Peak Water: What Happens When the Wells Go Dry?
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Peak oil has generated headlines in recent years, but the real threat to our future is peak water. There are substitutes for oil, but not for water. We can produce food without oil, but not without water.
We drink on average four liters of water per day, in one form or another, but the food we eat each day requires 2,000 liters of water to produce, or 500 times as much. Getting enough water to drink is relatively easy, but finding enough to produce the ever-growing quantities of grain the world consumes is another matter.
Grain consumed directly supplies nearly half of our calories. That consumed indirectly as meat, milk and eggs supplies a large part of the remainder. Today, roughly 40 percent of the world grain harvest comes from irrigated land. It thus comes as no surprise that irrigation expansion has played a central role in tripling the world grain harvest over the last six decades.
During the last half of the twentieth century, the world’s irrigated area expanded from close to 250 million acres (100 million hectares) in 1950 to roughly 700 million in 2000. This near tripling of world irrigation within 50 years was historically unique. But since then the growth in irrigation has come to a near standstill, expanding only 10 percent between 2000 and 2010.
In looking at water and our future, we face many questions and few answers. Could the world be facing peak water? Or has it already peaked?
Farmers get their irrigation water either from rivers or from underground aquifers. Historically, beginning with the Sumerians some 6,000 years ago, irrigation water came from building dams across rivers, creating reservoirs that then enabled them to divert the water onto the land through a network of gravity-fed canals. This method of irrigation prevailed until the second half of the twentieth century, where with few sites remaining for building dams, the prospects for expanding surface irrigation faded. Farmers then turned to drilling wells to tap underground water resources.
In doing so, they learned that there are two types of aquifers: those that are replenishable through rainfall, which are in the majority, and those that consist of water laid down eons ago, and thus do not recharge. The latter, known as fossil aquifers, include two strategically important ones, the deep aquifer under the North China Plain and the Ogallala aquifer under the U.S. Great Plains.
Tapping underground water resources helped expand world food production, but as the demand for grain continued climbing, so too did the amount of water pumped. Eventually the extraction of water began to exceed the recharge of aquifers from precipitation, and water tables began to fall. And then wells begin to go dry. In effect, overpumping creates a water-based food bubble, one that will burst when the aquifer is depleted and the rate of pumping is necessarily reduced to the rate of recharge.
Today some 18 countries, containing half the world’s people, are overpumping their aquifers. Among these are the big three grain producers—China, India and the U.S.—and several other populous countries, including Iran, Pakistan and Mexico.
During the last couple of decades, several of these countries have overpumped to the point that aquifers are being depleted and wells are going dry. They have passed not only peak water, but also peak grain production. Among the countries whose use of water has peaked and begun to decline are Saudi Arabia, Syria, Iraq and Yemen. In these countries peak grain has followed peak water.
Nowhere are falling water tables and the shrinkage of irrigated agriculture more dramatic than in Saudi Arabia, a country as water-poor as it is oil-rich. After the Arab oil export embargo in 1973, the Saudis realized they were vulnerable to a counter-embargo on grain. To become self-sufficient in wheat, they developed a heavily subsidized irrigated agriculture based heavily on pumping water from fossil aquifers.
After being self-sufficient in wheat for over 20 years, the Saudis announced in early 2008 that, with their aquifers largely depleted, they would reduce wheat planting by one eighth each year until 2016, when production would end. By then Saudi Arabia projects it will be importing some 15 million tons of wheat, rice, corn and barley to feed its 30 million people. It is the first country to publicly project how aquifer depletion will shrink its grain harvest.
Syria, a country of 22 million people riddled by civil war, is also overpumping its underground water. Its grain production peaked in 2001 and during the years since has dropped 32 percent. It, too, is becoming heavily dependent on imported grain.
In neighboring Iraq, grain production has plateaued over the last decade. In 2012 it was dependent on the world market for two thirds of its consumption. In addition to aquifer depletion, both Syria and Iraq are also suffering from a reduced flow in the Tigris and Euphrates rivers as upstream Turkey claims more water for its own use.
In Yemen, a nation of 24 million people that shares a long border with Saudi Arabia, the water table is falling by roughly six feet a year as water use outstrips aquifer recharge. With one of the world’s fastest-growing populations and with water tables falling throughout the country, Yemen is fast becoming a hydrological basket case. Grain production has fallen by nearly half over the last 40 years. By 2015, irrigated fields will be a rarity and the country will be importing virtually all of its grain. Living on borrowed water and borrowed time, Yemen could disintegrate into a group of tribal fiefdoms warring over water.
Thus in the Arab Middle East the world is seeing the collision between population growth and water supply at the regional level. For the first time in history, grain production is dropping in a geographic region with nothing in sight to arrest the decline. Because of the failure of governments in the region to mesh population and water policies, each day now brings 9,000 more people to feed and less irrigation water with which to feed them.
