Building coastal resilience in Portsmouth: A city under siege by the sea

Portsmouth, a historic city on England’s southern coast, finds itself on the front line of the climate crisis. The city’s venerable coastal defences, many reaching the end of their serviceable lives, are under threat from rising sea levels and increased coastal flooding. Portsmouth’s dual-fronted battle against time and tide reveals a city galvanized, innovating and adapting to safeguard its future. Here we explore Portsmouth’s bold moves, providing a blueprint for coastal cities worldwide grappling with similar threats. By Climate Champions | June 27, 2023

The coastal city of Portsmouth is under siege. The city’s North Portsea Island and Southsea regions, each with their unique topographies and ageing defence systems, face increasing flood risk due to climate change. The city’s coastal heritage, including its Scheduled Ancient Monuments such as the 17th-century Long Curtain Moat, Kings Bastion, Spur Redoubt, and the historic Southsea Castle, is also at risk. The forecasted sea-level rise of one meter by 2100 could inundate the majority of the existing defences annually, a stark reminder of the growing urgency.

In response, Portsmouth launched the Southsea Coastal Scheme, the UK’s largest local authority-led coastal defence project. This ambitious project aims to protect 10,000 homes and 704 commercial properties over the next century. More than just a robust defensive mechanism, the scheme blends its components seamlessly into the city’s landscape, preserving Portsmouth’s unique character, and safeguarding its cherished historical sites. The project’s six sub-frontages – Long Curtain Moat, Clarence Pier, Southsea Common, Southsea Castle, South Parade Pier, and Canoe Lake – are designed with mixed defences strategically blended with existing structures and significant historical assets.

Portsmouth’s resilience project stands as a testament to innovation. Artificial tide pools, mimicking natural ecosystems found on rocky coastlines, are installed to promote marine life colonization. Recycling is a priority; materials from existing structures are reused in new sea defences, minimizing waste. The scheme balances robust defence with a commitment to environmental sustainability, ensuring Portsmouth’s coastline remains a haven for both its human and marine residents.

The North Portsea Island scheme

The North Portsea Island flood defence scheme, covering 8.4km of Portsmouth’s coastline, is designed to provide a ‘1 in 500 year’ standard of protection against flooding. The scheme includes a specially textured seawall, which, once established, will provide a platform for local marine species to thrive. This approach proves that adapting to climate change can coexist with enhancing biodiversity.

Portsmouth’s initiatives have not gone unnoticed. The city is now part of the Cities Race to Resilience, a global initiative to rally cities towards building climate resilience. Portsmouth committed to a broad climate risk and vulnerability assessment, aiming to fully understand the climate risks to its residents, businesses, and public services, from which a climate change adaptation action plan will be developed.

Through its efforts, Portsmouth envisions creating resilient spaces that are safe, environmentally sustainable, and socially inclusive. They are not only combating climate change but also enhancing the cityscape with increased provisions for cyclists and pedestrians.


The Race to Resilience is the global sibling campaign to Race to Zero launched by the COP27 Presidency and High-Level Climate Champions to rally leadership and support from businesses, cities, regions and investors to help frontline communities build resilience and adapt to the accelerating impacts of climate change. The Race to Resilience campaign sets out to catalyse a step-change in global ambition for climate resilience, putting people and nature first in pursuit of a resilient world where communities don’t just survive climate shocks but thrive in spite of them. The Race to Resilience aims to catalyse action by non-state actors to build the resilience of 4 billion people from vulnerable groups and communities to climate risks by 2030.

Find out more here 

Cities Race to Resilience 

The Cities Race to Resilience is one of the initiatives under the Race to Resilience campaign, focused on driving cities to join and pledge their commitment to the global fight against climate change. The Cities Race to Resilience offers cities themselves the unique opportunity to showcase action and drive ambition, according to their own contextually relevant local landscape.

Find out more here. 


Race to Resilience

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