California is struggling through its fourth year of extreme drought in one of the driest periods in 1,200 years. In April, Gov. Jerry Brown issued water restrictions for the first time in California’s history, making it the last state in the West to seriously restrict groundwater use. In June, Californians cut their water use 27.3 percent, exceeding the governor’s 25 percent mandate. With agriculture typically using 80 percent of California’s surface water allocated for human use, strict water cutbacks on irrigation and livestock production have also now been imposed on many farmers in northern and central California, including some holding the state’s oldest water rights.
In normal times, groundwater accounts for 40 percent of the state’s freshwater use; in 2014, groundwater provided 65 percent.
This is largely because farmers like those in the Central Valley, which produces a quarter of the nation’s food, are growing high value water-hungry crops such as almonds, walnuts, tomatoes and oranges. To irrigate these crops during the drought, farmers are drilling wells deeper and deeper to tap groundwater as the water table drops two feet a year in some parts of the Central Valley. Jay Famiglietti, senior water cycle scientist at NASA’s Jet Propulsion Laboratory, said that by the end of 2015, groundwater might account for all of California’s water use.
Groundwater is water found beneath the Earth’s surface in spaces in soil and rock formations.
The depth at which these spaces in soil and rock are saturated with water is called the water table. An aquifer is any geological formation that contains or channels groundwater. Groundwater moves freely underground and is naturally replenished from precipitation, streams and rivers, but some aquifers formed eons ago will never be replenished in the human time frame.
Groundwater is often likened to a bank account, but perhaps a more apt metaphor is a trust fund you inherit—if you withdraw more money than the interest it earns, you are eating into your principal and will eventually have financial problems.
In essence, this is what is happening in California, which pumps more groundwater annually than any other state, and in many other parts of the United States and the world. One study found that between 1990 and 2010, global use of groundwater increased an average of 3 percent per year, especially in North America, Central America and parts of Asia, mainly to produce food for the world’s growing population. When groundwater is depleted, it can take tens to hundreds of years for it to reestablish its sustainable level, if at all, and when it is overdrawn, there can be serious consequences.
Overpumping groundwater can cause water tables to fall, as is happening in California, which means that some wells will no longer reach water. This forces wells to be drilled deeper, which costs more and requires more energy. It can cause land subsidence, because as water is removed from the soil, it collapses and drops.
Since groundwater that is very deep or below the oceans is saline, overpumping can cause the saltwater to move inland or upwards, resulting in saltwater intrusion, which can contaminate fresh drinking water. And when aquifers are overpumped, they can collapse, forever reducing their capacity to store water. (According to the Center for Investigative Reporting, California has lost 6 trillion gallons of water capacity because of structural damage to its aquifers.) Since much of the water in streams and rivers seeps up from groundwater, groundwater overpumping can also mean less water for lakes and rivers, which can affect vegetation and wildlife. The extent of the damage from overpumping depends on how much water is removed and replenished, and the physical characteristics of the aquifer. In addition, a 2012 Japanese study found that pumped groundwater which ends up in the ocean is a key factor in sea-level rise.
Groundwater is the main source of fresh water for two billion people in the world, and as the climate changes, impacting weather patterns and surface water sources, it is becoming increasingly important as a source of fresh water. The numbers that have been commonly cited of how much groundwater exists underground come from rough calculations done in 1969 and 1974 that overestimated the amount of water there is.
A new study about the state of the world’s aquifers found that 21 of the world’s 37 largest aquifers are overdrawn; 13 have declined so rapidly that they are in critical condition, with the most stressed aquifers found in poor, highly populated areas such as northwest India, Pakistan and North Africa.
The study was based on recent data gathered by NASA’s GRACE (Gravity Recovery and Climate Experiment) program, which uses two satellites to send back information about changes in Earth’s gravity caused by movement of water on or below its surface. The data revealed that some aquifers are much smaller than originally believed; the new regional estimates vary significantly from the estimates done 40 years ago, underscoring the great uncertainty about how much groundwater is available. Unfortunately, while GRACE can detect changes, it cannot tell how much groundwater the aquifers hold, so no one knows the exact amount of groundwater that exists.
The planet’s most stressed aquifer is the Arabian Aquifer; other threatened aquifers include the Indus Basin in India and Pakistan, the Murzuk-Djado Basin in Libya and Nigeria, and the Canning Aquifer in northwest Australia. The danger of overdrawing aquifers, aside from water scarcity, is that a string of consequences can ensue. For example, Saudi Arabia used to produce its own wheat by tapping water from aquifers under the desert, but by 2008 its aquifers were almost depleted. According to Lester Brown, founder and president of the now-shuttered Earth Policy Institute, “the Saudis will likely harvest their last wheat crop by 2016…and will then be totally dependent on imported grain to feed nearly 30 million people.” In Yemen, water tables are falling 6.5 feet a year, grain production has been halved in the last 40 years, and the country must now import over 80 percent of its grain. In China, water tables are dropping under the North China Plain, which produces half of China’s wheat and a third of its corn. Falling water tables jeopardize water supplies, which could result in food shortages, higher food prices, and potentially, social instability. According to Brown, not one country has successfully stopped the fall of its water tables.