Other countries with much larger populations are also near or beyond peak water. In Iran, a country with 77 million people, grain production dropped 10 percent between 2007 and 2012 as irrigation wells started to go dry. One-quarter of its current grain harvest is based on overpumping. With its population growing by a million people per year, it, too, faces a day of reckoning.
Pakistan, with a population of 182 million that is growing by 3 million per year, is also mining its underground water. Most of its irrigation water comes from the Indus river system, but in the Pakistani part of the fertile Punjab plain, the drop in water tables appears to be similar to the better-known fall that is occurring in India.
Observation wells near the twin cities of Islamabad and Rawalpindi showed a fall in the water table between 1982 and 2000 that ranged from three to six feet a year. In the Pakistani province of Balochistan, which borders Afghanistan, water tables around the capital, Quetta, are falling by 3.5 meters (11.5 feet) per year—pointing to the day when the city will run out of water. Sardar Riaz A. Khan, former director of Pakistan’s Arid Zone Research Institute in Quetta, reports that six of Balochistan’s seven basins have exhausted their groundwater supplies, leaving their irrigated lands barren.
In a World Bank study, water expert John Briscoe says: “Pakistan is already one of the most water-stressed countries in the world, a situation which is going to degrade into outright water scarcity due to high population growth.” He then notes that “the survival of a modern and growing Pakistan is threatened by water.”
In Mexico—home to a population of 122 million that is projected to reach 156 million by 2050—the demand for water is outstripping supply. Mexico City’s water problems are well known. Rural areas are also suffering. In the agricultural state of Guanajuato, the water table is falling by six feet or more a year. In the northwestern wheat-growing state of Sonora, farmers once pumped water from the Hermosillo aquifer at a depth of 40 feet. Today they pump from over 400 feet. Mexico may be near peak water use. Peak grain may be imminent.
In addition to these small and midsize countries, aquifer depletion now also threatens harvests in the big three grain producers—China, India and the U.S.—that together produce half of the world’s grain. The question is not whether water shortages will affect future harvests in these countries, but rather when they will do so.
Among the big three, dependence on irrigation varies widely. Some four fifths of China’s grain harvest comes from irrigated land, most of it drawing on surface water, principally the Yellow and Yangtze rivers. For India, three fifths of its grain is irrigated, mostly with groundwater. For the U.S., only one-fifth of the harvest is from irrigated land. The bulk of the grain crop is rain-fed, produced in the highly productive Midwestern Corn Belt where there is little or no irrigation.
Falling water tables are already adversely affecting harvest prospects in China, which rivals the U.S. as the world’s largest grain producer. A groundwater survey released in Beijing in 2001 indicated that the water table under the North China Plain, an area that produces half of the country’s wheat and a third of its corn, was falling fast. Overpumping has largely depleted the shallow aquifer, forcing well-drillers to turn to the region’s deep aquifer, which is not replenishable.
The survey reported that under Hebei Province in the heart of the North China Plain, the average level of the deep aquifer was dropping nearly 10 feet per year. Around some cities in the province, it was falling twice as fast. He Qingcheng, head of the groundwater monitoring team, notes that as the deep aquifer is depleted, the region is losing its last water reserve—its only safety cushion.
In 2010, He Qingcheng reported that Beijing was drilling down 1,000 feet to reach an aquifer, five times deeper than 20 years ago. His concerns are mirrored in the unusually strong language of a World Bank report on China’s water situation that foresees “catastrophic consequences for future generations” unless water use and supply can quickly be brought back into balance.
As serious as water shortages are in China, they are even more alarming in India, where the margin between food consumption and survival is so precarious. In India, whose population is growing by 15 million per year, irrigation depends heavily on underground water. And since there are no restrictions on well drilling, farmers have drilled more than 27 million irrigation wells and are pumping vast amounts of underground water.
In this global epicenter of well drilling, pumps powered by heavily subsidized electricity are dropping water tables at an alarming rate. Among the states most affected are Punjab, Haryana, Rajasthan and Gujarat in the north and Tamil Nadu in the south. In North Gujarat the water table is falling by 20 feet per year. In Tamil Nadu, a state of 72 million people, water tables are falling everywhere. Kuppannan Palanisami of Tamil Nadu Agricultural University noted in 2004 that 95 percent of the wells owned by small farmers have dried up, reducing the irrigated area in the state by half over the preceding decade.
India’s grain harvest has been expanding rapidly in recent years, but in part for the wrong reason, namely massive overpumping. A World Bank study estimates that 15 percent of India’s food supply is produced by mining groundwater. Stated otherwise, 175 million Indians are now fed with grain produced with the unsustainable use of water. As early as 2004, Fred Pearce reported in New Scientist that “half of India’s traditional hand-dug wells and millions of shallower tube wells have already dried up, bringing a spate of suicides among those who rely on them. Electricity blackouts are reaching epidemic proportions in states where half of the electricity is used to pump water from depths of up to a kilometer.”
