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Imagine a sponge. Swipe on a wet surface and it will absorb water; Squeeze and the water will drip.

Now imagine a city made up of sponges or spongy surfaces that can absorb rainwater, overflowing rivers or ocean storms and release stored water during a drought.

Engineers, architects, urban planners and officials around the world are looking for ways to retrofit or rebuild cities to better deal with water – basically acting like a sponge. While water management has always been a basic service in cities, climate change, along with urban expansion, is exacerbating wetlands and floodplains, flooding and drought at the same time.

excessive precipitation becomes more frequent and intense, and drought is more likely and severe. Impermeable asphalt surfaces, such as concrete and asphalt, trap water without leaving any room to escape and prevent the accumulation of groundwater that will later be used for drinking, cooking and cleaning. (Moreover, concrete production contributes significantly to climate change and is approximately 8 percent of global greenhouse gas emissions.) Many cities are also coastal and low-lying, so face an additional front in the war against water as sea levels rise.

That’s why authorities around the world are moving from traditional, rigid infrastructure of flood barriers, concrete walls, culverts and sewer systems to solutions that mimic nature. They build green roofs and parks; restoring wetlands, ditches and rivers; excavation of storage ponds; and more. These types of projects, which are called by various names such as sponge cities, permeable cities or blue-green infrastructure, are also improve the quality of life of city residents.

Instead of struggling to get rid of water quickly, sponge cities slow the water, absorb the rain and stop the flow, which is a major source of pollution in urban waterways.

“Climate change will mean that any storm, drought or natural disaster will easily outpace what we designed,” said Yu Kongjian, a landscape architect at Peking University and founder of the firm. TurenscapeThe person who popularized the term “sponge city”. “We’re very dependent on that infrastructure, so whenever a natural disaster happens, it’s overwhelmingly devastating.”

Mr. Yu said that the sponge development philosophy is not a new concept, but a way of living in cities that use its natural properties, take into account their climate and apply locally appropriate solutions.

China is under pressure to find a way to deal with water. in July approx. 300 people died During floods in central China, particularly in Zhengzhou, 14 people drowned in the subway; one An estimated one million people were displaced. in 2012 77 people died in Beijing when heavy rain hits the city.

In 2015, the Chinese government announced ambitious plans for sponge country. by 2030, 80% of cities they will be able to collect and recycle 70 percent of rainwater. Localities set their own goals; For example, Zhengzhou aims to make 90 percent of its core urban area spongy by 2030.

Because of its central government and funding, China is better equipped to implement ambitious solutions to flooding. China is also adept at large-scale urban construction, 600 cities built To adapt to the increasing urban population in recent years.

But the flooding problem is not limited to China. Record rainfall during two storms in New York in 2021 flooded subways, highways and basements, and kill 13 people. Cities all over the world face such tragedies. Here are a few examples of how other cities are using sponge solutions.

Wuhan, China

Due to the virus that causes Covid-19, Wuhan, which everyone knows now, was known as the “city of 100 lakes” with more than 100 lakes and ponds. But paving and construction have reduced the footprint of lakes and ponds by more than 60 percent in the last century.

Located at the confluence of the Yangtze, Han and some small rivers, Wuhan has experienced long periods of flooding, especially during the monsoon season. Now that there is less room for water to go, canalized rivers and concrete have transformed floodplains into basins.

In 2016, rainstorms killed 14 people in the city and caused nearly $360 million in damage. The disaster added urgency to existing plans to make Wuhan a pilot sponge city. Since then, about 390 infrastructure projects have been built in about 15 square miles of Wuhan, primarily in the Qingshan and Sixin areas, costing around $2 billion.

One of them is the Yangtze River Beach Park. To the embankments that once surrounded the river, the project added light vegetation and permeable surfaces for more than four miles; 45,000 trees, 125 square miles of bush and 150 square miles of grass; 15 football fields; and seven swimming pools. The park currently sequesters 725 tons of carbon dioxide per year, reduces temperatures by more than 5 degrees Fahrenheit compared to the rest of the city, and more than doubles the value of the land. a study.

The study also found that these solutions cost about $600 million less than traditional hard infrastructure projects, and provide protection against a 30-year storm rather than a 10-year storm, says one expert. He told The Guardian.

Malmo, Sweden

In the 1990s, engineers in the Augustenborg district of Malmo began separating stormwater from wastewater by allowing stormwater to flow through open channels to avoid drowning the sewer system in the event of a major storm. By doing this, Augustenborg was able to avoid a catastrophic flood.

Pipes run through buildings to open gutters that connect to concrete channels large enough to hold water from flooding every 25 years. These channels merge with ponds. Concrete “stones” at the bottom slow the flow and form small eddies, providing oxygen for plant growth. The water then moves from one marshy area to another pond and eventually pipes that keep the water out of the sewer system.

According to Per-Arne Nilsson, a senior strategist in Malmo’s environmental department, Augustenborg is doing much better during the flood than other parts of Malmo.

This project took shape in Augustenborg partly because the land and buildings belonged to the city, but also because the neighborhood was in economic decline. Mr Nilsson added that city officials see the sponge project as a way to deal with water, but also to increase land values, stabilize investments, and serve and benefit historically neglected people.

Philadelphia

In 2011 Philadelphia, “Green City, Clean Waters” plan is a 25-year, $4.5 billion project to reduce the city’s 13 billion gallon runoff and expand stormwater treatment using green and traditional infrastructure elements. The project came about under a mandate from the Environmental Protection Agency that enacted the federal Clean Water Act.

Ten years after the project, the city has “greened” 2,200 acres and reduced flow by three billion gallons. It is on track to meet its goal of reducing runoff by 85 percent, or eight billion gallons, by 2036. Its strategies include rain gardens, green roofs, restored wetlands and other green infrastructure.

The holistic approach was deliberate, officials said. “One of our biggest lessons in the last 10 years is that you don’t just take on a project like this about rainwater,” said Jessica K. Brooks, head of the green stormwater infrastructure implementation unit for the water department. Instead, they look at the whole city and how the parts that make it up work together.

“One of the keys is to get the residents on board to help,” he said.

And like Malmo, they are using the project to address issues of fairness and equality.

“Wherever we work, we adapt it to that neighborhood so the benefits we get are just what that neighborhood needs,” Brooks said, “because equality is such an important part of what we do.”