Water Security is National Security

Water resources and how they are managed impact almost all aspects of society and the economy, in particular health, food production and security, domestic water supply and sanitation, energy, industry, and the functioning of ecosystems. Under present climate variability, water stress is already high, particularly in many developing countries, and climate change adds even more urgency for action. Without improved water resources management, the progress towards poverty reduction targets, the Millennium Development Goals, and sustainable development in all its economic, social and environ- mental dimensions, will be jeopardized. UN Water.Org

Sunday, July 5, 2015

New NASA data show how the world is running out of water

The world’s largest underground aquifers – a source of fresh water for hundreds of millions of people — are being depleted at alarming rates, according to new NASA satellite data that provides the most detailed picture yet of vital water reserves hidden under the Earth’s surface.

Twenty-one of the world’s 37 largest aquifers — in locations from India and China to the United States and France — have passed their sustainability tipping points, meaning more water was removed than replaced during the decade-long study period, researchers announced Tuesday. Thirteen aquifers declined at rates that put them into the most troubled category. The researchers said this indicated a long-term problem that’s likely to worsen as reliance on aquifers grows.

Scientists had long suspected that humans were taxing the world’s underground water supply, but the NASA data was the first detailed assessment to demonstrate that major aquifers were indeed struggling to keep pace with demands from agriculture, growing populations, and industries such as mining.

“The situation is quite critical,” said Jay Famiglietti, senior water scientist at NASA’s Jet Propulsion Laboratory in California and principal investigator of the University of California Irvine-led studies.

Underground aquifers supply 35 percent of the water used by humans worldwide. Demand is even greater in times of drought. Rain-starved California is currently tapping aquifers for 60 percent of its water use as its rivers and above-ground reservoirs dry up, a steep increase from the usual 40 percent. Some expect water from aquifers will account for virtually every drop of the state’s fresh water supply by year end

The aquifers under the most stress are in poor, densely populated regions, such as northwest India, Pakistan and North Africa, where alternatives are limited and water shortages could quickly lead to instability.

The researchers used NASA’s GRACE satellites to take precise measurements of the world’s groundwater aquifers. The satellites detected subtle changes in the Earth’s gravitational pull, noting where the heavier weight of water exerted a greater pull on the orbiting spacecraft. Slight changes in aquifer water levels were charted over a decade, from 2003 to 2013.

“This has really been our first chance to see how these large reservoirs change over time,” said Gordon Grant, a research hydrologist at Oregon State University, who was not involved in the studies.

But the NASA satellites could not measure the total capacity of the aquifers. The size of these tucked-away water supplies remains something of a mystery. Still, the satellite data indicated that some aquifers may be much smaller than previously believed, and most estimates of aquifer reserves have “uncertainty ranges across orders of magnitude,” according to the research.

Aquifers can take thousands of years to fill up and only slowly recharge with water from snowmelt and rains. Now, as drilling for water has taken off across the globe, the hidden water reservoirs are being stressed.

“The water table is dropping all over the world,” Famiglietti said. “There’s not an infinite supply of water.”

The health of the world’s aquifers varied widely, mostly dependent on how they were used. In Australia, for example, the Canning Basin in the country’s western end had the third-highest rate of depletion in the world. But the Great Artesian Basin to the east was among the healthiest.

The difference, the studies found, is likely attributable to heavy gold and iron ore mining and oil and gas exploration near the Canning Basin. Those are water-intensive activities.

The world’s most stressed aquifer — defined as suffering rapid depletion with little or no sign of recharging — was the Arabian Aquifer, a water source used by more than 60 million people. That was followed by the Indus Basin in India and Pakistan, then the Murzuk-Djado Basin in Libya and Niger.

California’s Central Valley Aquifer was the most troubled in the United States. It is being drained to irrigate farm fields, where drought has led to an explosion in the number of water wells being drilled. California only last year passed its first extensive groundwater regulations. But the new law could take two decades to take full effect.

Also running a negative balance was the Atlantic and Gulf Coastal Plains Aquifer, which stretches across the southeast coast and Florida. But three other aquifers in the middle of the country appeared to be in relatively good shape.

Some groundwater filters back down to aquifers, such as with field irrigation. But most of it is lost to evaporation or ends up being deposited in oceans, making it harder to use. A 2012 study by Japanese researchers attributed up to 40 percent of the observed sea-level rise in recent decades to groundwater that had been pumped out, used by humans and ended up in the ocean.

