Wetlands can cool city air by 4.7 degrees Celsius during heatwaves, according to the most comprehensive review of its kind. In a list of various city features, such waterways ranked second for their cooling abilities.
Water is the driving force of all nature. And it seems to take on an added significance in summer when heatwaves roll across the nation. Water cools us and sustains us, but we are abusing it.
Water in the form of wetlands can cool city air by almost 5 degrees Celsius during heatwaves, according to a new review and the most comprehensive of its kind. But a recent analysis shows that human pressures—such as dam construction, global warming and large-scale irrigation—have altered freshwater resources to such an extent that their capacity to regulate vital climatic and ecological processes is at risk.
One of the first steps we can take to better safeguard our waters is to make sure that they have legal rights and that they are not being violated. Luckily, machine learning can now be used to more accurately predict which wetlands and waterways are protected by the Clean Water Act of 1972. Unfortunately, though, a recent analysis found that a 2020 Trump administration rule removed Clean Water Act protection for one-fourth of U.S. wetlands and one-fifth of U.S. streams, and it also deregulated 30% of watersheds that supply drinking water to household taps.
Hopefully, a better understanding of freshwater dynamics will help guide the creation of new policies to help mitigate the harms we’ve caused to our waterways and wetlands.
As an urban cooling agent, botanical gardens ranked first, causing temperatures to be 5 degrees Celsius cooler than they would be without the gardens.
Cooling cities during heatwaves: botanical gardens, parks and wetlands
In February 2024, researchers from the University of Surrey Global Center for Clean Air Research in Guildford, England, looked at green spaces and waterways in cities and towns and analyzed if having such features cooled the air.
Among the key findings of the analysis, which was published in the journal The Innovation, were the following landscape features and how much each of them lowered the surrounding temperatures:
• Botanical gardens: -5 C average (variation: -2.2 C to -10 C)
• Wetlands: -4.7 C average (variation: -1.2 C to -12 C)
• Rain gardens: -4.5 C average (variation: -1.3 C to -7 C)
• Green walls: -4.1 C average (variation: -0.1 C to -18 C)
• Street trees: -3.8 C average (variation: -0.5 C to -12 C)
• City farms: -3.5 C average (variation: -3 C to -3.9 C)
• Parks: -3.2 C average (variation: -0.8 C to -10 C)
• Reservoirs: -2.9 C average (variation: -1.8 C to 5 C)
• Playgrounds: -2.9 C average (variation: -2.8 C to -3 C)
For the past century, humans have been pushing the Earth’s freshwater system far beyond the stable conditions that prevailed before industrialization. Exceptional conditions are now much more frequent and widespread than before.
While it has been known for some time that green spaces and water can cool down cities, this study provides the most comprehensive picture yet. What’s more, it explains why: from trees providing shade to evaporating water cooling the air.
The scientists say they hope their work will help city and town planners around the world confront the challenges of global heating.
Relieving pressure on freshwater systems: returning them to a stable state
It’s clear that wetlands and waterways are becoming more and more important as the Earth continues to warm. Sadly, however, they are in trouble.
Human pressures, such as dam construction, have altered freshwater resources to such an extent that their capacity to regulate essential ecological processes is no longer guaranteed.
In a study that was published in the science journal Nature Water in March 2024, scientists state that human activity has pushed variation in the planet’s freshwater cycle well outside of its preindustrial range, and its capacity to regulate vital climatic and ecological processes is no longer assured.
This is the first time that the global water cycle change has been assessed over such a long timescale with an appropriate reference baseline. Using data from hydrological models that combine all major human impacts on the freshwater cycle, an international research team calculated monthly streamflow and soil moisture at a spatial resolution of roughly 31 by 31 miles. As a baseline, they determined the conditions during the preindustrial period (1661–1860). They then compared the industrial period (1861–2005) against this baseline. Their analysis revealed an increase in the frequency of exceptionally dry or wet conditions, with deviations in soil moisture and streamflow.
