This isn't a forest.
Not really.
It's actually an urban park
in the densely populated city of Nanchang, China.
Filled with birds, native trees...
and volcanic rock on 137 acres of urban land.
It's called a sponge city.
And it's a type of natural infrastructure that architects around the world
are designing to help us combat and withstand a changing climate.
So what does it mean for a city to become spongy?
This video is presented by Delta Airlines.
Today, like everywhere else on the globe
cities are feeling the effects of climate change.
And they often don't have the right infrastructure
to help them survive its impacts.
Some neighborhoods in Houston don't have enough trees
to provide shade and relief from rising temperatures.
Meanwhile, rising sea levels threaten coastal cities, like Mumbai and Seoul
that don't often have the infrastructure
to handle more frequent flooding.
This is only made worse
by the fact that cities are covered with pavement
and other surfaces that can't absorb water.
Urbanization changes habitat.
So, when you build on a place
it removes vegetation and alters hydrology.
That's Dr. Charlie Nilon.
He told me that cities play a complicated role in the climate crisis...
especially when it comes to maintaining biodiversity.
Biodiversity is, simply put
the total number of plants and animals that occur someplace.
Biodiversity is one of our main support systems for human life on earth.
We rely on natural ecosystems
full of diverse plants, animals, and organisms
for essential things like clean water, food, and medicine.
And biodiversity is critical
to defending the Earth against climate change.
We need healthy forests to absorb carbon dioxide from the air
and enough native plants for pollinators to help crops flourish.
But studies show that as urban expansion continues
it can drive habitat losses
that directly put some species in danger...
profoundly impacting global biodiversity.
Cities have a big impact on what happens locally.
Cities capture a significant number of plant and animal species...
which are native.
So that, even in cities, there's a significant amount of biodiversity.
Which means they can play a role in saving
these local plant and animal species.
The really important thing to think about
is not so much how urbanization...
reduces biodiversity, but really
how in cities you can conserve biodiversity.
One way to do this is by creating environments
where nature can flourish.
Environments that can also help cities soak up excess water.
And that's where sponge cities come in.
In 2015, China launched a sponge city pilot program
in 30 cities across the country.
The goal of the program was to coordinate
and promote the construction of sponge cities...
which would improve urban drainage and flood prevention
and create a diverse biological environment.
Architects did this by supplementing the existing grey infrastructure
that relied on concrete pipes and dams
with natural solutions like gardens that are designed to capture rain
and native trees that suck up excess water through their roots.
In China, these ideas were taken from ancient drainage systems.
That's because for centuries
Chinese cities actually handled water pretty well
in part because they were built with nature in mind.
A study from the scientific journal Water
recreated some of these old practices.
Building roofs designed with sloped eaves allowed rainwater
to fall onto the permeable pavement below...
and exterior walls were lined with flowers and trees
to absorb rain and stormwater.
Today, natural solutions like these have been
reimplemented in major cities across China.
In Qian’an, a sewage pipe was replaced
with this natural infiltration system...
that uses vegetation beds to purify storm and rainwater.
Shanghai replaced concrete roads
and sidewalks with this permeable pavement
which is lined with vegetation to absorb excess water
into the soil underground.
And across Wuhan, dozens of urban gardens like these
were planted to absorb water before it overwhelms communities.
Most of these projects rely on introducing vegetation
in an urban area to soak up excess water.
This is a really great way to handle flooding
and it also supports urban biodiversity.
Because you're providing habitat for additional groups...
Plant and animal species.
Sometimes you can restore habitats that have been lost.
Despite these benefits, sponge cities can't fix everything.
The connection between climate change and flooding
is still being studied.
But when floods do happen
these spongy cities are only able to absorb excess water
up to a certain point.
In 2021, sponge city designs in Zhengzhou failed
when historic rainfall drenched the city.
More than 300 people died from the catastrophic flooding.
There are other limitations, too.
One review of sponge cities in Guian New District
found that national standards and codes for spongy infrastructure
are really difficult to enforce
because climate, hydrology, and even socio-economics
are vastly different from one city to the next.
So what might work in some cities won't necessarily
solve climate-related problems in others.
Plus, ambitious sponge city designs
like the sprawling parks built in China
are expensive and require a lot of space...
which most cities don't have.
So some US cities experimenting with natural infrastructure
like LA and Boston
are using the green space they already have.
By trying things like planting vegetation on curbs...
and creating green spaces along median strips.
One type of city design
certainly won't save us from climate change...
but they can make a difference in how we live with it.
We often talk about biodiversity
like it's far away, but it's actually right there.
And I think the more that people understand that
the kinds of things they do around where they live
that really matters.
People can do things to change cities.
They can do things to make cities different.
They can do things to make cities better.