatements about the impacts are rampant in the Himalayas as well, saying, “The idea that 1.4 billion people are going to be without water when the glaciers melt is just not the case. It’s a local problem; it’s a local question. There are places that are going to be more impacted than other places.”

Those aren’t messages that environmental activists will likely find easy to hear. Armstrong recalled giving a presentation in Kathmandu on his early findings to a less-than-appreciative audience.

“I didn’t agree with the doomsday predictions, and I didn’t have anything that was anywhere near spectacular,” Armstrong said. But, he added, “At the same time, it’s just basic Earth science, and we want to do a better job than we have been.”

The more modest numbers, they and other scientists stressed, don’t mean that glacier melt is unimportant to river basins. Rather, they said, they mean that the understanding of water systems throughout the Himalayan region must improve and water management decisions will need to be made at very local levels.

“We need to know at least where the water comes from,” Armstrong said. “How can we project into the future if we don’t know where the water comes from now?”

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

The vanishing Arctic lakes

Strange case of the vanishing Arctic lakes – environment – 17 October 2011 – New Scientist.

 

 

THE lake-spotted landscape of Canada is home to a watery mystery. According to a painstaking satellite survey of 1.3 million lakes stretching from coast to coast, the country lost 6700 square kilometres – or 1.2 per cent – of its water surface area between 2000 and 2009. Yet what we know about the physical processes at play suggests the lakes should be growing, not shrinking.

Whatever the cause, the loss could impact local wildlife and human populations. “It’s an important finding. We need to find out what’s driving it,” says Larry Hinzman, director of the International Arctic Research Center in Fairbanks, Alaska. The comprehensiveness of the study makes it significant, he says.

Ten years is long enough that this could be a sign of climate change, Hinzman says, “and it’s over a large enough area that it’s bound to have ecosystem and climate impacts”. Migratory water fowl, aquatic life, and indigenous people who rely on the lakes for food and water may all face challenges if the drying continues.

Shrinking Arctic lakes have been observed before, but only in the southern-most part of the Arctic, where warming trends have melted permafrost and allowed lakes to drain into the soil. The new survey, carried out by Mark Carroll at the University of Maryland in College Park, finds just the reverse: northern lakes appear to be shrinking, while southern ones are not (Geophysical Research Letters, DOI: 10.1029/2011GL049427).

This is surprising, says Hinzman, not least because evidence suggests that the northern region received higher-than-average amounts of rain during the study period. “You would expect more precipitation to lead to higher lake levels,” says atmospheric scientist Stephen Dery at the University of Northern British Columbia in Prince George. “But here, it doesn’t.”

Much of the lake water comes from the seasonal snow pack melt. In theory, warmer temperatures across the region should be decreasing the snow pack – which should also boost the lakes. Another factor at play could be the delicate balance between precipitation and evaporation which Arctic lake levels depend on: warmer temperatures and higher winds could cause more evaporation. Hinzman and Dery say melting permafrost may also be involved. That would allow lake water to soak into thawed soil, but Carroll is not aware of any evidence that the permafrost in the far north is melting yet.

The water loss could affect the amount of greenhouse gases emitted by the region’s ecosystems. When lakes dry up, the sediment in the newly exposed soil can release carbon dioxide. But standing water can also release methane, so the lake shrinkage could lower methane levels. It remains to be seen whether the net result is to boost global warming or if the impacts offset each other.

Major river basins have enough water to sustainably double food production in the coming decades

Major river basins have enough water to sustainably double food production in the coming decades.

ScienceDaily (Sep. 25, 2011) — While water-related conflicts and shortages abound throughout the rapidly changing societies of Africa, Asia and Latin America, there is clearly sufficient water to sustain food, energy, industrial and environmental needs during the 21st century, according to two special issues of the peer-reviewed journal, Water International (Volume 35, Issue 5 and Volume 36, Issue 1), released September 26 at the XIV World Water Congress.

