Adaptation in action: Setúbal’s retention basin proves its value in flood resilience

Water Management

Adaptation

As recent extreme weather events intensify across Southern Europe, devastating floods in Portugal have once again highlighted the urgent need for local adaptation and resilience measures. While several municipalities faced severe impacts from the latest “train of storms,” the city of Setúbal offers a compelling case study of how forward-looking climate adaptation planning can significantly mitigate disaster risks.

A signatory of the Covenant of Mayors since 2014, Setúbal has invested in structural flood prevention measures as part of its broader commitment to climate resilience. Its flagship intervention - a dual water retention basin system integrated into what appears to be an urban park - has now passed its first real stress test under extreme rainfall conditions.

A park to face floods and heatwaves

Located near the Livramento stream, the 19-hectare area known locally as Parque da Várzea was designed not merely as green urban space, but primarily as a flood retention basin. With the capacity to hold approximately 240,000 cubic metres of water - equivalent to around 100 Olympic-sized swimming pools - the system regulates flows from the Livramento and Figueira streams before they reach the city centre and the Sado estuary.

Setúbal’s geographical vulnerability makes such infrastructure essential. Situated at the mouth of the Sado River, with Atlantic tides at its doorstep and runoff descending from nearby hills, the city has historically been prone to flooding when heavy rainfall coincides with high tide. According to municipal Civil Protection authorities, previous decades saw repeated inundations of the downtown area.

The project’s first test

During the latest extreme weather episode, rainfall reached 22–25 mm in a short period - a significant volume. Yet the retention basin filled to less than 50% of its total capacity, successfully buffering peak flows and preventing the flooding scenarios that have historically affected the city. The system releases water gradually back into natural channels when tidal and river conditions permit, combining engineered drainage with natural soil absorption.

The €1.28 million project was co-financed with national and EU funds under the Programa Operacional Sustentabilidade e Eficiência no Uso de Recursos (POSEUR), European Regional Development Funds (FEDER) and Portugal 2020. The project was completed in 15 months and has been operational for seven years. Until now, it had not been tested under such intense meteorological conditions. Its performance during the recent storms has demonstrated the tangible value of anticipatory adaptation investments.

Lessons for Europe

The project’s strong performance during Portugal’s recent floods has drawn national media attention, positioning it as a positive example of effective climate adaptation for other municipalities to follow.

This case illustrates a core principle of the Covenant of Mayors framework: adaptation is most effective when embedded in long-term planning and multi-functional urban design. By combining green space with hydraulic engineering, Setúbal created infrastructure that delivers daily social and environmental benefits while serving as critical protective infrastructure during climate extremes.

As climate-related disasters become more frequent and severe, the experience of Setúbal shows that proactive adaptation measures are practical, lifesaving investments. While many areas in Portugal grappled with flood damage, this Covenant signatory demonstrated that resilience planning, when implemented with foresight and supported by EU cohesion funding, can significantly reduce vulnerability and safeguard communities.

Other Portuguese cities are also stepping up with similar initiatives - from this year’s Green Capital Guimarães, which has developed its own water retention basin, to Cascais and the capital Lisbon - all advancing adaptation measures to strengthen resilience against similar disasters.

More information:

ClimateAdapt Case study, featured as part of our #CitiesRefresh campaign

Articles in Portuguese:

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Publication date: 23 February 2026