As India’s water tables fall, larger farmers are using modified oil-drilling technology to reach water, going as deep as 1,000 feet in some locations. In communities where underground water sources have dried up entirely, all agriculture is now rain-fed and drinking water must be trucked in. Tushaar Shah of the International Water Management Institute says of India’s water situation: “When the balloon bursts, untold anarchy will be the lot of rural India.”
In the U.S., farmers are over-pumping in the Great Plains, including in several leading grain-producing states such as Texas, Oklahoma, Kansas, and Nebraska. In these states, irrigation has not only raised wheat yields but it has also enabled a shift from wheat to corn, a much higher-yielding crop. Kansas, for example, long known as the leading wheat state, now produces more corn than wheat.
Irrigated agriculture has thrived in these states, but the water is drawn from the Ogallala aquifer, a huge underground water body that stretches from Nebraska southwards to the Texas Panhandle. It is, unfortunately, a fossil aquifer, one that does not recharge. Once it is depleted, the wells go dry and farmers either go back to dryland farming or abandon farming altogether, depending on local conditions.
In Texas, a large grain and cattle state, whose northern part overlies the shallow end of the Ogallala, irrigated grain area peaked in 1975. Since then it has shrunk by two-thirds, with the most precipitous drop in recent years. In Kansas the peak came in 1982 and irrigated grain area has since fallen 41 percent. Nebraska, now also a leading corn-producing state, saw its irrigated area peak most recently, in 2007. Even though aquifer depletion is reducing grain output in several key states, it is not yet sufficient to reduce the overall U.S. grain harvest, the bulk of which is produced in the rain-fed Midwestern Corn Belt.
At the international level, water conflicts, such as the one in the Nile river basin between Egypt and the upstream countries, make the news. But within countries it is the competition for water between cities and farms that preoccupies political leaders. Indeed, in many countries farmers now face not only a shrinking water supply as aquifers are pumped dry, but also a shrinking share of that shrinking supply.
In large areas of the U.S., such as the southern Great Plains and the Southwest, virtually all water is now spoken for. The growing water needs of major cities and thousands of small towns often can be satisfied only by taking water from agriculture. As the value of water rises, more farmers are selling their irrigation rights to cities, letting their land dry up. Hardly a day goes by without the announcement of a new sale. Half or more of all sales are by individual farmers or their irrigation districts to cities and municipalities.
In the largest farm-to-city water transfer in U.S. history, farmers in California’s highly productive Imperial Valley agreed in 2003 to send San Diego County enough water to meet the household needs of close to one million people each year. The agreement spans 45 years. This could reduce food production in the Imperial Valley, a huge vegetable garden not only for California, but for countless other markets as well. Writing from the area in the New York Times, Felicity Barringer notes that many fear that “a century after Colorado River water allowed this land to be a cornucopia, unfettered urban water transfers could turn it back into a desert.”
Colorado, with a fast-growing population, has one of the world’s most active water markets. Cities and towns of all sizes are buying irrigation water rights from farmers and ranchers. In the Arkansas river basin, which occupies the southeastern quarter of the state, Colorado Springs and Aurora (a suburb of Denver) have already bought water rights to one-third of the basin’s farmland. Aurora has purchased rights to water that was once used to irrigate 19,000 acres of cropland in the Arkansas valley. The U.S. Geological Survey estimates that 400,000 acres of farmland dried up statewide between 2000 and 2005.
Colorado is not alone in losing irrigation water. Farmers in rural India are also losing their irrigation water to cities. This is strikingly evident in Chennai (formerly Madras), a city of 9 million on the east coast. As a result of the city government’s inability to supply water to many of its people, a thriving tank-truck industry has emerged that buys water from nearby farmers and hauls it to the city’s thirsty residents.
For farmers near cities, the market price of water typically far exceeds the value of the crops they can produce with it. Unfortunately the 13,000 privately owned tank trucks hauling water to Chennai are mining the region’s underground water resources. As water tables fall, eventually even the deeper wells will go dry, depriving rural communities of both their food supply and their livelihood.
In the competition for water between farmers on the one hand and cities and industries on the other, farmers always lose. The economics do not favor agriculture. In countries such as China, where industrial development and the jobs associated with it are an overriding national economic goal, agriculture is becoming the residual claimant on the water supply.
Where virtually all water has been claimed, cities can typically get more water only by taking it from irrigation. Countries then import grain to offset the loss of irrigated grain production. Since it takes 1,000 tons of water to produce one ton of grain, importing grain is the most efficient way to import water. Thus trading in grain futures is, in a sense, trading in water futures. To the extent that there is a world water market, it is embodied in the world grain market.
We can now see how overpumping, whether in the Middle East or the U.S. Great Plains, can lead to aquifer depletion and shrinking grain harvests. In short, peak water can lead to peak grain. For some countries this is no longer merely a theoretical possibility. It is a reality.
