Seville, in southern Spain, has a heat problem most cities can only dread as a future possibility. Summers here are already extreme — afternoon temperatures regularly exceed 42°C (108°F), emptying the streets and making outdoor life nearly impossible. The city holds the uncomfortable distinction of being the first in the world to officially name and categorise heatwaves. But naming them is one thing — surviving them is another.
The answer a team of researchers at the University of Seville has been developing for the past several years involves going underground. Qanats — networks of underground water channels originally developed in ancient Persia around 3,000 years ago — were used across the Islamic world to irrigate crops and cool homes in arid environments. The Cartuja Qanat project, installed in Seville's Isla de la Cartuja district on the site of the 1992 World Expo, has adapted this millennia-old technology for the 21st century. Rainwater and solar power cool the water underground at night; by day, solar-powered pumps bring it to the surface, where it cools the air in two public spaces: a newly built 750-square-metre agora and a renovated amphitheatre.
The €5 million project — 80% of it funded by the EU — requires zero external energy to run. In summer 2025, research showed indoor temperatures up to 12°C (22°F) lower than outside. The spaces have filled with life: tango classes, skateboarding teenagers, workers taking lunch breaks in the shade.
Delegations from California, Germany and Dubai have already visited. The system, researchers note, works best in dry climates and won't suit everywhere — but for cities baking in the kind of heat Seville already knows well, it represents something rare: a solution that is ancient, affordable, and entirely proven.