Famiglietti said problems with groundwater are exacerbated by global warming, which has caused the regions closest to the equator to get drier and more extreme latitudes to experience wetter and heavier rains. A self-reinforcing cycle begins. People living in mid-range latitudes not only pump more water from aquifers to contend with drier conditions, but that water — once removed from the ground — also then evaporates and gets recirculated to areas far north and south.

The studies were published Tuesday in the Water Resources Research journal.

Famiglietti said he hoped the findings would spur discussion and further research into how much groundwater is left.

“We need to get our heads together on how we manage groundwater,” he said, “because we’re running out of it.” More

 

 

Tuesday, June 30, 2015

Groundwater from aquifers important factor in food security

Thirsty cities, fields and livestock drink deeply from aquifers, natural sources of groundwater. But a study of three of the most-tapped aquifers in the United States shows that overdrawing from these resources could lead to difficult choices affecting not only domestic food security but also international markets.

University of Illinois professors of civil and environmental engineering Ximing Cai and Megan Konar, along with graduate student Landon Marston and Lehigh University professor Tara Troy, studied groundwater consumption from three main systems. Reliance on these aquifers intensified so much from 2000 to 2008 that it accounted for 93 percent of groundwater depletion in the U.S. They published their findings in the Proceedings of the National Academy of Sciences.

The U.S. Geological Survey identifies the Central Valley aquifer in California, the High Plains aquifer in the Great Plains states, and the Mississippi Embayment aquifer in the lower Midwest as being managed unsustainably, which means that is being extracted from the aquifer faster than it is replenishing.

"Deep groundwater is like natural gas. If you use it, it takes a while to recharge," Cai said. "Unsustainable usage means the water table is lowered, which makes it more difficult and more expensive to pump water since we have to keep going deeper. It also affects ecosystems associated with the water table, such as streams and wetlands."

The researchers tracked water consumption from the aquifers to see where the water was going, both in terms of geography and usage. For example, when water was used to irrigate a crop, the researchers tracked where those crops were shipped.

"When we think of water, we think of direct water, the water that comes out of our faucets. But we actually use a lot of embodied water in our everyday lives – the water footprint to produce a product," Konar said. "We looked at the water implicitly being transferred between states and countries in the products."

The researchers found that the vast majority – 91 percent – of embodied groundwater from these three aquifers stayed within the U.S. The remaining 9 percent was exported internationally. They identified the states most heavily reliant on each aquifer, and the breakdown of what was produced using water from each aquifer. For example, the largest percentage of water from the High Plains aquifer irrigated grains, while the largest contribution from the Central Valley aquifer in California went to producing meat. See the infographic for the detailed findings.

The researchers hope that having detailed information on how aquifer water is used, and the complex economic and environmental implications of that use, can help policy makers in their decisions about water resource management.

"The issue here is the tradeoffs. That's the difficulty for the decision makers," Cai said. "There is a tradeoff between the environment and economic profit, and there is a trade-off between the current use and future use. The environment is affected, the food markets are affected, the resources for fisheries are affected. That helps the decision makers understand the issue. I think this information is also important for the public to understand the issue."

The researchers feel that the study is also important for international leaders, as any decisions will affect global food production and prices. Although the international exports represented a small percent of the overall water consumption, the exported goods account for a large market share in the countries that import them, the study found.

Next, the researchers plan to study major watersheds in the U.S. to gain a more comprehensive picture of natural water resources in the United States. They are interested in detailing water use under variable conditions, both in terms of economic and environmental impact.

"Managing water resources for the future is especially important because future rainfall patterns are going to be more variable, with more droughts predicted," Konar said. "As we're seeing in California, they were really lucky to have aquifers to rely on during a drought. We don't want to deplete these aquifer supplies, so that when we get into these drought situations, we have some emergency backup." More

More information: "Virtual groundwater transfers from overexploited aquifers in the United States" PNAS 2015 ; published ahead of print June 29, 2015, DOI: 10.1073/pnas.1500457112

 

Thursday, June 25, 2015

The World’s Most Hostile International Water Basins

At the launch of A New Climate for Peace, a new report on climate-fragility risks produced for the G7 by a consortium of international partners including the Wilson Center, USAID Deputy Assistant Administrator Christian Holmes called water a common denominator for climate risk.

“How you manage your water programs…has a huge amount to do with how you mitigate the prospect for increased fragility,” he said. “Sometimes it’s the obvious that’s so easy to miss, and I think that the obvious on water as it relates to economic development is, essentially, the question of sustainable water supply.”