Thus far, aquifer depletion has translated into shrinking harvests only in smaller countries in the Middle East. When we look at middle-sized countries such as Iran, Mexico and Pakistan, with tightening water supplies, we see that Iran is already in deep trouble. It is feeling the effects of shrinking water supplies from overpumping. Pakistan may also have reached peak water. If so, peak grain may not be far behind. In Mexico, the water supply may have already peaked. With less water for irrigation, Mexico may be on the verge of a downturn in its grain harvest.
In summarizing prospects for the three big grain producers—the U.S., China and India—we see sharp contrasts. In the U.S., the irrigated grainland is starting to shrink largely as a result of depletion of the Ogallala aquifer, making it more difficult to rapidly increase overall grain production.
China, with four-fifths of its grain harvest coming from irrigated land, relies heavily on irrigation, but it is largely river water. A notable exception to this is the all-important North China Plain which relies heavily on underground water. With tight water supplies in northern China and with cities claiming more irrigation water, the shrinking water supply will likely reduce the harvest in some local situations. And before long it could more than offset production gains, leading to an absolute decline in China’s grain harvest.
Of the big three countries, the one most vulnerable to overpumping is India. Three-fifths of its grain harvest comes from irrigated land. And since only a minor share of its irrigation water comes from rivers, India is overwhelmingly dependent on underground water. Its millions of wells, each powered with a diesel engine or electric motor, are dropping water tables at an alarming rate. Accurate data are hard to come by, but India may have already passed peak water. The question is, will peak water be followed by peak grain or is there enough unrealized technological potential remaining to raise yields enough to offset any imminent losses from wells going dry?
The world has quietly transitioned into a situation where water, not land, has emerged as the principal constraint on expanding food supplies. There is a large area of land that could produce food if water were available.
Water scarcity is not our only challenge. Just as harvests are shrinking in some countries because of aquifer depletion, they are shrinking in other countries because of soil erosion. Among the more dramatic examples are Mongolia and Lesotho, which have each seen their grain area shrink as a result of soil erosion. And as a result of overplowing and overgrazing, two huge new dust bowls are forming in the world today, one in northwest China and the other in the Sahelian region of Africa. These giant dust bowls dwarf the U.S. Dust Bowl of the 1930s.
The bottom line is that water constraints—augmented by soil erosion, the loss of cropland to nonfarm uses, a plateauing of yields in major producing areas and climate change—are making it more difficult to expand world food production. The question raised is this: is it conceivable that the negative influences on future food production could one day offset the positive ones, leading to a cessation in the world grain harvest?
On Thursday, April 22, the world will celebrate Earth Day, the largest non-religious holiday on the globe.
This Earth Day falls at a critical turning point. It is the second Earth Day since the start of the coronavirus pandemic and follows a year of devastating climate disasters, such as the wildfires that scorched California and the hurricanes that battered Central America. But the day's organizers still have hope, and they have chosen a theme to match.
"At the heart of Earth Day's 2021 theme, Restore Our Earth, is optimism, a critically needed sentiment in a world ravaged by both climate change and the pandemic," EarthDay.org president Kathleen Rogers told USA TODAY.
Last Earth Day marked the first time that the holiday was celebrated digitally to prevent the spread of COVID-19. This will largely be the case this year as well.
"Most of our Earth Day events will be virtual with the exception of individual and small group cleanups through our 'Great Global Cleanup' program," EarthDay.org's Olivia Altman told USA TODAY.
Tuesday, April 20: A Global Youth Summit begins at 2:30 p.m. ET featuring young climate activists like Greta Thunberg and Alexandria Villaseñor. This will be followed at 7 p.m. ET by "We Shall Breathe," a virtual summit organized by the Hip Hop Caucus to look at issues like the climate crisis, pollution and the pandemic through an environmental justice lens.
Wednesday, April 22: Beginning at 7 a.m. ET, Education International will lead the "Teach for the Planet: Global Education Summit." Talks will be offered in multiple languages and across multiple time zones to emphasize the importance of education in fighting the climate crisis.
Thursday, April 22: On the day itself, EarthDay.org will host its second ever Earth Day Live digital event beginning at 12 p.m. ET. This event will feature discussions, performances and workshops focusing on the day's theme of restoring our Earth through natural solutions, technological innovations and new ideas.
"EARTHDAY.ORG looks forward to contributing to the success of this historic climate summit and making active progress to Restore Our Earth," Rogers said in a press release. "We must see every country rapidly raise their ambition across all climate issues — and that must include climate education which would lead to a green jobs-ready workforce, a green consumer movement, and an educated and civically engaged citizenry around the world."
EarthDay.org grew out of the first Earth Day in 1970, which drew 20 million U.S. residents to call for greater environmental protections. The movement has been credited with helping to establish the U.S. Environmental Protection Agency and to pass landmark environmental legislation like the Clean Air and Water Acts. It has since gone on to be a banner day for environmental action, such as the signing of the Paris agreement in 2016. More than one billion people in more than 192 countries celebrate Earth Day each year.