The report from the Challenge Program on Water and Food (CPWF) of the CGIAR finds that the “sleeping giant” of water challenges is not scarcity, but the inefficient use and inequitable distribution of the massive amounts of water that flow through the breadbaskets of key river basins such as the Nile, Ganges, Andes, Yellow, Niger and Volta.

“Water scarcity is not affecting our ability to grow enough food today,” said Alain Vidal, director of the CPWF. “Yes, there is scarcity in certain areas, but our findings show that the problem overall is a failure to make efficient and fair use of the water available in these river basins. This is ultimately a political challenge, not a resource concern.”

“Huge volumes of rainwater are lost or never used,” he added, “particularly in the rain-fed regions of sub-Saharan Africa. With modest improvements, we can generate two to three times more food than we are producing today.

While Africa has the biggest potential to increase food production, researchers identified large areas of arable land in Asia and Latin America where production is at least 10 percent below its potential. For example, in the Indus and Ganges, researchers found 23 percent of rice systems are producing about half of what they could sustainably yield.

The analysis — which involved five years of research by scientists in 30 countries around the world — is the most comprehensive effort to date to assess how, over vast regions, human societies are coping with the growing need for water to nurture crops and pastures, generate electricity, quench the thirst of rapidly growing urban centers, and sustain our environment. The findings also present a picture of the increasingly political role of water management in addressing these competing needs, especially in dealing with the most pressing problem facing humanity today: doubling food production in the developing world to feed a surging population, which, globally, is expected to expand from seven to 9.5 billion people by 2050.

The 10 river basins that were studied include: the Andes and São Francisco in South America; the Limpopo, Niger, Nile and Volta basins in Africa; and the Ganges, Indus, Karkheh, Mekong, and Yellow in Asia. The basins — distinct and gargantuan geographic areas defined by water flows from high-ground to streams that feed major river systems — cover 13.5 million square kilometers and are home to some 1.5 billion people, 470 million of whom are amongst the world’s poorest.

According to Vidal, the 10 basins were selected for study because they embody the full measure of water-related challenges in the developing world. The research examines the role of policy and governance in managing water resources in ways that reduce poverty and improve living standards for the greatest number of people

“The most surprising finding is that despite all of the pressures facing our basins today, there are relatively straightforward opportunities to satisfy our development needs and alleviate poverty for millions of people without exhausting our most precious natural resource,” said Dr. Simon Cook, of the International Center for Tropical Agriculture (CIAT) and Leader of the CPWF’s Basin Focal Research Project (BFRP).

For example, Cook and his colleagues found that if donors and government ministries put more emphasis on supporting rain-fed agriculture, food production can increase substantially and rapidly. In Africa, it was found that the vast majority of cropland is rainfed and researchers found that only about four percent of available water is captured for crops and livestock.

“With a major push to intensify rainfed agriculture, we could feed the world without increasing the strain on river basins systems,” said Cook.

The authors also note that boosting food production in the basins studied requires looking beyond crops to consider more efficient uses of water to improve livestock operations and fisheries. Water policies often ignore the role livestock and fish play in local livelihoods and diets. For example, the researchers found that in the Niger basin, freshwater fisheries support 900,000 people while 40 million people in the Mekong depend on fisheries for at least part of the year. In the Nile, researchers note that almost half of the water in the basin flows through livestock systems.

“The basin perspective is critical in order to assess the upstream and downstream impacts of water allocation policies, and to determine opportunities for optimizing the sum of benefits across many residents,” said Dennis Wichelns, Deputy Director General at the International Water Management Institute (IWMI), which was a major partner in the research.

The researchers contrast the poor use of water resources within river basins observed in many areas — which they refer to as “dead spots” for agriculture development — to “bright spots” of water efficiency. They said bright spots can be found in the large areas of the Ganges, Nile and Yellow River basins, where farmers and governments have responded to development challenges by vastly improving the amount of food produced from available water. They also single out “hot spots” — which can be found in the in the Indus, Yellow, Nile and Limpopo river basins — where there is mounting concern and conflict over sharing water resources and reaching consensus on development approaches.

