Seoul used 1 daylighted buried stream to solve urban heat issues across 10km of concrete highway; the result transformed an asphalt corridor into a cool public park

For decades, a busy highway cut through central Seoul. Beneath it, a small stream had disappeared under concrete. The city had covered the waterway during a period when roads and development were seen as signs of progress. Over time, the corridor became one of the city’s hottest and most crowded spaces.

Then Seoul made an unusual choice. Instead of adding another road or building more infrastructure, it removed the existing highway and uncovered the buried Cheonggyecheon stream. The change was not cosmetic. It altered how the space worked.

Water began flowing through the center of the city again. Concrete gave way to walking paths, trees, planting and public spaces. The restored corridor stretched for about 11 kilometres, creating a long green route through a dense urban district.


The environmental effect was also measurable. Research found that areas around the restored stream became cooler than comparable locations farther from it. The open water and vegetation helped change the local microclimate, while the removal of the highway reduced the dominance of asphalt and traffic.

Seoul Covered a Stream With Concrete. Then It Brought the Water Back: what existed before the restoration?

Before the restoration, Cheonggyecheon was largely hidden beneath roads and concrete infrastructure. The area had been shaped around an elevated expressway and a heavily paved urban environment, leaving little room for vegetation or aquatic life. The restoration removed that infrastructure and brought the stream back into the center of Seoul's urban landscape.

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The change created a very different corridor through the city. Instead of functioning mainly as a transport-dominated space, the area could once again accommodate flowing water, plants, wildlife and people. The environmental results became especially visible when researchers compared conditions before restoration in 2003 with those recorded by the end of 2008.

How much did biodiversity change?

The ecological shift was substantial. Overall biodiversity increased by 639 percent during that period, with plant species rising from 62 to 308. Fish species increased from four to 25, while bird species grew from six to 36.

The changes extended beyond the most visible wildlife. Aquatic invertebrate species increased from five to 53, and insect species rose from 15 to 192. Mammal species increased from two to four, while amphibian species doubled from four to eight. Together, those figures show how restoring a water corridor inside a dense city can create habitat for several interconnected groups of species.

The stream also became part of Seoul's flood-management infrastructure. The restored corridor provides protection for floods reaching a 200-year event and can sustain a flow rate of 118 millimeters per hour. That function matters because an urban stream is not simply a landscape feature; it can also provide space for water during intense rainfall.

Can a stream really cool a city?

The project produced another effect that is easier to feel than to see: cooler temperatures along the restored stream. Measurements found temperatures beside the water were 3.3°C to 5.9°C lower than along a parallel road located four to seven blocks away.

Several factors contributed to that difference. Removing the paved expressway reduced heat-absorbing surfaces, while the stream itself provided a cooling effect. More vegetation added shade and evapotranspiration, and wind speeds through the corridor increased by between 2.2 and 7.8 percent.

The air also became cleaner in terms of small-particle pollution. Concentrations fell by 35 percent, from 74 to 48 micrograms per cubic meter. Before restoration, residents in the area were reported to be more than twice as likely to suffer from respiratory disease as residents elsewhere in Seoul, giving the air-quality change a public-health dimension.

Did the restoration change how people moved through Seoul?

The transformation was not limited to environmental conditions. Between 2003 and the end of 2008, Seoul recorded a 15.1 percent increase in bus ridership and a 3.3 percent increase in subway ridership.

The restored corridor also became a destination in its own right. An average of about 64,000 people visited the stream each day, including roughly 1,408 foreign tourists. Those international visitors were estimated to contribute up to 2.1 billion won, or about $1.9 million, in visitor spending to Seoul's economy.

That combination is important because the project changed the function of a central piece of the city. A space once dominated by road infrastructure became a place people could visit, walk through and use as part of the urban environment.

What happened to nearby property and businesses?

The economic effects were particularly visible around the restored corridor. Properties within 50 meters of the project experienced land-price increases of 30 to 50 percent, roughly twice the rate of property increases elsewhere in Seoul.

Business activity also changed. Between 2002 and 2003, the number of businesses in the Cheonggyecheon area increased by 3.5 percent, twice the rate of business growth in downtown Seoul during the same period. The number of working people in the area rose by 0.8 percent, while downtown Seoul recorded a 2.6 percent decline.

Those figures show why urban restoration projects can have consequences far beyond ecology. Changing roads, public space and water infrastructure can also alter where people travel, where businesses operate and how valuable nearby land becomes.

Cheonggyecheon ultimately illustrates a different way of thinking about infrastructure in a dense city. The project did not treat flood protection, biodiversity, air quality, transportation and public space as completely separate concerns. By restoring a waterway and removing a major paved corridor, Seoul changed several parts of the urban environment at once.

The results from 2003 to 2008 do not mean every benefit came from the stream alone; transport patterns, surrounding development and other citywide changes also form part of the broader context. But the measured changes show how dramatically an urban corridor can function when water, vegetation and public space are given room alongside transportation and development.