The mineral-stained canyon walls and the plunging water levels at Lake Mead, the nation’s largest reservoir, are the most visible signs of the driest 14-year period in the Colorado River Basin’s historical record.
But the receding shorelines at the Basin’s major reservoirs—including Lake Mead, which fell to a record-low level this month, and Lake Powell, the second largest reservoir on the Colorado, 290 kilometers (180 miles) upstream from Mead—are an insignificant hydrological change compared to the monumental disruption taking place underground.
Satellite data show that in the last nine years, as a powerful drought held fast and river flows plummeted, the majority of the freshwater losses in the Basin—nearly 80 percent—came from water pumped out of aquifers.
The decrease in groundwater reserves is a volume of water equivalent to one and a half times the amount held in a full Lake Mead, according to a study published today in the journal Geophysical Research Letters.
“We didn’t think it would be this bad,” said Stephanie Castle, a researcher at the University of California, Irvine, and the study’s lead author. “Basin-wide groundwater losses are not well documented. The number was shocking.”
Scales in the Sky
The research team used data from the GRACE satellite mission to calculate the water balance for a Basin that spreads across seven states and reaches into Mexico.
Launched in 2002, GRACE is a pair of satellites that translate fluctuations in the Earth’s gravitational pull into changes in total water storage. Separate data sets are used to pull apart the contributions from snowpack, soil moisture, surface water and groundwater. GRACE data has been used to assess groundwater depletion in California and the Middle East, as well as flood potential in the Missouri River Basin.
Jay Famiglietti, an Earth systems professor at the University of California, Irvine, and a study co-author, calls the instruments “scales in the sky.”
For the study, the researchers looked at the period from December 2004 to November 2013. This time frame allowed them to isolate the effects of the drought on groundwater. By 2004, the Basin’s reservoirs were nearing record lows. Today, they are slightly, but not significantly lower, at 51 percent full.
The steepest rates of water loss occurred in 2013, which followed one of the driest years on record.
The total decline in the Basin’s water reserves was 64.8 cubic kilometers (52.5 million acre-feet), with 50.1 cubic kilometers (40.6 million acre-feet) from groundwater. The capacity of Lake Mead, for comparison, is 32 cubic kilometers (26 million acre-feet). At least 70 percent of the Basin’s water use is for irrigated agriculture.
Chuck Collum, Colorado River manager at the Central Arizona Project, which delivers more than half of Arizona’s Colorado River allocation, said the study was helpful.
“The study is useful in using GRACE to verify at a coarse scale what water managers in the Basin know,” Cullom told Circle of Blue.
To check their conclusions, the researchers compared the satellite data against measurements taken from individual wells. Measurements from nine U.S. Geological Survey wells and 65 Arizona Department of Water Resources wells showed similar trends at the smaller scale.
“That gives us confidence in what GRACE is seeing,” Castle said.
Still, GRACE data has limits. For one, the satellites cannot tell what share of the groundwater decline comes from an increase in pumping versus a decrease in the recharge rate, the amount that flows into an aquifer. In a drought, pumping would be expected to go up and recharge down, Famiglietti said.
GRACE also has spatial constraints. The satellites work best for land areas larger than 200,000 square kilometers (77,220 square miles), roughly the size of Nebraska. The satellites cannot pick out hotspots of groundwater depletion within the states.
“It’s difficult to break GRACE data down farther than we have,” Famiglietti told Circle of Blue. “We need additional data on the ground to tell what is happening.”
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Here are three new films to watch this Earth Week that will transport you from pole to pole and introduce you to the scientists and activists working to save our shared home.
1. The Year Earth Changed
Where to Watch: Apple TV+
When to Watch: From April 16
The coronavirus pandemic has brought home the stakes of humanity's impact on the environment. But the lockdowns also proved how quickly nature can recover when humans give it the space. Birds sang in empty cities, whales surfaced in Glacier Bay and capybara roamed the South American suburbs.
The Year Earth Changed captures this unique year with footage from more than 30 lockdowned cities between May 2020 to January 2021. Narrated by renowned wildlife broadcaster David Attenborough, the film explores what positive lessons we can take from the experience of a quieter, less trafficked world.
"What the film shows is that the natural world can bounce back remarkably quickly when we take a step back and reduce our impact as we did during lockdown," executive producer Alice Keens-Soper of BBC Studios Natural History Unit told EcoWatch. "If we are willing to make even small changes to our habits, the natural world can flourish. We need to learn how to co-exist with nature and understand that we are not separate from it- for example if we closed some of our beaches at for a few weeks during the turtle breeding we see that it can make a huge difference to their success. There are many ways that we can adapt our behavior to allow the natural world to thrive as it did in lockdown."
2. After Antarctica
Where to Watch: San Francisco International Film Festival
When to Watch: 12 a.m. PST April 9 to 11:59 p.m. April 18
In 1989, Will Steger led an international team of six scientists and explorers to be the first humans to cross Antarctica by dogsled. Steger and his team weren't just in it for the adventure. They also wanted to draw attention to the ways in which the climate crisis was already transforming the icy continent and to rally support for the renewal of the Antarctic Treaty, which would keep the continent safe from extractive industries.
In After Antarctica, award-winning filmmaker Tasha Van Zandt follows Steger 30 years later as he travels the Arctic this time, reflecting on his original journey and once again bringing awareness to changes in a polar landscape. The film intersperses this contemporary journey with footage from the original expedition, some of which has never been seen before.
"Will's life journey as an explorer and climate activist has led him not only to see more of the polar world than anyone else alive today, but to being an eyewitness to the changes occurring across both poles," Van Zandt told EcoWatch. "But now, these changes are happening in all of our own backyards and we have all become eyewitnesses. Through my journey with Will, I have learned that although we cannot always control change, we can change our response. I feel strongly that this is a message that resonates when we look at the current state of the world, as we each have power and control over how we choose to respond to hardships, and we all have the power to unite with others through collective action around a common goal."
After Antarctica is available to stream once you purchase a ticket to the San Francisco International Film Festival. If you miss it this weekend, it will screen again at the Minneapolis St. Paul International Film Festival from May 13 to May 23.
Tasha Van Zandt
3. The Race to Save the World
Where to Watch: Virtual Cinema
When to Watch: From Earth Day, April 22
While many films about the climate crisis seek to raise awareness about the extent of the problem, The Race to Save the World focuses on the people who are trying to stop it. The film tells the story of climate activists ranging from 15-year-old Aji to 72-year-old Miriam who are working to create a sustainable future. It follows them from the streets to the courtroom to their homes, and explores the impact of their advocacy on their personal lives and relationships.
Emmy award-winning documentary filmmaker Joe Gantz told EcoWatch that he wanted to make a film about climate change, but did not want to depress viewers with overwhelming statistics. Instead, he chose to inspire them by sharing the stories of people trying to make a difference.
"Unless millions of people take to the streets and make their voices heard for a livable future, the politicians are not going to get on board to help make the changes needed for a sustainable future," Gantz told Ecowatch. "I think that The Race To Save The World will energize and inspire people to take action so that future generations, as well as the plants, animals and ecosystems, can survive and thrive on this planet."
Check back with EcoWatch on the morning of Earth Day for a special preview of this inspiring film!