This legacy continues. The organization called the scheduling of Biden's summit a "clear acknowledgement of the power of Earth Day."
"This is a critical stepping stone for the U.S. to rejoin the world in combating the climate crisis. In concert with several planned parallel EARTHDAY.ORG events worldwide, Earth Day 2021 will accelerate global action on climate change," EarthDay.org wrote.
Super-emitters are individual sources such as leaking pipelines, landfills or dairy farms that produce a disproportionate amount of planet-warming emissions, especially methane and carbon dioxide. Carbon Mapper, the non-profit leading the effort, hopes to provide a more targeted guide to reducing emissions by launching special satellites that hunt for sources of climate pollution.
"What we've learned is that decision support systems that focus just at the level of nation states, or countries, are necessary but not sufficient. We really need to get down to the scale of individual facilities, and even individual pieces of equipment, if we're going to have an impact across civil society," Riley Duren, Carbon Mapper CEO and University of Arizona researcher, told BBC News. "Super-emitters are often intermittent but they are also disproportionately responsible for the total emissions. That suggests low-hanging fruit, because if you can identify and fix them you can get a big bang for your buck."
The new project, announced Thursday, is a partnership between multiple entities, including Carbon Mapper, the state of California, NASA's Jet Propulsion Laboratory (JPL) and Planet, a company that designs, builds and launches satellites, according to a press release. The project is being implemented in three stages.
The initial stage, which is already complete, involved the initial engineering development. NASA and Planet will work together in the second stage to build two satellites for a 2023 launch. The third phase will launch an entire constellation of satellites starting in 2025.
The satellites will include an imaging spectrometer built by NASA's JPL, NASA explained in a press release. This is a device that can break down visible light into hundreds of colors, providing a unique signature for chemicals such as methane and carbon dioxide. Most imaging spectrometers currently in orbit have larger pixel sizes, making it difficult to locate emission sources that are not always visible from the ground. However, Carbon Mapper spectrometers will have pixels of around 98 square feet, facilitating more detailed pin-pointing.
"This technology enables researchers to identify, study and quantify the strong gas emission sources," JPL Scientist Charles Miller said in the press release.
Once the data is collected, Carbon Mapper will make it available to industry and government actors via an open data portal to help repair leaks.
"These home-grown satellites are a game-changer," California Governor Gavin Newsom said of the project. "They provide California with a powerful, state-of-the-art tool to help us slash emissions of the super-pollutant methane — within our own borders and around the world. That's exactly the kind of dynamic, forward-thinking solution we need now to address the existential crisis of climate change."
By Jenna McGuire
Commonly used herbicides across the U.S. contain highly toxic undisclosed "inert" ingredients that are lethal to bumblebees, according to a new study published Friday in the Journal of Applied Ecology.
The study reviewed several herbicide products and found that most contained glyphosate, an ingredient best recognized from Roundup products and the most widely used herbicide in the U.S. and worldwide.
While the devastating impacts of glyphosate on bee populations are more broadly recognized, the toxicity levels of inert ingredients are less understood because they are not subjected to the same mandatory testing by the U.S. Environmental Protection Agency (EPA).
"Pesticides are manufactured and sold as formulations that contain a mixture of compounds, including one or more active ingredients and, potentially, many inert ingredients," explained the Center for Food Safety in a statement. "The inert ingredients are added to pesticides to aid in mixing and to enhance the products' ability to stick to plant leaves, among other purposes."
The study found that these inert substances can be highly toxic and even block bees' breathing capacity, essentially causing them to drown. While researchers found that some of the combinations of inert ingredients had no negative impacts on the bees, one of the herbicide formulations killed 96% of the bees within 24 hours.
According to the abstract of the study:
Bees exhibited 94% mortality with Roundup® Ready‐To‐Use® and 30% mortality with Roundup® ProActive®, over 24 hr. Weedol® did not cause significant mortality, demonstrating that the active ingredient, glyphosate, is not the cause of the mortality. The 96% mortality caused by Roundup® No Glyphosate supports this conclusion.
"This important new study exposes a fatal flaw in how pesticide products are regulated here in the U.S.," said Jess Tyler, a staff scientist at the Center for Biological Diversity. "Now the question is, will the Biden administration fix this problem, or will it allow the EPA to continue its past practice of ignoring the real-world harms of pesticides?"
According to the Center for Food Safety, there are currently 1,102 registered formulations that contain the active ingredient glyphosate, each with a proprietary mixture of inert ingredients. In 2017, the group filed a legal petition calling for the EPA to force companies to provide safety data on pesticide formulations that include inert ingredients.
"The EPA must begin requiring tests of every pesticide formulation for bee toxicity, divulge the identity of 'secret' formulation additives so scientists can study them, and prohibit application of Roundup herbicides to flowering plants when bees might be present and killed," said Bill Freese, science director at the Center for Food Safety. "Our legal petition gave the EPA a blueprint for acting on this issue of whole formulations. Now they need to take that blueprint and turn it into action, before it's too late for pollinators."