One of the most striking infographics from A New Climate for Peace touches on that question of supply. Using data from Oregon State University’s Transboundary Freshwater Dispute Database and adapted from a graphic that originally appeared in Popular Sciencelast year, the map shows the world’s most active – and tension-filled – international water basins.

Water is a common denominator for climate risk

The Transboundary Freshwater Dispute Database measures not only the frequency of hostile events in a basin, but cooperative ones as well, each on a sliding scale. Hostile events range from declarations of war (zero recorded from 1990 to 2008, the period of time encompassed by the graphic) to leaders using “language of discord.” Cooperative events range from “mild verbal support” to “voluntary unification into a single country.”

The total number of events is indicated by shades of blue – the darker the blue, the more transboundary events, both positive and negative. This is essentially the “hot list” of international water basins – which regions have the most official and unofficial chatter over water.

Circles superimposed on the basins represent the total number of hostile events. As the description text points out, however, “circle size does not automatically translate into conflict danger.” In some places, transboundary institutions and diplomatic frameworks allow different actors to work through their differences. Cooperative hostility, if you will. In the Danube River Basin, for example, the high number of “hostile” events is mitigated by strong cooperative incentives associated with European integration. Likewise in North America, where Canada, the United States, and Mexico share several basins with a high number of hostile events, there is little chance of violent conflict.

Water basins in South Asia, the Middle East, and East Africa are major hotspots with a high number of hostile events and weaker institutional frameworks to mitigate them. The Indus, Ganges-Brahmaputra-Meghna, Salween, Tigris-Euphrates, and Jordan basins witness a very high number of interactions, suggesting at least that continued dialogue could be a way forward to mitigate the risk of violent conflict or fragility. The Nile Basin has less activity reflecting the stalled negotiations between the basin’s 10 member states to replace colonial-era water agreements. The Mekong Basin, where the largest member, China, does not participate as a full member of the Mekong River Commission, shows less activity as well.

The map does a great job illustrating why it can be difficult to answer the question, where is the highest risk of water-related violence? Tensions between states and other freshwater basin actors isn’t necessarily a sign of impending violence if there’s a framework to resolve them. Likewise, lack of communication over a major natural resource can be a bad sign for cooperation when the resource in question is the Nile. More

More infographics from ‘A New Climate for Peace: Taking Action on Climate and Fragility Risks’ are available on NewClimateforPeace.org.

 

Wednesday, June 24, 2015

Century of Water Shortage Ahead? Lake Mead Drops Below Rationing Line For First Time in Its History.

Lake Mead Drops Below Rationing Line For First Time in Its History.

1075 feet. That’s the water level Lake Mead must stay above before mandatory multi-state water rationing goes into effect. A level just 25 feet above the highest intake pipe used to supply cities across the Desert Southwest. Last night water levels at the key national water storage facility fell below that hard line to 1074.99 feet — a record low never before seen in all of its history.

If water levels remain below the 1075 foot mark through January of 2016, then a multi-state rationing will go into effect (with most acute impacts for Arizona and Nevada). A rationing that will have serious consequences for desert cities across the Southwest, cities like Las Vegas which rely on Lake Mead for so much of their water.

Despite Lake Mead hitting the 1075 hard line, it appears that rationing may be forestalled through 2016. It’s a silver lining of all the severe summer storms that have rolled through the Colorado River Basin this spring and summer — pumping up water flows to Lake Mead and Lake Powell. A flush of much needed moisture that will, hopefully, prevent water rationing from going into effect during 2016. But prospects for the future, despite this temporary respite, are starting to look a bit grim.

Risk of Future Megadrought

The trend set in place by a human-forced warming of the Desert Southwest has resulted in an increasing number of dry years. The added heat forces water to evaporate more rapidly. So even when it does rain an average amount, moisture levels still fall. The result is not only an increase in single year droughts, but an increased risk of decadal droughts (called megadroughts).

As the years progress and more of the impacts of human-forced global warming become apparent, the drought impacts and severe drought risks are only expected to rise. For according to a recent Cornell University report (2014) the chance of a 10 year drought for the US Southwest under a moderate warming scenario (RCP 4.5) is 50% this century (greater for states like Texas, Oklahoma, New Mexico, Arizona, and Nevada — see graphic below). The chances of a 30 year drought range from 20-50 percent depending on the severity of the human greenhouse gas emission. More

 

Parched Caribbean faces widespread drought, water shortages

The worst drought in five years is creeping across the Caribbean, prompting officials around the region to brace for a bone dry summer.