Confronting the “Complete Fragmentation” of Water Management

Cook and his colleagues caution that while globally there is enough water to sustain human development and environmental needs, water-related conflicts will continue if particular issues like food security and energy production are considered in isolation from one another. Cook observed that in most areas there is a “complete fragmentation of how river basins are managed amongst different actors and even countries where the water needs of different sectors — agriculture, industry, environment and mining — are considered separately rather than as interrelated and interdependent.”

“In many cases, we need a complete rethink of how government ministries take advantage of the range of benefits coming from river basins, rather than focusing on one sector such as hydropower, irrigation or industry,” the authors stated.

Related Stories


The Problem with the Nation's Drinking Water Standards

Is It Safe to Drink? The Problem with the Nation’s Drinking Water Standards: Scientific American.

More than 6,000 chemicals pollute U.S. drinking water, yet the U.S. Environmental Protection Agency has added only one new pollutant to its regulatory roster in the past 15 years. Environmental groups have long raised questions about this track record, and the U.S. Government Accountability Office recently joined the chorus, releasing a report that charges the agency with taking actions that have “impeded … progress in helping assure the public of safe drinking water.”

Among other things, the GAO report says, the EPA relies on flawed data. To determine the level of a particular pollutant in drinking water—which the EPA does before making a regulatory ruling on it—the agency relies on analytic testing methods so insensitive that they cannot identify the contaminants at levels expected to cause health effects. In addition, since 1996 the EPA has been required to make regulatory decisions about five new pollutants each year, ruling on those that might pose the biggest threats to public health. The GAO report asserts that the agency has been ruling only on the “low-hanging fruit”—contaminants for which regulatory decisions are easy rather than those that might be the most dangerous. “They’re not actually doing anything to protect public health,” says Mae Wu, an attorney at the Natural Resources Defense Council.

For its part, the EPA has pledged to review the nation’s drinking-water standards and to add at least 16 new contaminants to the list of those it regulates. This past February the agency reversed a long-standing decision to not regulate the rocket-fuel ingredient perchlorate, making the chemical the first new drinking-water contaminant to be regulated since 1996. In its response to the GAO, the EPA stated that “no action” was necessary to better prioritize the contaminants on which the agency will rule in the future, nor did it acknowledge the need for improvements in data collection. The agency did, however, agree to consider improving its methods for alerting the public when there are drinking-water advisories.

Simulation shows it’s possible to tow an iceberg to drought areas

Simulation shows it’s possible to tow an iceberg to drought areas.

Iceberg

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Image credit: Trevor Williams.

(PhysOrg.com) — Way back in the 70’s Georges Mougin, then an engineering graduate, had a big idea. He suggested that icebergs floating around in the North Atlantic could be tethered and dragged south to places that were experiencing a severe drought, such as the Sahel of West Africa. Mougin received some backing funds from a Saudi prince but most “experts” at the time scoffed at his idea and the whole scheme was eventually shelved.

Cut to 2009 and French software firm Dassault Systemes, who thought maybe Mougin was on to something after all and contacted him to suggest modeling the whole idea on a computer. After applying 15 engineers to the problem, the team concluded that towing an from the waters around Newfoundland to the Canary Islands off the northwest coast of Africa, could be done, and would take under five months, though it would cost nearly ten million dollars.

In the simulation, as in a real world attempt, the selected iceberg would first be fitted with an insulating skirt to stave off melting; it would then be connected to a tugboat (and a kite sail) that would travel at about one knot (assuming assistance from ocean currents). In the simulated test, the iceberg arrived intact having lost only 38 percent of its seven ton mass.

A real world project would of course require hauling a much bigger berg; experts estimate a 30 million ton iceberg could provide fresh water for half a million people for up to a year. There would also be the problem of transporting the water from the berg in the ocean to the drought stricken people. The extraordinary costs for such a project would, it is assumed, come from the price tag for the skirt, five months of diesel fuel for the tugboat, the man hours involved and then finally, distribution of the fresh water at the destination.

Scientists estimate that some 40,000 icebergs break away from the polar ice caps each year, though only a fraction of them would be large enough to be worth the time and expense of dragging them to a place experiencing a drought, such as the devastating one currently going on in the Horn of Africa.