ATTN @EPA: Undisclosed "inert" ingredients in #pesticide products warrant further scrutiny! ➡️ A new study compared… https://t.co/bdFwXCVHsD— Center 4 Food Safety (@Center 4 Food Safety)1618592343.0
Roundup — also linked to cancer in humans — was originally produced by agrochemical giant Monsanto, which was acquired by the German pharmaceutical and biotech company Bayer in 2018.
The merger of the two companies was condemned by environmentalists and food safety groups who warned it would cultivate the greatest purveyor of genetically modified seeds and toxic pesticides in the world.
Reposted with permission from Common Dreams.
By Ayesha Tandon
New research shows that lake "stratification periods" – a seasonal separation of water into layers – will last longer in a warmer climate.
These longer periods of stratification could have "far-reaching implications" for lake ecosystems, the paper says, and can drive toxic algal blooms, fish die-offs and increased methane emissions.
The study, published in Nature Communications, finds that the average seasonal lake stratification period in the northern hemisphere could last almost two weeks longer by the end of the century, even under a low emission scenario. It finds that stratification could last over a month longer if emissions are extremely high.
If stratification periods continue to lengthen, "we can expect catastrophic changes to some lake ecosystems, which may have irreversible impacts on ecological communities," the lead author of the study tells Carbon Brief.
The study also finds that larger lakes will see more notable changes. For example, the North American Great Lakes, which house "irreplaceable biodiversity" and represent some of the world's largest freshwater ecosystems, are already experiencing "rapid changes" in their stratification periods, according to the study.
As temperatures rise in the spring, many lakes begin the process of "stratification." Warm air heats the surface of the lake, heating the top layer of water, which separates out from the cooler layers of water beneath.
The stratified layers do not mix easily and the greater the temperature difference between the layers, the less mixing there is. Lakes generally stratify between spring and autumn, when hot weather maintains the temperature gradient between warm surface water and colder water deeper down.
Dr Richard Woolway from the European Space Agency is the lead author of the paper, which finds that climate change is driving stratification to begin earlier and end later. He tells Carbon Brief that the impacts of stratification are "widespread and extensive," and that longer periods of stratification could have "irreversible impacts" on ecosystems.
For example, Dr Dominic Vachon – a postdoctoral fellow from the Climate Impacts Research Centre at Umea University, who was not involved in the study – explains that stratification can create a "physical barrier" that makes it harder for dissolved gases and particles to move between the layers of water.
This can prevent the oxygen from the surface of the water from sinking deeper into the lake and can lead to "deoxygenation" in the depths of the water, where oxygen levels are lower and respiration becomes more difficult.
Oxygen depletion can have "fatal consequences for living organisms," according to Dr Bertram Boehrer, a researcher at the Helmholtz Centre for Environmental Research, who was not involved in the study.
Lead author Woolway tells Carbon Brief that the decrease in oxygen levels at deeper depths traps fish in the warmer surface waters:
"Fish often migrate to deeper waters during the summer to escape warmer conditions at the surface – for example during a lake heatwave. A decrease in oxygen at depth will mean that fish will have no thermal refuge, as they often can't survive when oxygen concentrations are too low."
This can be very harmful for lake life and can even increase "fish die-off events" the study notes.
However, the impacts of stratification are not limited to fish. The study notes that a shift to earlier stratification in spring can also encourage communities of phytoplankton – a type of algae – to grow sooner, and can put them out of sync with the species that rely on them for food. This is called a "trophic mismatch."
Prof Catherine O'Reilly, a professor of geography, geology and the environment at Illinois State University, who was not involved in the study, adds that longer stratified periods could also "increase the likelihood of harmful algae blooms."
The impact of climate change on lakes also extends beyond ecosystems. Low oxygen levels in lakes can enhance the production of methane, which is "produced in and emitted from lakes at globally significant rates," according to the study.
Woolway explains that higher levels of warming could therefore create a positive climate feedback in lakes, where rising temperatures mean larger planet-warming emissions:
"Low oxygen levels at depth also promotes methane production in lake sediments, which can then be released to the surface either via bubbles or by diffusion, resulting in a positive feedback to climate change."
Onset and Breakup
In the study, the authors determine historical changes in lake stratification periods using long-term observational data from some of the "best-monitored lakes in the world" and daily simulations from a collection of lake models.
They also run simulations of future changes in lake stratification period under three different emission scenarios, to determine how the process could change in the future. The study focuses on lakes in the northern hemisphere.
The figure below shows the average change in lake stratification days between 1900 and 2099, compared to the 1970-1999 average. The plot shows historical measurements (black), and the low emission RCP2.6 (blue), mid emissions RCP6.0 (yellow) and extremely high emissions RCP8.5 (red) scenarios.
Change in lake stratification duration compared to the 1970-1999 average, for historical measurements (black), the low emission RCP2.6 (blue) moderate emissions RCP6.0 (yellow) and extremely high emissions RCP8.5 (red). Credit: Woolway et al (2021).