From Puerto Rico to Cuba to the eastern Caribbean island of St. Lucia, crops are withering, reservoirs are drying up and cattle are dying while forecasters worry that the situation could only grow worse in the coming months.

Thanks to El Nino, a warming of the tropical Pacific that affects global weather, and a quieter-than-normal hurricane season that began in June, forecasters expect a shorter wet season. That means less rain to help refill Puerto Rico's thirsty Carraizo and La Plata reservoirs as well as the La Plata river in the central island community of Naranjito. A tropical disturbance that hit the U.S. territory on Monday did not fill up those reservoirs as officials had anticipated.

Puerto Rico is among the Caribbean islands worst-hit by the , with more than 1.5 million people affected by the drought so far, according to the U.S. National Drought Mitigation Center.

Tens of thousands of people receive water only every third day under strict rationing recently imposed by the island government. Puerto Rico last week also activated National Guard troops to help distribute water and approved a resolution to impose fines on people and businesses for improper water use.

The Caribbean's last severe drought was in 2010. The current one could grow worse if the hurricane season ending in November produces scant rainfall and the region enters the dry season with parched reservoirs, said Cedric Van Meerbeeck, a climatologist with the Caribbean Institute for Meteorology and Hydrology.

"We might have serious water shortages ... for irrigation of crops, firefighting, domestic consumption or consumption by the hotel sector," he said.

The Caribbean isn't the only area in the Western Hemisphere dealing with extreme water shortages. Brazil has been struggling with its own severe drought that has drained reservoirs serving the metropolis of Sao Paulo.

In the Caribbean, the farm sector has lost more than $1 million in crops as well as tens of thousands of dollars in livestock, said Norman Gibson, scientific officer at the Trinidad-based Caribbean Agricultural Research and Development Institute.

On St. Lucia, which has been especially hard hit, farmers say crops including coconuts, cashews and oranges are withering.

"The outlook is very, very bad," said Anthony Herman, who oversees a local farm cooperative. "The trees are dying, the plants are dying ... It's stripping the very life of rivers."

Officials in Cuba say 75 percent of the island is enduring a drought that has killed cattle and destroyed thousands of hectares (acres) of crops including plantains, citrus, rice and beans. Recent heavy rains in some areas have alleviated the problem some, but all 200 government-run reservoirs are far below capacity.

In the nearby Dominican Republic, water shortages have been reported in hundreds of communities, said Martin Melendez, a civil engineer and hydrology expert who has worked as a government consultant. "We were 30 days away from the entire water system collapsing," he said.

The tourism sector has also been affected.

Most large hotels in Puerto Rico have big water tanks and some recycle wastewater to irrigate green areas, but many have curtailed water use, said Frank Comito, CEO of the Florida-based Caribbean Hotel & Tourism Association.

Other hotels have cut back on sprinkler time by up to 50 percent, said Carlos Martinez of Puerto Rico's Association of Hotels. "Everybody here is worried," he said. "They are selling water tanks like hot cakes ... and begging God for rain."

Guests at Puerto Rico's El Canario by the Lagoon hotel get a note with their room keys asking them to keep their showers short amid the water shortage. "We need your cooperation to avoid waste," says the message distributed at the front desk of the hotel in the popular Condado district.

At the Casa del Vega guesthouse in St. Lucia, tourists sometimes find the in their rooms turned off for the day, preventing them from taking a shower. "Even though we have a drought guests are not sympathetic to that," hotel manager Merlyn Compton said. More


 

Monday, May 25, 2015

Deciphering clues to prehistoric climate changes locked in cave deposits

It turns out that the steady dripping of water deep underground can reveal a surprising amount of information about the constantly changing cycles of heat and cold, precipitation and drought in the turbulent atmosphere above. The analysis of a stalagmite from a cave in north east India can detect the link between El Nino conditions in the Pacific Ocean and the Indian monsoon, a new study has found.

When the conversation turns to the weather and the climate, most people’s thoughts naturally drift upward toward the clouds, but Jessica Oster’s sink down into the subterranean world of stalactites and stalagmites.

That is because the assistant professor of earth and environmental sciences at Vanderbilt University is a member of a small group of earth scientists who are pioneering in the use of mineral cave deposits, collectively known as speleothems, as proxies for the prehistoric climate.

It turns out that the steady dripping of water deep underground can reveal a surprising amount of information about the constantly changing cycles of heat and cold, precipitation and drought in the turbulent atmosphere above.

