A case study in Barcelona mapped high-risk hotspots for major flood events as climate change increases stormwater frequency. It highlighted social vulnerability as a major factor that must be addressed.
By 2050, nearly 70% of the world’s population is projected to live in cities. Urban populations are growing, putting ever more people at risk from extreme climate-driven events related to stormwater, including surface water flooding and combined sewer overflows.
Increasing the resilience of cities to such events is critical. This forms part of major European Union policy initiatives such as the EU Adaptation Strategy, through which the bloc aims for climate resilience by 2050, and the new European Water Resilience Strategy, which aims to restore and protect the water cycle to ensure flood resilience. Effective water management in cities is also a priority for EU legislation and funding: the Floods Directive requires EU member states to identify at-risk areas and plan coordinated mitigation, and the EU’s Cohesion Policy provides financing to reduce social and economic disparities and encourage investment in climate adaptation.
To improve policy impact, better information is needed on the specific risks and vulnerabilities facing European cities. New research considers the case study of Barcelona, Spain, a coastal city exposed to significant flood risk. It examines climate risk not purely as a physical system but as an integrated ‘Social-Ecological-Technological System’ (SETS). This approach takes an overview of interconnected factors such as the consumption of contaminated water, the harm to aquatic ecosystems and street drainage.
The researchers looked at the city’s exposure to sewer overflows and surface water flooding, and the threat levels these pose, and created an urban risk index, calculating the hazards of each event using hydrological and hydraulic modelling for sewer overflows and flooding, and historical observations for sewers.
To assess the exposure risk to city dwellers, they investigated population density, proximity to public beaches and sewer points. They evaluated social vulnerability by considering income, government welfare needs, language, and the ratio of minors and senior citizens. They looked at ecological vulnerability including connectivity, biodiversity and green spaces, and technological vulnerability including urban surfaces and sewer capacity. They analysed connections between vulnerabilities, hazards and exposures, and used this information to map high-risk communities and hotspots.
The researchers found that the major factor determining overall water-related risk in Barcelona was social vulnerability, with “disproportionate impacts” hitting vulnerable communities – specifically older people and children; and people who are poorer, less healthy or from minority ethnic groups. Other factors increasing risk were sparse vegetation and ageing drainage systems identified as “technological lock-ins” in the sewer system, meaning that approaches which were once considered cutting-edge – such as storing run-off during rain events – were now outdated, and smart technologies were needed.
The findings highlight the difficulty of future-proofing cities against more extreme events without also considering the underlying problems that may affect the success of a chosen intervention. They act as a proof of concept for using a SETS approach to inform policy to increase a city’s climate resilience, the researchers concluded. This could mean a move away from focusing purely on technological considerations. They suggested that an integrated approach to flood risk management could be employed – one that would reduce hazards whilst also reducing vulnerabilities. An example of such an approach could be to strategically develop green spaces in economically disadvantaged areas.
The approach used would be applicable to other cities with similar problems. The researchers propose a series of policy recommendations to reduce the risks associated with extreme climate events.
These included a move to greater social equity in climate adaptation, with policies specifically aimed at helping vulnerable communities; modernising urban water systems to include smart technologies such as decentralised rainwater harvesting; improving access to data around urban water systems; and investing in green infrastructure such as rain gardens, green roofs and urban wetlands to mitigate runoff.