The plot shows that the average lake stratification period has already lengthened. However, the study adds that some lakes are seeing more significant impacts than others.
For example, Blelham Tarn – the most well-monitored lake in the English Lake District – is now stratifying 24 days earlier and maintaining its stratification for an extra 18 days compared to its 1963-1972 averages, the study finds. Woolway tells Carbon Brief that as a result, the lake is already showing signs of oxygen depletion.
Climate change is increasing average stratification duration in lakes, the findings show, by moving the onset of stratification earlier and pushing the stratification "breakup" later. The table below shows projected changes in the onset, breakup and overall length of lake stratification under different emission scenarios, compared to a 1970-1999 baseline.
The table shows that even under the low emission scenario, the lake stratification period is expected to be 13 days longer by the end of the century. However, in the extremely high emissions scenario, it could be 33 days longer.
The table also shows that stratification onset has changed more significantly than stratification breakup. The reasons why are revealed by looking at the drivers of stratification more closely.
Warmer Weather and Weaker Winds
The timing of stratification onset and breakup in lakes is driven by two main factors – temperature and wind speed.
The impact of temperature on lake stratification is based on the fact that warm water is less dense than cool water, Woolway tells Carbon Brief:
"Warming of the water's surface by increasing air temperature causes the density of water to decrease and likewise results in distinct thermal layers within a lake to form – cooler, denser water settles to the bottom of the lake, while warmer, lighter water forms a layer on top."
This means that, as climate change causes temperatures to rise, lakes will begin to stratify earlier and remain stratified for longer. Lakes in higher altitudes are also likely to see greater changes in stratification, Woolway tells Carbon Brief, because "the prolonging of summer is very apparent in high latitude regions."
The figure below shows the expected increase in stratification duration from lakes in the northern hemisphere under the low (left), mid (center), and high (right) emission scenarios. Deeper colors indicate a larger increase in stratification period.
Expected increase in stratification duration in lakes in the northern hemisphere under the low (left), mid (centre) and high (right) emissions scenarios. Credit: Woolway et al (2021).
The figure shows that the expected impact of climate change on stratification duration becomes more pronounced at more northerly high latitudes.
The second factor is wind speed, Woolway explains:
"Wind speed also affects the timing of stratification onset and breakdown, with stronger winds acting to mix the water column, thus acting against the stratifying effect of increasing air temperature."
According to the study, wind speed is expected to decrease slightly as the planet warms. The authors note that the expected changes in near-surface wind speed are "relatively minor" compared to the likely temperature increase, but they add that it may still cause "substantial" changes in stratification.
The study finds that air temperature is the most important factor behind when a lake will begin to stratify. However, when looking at stratification breakup, it finds that wind speed is a more important driver.
Meanwhile, Vachon says that wind speeds also have implications for methane emissions from lakes. He notes that stratification prevents the methane produced on the bottom of the lake from rising and that, when the stratification period ends, methane is allowed to rise to the surface. However, according to Vachon, the speed of stratification breakup will affect how much methane is released into the atmosphere:
"My work has suggested that the amount of accumulated methane in bottom waters that will be finally emitted is related to how quickly the stratification break-up occurs. For example, a slow and progressive stratification break-up will most likely allow water oxygenation and allow the bacteria to oxidise methane into carbon dioxide. However, a stratification break-up that occurs rapidly – for example after storm events with high wind speed – will allow the accumulated methane to be emitted to the atmosphere more efficiently."
Finally, the study finds that large lakes take longer to stratify in spring and typically remain stratified for longer in the autumn – due to their higher volume of water. For example, the authors highlight the North American Great Lakes, which house "irreplaceable biodiversity" and represent some of the world's largest freshwater ecosystems.
These lakes have been stratifying 3.5 days earlier every decade since 1980, the authors find, and their stratification onset can vary by up to 48 days between some extreme years.
O'Reilly tells Carbon Brief that "it's clear that these changes will be moving lakes into uncharted territory" and adds that the paper "provides a framework for thinking about how much lakes will change under future climate scenarios."
Reposted with permission from Carbon Brief.
By Robert Glennon
Interstate water disputes are as American as apple pie. States often think a neighboring state is using more than its fair share from a river, lake or aquifer that crosses borders.
Currently the U.S. Supreme Court has on its docket a case between Texas, New Mexico and Colorado and another one between Mississippi and Tennessee. The court has already ruled this term on cases pitting Texas against New Mexico and Florida against Georgia.
Climate stresses are raising the stakes. Rising temperatures require farmers to use more water to grow the same amount of crops. Prolonged and severe droughts decrease available supplies. Wildfires are burning hotter and lasting longer. Fires bake the soil, reducing forests' ability to hold water, increasing evaporation from barren land and compromising water supplies.