Mougin, newly reinvigorated by the results of the recent study, at age 86, is now trying to raise money for a real-world test of the idea.

'Super sand' to help clean up dirty drinking water

BBC News – ‘Super sand’ to help clean up dirty drinking water.

Contaminated water can be cleaned much more effectively using a novel, cheap material, say researchers.

Dubbed “super sand”, it could become a low-cost way to purify water in the developing world.

The technology involves coating grains of sand in an oxide of a widely available material called graphite – commonly used as lead in pencils.

The team describes the work in the American Chemical Society journal Applied Materials and Interfaces.

In many countries around the world, access to clean drinking water and sanitation facilities is still limited.

The World Health Organization states that “just 60% of the population in Sub-Saharan African and 50% of the population in Oceania [islands in the tropical Pacific Ocean] use improved sources of drinking-water.”

The graphite-coated sand grains might be a solution – especially as people have already used sand to purify water since ancient times.

Coating the sand

But with ordinary sand, filtering techniques can be tricky.

Start Quote

Given that this can be synthesized using room temperature processes and also from cheap graphite sources, it is likely to be cost-efficient”

Mainak Majumder Monash University, Australia

Wei Gao from Rice university in Texas, US, told BBC News that regular coarse sand was a lot less effective than fine sand when water was contaminated with pathogens, organic contaminants and heavy metal ions.

While fine sand is slightly better, water drains through it very slowly.

“Our product combines coarse sand with functional carbon material that could offer higher retention for those pollutants, and at the same time gives good throughput,” explained the researcher.

She said that the technique the team has developed to make the sand involves dispersing graphite oxide into water and mixing it with regular sand.

“We then heat the whole mixture up to 105C for a couple of hours to evaporate the water, and use the final product – ‘coated sand’ – to purify polluted water.”

Cost-efficient

Sand “Super sand” is made using regular sand – and it could become a low-cost way to purify water

The lead scientist of the study, Professor Pulickel Ajayan, said it was possible to modify the graphite oxide in order to make it more selective and sensitive to certain pollutants – such as organic contaminants or specific metals in dirty water.

Another team member, Dr Mainak Majumder from Monash University in Melbourne, Australia, said it had another advantage – it was cheap.

“This material demonstrates comparable performance to some commercially available activated carbon materials,” he said.

“But given that this can be synthesized using room temperature processes and also from cheap graphite sources, it is likely to be cost-efficient.”

He pointed out that in Australia many mining companies extract graphite and they produce a lot of graphite-rich waste.

“This waste can be harnessed for water purification,” he said.

Flood disrupts Minot water supply

Flood disrupts Minot water supply – CNN.com.

Gordon Valgren, right, cleans debris from his flood-damaged home Monday in Minot, North Dakota.

Gordon Valgren, right, cleans debris from his flood-damaged home Monday in Minot, North Dakota.
STORY HIGHLIGHTS
  • Minot, North Dakota, residents are under orders to conserve water
  • Floodwaters apparently broke a water main on Monday
  • Flooding also is affecting Burlington, North Dakota

Is severe weather happening where you are? Share your story.

(CNN) — Residents of flooded Minot, North Dakota, remained under orders to limit their water use Tuesday, a day after rushing floodwaters apparently broke a main water line, a city spokesman said.

Utility crews were able to wade to the site of the break and divert the water flow, but it would likely be Tuesday night or Wednesday before they could install a new line to restore normal flow, said Dean Lenertz, a spokesman for the city.

About a third of Minot’s population of nearly 36,000 has been evacuated due to record flooding from the Souris River, which bisects the city.

The main north-south route through the city, the Broadway Bridge, has been closed to traffic other than emergency vehicles and those involved in the flood fight, leading to traffic jams, Lenertz said.

“It’s a two- to three-hour commute in the mornings and evenings to get from one area to another,” he said.

Floodwaters crest, fears remain
Flooding called heartbreaking

The Souris crested over the weekend at nearly 13 feet over flood stage. It has since fallen about a foot but remains more than 2½ feet above the previous record flood from 1881, according to the National Weather Service.

