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

===== 4.4.2.3.3 Cost of ecosystem-based adaptation =====

There is ''limited evidence and low agreement'' on the costs of ecosystem-based measures to make generally valid estimations of the unit costs across large spatial scales. The total cost of an ecosystem-based measure includes capital costs, maintenance costs, the cost of land and, in some situations, permitting costs (Bilkovic, 2017 <sup>[[#fn:r1666|1666]]</sup> ). The costs of restoring and maintaining coastal habitats depend on coastal setting, habitat type and project conditions. In general, unit restoration costs are lowest for mangroves, higher for salt marshes and oyster reefs, and highest for seagrass beds and coral reefs (Table 4.8).

The conservation of coral reefs and other coastal habitats may also entail substantial opportunity costs because alternative uses of this land, such as through agricultural production, industry and settlements, are generally of high economic value (Stewart et al., 2003 <sup>[[#fn:r1667|1667]]</sup> ; Balmford et al., 2004 <sup>[[#fn:r1668|1668]]</sup> ; Adams et al., 2011 <sup>[[#fn:r1669|1669]]</sup> ; Hunt, 2013 <sup>[[#fn:r1670|1670]]</sup> ). The high value of these alternative uses are the reason why globally, coastal ecosystems are amongst the ecosystems that face the highest rates of anthropogenic destruction, with estimated annual losses of 1–3% of mangroves area, 2–5% seagrass area and 4–9% corals (Duarte et al., 2013 <sup>[[#fn:r1671|1671]]</sup> ). Conserving these areas means reversing these trends.

Under the right conditions, and to some extent, EbA measures are free of maintenance costs, because they respond and adapt to changes in their coastal environment. However, maintenance can become important in the aftermath of damage by storms or human action, for example, when wetlands and reefs can be damaged by high winds, waves and surges, or affected by dredging operations (Smith III et al., 2009 <sup>[[#fn:r1672|1672]]</sup> ; Puotinen et al., 2016 <sup>[[#fn:r1673|1673]]</sup> ). At present, there is limited evidence about the conditions under which EbA measures can self-adapt and when they require human intervention to recover.

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'''Table 4.8:''' Costs of ecosystem-based adaptation (EbA). MPA is marine protected area.

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{| class="wikitable"
|-
| Type of measure
| Capital Costs
| Maintenance Costs
|-
| Wetland Conservation
| No data available
| Thinning, clearing debris after storms, etc.: Mangrove: 5000 USD ha –1 yr –1 in Florida (Lewis, 2001) to 11,000 ha –1 yr –1 (Aerts, 2018).
For mangroves globally, 7–85 USD ha –1 yr –1 (Aerts et al., 2018a);

For marshes in the Wadden Sea, 25 USD m –1 yr –1 (Vuik et al., 2019).

|-
| Wetland Restoration (Marshes/Mangroves, Maritime Forests)
| Wetlands: 85,000 – 230,000 USD ha –1 (Aerts et al., 2018a); Mangroves: USD 9000 ha –1 (median; Bayraktarov et al., 2016);
2000 – 13,000 USD ha –1 in American Samoa (Gilman and Ellison, 2007); Salt Marshes: 67,000 USD ha –1 (Bayraktarov et al., 2016); Brushwood dams for marsh restoration 150 m –1 (Vuik et al., 2019).

| Similar to maintenance costs for Wetland Conservation
|-
| Reef Conservation (Coral/ Oyster)
| For example, start-up costs for Reef MPAs: 96 – 40,000 USD km -2 (McCrea-Strub et al., 2011).
| For MPAs, 12 million USD yr -1 for the Great Barrier Reef (Balmford et al., 2004).
|-
| Reef Restoration (Coral/ Oyster)
| 165,600 USD ha –1 (median; Bayraktarov et al., 2016); Oyster Reefs: 66,800 USD ha –1 (median; Bayraktarov et al., 2016); Artificial Reefs in the UK 30,000–90,000 USD 100 m –1 (Aerts et al., 2018a)
| Similar to maintenance costs for Reef Conservation
|}
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