In the U.S., GRACE’s data revealed that the most stressed aquifers are the Central Valley Aquifer in California, with the Atlantic and Gulf Coastal Plain Aquifer across the southeast also highly stressed. The High Plains Aquifer (including the Ogallala Aquifer) has depleted the greatest amount of groundwater in the U.S.— it is being pumped at 10 times the rate of replenishment.
There are some areas where groundwater levels are rising, however. Upmanu Lall, professor of engineering and director of the Earth Institute’s Columbia Water Center, said, “This is mainly because they had problems with groundwater depletion in the past and moved out the crops that used to grow there.” Perhaps a sign of things to come is that some northern San Diego County farmers have begun to change over from water-guzzling citrus and avocados to vineyards, because grapes consume 25 percent less water.
State laws regulate groundwater use in the U.S., though the federal Environmental Protection Agency and states together oversee groundwater pollution. In California, laws governing the use of surface waters go back to the 1870s, and the principle of “first in time, first in right” prevails, i.e. the first person to stake a claim gets rights to the water so long as it is put to beneficial use. “For groundwater, there are no definite regulations,” said Lall. “The rights usually go with the land. But since groundwater flows underground, you can be getting water from elsewhere.”
During the 1970s, the Central Valley had land subsidence of 30 feet because of overpumping, said Lall. After groundwater pumping was curtailed, groundwater levels were restored (though the land never recovered).
Since 1995, however, California has been in and out of droughts, and groundwater pumping has increased because some people don’t have access to surface water, and because tapping groundwater is less expensive than surface water, which incorporates the cost of infrastructure and treatment into its price. California’s new groundwater law does not require water authorities to devise sustainable groundwater strategies until 2020 or to balance the amount of water extracted with what is replenished until 2040. Hopefully, the groundwater will last that long.
How can groundwater be managed sustainably? Lall suggests that there should be equitable use and pricing. “If there is a lot of groundwater available and there is no stress on the aquifer, the cost can be cheap,” he said. “But if you are depleting groundwater, you are withdrawing water from future users, and you should pay for it. Pricing should reflect supply and demand.”
Lall also recommends the conjunctive use of surface water and groundwater, that is, coordinating the development of both resources to maximize the supply of fresh water. Because they are essentially connected, they need to be managed as one entity. This might involve storing more surface water underground during wet years and pumping more groundwater from the reserve in dry years. Storage can be accomplished through injecting water into wells or diverting water into natural or constructed areas where it can collect and seep into the ground over time.
In 2014, the Columbia Water Center received a $2.1 million National Science Foundation grant for its America’s Water initiative. The center will study the history and current state of the nation’s water use, its resources and infrastructure. It will then develop a model to help prepare the country for water scenarios of the future, taking into consideration the potential to expand water capacity, energy infrastructure, possible redistribution of crops, irrigation technology, water rights, groundwater levels, ecological needs, government policies, international trade, demographics, economics and climate change. While there are state water plans, no national water plan exists today. Lall said that one goal of America’s Water is to “develop on a county and river basin-scale, an understanding of the real value of water under drought and normal conditions, of where we should grow food, and where energy facilities should be located.”
In the U.S., areas near large cities in the Midwest and the South also have significant groundwater depletion, and as the world becomes increasingly urbanized, providing water to growing urban populations presents many challenges. The Columbia Water Center is developing a future project for city water use called One Water. Currently, our water system operates three discreet systems for drinking water, wastewater and stormwater. Studies have shown that the nation’s drinking water and wastewater utilities need as much as $1.2 trillion to replace aging infrastructure by 2030. One Water will reenvision the water system and study how to invest in unifying it instead of spending enormous sums to replace the infrastructure and inefficient systems that exist today.
The Visionaire condominium in New York’s Battery Park City is an example of how this could be implemented. The building collects rainwater from the roof and wastewater from the building; in the basement, the wastewater is treated by a reactor, and then passes through a disinfection system. The recycled water goes back into the building where it is used, not for drinking, but for all other functions. One Water will try to determine at what scale and with what kind of sensors a unified water system could be implemented, as well as its implications.
“The question is, what’s a good strategy for new cities or expanding cities in terms of solving these kinds of problems?” Lall asked. “Do you continue to extend yourself further and further out into the hinterland and take other people’s water, which is what New York City and Beijing are doing, or do you try to come up with a strategy where you have as much sustainability locally as you can?”