Lenertz said it will likely be at least a week, perhaps two, before residents of the estimated 4,000 homes flooded in the city will be able to return home and assess the damage.

Residents of Burlington, North Dakota, are also being affected by flooding, but not from the Souris. There, the water being released from Garrison Reservoir into Missouri River is causing the problems.

About 4,000 people have been forced out of about 800 homes there, according to iReporter Mark Armstrong, who is a Burleigh County commissioner.

Flooding problems have been ongoing there for five weeks, he said.

Eight million gallons of water drained from reservoir after man urinates in it

Eight million gallons of water drained from reservoir after man urinates in it – Telegraph.

The operation is costing the state’s taxpayers $36,000 (£22,000) and was ordered after Joshua Seater, 21, was caught on a security camera relieving himself in the pristine lake.

Health experts said the incident would not have caused any harm to people in the city of Portland, who are supplied with drinking water from the reservoir.

They said the average human bladder holds only six to eight ounces, and the urine would have been vastly diluted.

But David Shaff, an administrator at the Portland Water Bureau, defended the decision to empty the lake.

“There are people who will say it’s an over reaction. I don’t think so. I think what you have to deal with here is the ‘yuck’ factor,” he said.

“I can imagine how many people would be saying ‘I made orange juice with that water this morning.’ “Do you want to drink pee? Most people are going to be pretty damn squeamish about that.”

Mr Seater had been out drinking with friends when he decided to relieve himself in the open air reservoir at 1.30am.

He has not been arrested or charged with a crime, but may ultimately face a fine.

He apologised publicly for his behaviour, adding: “It was a stupid thing to do. I didn’t know it was a water supply, I thought it was a sewage plant.

“I wouldn’t mind paying for it but I don’t have a job right now. I’m willing to do community service to clean up the place because I feel bad and feel pretty stupid.” Sergeant Pete Simpson, of Portland Police, said: “It’s really an unfortunate incident that probably could have been avoided if he had just chosen a bush.”

Virtual water cannot remedy freshwater shortage

Virtual water cannot remedy freshwater shortage.

ScienceDaily (June 6, 2011) — The implementation of virtual water into trading deals has been suggested as a realistic solution to solving the global inequality of renewable freshwater, but new research suggests that it may not be as revolutionary as first thought.

In a study published June 7, in IOP Publishing’s journal Environmental Research Letters, researchers have claimed that virtual water is unlikely to increase water use equality, primarily because the existing amount of virtual water is not large enough to overcome the inequalities that exist.

Lead author David Seekell, of the University of Virginia, said, “Virtual water is unlikely to overcome these constraints because there just isn’t enough to go around.”

80 per cent of humanity currently lives in regions where water security is threatened, meaning that as the global population grows against a finite volume of freshwater, a more equal distribution of water use between countries will be needed.

Virtual water — the amount of water it takes to produce goods or a service — has been suggested as a possible solution to this growing problem by using virtual water values to inform international trade deals.

Most goods carry a virtual water value — for example, producing one kilogram of beef requires 15 thousand litres of water — which can act as a significant tool for addressing a country’s input and output of water.

For example, a trade deal could be struck where products with a high virtual water value, such as oranges, could be exported from countries where there is an efficient and abundant water supply, into a country where the requirement of water to grow that particular product is more of a burden.

This would allow the receiving country to save on water, relieving the pressure on their limited water resources, and allowing the water to be used elsewhere in its infrastructure.

This study, performed by researchers at the University of Virginia, assessed the inequality in water use between countries and examined how different uses, such as industrial, household, and for agricultural products consumed domestically, contributed to the overall inequality.

To do this, the authors compared United Nations statistics on both social and human development statuses with water usage statistics for a range of countries.

Their study concludes that virtual water transfers are not sufficient to equalise water use among nations because water used for agriculture consumed domestically dominates a nation’s water needs and cannot be completely compensated by current volumes of virtual water transfers.

