Why so many buildings in Singapore are covered in plants

• Singapore is trying to fight rising temperatures partly by making its buildings greener, literally.
• This involves covering rooftops and vertical facades with gardens.

As the world heats up — and the urban built environment makes things worse — Singapore is at the leading edge of efforts to cool cities.

The hot and humid city-state is among the most densely populated in the world, and it's seeing its temperatures rise particularly quickly. The country approaches this task in various ways — from designing buildings to facilitate airflow to painting rooftops with reflective coats. One central strategy is to literally make the city greener by covering rooftops and the facades of buildings with plants.

Cities often suffer from the urban heat-island effect, when the built environment makes cities hotter than neighboring rural areas. Buildings and asphalt absorb heat, while cars and other vehicles emit even more heat, and a lack of greenery in cities exacerbates the issues. Plants cool buildings and cities by absorbing sunlight, creating shade, and releasing water that cools the air. Of course, they also absorb carbon dioxide, a greenhouse gas that contributes to the climate crisis.

Under its Skyrise Greenery Incentive Scheme, Singapore pays property owners up to 50% of the cost of installing green rooftops and facades. This amounts to up to $200 a square meter for roofs and $500 a square meter for vertical plantings, according to the government.

The greenery also reduces buildings' carbon footprint and saves property owners on air conditioning and other energy costs. And the green buildings can attract tourists looking to patronize eco-friendly businesses.

Many of these plant-covered structures have received international attention. One skyscraper that opened in Singapore last year has more than 80,000 trees and plants on it. The city-state's Nanyang Technological University has been celebrated for its green roofs. And a mixed-used complex with extensive green roofs won the 2018 World Architecture Festival's award for building of the year.

This is all part of Singapore's decadeslong effort to become the "Garden City." Its Green Plan 2030 sets out a series of ambitious environmental goals, including doubling the rate at which trees are planted between 2020 and 2030, making at least 80% of its buildings green, and creating 200 hectares of green roofs by 2030. Singapore is also investing in a network of "green corridors," streets lined thickly with trees that also help to provide shade and moisture, naturally air conditioning the city. Some public buses have even adopted green roofs.

Singapore is not the only place investing heavily in planting more greenery to reduce temperatures and boost energy efficiency. The city of Basel, Switzerland, has been incentivizing green roof construction since the 1990s, and as of 2019, it had more green roof space per capita than any place on earth. Toronto passed a law in 2009 requiring that buildings of a certain size have green roofs.