As water seeps down through the ground it picks up minerals, most commonly calcium carbonate. When this mineral-rich water drips into caves, it leaves mineral deposits behind that form layers which grow during wet periods and form dusty skins when the water dries up.

Today, scientists can date these layers with extreme precision based on the radioactive decay of uranium into its daughter product thorium. Variations in the thickness of the layers is determined by a combination of the amount of water seeping into the cave and the concentration of carbon dioxide in the cave’s atmosphere so, when conditions are right, they can provide a measure of how the amount of precipitation above the cave varies over time. By analyzing the ratios of heavy to light isotopes of oxygen present in the layers, the researchers can track changes in the temperature at which the water originally condensed into droplets in the atmosphere changes and whether the rainfall’s point of origin was local or if traveled a long way before falling to the ground.

The value of this information is illustrated by the results of a study published May 19 in the journal Geophysical Research Letters by Oster’s group, working with colleagues from the Berkeley Geochronology Center, the Smithsonian Institution National Museum of Natural History and the University of Cambridge titled “Northeast Indian stalagmite records Pacific decadal climate change: Implications for moisture transport and drought in India.”

In the study, Oster and her team made a detailed record of the last 50 years of growth of a stalagmite that formed in Mawmluh Cave in the East Khasi Hills district in the northeastern Indian state of Meghalaya, an area credited as the rainiest place on Earth.

Studies of historical records in India suggest that reduced monsoon rainfall in central India has occurred when the sea surface temperatures in specific regions of the Pacific Ocean were warmer than normal. These naturally recurring sea surface temperature “anomalies” are known as the El Niño Modoki, which occurs in the central Pacific, and the Pacific Decadal Oscillation, which takes place in the northern Pacific. (By contrast, the historical record indicates that the traditional El Niño, which occurs in the eastern Pacific, has little effect on rainfall levels in the subcontinent.)

When the researchers analyzed the Mawmluh stalagmite record, the results were consistent with the historical record. Specifically, they found that during El Niño Modoki events, when drought was occurring in central India, the mineral chemistry suggested more localized storm events occurred above the cave, while during the non-El Niño periods, the water that seeped into the cave had traveled much farther before it fell, which is the typical monsoon pattern.

“Now that we have shown that the Mawmluh cave record agrees with the instrumental record for the last 50 years, we hope to use it to investigate relationships between the Indian monsoon and El Niño during prehistoric times such as the Holocene,” said Oster.

The Holocene Climate Optimum was a period of global climate warming that occurred between six to nine thousand years ago. At that time, the global average temperatures were somewhere between four to six degrees Celsius higher than they are today. That is the range of warming that climatologists are predicting due to the build-up of greenhouse gases in the atmosphere from human activity. So information about the behavior of the monsoon during the Holocene could provide clues to how it is likely to behave in the future. This knowledge could be very important for the 600 million people living on the Indian subcontinent who rely on the monsoon, which provides the area with 75 percent of its annual rainfall.

“The study actually grew out of an accidental discovery,” said Oster. Vanderbilt graduate student Chris Myers visited the cave, which co-author Sebastian Breitenbach from Cambridge has been studying for several years, to see if it contained enough broken speleothems so they could use them to date major prehistoric earthquakes in the area.

Myers found a number of columns that appear to have broken off in the magnitude 8.6 earthquake that hit Assam, Tibet in 1950. But he also discovered a number of new stalagmites that had begun growing on the broken bases. When he examined these in detail he found that they had very thick layers and high concentrates of uranium, which made them perfect for analysis.

Because of the large amount of water running into the cave, the stalagmite they choose to analyze had grown about 2.5 centimeters in 50 years. (If that seems slow, compare it with growth rates of a few millimeters in a thousand years found in caves in arid regions like the Sierra Nevada.) As a result, the annual layers averaged about 0.4 millimeters thick — wide enough for the researchers to get seven to eight samples per layer, which is slightly better than one measurement every two months. The amount of information about the climate that scientists can extract from the stalagmites and stalactites in a cave is amazing. But the value of this approach increases substantially as the number of caves that can act as climate proxies increases.

It is not a simple task. Because each cave is unique, the scientists have to study it for several years before they understand it well enough to use it as a proxy. For example, they must establish how long it takes water to move from the surface down to the cave, a factor that can vary from days to months.

Efforts to use the mineral deposits in caves as climate proxies began in the 1990’s. Currently, there are only a few dozen scientists who are pursuing this line of research and they have analyzed the mineral deposits from 100 to 200 caves in this fashion.

