Editing IPCC:AR6/WGII/Chapter-13 (section)

===== 13.2.2.1.1 Coastal flood risk management =====

<div id="h4-7-siblings" class="h4-siblings"></div>

Further protection against coastal flooding is considered economically beneficial for densely populated areas ( [[#Lincke--2018|Lincke and Hinkel, 2018]] ; [[#Tiggeloven--2020|Tiggeloven et al., 2020]] ). At least 83% of flood damages due to coastal flooding could be avoided by elevating dykes along ~23–32% of Europe’s coastline by 2100 (RCP4.5-SSP1, RCP8.5-SSP5) ( [[#Vousdoukas--2020|Vousdoukas et al., 2020]] ). Limitations of building flood defences include cost–benefit considerations in rural areas, available land and social acceptability in densely populated areas ( [[#Haasnoot--2018|Haasnoot et al., 2018]] ; [[#Hinkel--2018|Hinkel et al., 2018]] ; [[#Meyerhoff--2021|Meyerhoff et al., 2021]] ).

Nature-based Solutions (NbS) (e.g., wetlands) and sediment-based solutions (e.g., sand nourishment) are increasingly considered for environmental, economic and/or societal reasons (Cross-Chapter Box NATURAL in Chapter 2; [[#Stive--2013|Stive et al., 2013]] ; [[#Pranzini--2015|Pranzini et al., 2015]] ; [[#Pinto--2020|Pinto et al., 2020]] ; [[#de%20Schipper--2021|de Schipper et al., 2021]] ). Coastal wetlands can be effective to reduce wave height and form habitats, but their feasibility and effectiveness is limited for densely populated areas with competing land use, runoff of pollution, sediment-starved deltas like the Rhine Delta ( [[#Edmonds--2020|Edmonds et al., 2020]] ) and rapid SLR ( [[#Kirwan--2016|Kirwan et al., 2016]] ; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ; [[#Haasnoot--2020b|Haasnoot et al., 2020b]] ). While losses of wetlands could be minor if warming stays below 1.7°C GWL, at high warming or SLR above 0.5 m large-scale losses of these habitats will impact their ecological importance, ecosystem function ( [[#13.4|Section 13.4]] ; KR 1, [[#13.10.2|Section 13.10.2]] ) and their ability to protect coastlines ( [[#Roebeling--2013|Roebeling et al., 2013]] ; [[#van%20der%20Spek--2018|van der Spek, 2018]] ; [[#Wang--2018|Wang et al., 2018]] ; [[#Xi--2021|Xi et al., 2021]] ). A combination with structural defences could reduce risk in urbanised coastal regions ( ''high confidence'' ). Accommodation through elevated or floating houses have been implemented and proposed locally within cities as part of a hybrid strategy together with protection and as a way of innovative urban development ( [[#13.6.2|Section 13.6.2]] ; Cross-Chapter Paper 2; [[#Penning-Rowsell--2020|Penning-Rowsell, 2020]] ; [[#Storbjörk--2021|Storbjörk and Hjerpe, 2021]] ).

Avoidance through restricting new developments in flood prone areas is applied along the coast of WCE and SEU ( [[#Harman--2015|Harman et al., 2015]] ; [[#Lincke--2020|Lincke et al., 2020]] ) and is considered a low-cost alternative to coastal defence at lower SLR. In SEU, an integrated coastal zone management (ICZM) protocol has been developed which requires a setback zone of 100 m from the coast in unprotected areas. Setback zones are projected to reduce impacts considerably in urbanised regions ( [[#Lincke--2020|Lincke et al., 2020]] ). Planned relocation is increasingly considered as a realistic adaptation option in cases of extreme SLR ( [[#Haasnoot--2021a|Haasnoot et al., 2021a]] ; [[#Lincke--2021|Lincke and Hinkel, 2021]] ; [[#Mach--2021|Mach and Siders, 2021]] ), for example, UK Shoreline Management Plans ( [[#Nicholls--2013|Nicholls et al., 2013]] ; [[#Buser--2020|Buser, 2020]] ). Retreat is rarely applied in Europe ( ''medium confidence'' ), though it can have greater benefit-to-cost outcomes than protection, particularly in less populated parts of Europe ( [[#Lincke--2021|Lincke and Hinkel, 2021]] ). Along parts of the coast in the UK (e.g., The Wash), Germany (e.g., Langeoog Island) and the Netherlands (e.g., Westerschelde) retreat has been applied to restore salt marshes and to aid coastal defence ( [[#Haasnoot--2019|Haasnoot et al., 2019]] ; [[#Kiesel--2020|Kiesel et al., 2020]] ; [[#Lincke--2021|Lincke and Hinkel, 2021]] ).

<div id="13.2.2.1.2" class="h4-container"></div>

<span id="riverine-and-pluvial-flood-risk-management"></span>