Editing IPCC:AR6/SROCC/Chapter-5 (section)

===== 5.5.2.1.3 Adaptation in mangroves and other coastal ecosystems =====

Mangroves provide significant ecosystem services, including localised coastal protection from extreme storm events (Section 5.4.1), supporting services through increased sedimentation rates (Hayden and Granek, 2015 <sup>[[#fn:r1960|1960]]</sup> ) and provisioning services for local communities, for example, habitats for nurseries to support fisheries. Mangroves provide limited carbon mitigation, in terms of global emissions reduction, and substantial job creation (Table 5.7) co-benefits (for example through Reducing Emissions from Deforestation and Forest Degradation programmes) when managed properly (Section 5.4.1, 5.5.1.1), and there is evidence of their value in supporting aquaculture and fishery initiatives (Huxham et al., 2015 <sup>[[#fn:r1961|1961]]</sup> ; Ahmed and Glaser, 2016a <sup>[[#fn:r1962|1962]]</sup> ).

Mangrove EbA responses most commonly reported included ecosystem restoration (Sierra-Correa and Cantera Kintz, 2015 <sup>[[#fn:r1963|1963]]</sup> ; Romañach et al., 2018 <sup>[[#fn:r1964|1964]]</sup> ) and management such as mangroves re-planting through community participation programmes (Nanlohy et al., 2015 <sup>[[#fn:r1965|1965]]</sup> ; Nguyen et al., 2017 <sup>[[#fn:r1966|1966]]</sup> ; Triyanti et al., 2017 <sup>[[#fn:r1967|1967]]</sup> ). Mangrove EbA has been reported to provide multiple co-benefits in terms of improvement in support for coastal physical processes, including: shoreline stabilisation (Hayden and Granek, 2015 <sup>[[#fn:r1968|1968]]</sup> ; Nanlohy et al., 2015 <sup>[[#fn:r1969|1969]]</sup> ); ecological functioning (Sierra-Correa and Cantera Kintz, 2015 <sup>[[#fn:r1970|1970]]</sup> ; Miller et al., 2017 <sup>[[#fn:r1971|1971]]</sup> ) with improved ecosystem services (Alongi, 2015 <sup>[[#fn:r1972|1972]]</sup> ; Nanlohy et al., 2015 <sup>[[#fn:r1973|1973]]</sup> ; Palacios and Cantera, 2017 <sup>[[#fn:r1974|1974]]</sup> ); carbon mitigation (5.5.1.1); supporting livelihoods (Nanlohy et al., 2015 <sup>[[#fn:r1975|1975]]</sup> ; Nguyen et al., 2017 <sup>[[#fn:r1976|1976]]</sup> ); and reductions in coastal infrastructure damage and community vulnerability to climate change impacts. Managed retreat to counter coastal squeeze (Section 5.3) through improved governance, creation of finance and land use planning can allow mangroves to move up the shoreline contour or down the latitudinal gradient (Sierra-Correa and Cantera Kintz, 2015 <sup>[[#fn:r1977|1977]]</sup> ; Ward et al., 2016 <sup>[[#fn:r1978|1978]]</sup> ; Romañach et al., 2018 <sup>[[#fn:r1979|1979]]</sup> ). Therefore, mangrove EbA responses can strengthen coastal ecosystem services through shoreline stabilisation and provide multiple co-benefits for coastal communities, like job creation and improved access to ecosystem services ( ''high confidence'' ).

There are, however, examples where community mangrove restoration projects have resulted in maladaptive outcomes, in which the resulting ecosystem degradation could not provide the ecosystem services required (Nguyen et al., 2017 <sup>[[#fn:r1980|1980]]</sup> ; Romañach et al., 2018 <sup>[[#fn:r1981|1981]]</sup> ). Such maladaptation can be a result of poor governance processes or a lack of community compliance with restoration plans. These examples emphasise the value of designing effective governance to implement adaptation responses with broad community participation to improve the climate risk reduction outcomes and co-benefits (Sierra-Correa and Cantera Kintz, 2015 <sup>[[#fn:r1982|1982]]</sup> ; Nguyen et al., 2017 <sup>[[#fn:r1983|1983]]</sup> ) ( ''medium evidence, high agreement'' ).

