Editing IPCC:AR6/WGII/Cross-Chapter-Paper-2 (section)

=== CCP2.3.3 Accommodation of the Built Environment ===

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The most effective solution for limiting the growth of climate risks in C&amp;S by the sea is to avoid new development in coastal locations prone to major flooding and/or SLR impacts ( ''very high confidence'' ; Cross-Chapter Box SLR in Chapter 3; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ; [[#Doberstein--2019|Doberstein et al., 2019]] ). For existing C&amp;S, accommodation includes biophysical and institutional responses to reduce exposure and/or vulnerability of coastal residents, human activities, ecosystems and the built environment, enabling continued habitation of coastal C&amp;S ( [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ). Next to hard protection, accommodation is the most widely used adaptation strategy across all archetypes to date ( ''high confidence'' ; [[#Sayers--2015|Sayers et al., 2015]] ; [[#Olazabal--2019|Olazabal et al., 2019]] ; [[#Le--2020|Le, 2020]] ). Measures include elevation or flood proofing of houses and other infrastructure ( [[#Garschagen--2015|Garschagen, 2015]] ; [[#Aerts--2018|Aerts et al., 2018]] ; [[#Buchori--2018|Buchori et al., 2018]] ; [[#Jamero--2018|Jamero et al., 2018]] ; [[#Tamura--2019|Tamura et al., 2019]] ), spatial planning (e.g., [[#Duy--2018|Duy et al., 2018]] ), amphibious building designs ( [[#Nilubon--2016|Nilubon et al., 2016]] ), increasing water storage and/or drainage capacity within C&amp;S ( [[#Chan--2018|Chan et al., 2018]] ), early warning systems and disaster responses ( [[#Hissel--2014|Hissel et al., 2014]] ) and slum upgrading ( [[#Jain--2017|Jain et al., 2017]] ; [[#Olthuis--2020|Olthuis et al., 2020]] ).

Raising land, or individual buildings, can avert flooding and be accomplished artificially or by nature-based interventions through river diversion and control in estuarine and deltaic archetypes ( [[#Nittrouer--2012|Nittrouer et al., 2012]] ; [[#Auerbach--2015|Auerbach et al., 2015]] ; [[#Day--2016|Day et al., 2016]] ; [[#Sánchez-Arcilla--2016|Sánchez-Arcilla et al., 2016]] ; [[#Hiatt--2019|Hiatt et al., 2019]] ; [[#Cornwall--2021|Cornwall, 2021]] ). Nature-based land elevation is limited by sediment supply and can address SLR rates of up to 10 mm yr–1 ( [[#Kleinhans--2010|Kleinhans et al., 2010]] ; [[#Kirwan--2016|Kirwan et al., 2016]] ; [[#IPCC--2019|IPCC, 2019]] ). It also assumes that existing land-use patterns permit land raising (e.g., in rural or newly developed areas; [[#Scussolini--2017|Scussolini et al., 2017]] ). Artificial land raising can achieve significant elevations and be implemented over a large spatial scale ( [[#Esteban--2015|Esteban et al., 2015]] ; [[#Esteban--2019|Esteban et al., 2019]] ). Raising land can be cost beneficial for small areas or where lower safety levels are satisfactory, but protection is usually more economical for larger areas, although both strategies are often combined ( [[#Lendering--2020|Lendering et al., 2020]] ).

Accommodation measures can be very effective for current conditions and small changes in SLR ( [[#Laurice%20Jamero--2017|Laurice Jamero et al., 2017]] ; [[#Scussolini--2017|Scussolini et al., 2017]] ; [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ; [[#Du--2020|Du et al., 2020]] ; [[#Haasnoot--2021a|Haasnoot et al., 2021a]] ), and buy time to prepare for more significant changes in sea level and other climate-compounded coastal hazards. However, limits to this strategy occur comparatively soon in some locations, possibly requiring protection in the medium term and retreat in the long run and beyond 2100, particularly in scenarios of dramatic SLR ( [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ). For the foreseeable future, accommodation can play an important role in combination with protective measures to form hybrid interventions, with higher effectiveness than either approach in isolation ( [[#Du--2020|Du et al., 2020]] ). Accommodation can play an increasingly important role where hard protection is neither technically nor financially viable, but detailed studies about expected trends of accommodation are lacking ( [[#Oppenheimer--2019|Oppenheimer et al., 2019]] ).

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