Europe

Rows of black pipes run along the ceiling and down the bare concrete walls. These, in turn, connect to bright blue and green tubes and enormous silver pumps. In a control room to the side, an array of monitors display the heat, humidity and wind speed above.

“We have deployed several types of cooling systems here, each one used depending on climatic conditions,” says Maria de la Paz Montero Gutiérrez, a researcher at the University of Seville, from down in the building’s bowels where she is helping supervise the project.

In 2020, authorities began to install these cooling systems in two public spaces in the Isla de La Cartuja neighborhood of what is one of Europe’s hottest cities. Every day about 30,000 people come to work and study in this northwestern district, which is mostly non-residential and home to university campuses, museums, and businesses.

Under the EU-funded project CartujaQanat, the so-called “qanats” – networks of underground aqueducts – were constructed in a newly-built 750-square meter site known as the Agora, which is large enough to fit about 400 people, as well as in a renovated amphitheater from the ‘90s that has a capacity of about 200 people.

The design of the CartujaQanat. (Rendering courtesy University of Seville)

The system, created millennia ago but updated for the 21st century, works by cooling water underground in the naturally low temperatures at night. To cool water more quickly, some is also sent to the roof via solar-powered pumps and sprayed out of nozzles in a thin layer through a method known as a “falling film,” before draining back down underground.

By day, as outdoor temperatures peak, the cool water is sent above ground into the ceiling to counteract the heat. Water is also funneled into subterranean pipes that cool air (up to 36,000 square meters an hour), which is then released via ducts in the public spaces. Outside, mist is sprayed in order to lower temperatures through evaporation.

“We have half re-invented the qanats, taking from their engineering ingenuity,” says head of the multi-stakeholder project, Lucas Perea Gil, whose team began operating the cooling system in 2022, running seasonally from March to October every year.

Maria de la Paz Montero Gutiérrez, a researcher at the University of Seville helping to supervise the project. (Photo by Peter Yeung)

The original qanats, according to Nilou Vakil, an associate professor of architecture at the University of Kansas, date back 3,000 years to ancient Persia, or modern day Iran. The same system has been used in many regions across the Islamic world, from Balochistan to Jordan.

Historically, she says, they were used in arid areas to transport water from underground sources to irrigate crops and feed animals, but also for cooling homes.

“That’s how they were able to create civilization in places you couldn’t have humans living in before,” explains Vakil, who has researched the history of the qanats. “They allowed people to live with heat before the arrival of electricity.”

The project also represents something of a revival of past local practices. Similar water management technologies were deployed by the Moors across Andalusia, including at Granada’s Alhambra, several hundred years ago.

Seville’s low-emission solution is an encouraging response to the rising threat of extreme urban heat in Spain’s fourth largest city, home to 1.5 million people. Last year, Seville broke a record after recording 30 days above 40C (104F) – compared with an average of 12.8 days a year over the previous decade. 

The city gets so hot these days it’s earned the unenviable nickname of the “Frying Pan of Spain.” And scientists project that due to manmade climate change, by 2050, Seville is likely to hit summer peaks of 50C (122F) while suffering an average 20% decline in rainfall.

That extreme heat, an increasing reality for cities around the world, is already causing serious harm to the population. The Carlos III Health Institute estimated that about 1,180 people died because of high temperatures during a heatwave in Spain between May and July last year. Meanwhile, researchers have calculated that more than 11,000 people died due to extreme heat in Spain during summer 2022.

“It’s a really serious health issue,” says Anna Beswick, a policy fellow at the London School of Economics working on climate adaptation and resilience. “Global average temperatures are rising, and so are extreme temperatures. Cities have specific vulnerabilities since they hold and retain heat more than other areas.”