The city of Seville is accustomed to extreme heat, so much so that it is often called the "frying pan of Spain." 

On summer afternoons, the air is so warm that the streets of this historic town in southern Spain become empty, as merely breathing outside becomes extremely difficult. And it could be even worse in the future. 

With climate change, heat waves are happening earlier in the year and are becoming more intense. In June, a record high of 46 C was recorded in Huelva, near the Portuguese border, confirming that 2025 had the hottest June ever recorded in Spain. 

By 2050, Seville could record summer peaks of 50 C and a 20 per cent reduction in rainfall, according to a study conducted by Eltiempo.es, a Spanish weather news network. The city, therefore, has no choice but to adapt. 

By developing several solutions around the innovative use of water, Seville is now at the forefront of cities that have found ways to deal with increasing heat and was recently named a winner of the 2025 edition of Haciendo misión, a competition between Spanish cities on the climate transition.

On the Isla de la Cartuja, the Seville neighbourhood that hosted Expo '92, a group of researchers have implanted an ancient technique for cooling indoor urban spaces.

Called qanat, this technique was invented by Persians around 3,000 years ago to improve irrigation, lower ambient temperatures and provide drinking water to animals in arid regions. 

"Basically, we are using this ancient, proven technique to adapt it to our 21st century," said María de la Paz Montero Gutiérrez, a researcher on the project called Cartuja Qanat. 

Located approximately 20 to 200 metres below the desert surface, the system consists of a series of underground canals built on a slight slope that carry water from higher to lower elevations by gravity.

Two qanats were installed in Seville on either side of an agora, or gathering place, which is the size of two football pitches. During the night, the groundwater is cooled by naturally lower temperatures. Solar-powered pumps propel the cooled water to the surface during the day, where it is then pushed by vertical vents, allowing it to reduce the ground temperature from six to 10 degrees Celsius.

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Gutiérrez says they "modernized the Persian technique by integrating rainwater and electricity generated from solar panels. The entire project is therefore completely self-sufficient without relying on energy-intensive technologies." 

The space — which includes an agora and an amphitheatre — has become a true oasis, which accommodates locals who come there to take a refreshing break or for sporting activities and events. 

"If you come here in the middle of the agora, you can feel fresh air and breathe normally, while outside it's impossible during afternoons," Gutiérrez said. "This model is truly proof that sustainable solutions exist." 

The vegetation planted on the interior walls of the building, the white exterior that reflects heat and the orientation of the entrance doors also contribute to reducing the temperature. 

Since its implementation in 2021, the project, which cost about five million euros to install, has attracted visitors from all over the world curious to learn more. Delegations from California, Germany and Dubai have come to draw inspiration.

"This Persian technique could technically be implanted everywhere," said José Sánchez Ramos, a professor in energy engineering at the University of Seville. 

However, one of the major challenges remains convincing developers to include this solution in their projects, because it requires additional costs, from construction to maintenance.

Bioclimatic schools

Another water-based cooling solution helps students cope with high temperatures well beyond summer, as the Andalusian regional government has decided to implement bioclimatic air conditioning systems in schools.

"It's a system that works in a very simple way just with the water evaporation," explained Manuel Cortés Romero, general director of the Andalusian public agency for education. 

To do this, an adiabatic cooling machine must be installed on the school's roof. This system, which works with solar panels and water, absorbs hot outside air and then cools it inside the machine. During the process to transform the water from liquid to a gas, the evaporated water simultaneously humidifies and cools the airflow. 

The fresh air is then distributed throughout the school through numerous vertical vents. This technique allows the interior temperature to be reduced by up to 12 C, even when the windows are open. 

It has been implemented in more than 450 schools across the Andalusia region — including 131 around Seville — and every new school is built with this system.

"We really see the difference in the students' behaviour," said one of the employees of the IES Cristóbal de Monroy, a secondary school in the suburbs of Seville. "Before, there were a lot of behavioural and attention problems because of the heat, but now this system makes all the difference."

The cost of the installation at the IES Cristobal de Monroy, which has 1,300 students, was half a million euros. 

"It's almost the same price as the air conditioner, but the difference is the cost of the monthly electricity bill. It's about one-tenth of what a normal system would be, because this system requires minimal electrical power," said Romero. 

He said this can be replicated elsewhere. The challenge is explaining this technique well, because people may seem skeptical at first. 

"At the very beginning, no one really knew about it, and the parents were a little skeptical because they were not familiar with this specific technique," said Romero. "Seeing the results, everyone is now convinced of the comfort that this technique brings to the students."

Adapting urban spaces

Seville is also implementing solutions to adapt urban planning to heat waves, from street shades to the reduction of asphalt surfaces or the use of light and permeable urban surfaces to limit the urban heat island effect. 

The latter phenomenon occurs when heat is retained by materials and surfaces and then radiated into the surrounding area, causing the city to experience much warmer temperatures than neighbouring rural areas.

Cruz Roja Avenue is at the heart of this strategy. The Life Watercool project, which cost about 3.7 million euros, aims to mitigate urban heat through evapotranspiration.

The avenue has been transformed from a busy thoroughfare into a pedestrian zone with shade that allows runoff water to be collected, stored in a reservoir and then pumped into public spaces.

"This groundwater cooling system allows us to irrigate new trees that create shade but also to use the water for a fountain in a public square. It also allows us to distribute fresh air via vertical vents in the public square and in the courtyard of a nearby school," said Teresa Palomo Amores, project manager of Life Watercool.

The location of the fountain has also been studied to allow for the cooling of the hot air that will reach the square. "The union of all the technologies will allow us to reduce by three or four degrees the temperature in this square."

One of the objectives of the project, which will be fully operational next autumn, is to implement multiple solutions that can help cities anywhere in the world adapt to a warming climate. 

"It's a very long process with many steps, but it's not impossible," said Amores. "First, you need to develop a removable cover to reduce sun radiation and to adapt to the trees that will grow. Then you need to put a pavement with high reflection, which will reduce the ground temperature, unlike asphalt. And later, the whole water system must be organized."

The researchers will now study how cooling this public square could also cool the surrounding residents.