During our recent field trip to one of Barcelona’s underground water retention tanks, located next to Placa Espanya, we were able to see firsthand one of the ways this impressive city is adapting to the increased risk of flooding caused by climate change. We were guided by a member of the Ajuntament de Barcelona on a tour beneath the streets of the city. They guided us around this immense underground infrastructure, and expertly informed us about how the system works.
The visit was a great way to see a specific example of how the city of Barcelona has adapted to withstand future climate events, making the city safer and better prepared for climate change. The experience gave an insight into how the city manages its waste and stormwater, dealing with the climatic challenges and urban pressures it currently faces.
What stood out the most during the site visit was how vast the underground drainage system is in Barcelona. The city has 13 underground stormwater tanks scattered across various locations under the city. All combined, the stormwater retention tanks can hold over 500,000 m3 of water and in the coming years, this capacity is expected to be expanded. They plan to build 38 new stormwater retention tanks in response to future climate change threats becoming more severe and common. The system uses sensors for real-time monitoring of the stormwater level and uses radar forecasting to effectively manage and store incoming water.
The drainage system has over 200 sensors and 24 rain gauges to monitor the conditions and respond efficiently to extreme climate events. There is a 5-level warning system used based on 20 and 60-minute rainfall statistics, depending on the quantity of rainfall detected by the sensors one of the 5 warning systems would be triggered. Level 1 is light rainfall, levels 2 and 3 are moderate rainfall and levels 4 and 5 are severe events. When the system detects a level 4 or 5 event, this is communicated to civil protection, who will decide whether they need to alert the public. This allows for a fast and effective warning system during extreme weather events. During such events, if necessary, the capacity of the tanks can be expanded in order to withstand the higher volume of rainfall. The stormwater will then be stored and treated, reducing the amount of contaminated water that spills into the Mediterranean Sea.
The tanks also have an innovative cleaning system, using subsoil water to clean them. Water is released manually and washes over the floor of the tanks which is later drained. This is a great way the Ajuntament de Barcelona is reducing the use of treated water in the city by repurposing the subsoil water. Furthermore, another notable effort made by the Ajuntament de Barcelona to deal with the flooding issue in the city is the implementation of Sustainable Urban Drainage Systems (SUDS). Some examples of the SUDS in Barcelona include green roofs, green drainage elements in the streets, and 10 small dams in the mountains, which also help deal with surface runoff and water management.
Although Barcelona’s drainage system is advanced, there are still some downsides. The system struggles to contain all the water during extreme weather events such as flash floods or times of high surface runoff caused by the abundance of impermeable surfaces in the city. This can cause spillages of untreated water into the ocean, contaminating marine ecosystems offshore of Barcelona and causing environmental and public health complications.
Our site visit to Barcelona’s underground stormwater storage system was an eye-opening experience, seeing firsthand one of the ways the city has adapted for extreme climate events and having a tour around the facility guided by a member of the Ajuntament de Barcelona was very informative and interesting. It showed us a great example of how grey infrastructure can be sustainable and tackle the pressing challenges faced by the city. It also showed how Barcelona is preparing for future climate change uncertainties, mentioning the plans to construct more stormwater tanks in the city and expanding the size of the underground tunnels to cope with predicted increased capacity.
This experience has broadened my perspective on what is possible to implement in a city. This infrastructure works very well in conjunction with other mitigation and adaptation strategies such as nature-based solutions in the city. These strategies co-benefit and increase the effectiveness of the city in dealing with extreme weather events, protecting the public and city infrastructure. This infrastructure would benefit other urban areas suffering from similar climate hazards to reduce the risk of future disasters, safeguarding the people and ecosystems.
Ricardo Chinea-Pegler, Master student.