Editing IPCC:AR6/SROCC/Chapter-4 (section)

===== 4.4.2.2.1 Observed hard and sediment-based protection across geographies =====

Coastal protection through hard measures is widespread around the world, although it is difficult to provide estimates on how many people benefit from them. Currently, at least 20 million people living below normal high tides are protected by hard structures (and drainage) in countries such as Belgium, Canada, China, Germany, Italy, Japan, the Netherlands, Poland, Thailand, the UK, and the USA (Nicholls, 2010). Many more people living above high tides are also protected against ESL by hard structures in major cities around the world. There is a concentration of these measures in northwest Europe and East Asia, although extensive defences are also found in and around many coastal cities and deltas. For example, large scale coastal protection exists in Vancouver (Canada), Alexandria (Egypt) and Keta (Ghana; Nairn et al., 1999 <sup>[[#fn:r1544|1544]]</sup> ) and 6000 km of polder dikes in coastal Bangladesh. Gittman et al. (2015) estimate that 14% of the total US coastline has been armoured, with New Orleans being an example of an area below sea level dependent on extensive engineered protection (Kates et al., 2006 <sup>[[#fn:r1545|1545]]</sup> ; Rosenzweig and Solecki, 2014 <sup>[[#fn:r1546|1546]]</sup> ; Cooper et al., 2016 <sup>[[#fn:r1547|1547]]</sup> ). Defences built and raised for tsunami protection, such as post-2011 in Japan (Raby et al., 2015 <sup>[[#fn:r1548|1548]]</sup> ), also provide protection against SLR.

The application of sediment-based protection measures also has a long history, offering multiple benefits in terms of enhancing safety, recreation and natural systems (JSCE, 2000 <sup>[[#fn:r1549|1549]]</sup> ; Dean, 2002 <sup>[[#fn:r1550|1550]]</sup> ; Hanson et al., 2002 <sup>[[#fn:r1551|1551]]</sup> ; Cooke et al., 2012 <sup>[[#fn:r1552|1552]]</sup> ). About 24% of the world’s sandy beaches are currently eroding by rates faster than 0.5 m yr–1 (Luijendijk et al., 2018 <sup>[[#fn:r1553|1553]]</sup> ). In the USA, Europe and Australia, these responses are often driven by the recreational value of beaches and the high economic benefits associated with beach tourism. More recently, sediment-based measures are implemented as effective and yet flexible measures to address SLR (Kabat et al., 2009 <sup>[[#fn:r1554|1554]]</sup> ) and experiments are being conducted with innovative decadal scale application of sediments such as the sand engine in the Netherlands (Stive et al., 2013 <sup>[[#fn:r1555|1555]]</sup> ).

There is high confidence that most major upgrades in defences happen after coastal disasters (Box 4.1). Dikes were raised and reienforced after the devastating coastal flood of 1953 in the Netherlands and the UK, and in 1962 in Germany. In New Orleans, investments in the order of 15 billion USD, including a major storm surge barrier, followed Hurricane Katrina in 2005 (Fischetti, 2015 <sup>[[#fn:r1556|1556]]</sup> ), and in New York the Federal Government made available 16 billion USD for disaster recovery and adaptation after Superstorm Sandy in 2012 (NYC, 2015). Examples in which SLR has been considered proactively in the planning process include SLR safety margins in, for example, the UK, Germany and France, upgrading defences according to cost-benefit analysis in the Netherlands, and SLR guidance in the USA (USACE, 2011 <sup>[[#fn:r1557|1557]]</sup> ).

<div id="section-4-4-2-2hard-and-sediment-based-protection-block-2"></div>

<span id="projected-hard-and-sediment-based-protection"></span>