Story Source:

The above story is based on materials provided by Vanderbilt University. The original article was written by David Salisbury. Note: Materials may be edited for content and length.

Journal Reference:

  1. Christopher G. Myers, Jessica L. Oster, Warren D. Sharp, Ralf Bennartz, Neil P. Kelley, Aaron K. Covey, Sebastian F.M. Breitenbach. Northeast Indian stalagmite records Pacific decadal climate change: Implications for moisture transport and drought in India. Geophysical Research Letters, 2015; DOI: 10.1002/2015GL063826

 

Saturday, May 9, 2015

Dry Heat

Last week, Lake Mead, which sits on the border of Nevada and Arizona, set a new record low—the first time since the construction of the Hoover Dam in the 1930s that the lake’s surface has dipped below 1,080 feet above sea level.

The West’s drought is so bad that official plans for water rationing have now begun—with Arizona’s farmers first on the chopping block. Yes, despite the drought’s epicenter in California, it’s Arizona that will bear the brunt of the West’s epic dry spell.

The huge Lake Mead—which used to be the nation’s largest reservoir—serves as the main water storage facility on the Colorado River. Amid one of the worst droughts in millennia, record lows at Lake Mead are becoming an annual event—last year’s low was 7 feet higher than this year’s expected June nadir, 1,073 feet.

If, come Jan. 1, Lake Mead’s level is below 1,075 feet, the U.S. Bureau of Reclamation, which manages the river, will declare an official shortage for the first time ever—setting into motion a series of already agreed-upon mandatory cuts in water outlays, primarily to Arizona. (Nevada and Mexico will also receive smaller cuts.) The latest forecasts give a 33 percent chance of this happening. There’s a greater than 75 percent chance of the same scenario on Jan. 1, 2017. Barring a sudden unexpected end to the drought, official shortage conditions are likely for the indefinite future.

Why Arizona? In exchange for agreeing to be the first in line for rationing when a shortage occurs, Arizona was permitted in the 1960s to build the Central Arizona Project, which diverts Colorado River water 336 miles over 3,000 feet of mountain ranges all the way to Tucson. It’s the longest and costliest aqueduct in American history, and Arizona couldn’t exist in its modern state without it. Now that a shortage is imminent, another fundamental change in the status quo is on the way. As in California, the current drought may take a considerable and lasting toll on Arizona, especially for the state’s farmers.

“We need to stop growing alfalfa in the deserts in the summertime.”

Robert Glennon, water policy expert at the University of Arizona

“A call on the river will be significant,” Joe Sigg, director of government relations for Arizona Farm Bureau, told the Arizona Daily Star. “It will be a complete change in a farmer’s business model.” A “call” refers to the mandatory cutbacks in water deliveries for certain low-priority users of the Colorado. Arizona law prioritizes cities, industry, and tribal interests above agriculture, so farmers will see the biggest cuts. And those who are lucky enough to keep their water will pay more for it.

According to Robert Glennon, a water policy expert at the University of Arizona, the current situation was inevitable. “It’s really no surprise that this day was coming, for the simple reason that the Colorado River is overallocated,” Glennon told me over the phone last week. Glennon explained that the original Colorado River compact of 1922, which governs how seven states and Mexico use the river, was negotiated during “the wettest 10-year period in the last 1,000 years.” That law portioned out about 25 percent more water than regularly flows, so even in “normal” years, big reservoirs like Lake Mead are in a long-term decline. “We’ve been saved from the disaster because Arizona and these other states were not using all their water,” Glennon said.

They are now. Since around 2000, Arizona has been withdrawing its full allotment from the Colorado River, and it’s impossible to overstate how important the Colorado has become to the state. About 40 percent of Arizona’s water comes from the Colorado, and state officials partially attribute a nearly 20-fold increase in the state’s economy over the last 50 years to increased access to the river.

On April 22, Arizona held a public meeting to prepare for an eventual shortage declaration, which could come as soon as this August. The latest rules that govern a shortage, established in 2007 by an agreement among the states, say that Arizona will have to contend with a 20 percent cut in water in 2016 should Lake Mead fall below 1,075 feet, which will decrease the amount available to central Arizona’s farmers by about half. At 1,050 feet, central Arizona’s farmers will take a three-quarters cut in water. At 1,025 feet, agriculture would have to make due largely without water from the Colorado River. That would probably require at least a temporary end to large-scale farming in central Arizona. Below 1,025 feet, the only thing Colorado River states have agreed to so far is a further round of negotiations. In that emergency scenario, no one really knows what might happen. More