In April 2024, more than 9 million residents of Colombia's capital, Bogota, were told to collect rainwater – if the city was lucky enough to experience a storm.
The Chingaza reservoir system, fed by the Guatiquía River, provides 70% of the region's water, but water levels have reached extremely low levels.
To get what's left through a drought with no end in sight, authorities have divided the city into nine zones. Each day, one of the areas will dry for 24 hours. None of the toilets flushed. There was not a glass of water to pour from the tap. Dishes must not be washed.
Bogotá Mayor Carlos Galán told residents they should prepare to endure water restrictions for a year.
“Our call is to care for every drop,” the mayor's office said, according to CBS News.
A month later, 2,000 miles away in Mexico, water levels in the Cusamara reservoir system reached record lows. These water reserves provide a large portion of Mexico City's 22 million residents who face forced rationing.
The stories of Bogota and Mexico City reflect the stories of cities around the world. The amount of water stored in lakes around the world has continued to decrease dramatically since 1992, according to a 2023 study published in the prestigious research journal Science. Over the past 30 years, the freshwater lake has lost an average of 600 cubic kilometers of water storage per year, which is 17 times the capacity of Lake Mead, the largest reservoir in the United States.
global crisis
Researchers found that the cause is a combination of human overuse and unprecedented climate change.
Rising temperatures, accelerated evaporation, unpredictable changes in rain and snow patterns, and the runoff caused by these events are making urban water sources increasingly unstable.
These factors, combined with unsustainable water consumption, have contributed to approximately half of the water losses over the past 30 years. They have pushed cities around the world toward “Day Zero,” when water supplies will run out and taps will run dry.
But understanding which stressors have the greatest impact on each water system is the cornerstone of developing solutions.
A cautionary tale from the Aral Sea
In living memory, the Aral Sea, which straddles the border between Uzbekistan and Kazakhstan, is the fourth largest lake in the world.
Starting in the early 1960s, engineers diverted large amounts of water from the Aral Sea to irrigate one of the world's largest cotton-growing regions. Over the next three decades, the lake shrank rapidly.
The decision makes the Aral Sea a model for what happens when humans overuse water in arid areas.
Today, the lake is only one-tenth its size in 1920. If there were no rusty fishing boats in the gray-brown desert, there would be no reason to believe that the surrounding area was a lake bed.
A similar situation is playing out in dozens of critical waterways, from Chile's Maipo River, which supplies 80 percent of Santiago's water, to the United States' Colorado River, which supplies water to 40 million people. Both rivers have been over-committed and over-exploited by expanding cities and agricultural operations.
How does climate change affect water supplies?
Even the best-laid plans can be thwarted by the uncertainty caused by climate change. Evaporation poses a major threat to global drinking water supplies due to rising temperatures.
Evaporation from reservoirs and natural lakes increased by nearly 60% between 1985 and 2018, exceeding scientists' previous expectations, according to a 2022 study published in Nature Communications.
In central Argentina, a salt lake called Laguna Mar Chiquita, or “Little Sea Lake,” illustrates how the pressures of climate change interact with overconsumption. Lack of rainfall and high temperatures mean reduced water supplies from the three rivers that feed Lake Marchquita. With no rain to irrigate crops, farmers divert more water from the lake than usual so their plants don't die. The heat intensifies evaporation, increasing pressure on the lake. In the summers of 2022 and 2023, Argentina set a record 10 heat waves.
The Colorado River, which supplies water to seven Western states, nearly 30 Native American tribes and two Mexican states, faces similar threats. The river irrigates 15% of U.S. agriculture, including about 90% of vegetables grown in the winter. The American West has endured a quarter-century of extreme drought, but two consecutive wet winters have failed to alleviate the situation.
As a result, more water is used than entered.
The U.S. Department of the Interior monitors Lake Mead, which is fed by the Colorado River. If experts expect reservoir levels to drop below a certain point, federal agencies will release less water, leaving less water for downstream shareholders in both countries. In 2022, this happens for the first time.
Arizona, Nevada and Mexico have all faced cuts to their share of the Colorado River in recent years, a trend expected to continue through 2024.
Parker Williams, a hydroclimatologist at the University of California, Los Angeles, told the Los Angeles Times: “A warmer climate means a drier climate, and without compensatory increases in precipitation, which has not happened yet, water for humans and ecosystems will will decrease.
What can cities do in the face of reduced water supplies?
We have undertaken a series of ongoing small-scale efforts to avoid Day Zero.
Reducing water use is the most obvious line of defense. In 2018, a crisis was narrowly averted in Cape Town, South Africa, and people around the world watched as it unfolded. In response, city officials implemented tough restrictions that reduced water use by 50% from 2015 levels. These efforts, coupled with the return of seasonal rains, have kept the city's water supply from running out.
Some states have made changes to their water infrastructure to reduce losses from evaporation and overuse, such as Las Vegas’ ineffective lawn ban.
At the Pasauna Reservoir in southern Brazil, floating solar panels have the potential to be a win-win. These sparkling flakes reduce evaporation from reservoirs by 60% while providing renewable energy to homes, businesses and industry. Floating covers and shade balls have the same effect of preventing evaporation, especially for reservoirs in arid climates. While these technologies promise to reduce evaporation, ongoing research is evaluating side effects, such as compromised water quality.
“Understanding the primary stressors of lake water loss is often a prerequisite for management solutions,” Fangfang Yao, a postdoctoral researcher at the Cooperative Institute for Environmental Sciences who led the study, told Yale Climate Connections.
Tackling climate change is also an essential part of the solution. “Reducing greenhouse gas emissions domestically and internationally will help reduce further water loss through evaporation,” Yao said.
Petacci asked. is a climate science researcher at the Aspen Institute on Global Change. Caitlin Sullivan is a freelance journalist. She covers health, science and the environment. This article was written in collaboration with Energy Innovation and the Aspen Institute on Global Change. Both organizations are Yale Climate Connect content sharing partners.
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