Mangrove and other coastal ecosystems restoration and management can be applied through reducing non-climatic hazards (Gilman et al., 2008 <sup>[[#fn:r1984|1984]]</sup> ; Ataur Rahman and Rahman, 2015 <sup>[[#fn:r1985|1985]]</sup> ; Sierra-Correa and Cantera Kintz, 2015 <sup>[[#fn:r1986|1986]]</sup> ; Ahmed and Glaser, 2016a <sup>[[#fn:r1987|1987]]</sup> ; Nguyen et al., 2017 <sup>[[#fn:r1988|1988]]</sup> ; Romañach et al., 2018 <sup>[[#fn:r1989|1989]]</sup> ). Coastal and catchment development, including wetland transformation and degradation (Miloshis and Fairfield, 2015 <sup>[[#fn:r1990|1990]]</sup> ; Schaeffer-Novelli et al., 2016 <sup>[[#fn:r1991|1991]]</sup> ; Watson et al., 2017a <sup>[[#fn:r1992|1992]]</sup> ; Schuerch et al., 2018 <sup>[[#fn:r1993|1993]]</sup> ), the disruption of physical processes impacting sedimentation rates (Watson et al., 2017a <sup>[[#fn:r1994|1994]]</sup> ) and coastal squeeze compound coastal climate change impacts like erosion, flooding and saltwater intrusion (Ondiviela et al., 2014 <sup>[[#fn:r1995|1995]]</sup> ; Miloshis and Fairfield, 2015 <sup>[[#fn:r1996|1996]]</sup> ; Schaeffer-Novelli et al., 2016 <sup>[[#fn:r1997|1997]]</sup> ; Wigand et al., 2017 <sup>[[#fn:r1998|1998]]</sup> ) (Section 5.3). This reduces the ability of these ecosystems to provide protection from wave and storm impacts, whilst positive feedbacks may occur that cause a net release of carbon into the atmosphere, for example, in salt marshes (Wong et al., 2014a <sup>[[#fn:r1999|1999]]</sup> ) (Section 5.4.1). In some cases, effective interventions requires management at a broad spatial scale that includes a variety of ecosystems, for example, including ecosystems like mussel beds on the seaward side of seagrass beds to reduce wave energy and erosion (Ondiviela et al., 2014 <sup>[[#fn:r2000|2000]]</sup> ). Where sediment accretion matches the SLR rate, wetlands and salt marshes provide effective coastal protection and other important ecosystem services ( ''high confidence'' ).

Coastal dune systems are widely transformed globally. Human disturbance and the limited stabilising ability of dune vegetation are key causes of degradation (Onaka et al., 2015 <sup>[[#fn:r2001|2001]]</sup> ; Ranasinghe, 2016 <sup>[[#fn:r2002|2002]]</sup> ; MacDonald et al., 2017 <sup>[[#fn:r2003|2003]]</sup> ; Pranzini, 2017 <sup>[[#fn:r2004|2004]]</sup> ; Salgado and Martinez, 2017 <sup>[[#fn:r2005|2005]]</sup> ; Vikolainen et al., 2017 <sup>[[#fn:r2006|2006]]</sup> ; Gracia et al., 2018 <sup>[[#fn:r2007|2007]]</sup> ), while restoration efforts can be supported by both hard (Sutton-Grier et al., 2015 <sup>[[#fn:r2008|2008]]</sup> ; Pranzini, 2017 <sup>[[#fn:r2009|2009]]</sup> ) and soft (Sutton-Grier et al., 2015 <sup>[[#fn:r2010|2010]]</sup> ; Vikolainen et al., 2017 <sup>[[#fn:r2011|2011]]</sup> ) engineering responses. Reduced coastal erosion (Sánchez-Arcilla et al., 2016 <sup>[[#fn:r2012|2012]]</sup> ; Goreau and Prong, 2017 <sup>[[#fn:r2013|2013]]</sup> ; Vikolainen et al., 2017 <sup>[[#fn:r2014|2014]]</sup> ; Carro, 2018 <sup>[[#fn:r2015|2015]]</sup> ; Gracia et al., 2018 <sup>[[#fn:r2016|2016]]</sup> ) and flood risk (Onaka et al., 2015 <sup>[[#fn:r2017|2017]]</sup> ; MacDonald et al., 2017 <sup>[[#fn:r2018|2018]]</sup> ; Nehren et al., 2017 <sup>[[#fn:r2019|2019]]</sup> ) through maintaining dunes as natural buffers against wave energy (Nehren et al., 2017 <sup>[[#fn:r2020|2020]]</sup> ) can increase resilience to climate change impacts (Sutton-Grier et al., 2015 <sup>[[#fn:r2021|2021]]</sup> ; Magnan and Duvat, 2018 <sup>[[#fn:r2022|2022]]</sup> ). Engineered responses and sand replenishment are considered complementary approaches (Onaka et al., 2015 <sup>[[#fn:r2023|2023]]</sup> ; Martínez et al., 2017 <sup>[[#fn:r2024|2024]]</sup> ). Section 4.4.4.1 provides an overview of sediment-based adaptation response measures, including cost estimates for beach nourishment and dune maintenance, a discussion of co-benefits and drawbacks of combining hard and soft infrastructure measures, and challenges with sourcing sediment for beach replenishment. In some cases dune restoration and sand replenishment projects have not been successful, due to fire damage (Shumack and Hesse, 2017 <sup>[[#fn:r2025|2025]]</sup> ) or the rapid loss of sand within replenishment schemes due to coastal processes and stakeholder rejection of adaptation activities (Pranzini, 2017 <sup>[[#fn:r2026|2026]]</sup> ). Coastal dune restoration and beach replenishment are effective responses against coastal erosion and flooding, where sufficient materials and space to implement are available ( ''medium confidence'' ).

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