Professor Alison Raby, Professor in Environmental Fluid Mechanics and Professor Gerd Masselink, Professor of Coastal Geomorphology.
Climate change means warmer temperatures lend greater energy for storms to become more intense in tropical regions. In the mid-latitudes, such as around the UK, the increased impact of climate change is less about temperature and more about sea-level rise, which will exacerbate the adverse impacts of storm events along our coast, namely flooding and erosion.
The UN reports that coastal communities represent around 40% of the global population, with two-thirds of cities with populations over 5 million located at risk of sea-level rise.
You might imagine sea-level rise to be a slow approach of water, like an overflowing bath seeping across the floor to gradually drown our cities and islands. But the reality is that much of the harm is inflicted by storm waves, as rising sea level allows them to batter coastlines at a higher elevation, accelerating coastal erosion.
Sea-level rise and coastal erosion aren’t much of a problem for natural coastlines. Those respond by retreating from the sea. Imagine a beach-dune system backed by a saltmarsh. As sea level rises, the dunes will erode to become beach with some of their sand blowing into the saltmarsh, turning the saltmarsh into dunes. The terrestrial environment behind will flood due to sea-level rise to become a new saltmarsh and, thus, the coastline has gradually shifted. Although the coastline has retreated, there is no loss of habitat or coastal ecosystem.
Problems associated with coastal retreat only arise along developed coastlines with protection structures. These structures prevent the natural adaptation process and are responsible for ‘coastal squeeze’, whereby the coastline can’t move landward and coastal habitats are squeezed against the coastal structures. This leads to beaches and saltmarshes becoming progressively narrower, and their ecosystems, habitats, biodiversity and natural capital are gradually lost.
Tackle global climate change. Reduce greenhouse gas emissions and stop the root causes of sea-level rise and enhanced coastal erosion and flooding. But even if we become carbon neutral by 2050, as we will no doubt hear many times from the UK government during COP26, it will take decades, even centuries, for sea-level rise to cease.
That leaves us with a short-term path of adapting to rising sea level and increased storm impacts.
Over centuries in the UK, we’ve engineered an extensive array of sea defences to hide behind. But they’re not invincible structures; many are fairly simple Victorian blockwork structures that are degrading, sometimes dramatically, under storm wave action. Their rudimentary designs contrast with those found in historic rock lighthouses, where our research on the wave loading and structural response has provided an insight into their survivability. We can apply the tools developed through those investigations to monitor and inform the design of future coastal defences to improve their resilience.
But gone are the days where we see adapting to sea-level rise and storm impacts as a problem for only engineers to address, and where we pitch engineering against coastal ecology. The importance, and societal, environmental and economic benefits, of building in harmony with nature through a holistic approach has never been more critical. Where we do have to build concrete structures, we are demonstrating that ecological engineering can be an effective way of incorporating natural habitats into coastal structures, and therefore start to mitigate some of the habitat loss such development inevitably causes.
Adaptations can also mean focusing on ‘green’ or ‘nature-based’ solutions, like reinstating saltmarshes and mangroves. Not only are these interventions incredibly effective and add biodiversity, they often provide additional benefits including carbon capture, thereby directly addressing the cause of climate change.
Sea-level rise is a major threat to communities living on coral reef islands such as the low-lying Maldives. Just a few centimetres of rise will significantly increase the risk of coastal flooding. The islands are made of sand- and gravel-sized material from the surrounding living coral reef system, with the islands generally formed under large wave conditions. Coastal protection structures are the only way to protect the islands from flooding, but they can’t keep the sea at bay forever. There’s a real risk that the communities will have to relocate at some point.
Building defences here doesn’t consider that the flooding it is trying to prevent, is the very reason those islands exist; in a way, the flooding is a natural adaptation strategy from the island itself. We’re trying to understand this overtopping process and how the islands grow, to incorporate into the adaptations toolbox at our disposal for protecting coral reef islands.
Whether deliberating the Maldives or the UK, we need to accept that the coast is dynamic and avoid placing infrastructure too close to the shoreline.
In countries with a very long coastline, it is impossible to protect every inch of it. How do you select which parts to defend and which to concede? How do you tell a community that their home cannot, or will not, be saved?
It cannot be left to scientists and engineers alone to support coastal communities in understanding the magnitude of the issue facing their homes. We can predict where the coast is most vulnerable and which structures may survive storm waves, and provide expertise in searching for a solution. But these solutions can only be implemented when we work with social scientists, policymakers, science communicators, and those most affected by the changes.
It is vital that local communities are involved as they are most affected by climate change impacts and have the most to gain from appropriate management solutions. Implementing those solutions needs governments who will support communities, especially if faced with the last resort of having to relocate further in-land.
COP26 must be more than a talking shop to prevent burdening future generations with the same dilemmas. Through initiatives like Coastal Change Management Areas, a concept we’re currently working on with local authorities, we’re identifying which areas are likely to be under threat from sea-level rise, flooding or erosion in the next 50-100 years. This will be used to inform planning policy to prevent permanent infrastructure in that buffer zone and combat aspects of coastal squeeze.
It is only through adopting a whole-system approach to the coast, bringing in multiple perspectives and academic disciplines, that we can hope to successfully adapt to the challenges of sea-level rise.
Professor Alison Raby and Professor Gerd Masselink discuss how we need to protect coastal habitats and communities from the effects of climate change
Alison Raby is Professor of Environmental Fluid Mechanics and Head of the COAST Engineering Research Group. She is an expert on the interactions of extreme waves with coastal structures. Gerd Masselink is Professor of Coastal Geomorphology and Head of the Coastal Processes Research Group (CPRG). He is one of the world’s leading authorities on the coastal impacts of extreme storms.
The COP26 summit, held in Glasgow, Scotland from 31 October to 12 November 2021, brought parties together to accelerate action towards the goals of the Paris Agreement and the UN Framework Convention on climate change.
The University of Plymouth is proud to be a part of the COP26 Universities Network whose mission it is to ensure that the UK academic sector plays its role in delivering a successful COP26, in order to deliver a zero-carbon, resilient world.
