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

===== 4.4.2.3.1 Observed ecosystem-based adaptation across geographies =====

Relative to hard adaptation measures whose global distribution is not known in detail (Scussolini et al., 2015 <sup>[[#fn:r1644|1644]]</sup> ), the current global distribution of coastal ecosystems is well-studied (e.g., for saltmarshes and mangroves, respectively; Giri et al., 2011 <sup>[[#fn:r1645|1645]]</sup> ; Mcowen et al., 2017 <sup>[[#fn:r1646|1646]]</sup> ). EbA, by definition, can only exist and function where the environmental conditions are appropriate for a given ecosystem. Mangroves, salt marshes and reefs occur along about 40–50% of the world’s coastlines (Wessel and Smith, 1996 <sup>[[#fn:r1647|1647]]</sup> ; Burke, 2011 <sup>[[#fn:r1648|1648]]</sup> ; Giri et al., 2011 <sup>[[#fn:r1649|1649]]</sup> ; Mcowen et al., 2017 <sup>[[#fn:r1650|1650]]</sup> ). However, there is no clear estimate on the global length of coastline covered by ecosystems relevant for EbA in the face of SLR in part because of a mismatch between the spatial resolutions of different estimates available. Mangroves occur on tropical and subtropical coasts, and cover 138,000–152,000 km <sup>2</sup> across about 120 countries (Spalding et al., 2010 <sup>[[#fn:r1651|1651]]</sup> ; Giri et al., 2011 <sup>[[#fn:r1652|1652]]</sup> ). At least 150,000 km of coastline in over 100 countries benefit from the presence of coral reefs (Burke, 2011 <sup>[[#fn:r1653|1653]]</sup> ) and these are estimated to protect over 100 million people from wave-induced flooding globally (Ferrario et al., 2014 <sup>[[#fn:r1654|1654]]</sup> ). The extent of other coastal habitats is less well known: salt marshes are estimated to occur in 99 countries, especially in temperature to high latitude locations, with nearly 5,500,000 ha mapped across 43 countries (Mcowen et al., 2017 <sup>[[#fn:r1655|1655]]</sup> ).

Since AR5 there has been growing recognition of the value of conserving existing coastal ecosystems, and where possible restoring them, for the flood protection and multiple other benefits they provide (Temmerman et al., 2013 <sup>[[#fn:r1656|1656]]</sup> ; Arkema et al., 2015 <sup>[[#fn:r1657|1657]]</sup> ). In parallel, EbA measures are increasingly being incorporated and required within national plans, strategies and targets (Lo, 2016), international adaptation funding mechanisms, such as the Adaptation Fund (AF; e.g., in Sri Lanka and India; Epple et al., 2016 <sup>[[#fn:r1658|1658]]</sup> ), and national natural capital valuations (Beck and Lange, 2016 <sup>[[#fn:r1659|1659]]</sup> ). Given their relative novelty, there is widespread interest in building and collecting knowledge of EbA implementation case-studies and examples (Table 4.7). Meanwhile, coastal communities around the globe are already implementing EbA responses at local scales, with emphasis on community participation and ownership and local priorities, needs and capacities (Reid, 2016 <sup>[[#fn:r1660|1660]]</sup> ; see Section 4.4.4.4).

EbA has been used as an integral part of some retreat, advance and accommodation responses. For example, on coastlines where high-risk properties are relocated inland, space can be made for ecosystem restoration to enhance natural biodiversity and provide coastal protection (French, 2006 <sup>[[#fn:r1661|1661]]</sup> ; Coastal Protection and Restoration Authority of Louisiana, 2017 <sup>[[#fn:r1662|1662]]</sup> ). There are also examples of ecosystem restoration to advance coastlines and build land elevation (Chung, 2006 <sup>[[#fn:r1663|1663]]</sup> ). EbA can also be an element of accommodation responses by, for example, restoring or creating marshes to provide space for flood water (Temmerman et al., 2013 <sup>[[#fn:r1664|1664]]</sup> ).

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