Seville is one of the hottest cities in Europe. Summers regularly push past 40°C (104°F), and climate change is making the heat more intense, more frequent, and longer-lasting. The city regularly breaks temperature records — and the people who live and work there feel it.
The response Seville has reached for isn't cutting-edge. It's 3,000 years old.
The Ancient Solution
Qanats are underground water channels developed by Persian engineers as far back as the early first millennium BCE. They work by carrying water from underground aquifers or cooled night-time sources through tunnels that stay naturally cool at depth — typically 20 to 200 metres below the surface — and channel it toward where it's needed, using gravity alone.
The genius of the system is passive cooling. Water moving underground stays cold. That cold water, brought closer to the surface, chills the ground above it. The ambient air temperature around qanat outlets drops significantly — without compressors, refrigerants, or electricity-hungry cooling systems.
The technology spread from Persia across the Islamic world and into Spain during the Moorish period. Some ancient qanat networks still exist across Iran, Morocco, and Afghanistan — still functioning after millennia. Seville is now reimagining the concept for a climate crisis it didn't anticipate.
CartujaQanat: Ancient Meets Modern
The project, named CartujaQanat, is a contemporary architectural experiment installed in Seville's Isla de la Cartuja neighbourhood — partially funded by the European Union. It uses underground channels to cool water naturally overnight. During the day, solar-powered pumps circulate the cooled water, which reduces ground and ambient air temperatures in surrounding public spaces by an estimated 6 to 10 degrees Celsius.
The combination of ancient principle and modern power source is deliberate: the qanat's passive cooling logic is preserved, but solar energy replaces gravity as the circulation mechanism, making the system adaptable to urban environments where ancient-style gravity-fed channels aren't possible.
The result: cooler streets, cooler squares, cooler outdoor spaces — without air conditioning units humming on every wall, without massive electricity consumption, and without the urban heat island effect that conventional cooling systems worsen by pumping heat back into the surrounding air.
Cities Are Rediscovering What Civilisations Knew
Seville isn't alone. Cities across the world — Athens, Medellín, Singapore, Phoenix — are experimenting with passive and nature-based cooling strategies as urban heat becomes a public health emergency. Green roofs, water features, tree canopy coverage, and reflective surfaces are all part of the toolkit.
But qanats represent something different: a technology that was already proven across millennia of use in climates far hotter than medieval Europe, now being rediscovered precisely because modern engineering often missed what ancient builders understood instinctively about heat, water, and the earth beneath our feet.
In Seville, the oldest solution in the room might turn out to be the most effective one.
For more on the surprising ways nature and ancient wisdom are solving modern problems, read about beavers turning riverbeds into carbon sinks and the ancient freshwater reservoir discovered under the Great Salt Lake.
Sources: Al Jazeera, April 2024 · Fast Company · CBC News · PreventionWeb · The Cooldown · Monocle