Seekell continued, “Even if it cannot completely equalise water use between countries, virtual water may stand to contribute to this effort if there is increased transfer from high water use to low water use countries, but the danger here is that these transfers effectively prop up populations above the carrying capacity of their natural resources and this could actually erode a population’s long-term resilience to drought or other disasters.

“There are a myriad of political and economic barriers to trade, and because water is not usually a deciding factor in trade decisions, it is unlikely that global trade will ever be viewed as efficient from a water use point of view.”

African land grab could lead to future water conflicts

African land grab could lead to future water conflicts – environment – 26 May 2011 – New Scientist.

IS THIS the face of future water conflicts? China, India and Saudi Arabia have lately leased vast tracts of land in sub-Saharan Africa at knockdown prices. Their primary aim is to grow food abroad using the water that African countries don’t have the infrastructure to exploit. Doing so is cheaper and easier than using water resources back home. But it is a plan that could well backfire.

“There is no doubt that this is not just about land, this is about water,” says Philip Woodhouse of the University of Manchester, UK.

Take Saudi Arabia, for instance. Between 2004 and 2009, it leased 376,000 hectares of land in Sudan to grow wheat and rice. At the same time the country cut back on wheat production on home soil, which is irrigated with water from aquifers that are no longer replenished – a finite resource.

Meanwhile, firms from China and India have leased hundreds of thousands of hectares of farmland in Ethiopia. Both China and India have well-developed irrigation systems, but Woodhouse says their further development – moving water from the water-rich south to northern China, for instance – is likely to be more costly than leasing land in Africa, making the land-grab a tempting option.

But why bother leasing land instead of simply importing food? Such imports are equivalent to importing “virtual water”, since food production accounts for nearly 80 per cent of annual freshwater usage. A new study into how this virtual water moves around the world offers an explanation for the leasing strategy. Ignacio Rodriguez-Iturbe of Princeton University and Samir Suweis of the Swiss Federal Institute of Technology in Lausanne have built the first mathematical model of the global virtual water trade network, using the UN Food and Agricultural Organization’s data on trade in barley, corn, rice, soya beans, wheat, beef, pork, and poultry in 2000. They combined this with a fine-grained hydrological model (Geophysical Research Letters, DOI: 10.1029/2011GL046837).

The model shows that a small number of countries have a large number of connections to other countries, offering them a steady and cheap supply of virtual water even if some connections are compromised by drought or political upheaval. A much larger number of countries have very few connections and so are vulnerable to market forces.

Most importantly, the model shows that about 80 per cent of the water flows over only about 4 per cent of the links, which Rodriguez-Iturbe calls the “rich club phenomenon”. In total, the model shows that in 2000, there were 6033 links between 166 nations. Yet 5 per cent of worldwide water flow was channelled through just one link between two “rich club” members – the US and Japan.

The power of the rich club may yet increase. The model allows the team to forecast future scenarios – for example, how the network will change as droughts and spells of violent precipitation intensify due to climate change. Predictably, this will only intensify the monopoly, says Suweis. “The rich get richer.”

China and India are not currently major players in the virtual water network on a per capita basis, and as the network evolves they could find themselves increasingly vulnerable to market forces and end up paying more for the food they import. Leasing land elsewhere is an attempt to secure their food and water supply in a changing world. But it could be a short-sighted move.

Last year, Paolo D’Odorico of the University of Virginia at Charlottesville showed that a rise in the virtual water trade makes societies less resilient to severe droughts (Geophysical Research Letters, DOI: 10.1029/2010GL043167). “[It] causes a disconnect between societies and the water they use,” says D’Odorico. The net effect is that populations in nations that import water can grow without restraint since they are not limited by water scarcity at home.

Although this could be seen as a good thing, it will lead to greater exploitation of the world’s fresh water. The unused supplies in some areas that are crucial in case of major droughts in other areas will dry up. “In case of major droughts we [will] have less resources available to cope with the water crisis,” says D’Odorico.

In the end, then, the hunt for water that is driving emerging economies to rent African land to grow their crops could come back to haunt them.