WHY A NEXUS APPROACH?

Future sea level rise combined with storm surges and heavy rainfall will increase compound flood risks. Unavoidable sea level rise will bring cascading and compounding impacts resulting in losses of coastal ecosystems and ecosystem services, groundwater salinization, flooding and damages to coastal infrastructure that cascade into risks to livelihoods, settlements, health, well-being, food and water security, and cultural values in the near to long-term [link]. When sea levels rise as rapidly as they have been, even a small increase can have devastating effects on coastal habitats farther inland. It can cause destructive erosion, wetland flooding, aquifer and agricultural soil contamination with salt, and lost habitat for fish, birds, and plants. Already, flooding in low-lying coastal areas is forcing people to migrate to higher ground, and millions more are vulnerable to flood risk and other climate change effects. The prospect of higher coastal water levels threatens essential services such as port transport infrastructures since much of the underlying communications infrastructure lies in the path of rising seas [link].

Sea level rise poses a distinctive and severe adaptation challenge as it implies dealing with slow onset changes and increased frequency and magnitude of extreme sea level events, which will escalate in the coming decades. Such adaptation challenges would occur much earlier under high rates of sea level rise, in particular, if low-likelihood, high-impact outcomes associated with collapsing ice sheets occur. Responses to ongoing sea level rise and land subsidence in low-lying coastal cities and settlements, and small islands include protection, accommodation, advance and planned relocation. These responses are more effective if combined and/or sequenced, planned well ahead, aligned with sociocultural values and development priorities, and underpinned by inclusive community engagement processes [link]. Coastal areas are more than just places to live - they are key to our economy and way of life. Marine transportation of goods, offshore energy drilling, seafood cultivation, mineral extraction, tourism, and other coastal activities are integral to the nation's economy, generating more than half of the national gross domestic product (GDP). Coastal cities all over the world are expected to face problems combined with strong hurricanes and storm surges; sea level rise is even more threatening. Coastal cities and settlements play a crucial role in moving toward higher climate-resilient development, given firstly, almost 11% of the global population – 896 million people – lived within the Low Elevation Coastal Zone in 2020, potentially increasing to more than 1 billion people by 2050, and these people, and associated development and coastal ecosystems, face escalating climate compounded risks, including sea level rise [link]. As a result of these risks, many coastal cities are already planning adaptation measures to cope with the long-term prospects of higher sea levels, often at considerable cost. Cities are deploying a broad range of strategies to adapt infrastructure to flooding, with hard engineering approaches (e.g., dikes and seawalls) increasingly complementing soft approaches, including planning and use of nature-based solutions, emphasizing natural and social capital [link].

Coastal impacts of SLR can be avoided by preventing new development in exposed coastal locations. For existing developments, a range of near-term adaptation options exists, including (1) engineered, sediment or ecosystem-based protection; (2) accommodation and land use planning to reduce the vulnerability of people and infrastructure; (3) advance through, e.g., land reclamation; and (4) retreat through planned relocation or displacements and migrations due to SLR [link].

Rising sea levels, as a result of climate change, mean that coasts are eroding at a fast rate, and storm surges are more likely to cause damaging coastal flooding. Natural coastal vegetation, such as saltmarsh and mangrove swamps, can, in the right places, stabilize the shoreline and act as a buffer, absorbing the force of waves. On a natural coast, the shoreline will move inland, and as the sea level rises, the coastal vegetation will gradually move inland with it. This contrasts with hard coastal defenses such as sea walls and banks, which can be overwhelmed and fail. In many places, however, coastal habitats have been cleared, and where there are hard sea defences behind the coastal zone, the vegetation disappears as the coast erodes rather than moving inland. This is often referred to as ‘coastal squeeze’ as the vegetation is squeezed between the sea and the sea wall. Restoring coastal habitats and removing hard sea defences can help reduce the risks of catastrophic flooding [link]. Whether it's protection, accommodation or relocation, coastal adaptation projects take time to put in place, and so does coastal governance to address sea-level rise: often several years and sometimes decades. Coastal adaptation practitioners need to consider these lead times to avoid running out of time when sea-level rise or sea-level rise rates will exceed local coping capacities [link]. 

Coastal adaptation is more efficient when clear objectives are set out, and measures are planned, implemented and evaluated in a sequenced way while ensuring that relevant stakeholders are involved in the decision-making process [link]. While adapting to sea-level rise, coastal communities will need to address other social, economic and environmental challenges. The IPCC defines climate resilient development as “the process of implementing greenhouse gas mitigation and adaptation measures to support sustainable development for all” [link]. In other words, meeting sustainable development goals [link]. Each coastal area is different, but all are confronted with the same domain and the same challenge to find a pathway toward sustainability. To ensure that coastal adaptation benefits all and provides equitable and just outcomes, adaptation should be considered part of the broader challenge to meet sustainable development goals [link].