Dry and wet deviations have consistently occurred over substantially larger areas since the early 20th century than during the preindustrial period. Overall, the global land area experiencing deviations has nearly doubled compared with preindustrial conditions.
In many regions with a long history of human occupation and agriculture, such as along the Nile River, irrigation has caused exceptionally dry streamflows and wet soil-moisture conditions.
Exceptionally dry streamflow and soil-moisture conditions became more frequent in many tropical and subtropical regions, while many boreal and temperate regions saw an increase in exceptionally wet conditions, especially in terms of soil moisture. These patterns match changes seen in water availability due to climate change.
There were more complex patterns in many regions with a long history of human agriculture and land use. For example, the Indus, Mississippi and Nile River Basins have experienced exceptionally dry streamflow and wet soil-moisture conditions, indicating changes driven by irrigation.
With this comprehensive view of the changes in soil moisture and streamflow, researchers are better equipped to investigate the causes and consequences of the changes in the freshwater cycle. Understanding these dynamics in greater detail could help guide policies to mitigate the resulting harm, although the immediate priority is decreasing human-driven pressures on freshwater systems, which are vital to life on Earth, conclude the researchers.
The 1972 Clean Water Act protects the “waters of the United States,” but it does not precisely define which streams and wetlands this phrase covers, leaving it to courts, presidential administrations and regulators to decide.
Predicting coverage of the Clean Water Act: deregulating drinking water, streams and wetlands
Just when we need to augment, protect and value our wetlands and waters, we are doing the opposite, concludes a recent study led by a team at the University of California, Berkeley.
The 1972 Clean Water Act protects the “waters of the United States,” but it does not precisely define which streams and wetlands this phrase covers, leaving it to courts, presidential administrations and regulators to decide. As a result, the exact coverage of Clean Water Act rules is difficult to estimate. So, the University of California, Berkeley, team used machine learning to more accurately predict which waterways are protected by the act.
The machine-learning model predicted regulation across the U.S. under a 2020 Trump administration rule and its predecessor, the Supreme Court’s Rapanos ruling, which had previously guided decisions. It was found that the 2020 Trump administration rule removed Clean Water Act protections from one-fourth of U.S. wetlands and one-fifth of U.S. streams—690,000 stream miles, more than every stream in California, Florida, Illinois, New York, Ohio, Pennsylvania and Texas combined—and it deregulated 30% of watersheds that supply drinking water to household taps. The wetlands deregulated under the 2020 rule provided more than $250 billion in flood prevention benefits to nearby buildings, say the study’s authors.
A 2020 rule deregulated 690,000 stream miles, more than every stream in California, Florida, Illinois, New York, Ohio, Pennsylvania and Texas combined.
Prior analyses assumed that streams and wetlands sharing certain geophysical characteristics were regulated, without scrutinizing data on what was truly regulated, an approach the Environmental Protection Agency and the U.S. Army Corps of Engineers called “highly unreliable.”
It’s believed that the machine-learning model’s predictions could save more than $1 billion annually in permitting costs for developers and regulators by providing immediate calculations of the probability that a site is regulated, rather than waiting months through the uncertain process for obtaining permits.
In 2023, a President Biden White House rule expanded the Clean Water Act’s jurisdiction. The Supreme Court’s 2023 Sackett decision then contracted it. Once Sackett is fully implemented, this machine-learning methodology can clarify its scope.
Unaltered waterways support biodiversity, help control floods and provide clean drinking water. Rivers, such as the Colorado, are also vital to our food supply. The Colorado River irrigates almost 90% of our nation’s winter vegetable crops. We need to take our waters far more seriously.
Valuing water: wells and their worth
This recent game of regulatory ping-pong certainly has had staggering effects on environmental protections. In this era of ever-lengthening heatwaves, we need to take our cooling waters far more seriously.
In his very folksy way, Benjamin Franklin once said, “When the well is dry, we’ll know the worth of water.”
That “well”—whether it’s situated in our neighborhoods or on a global level—may be very close to parched.
Here’s to finding your true places and natural habitats,
Candy