As a longtime observer of interstate water negotiations, I see a basic problem: In some cases, more water rights exist on paper than as wet water – even before factoring in shortages caused by climate change and other stresses. In my view, states should put at least as much effort into reducing water use as they do into litigation, because there are no guaranteed winners in water lawsuits.
Alabama, pay attention to Supreme Court ruling against Florida in water war #Water #SDG6 https://t.co/wIjdoY6Ccr— Noah J. Sabich (@Noah J. Sabich)1617800452.0
Dry Times in the West
The situation is most urgent in California and the Southwest, which currently face "extreme or exceptional" drought conditions. California's reservoirs are half-empty at the end of the rainy season. The Sierra snowpack sits at 60% of normal. In March 2021, federal and state agencies that oversee California's Central Valley Project and State Water Project – regional water systems that each cover hundreds of miles – issued "remarkably bleak warnings" about cutbacks to farmers' water allocations.
The Colorado River Basin is mired in a drought that began in 2000. Experts disagree as to how long it could last. What's certain is that the "Law of the River" – the body of rules, regulations and laws governing the Colorado River – has allocated more water to the states than the river reliably provides.
The 1922 Colorado River Compact allocated 7.5 million acre-feet (one acre-foot is roughly 325,000 gallons) to California, Nevada and Arizona, and another 7.5 million acre-feet to Utah, Wyoming, Colorado and New Mexico. A treaty with Mexico secured that country 1.5 million acre-feet, for a total of 16.5 million acre-feet. However, estimates based on tree ring analysis have determined that the actual yearly flow of the river over the last 1,200 years is roughly 14.6 million acre-feet.
The inevitable train wreck has not yet happened, for two reasons. First, Lakes Mead and Powell – the two largest reservoirs on the Colorado – can hold a combined 56 million acre-feet, roughly four times the river's annual flow.
But diversions and increased evaporation due to drought are reducing water levels in the reservoirs. As of Dec. 16, 2020, both lakes were less than half full.
Second, the Upper Basin states – Utah, Wyoming, Colorado and New Mexico – have never used their full allotment. Now, however, they want to use more water. Wyoming has several new dams on the drawing board. So does Colorado, which is also planning a new diversion from the headwaters of the Colorado River to Denver and other cities on the Rocky Mountains' east slope.
Utah Stakes a Claim
The most controversial proposal comes from one of the nation's fastest-growing areas: St. George, Utah, home to approximately 90,000 residents and lots of golf courses. St. George has very high water consumption rates and very low water prices. The city is proposing to augment its water supply with a 140-mile pipeline from Lake Powell, which would carry 86,000 acre-feet per year.
Truth be told, that's not a lot of water, and it would not exceed Utah's unused allocation from the Colorado River. But the six other Colorado River Basin states have protested as though St. George were asking for their firstborn child.
In a joint letter dated Sept. 8, 2020, the other states implored the Interior Department to refrain from issuing a final environmental review of the pipeline until all seven states could "reach consensus regarding legal and operational concerns." The letter explicitly threatened a high "probability of multi-year litigation."
Utah blinked. Having earlier insisted on an expedited pipeline review, the state asked federal officials on Sept. 24, 2020 to delay a decision. But Utah has not given up: In March 2021, Gov. Spencer Cox signed a bill creating a Colorado River Authority of Utah, armed with a $9 million legal defense fund, to protect Utah's share of Colorado River water. One observer predicted "huge, huge litigation."
How huge could it be? In 1930, Arizona sued California in an epic battle that did not end until 2006. Arizona prevailed by finally securing a fixed allocation from the water apportioned to California, Nevada and Arizona.
Litigation or Conservation
Before Utah takes the precipitous step of appealing to the Supreme Court under the court's original jurisdiction over disputes between states, it might explore other solutions. Water conservation and reuse make obvious sense in St. George, where per-person water consumption is among the nation's highest.
St. George could emulate its neighbor, Las Vegas, which has paid residents up to $3 per square foot to rip out lawns and replace them with native desert landscaping. In April 2021 Las Vegas went further, asking the Nevada Legislature to outlaw ornamental grass.
The Southern Nevada Water Authority estimates that the Las Vegas metropolitan area has eight square miles of "nonfunctional turf" – grass that no one ever walks on except the person who cuts it. Removing it would reduce the region's water consumption by 15%.
Water rights litigation is fraught with uncertainty. Just ask Florida, which thought it had a strong case that Georgia's water diversions from the Apalachicola-Chattahoochee-Flint River Basin were harming its oyster fishery downstream.
That case extended over 20 years before the U.S. Supreme Court ended the final chapter in April 2021. The court used a procedural rule that places the burden on plaintiffs to provide "clear and convincing evidence." Florida failed to convince the court, and walked away with nothing.
Robert Glennon is a Regents Professor and Morris K. Udall Professor of Law & Public Policy, University of Arizona.
Disclosure statement: Robert Glennon received funding from the National Science Foundation in the 1990s and 2000s.
Reposted with permission from The Conversation.