Key Messages 
  • Coastal zones face multiple risks from climate change (e.g. sea level rise, storm surges, wind-storms, coastal erosion, and salt water intrusion).
  • Most impact assessment studies assume highly effective adaptation and ignore the costs of policy development and implementation, which leads to an under-estimation of the cost of adaptation.
  • The concept of adaptive management is gaining traction, together with low-regret measures, iterative risk management and robust decision-making. Applications of real options analysis has been carried out to evaluate the value of maintaining flexibility for engineered structures.

Context

The risks to coastal zones from climate change are primarily related to sea level rise, but also storm surges, wind-storms, flooding, loss of land, coastal erosion, salt water intrusion and impacts on coastal wetlands. Adaptation options to these risks are mostly based on protection, retreat or accepting the risk (e.g. “living with water”).

Policy and methodological developments 

Global and national assessments

Many studies employ the Dynamic Interactive Vulnerability Assessment (DIVA) model, which simulates global and regional sea level rise and examines the costs of physical barriers to address flood risks and shoreline management to address coastal erosion. The DIVA model has been used at the global scale (UNFCCC, 2007; World Bank, 2011), for regional studies in Africa (Brown et al., 2009) and Europe (Hinkel et al., 2010), and for national studies (Brown et al., 2011; SEI, 2009; IBD/ECLAC, 2014; GCAP, 2011; Markandya and Mishra, 2010). Most recently, Hinkel et al. (2014) estimated additional global annual investment and maintenance costs for coastal protection toin 2100 between USD 12-31 billion for a low warming scenario (RCP2.6), and USD 27-71 billion in a high warming scenario (RCP8.5).

Similar studies have also been carried out at the national level, in Canada (Stanton, Davis and Fencl, 2010), Brazil (Margulis and Dubeux, 2010), Germany (Tröltzsch et al., 2012), the UK (Evans et al., 2004) and the US (Neumann et al., 2011). These studies all reach the conclusion that coastal protection is a low cost way to reduce damage from climate change, and leaves low residual damage. The studies also note that the benefit-to-cost ratios will generally increase towards 2100. However, it should be noted that these studies often only cover part of the adaptation costs, as they often fail to include wind storm damage, salinization, port infrastructure, tourism, ecosystems and dike maintenance costs. In addition, they often assume no adaptation deficit and good levels of existing protection, a questionable assumption in many developing countries.

Studies on alternatives to engineered coastal defences

For many OECD countries, there is growing interest in effective alternatives to engineered coastal defences. This can include spatial planning options (de Bruin et al., 2014) or ecosystem-based protection in the form of sand dunes, offshore sand banks and managed retreat. These approaches are particularly advantageous, providing not only numerous co-benefits, but also flexibility against future climate uncertainty. Studies have looked at salt marshes (De Bel, Schomaker and van Harpen, 2011); compared sand dunes against hard structural protection (de Bruin et al., 2012); and compared wetland restoration with enhanced building codes for flood management (Aerts et al., 2013; Aerts et al., 2014).

Low-regret adaptation

Recently, studies have begun to focus on early low-regret options or iterative adaptation approaches. Low/no-regret adaptation options are generally advantageous for early adaptation, offering immediate benefits which can lay the foundation for future resilience. In the context of coastal zones, there are a variety of such options which have been studied. Climate services, forecasting and early warning systems often have high benefit-to-cost ratios in both developed countries (Lazo and Waldman, 2011; Considine et al., 2004; both on US hurricane risk) and in developing countries (Paul, 2009 for Bangladesh; Subbiah, Bildan and Narasimhan, 2008 for South-East Asia).

Disaster risk management and emergency plans have also shown high benefit-to-cost ratios for current risks and future climate change. Natural coastal buffer zones, like mangrove conservation, have also been studied in Samoa (ECA, 2009), the Caribbean (CCRIF, 2010) and the United States (World Bank, 2011). Risk transfer, such as insurance, reserve funds and risk pools can be especially important for extreme events (IPCC, 2012; CCRIF, 2010; Mechler, 2012).

There are other options which focus on building early resilience to longer-term climate change; however their low-regret characteristics can vary. This includes: climate risk screening; land-use planning and set-back zones; and building codes.

Main implications and recommendations 

There is a comprehensive coverage of studies on the costs and benefits of adaptation in coastal zones, focusing on flooding and erosion, Studies have been done at global, national and local level, mainly through impact assessment studies.

Most impact assessment studies assume highly effective adaptation and ignore the costs of policy development and implementation. Newer policy studies (EA, 2009; 2011) have calculated adaptation costs many times higher than existing impact assessments for the same area (Brown et al., 2011).

Robust decision-making support tools have been applied in some recent studies. In the Netherlands, van der Pol et al. (2013) carried out real options analysis for dike heightening. Kontogianni et al. (2013) studied the value of maintaining flexibility for engineered structures in Greece. Groves and Sharon (2013) applied robust decision making in a study for planning coastal resilience in Louisiana in the United States. The concept of adaptive management is also gaining traction in OECD countries, together with greater attention to low-regret measures and iterative risk management. Such approaches are present in the Netherlands as part of the Delta programme (Delta Programme, 2014; Kind, 2014; Eijgenraam et al., 2014) and in the UK under the Thames Estuary 2100 project (EA, 2009; EA, 2011).

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