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

=== CCP2.1.2 Urbanisation in Coastal Systems: Coastal City and Settlement Archetypes ===

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This assessment uses an archetype framework categorizing coastal C&amp;S according to geomorphological characteristics, urban growth, economic resources and inequalities (Figure CCP2.1). Three broadly defined coastal settlement geomorphologies are used in each row: open coasts (a coast with sediment without river mouths) and two transitional coastal zones with river mouths, distinguishing between estuaries (a wetland receiving sediment from both fluvial and marine sources, which is affected by tide, wave and river processes) and deltas (a wetland where fluvial sediment is supplied and deposited more rapidly than it can be redistributed by basin processes such as waves and tides; [[#Bhattacharya--1978|Bhattacharya, 1978]] ; [[#Barragán--2015|Barragán and de Andrés, 2015]] ; [[#Kay--2017|Kay and Alder, 2017]] ; [[#Haasnoot--2019|Haasnoot et al., 2019]] ; [[#Sterzel--2020|Sterzel et al., 2020]] ). Small island C&amp;S are not singled out in this typology, because their coastlines often include the geomorphic features listed above, or require a different adaptation approach at larger spatial scales ( [[#Haasnoot--2019|Haasnoot et al., 2019]] ). Several coastal C&amp;S have a combination of two typologies, for example, Maputo-Matola, Mozambique and Mumbai, India, having both open and transitional riverine coasts, and can be classed as mixed. We also acknowledge that several coastal C&amp;S may have areas sited in mountainous topography that abruptly rises from the coast (e.g., along the Mediterranean), but generally these cities have narrow, densely populated coastlines exhibiting these three archetypal categories ( [[#Blackburn--2019|Blackburn et al., 2019]] ). Arctic settlements are addressed separately in this cross-chapter paper.

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'''Figure CCP2.1 |''' '''Archetypal cities and settlements (C&amp;S) affected by ocean, terrestrial, geological, atmospheric and hydrological hazards driven by climate change.''' Coastal C&amp;S are grouped by physical geomorphology along estuarine, deltaic or open coasts ( [[#Barragán--2015|Barragán and de Andrés, 2015]] ; [[#Kay--2017|Kay and Alder, 2017]] ; [[#Haasnoot--2019|Haasnoot et al., 2019]] ). C&amp;S are also classified according to relative inequality (e.g., urban Gini coefficient or poverty rates) and growth rates (e.g., recent population growth and increasing density of urban form or built-up areas over the past decade; [[#OECD--2018|OECD, 2018]] ; ''[[#CEIC--2021|CEIC, 2021]]'' ; [[#OECD--2020|OECD, 2020]] ). Settlement types (e.g., informal, low-density or high-density developments) and economic resources (e.g., urban per capita gross domestic product) are also reflected in their respective categories. The bottom map shows location, 2020 population size and geomorphological types.

Coastal C&amp;S within these geomorphological categories are further distinguished according to higher or lower rates of urban growth and inequality, which can be estimated through population growth from national census data or areal extent of urban development ( [[#CEIC--2021|CEIC, 2021]] ), as well as by relative urban inequalities estimated by Gini coefficient data and urban–rural poverty rates ( [[#OECD--2018|OECD, 2018]] ; [[#OECD--2020|OECD, 2020]] ). Combining geomorphological and socioeconomic data accounts for urban–rural interconnections and differences, with levels of capital generation, diversity of economic functions and human development indices having previously been used to discern cultural, economic, administrative and political differences between cities and their hinterland ( [[#Blackburn--2019|Blackburn et al., 2019]] ; [[#Rocle--2020|Rocle et al., 2020]] ). For instance, the ecological, cultural and economic footprint of tertiary sectors, for example, coastal tourism associated with the Australian Great Barrier Reef, stretches far beyond the nearest onshore settlement of Cairns ( [[#Bohnet--2010|Bohnet and Pert, 2010]] ; [[#Brodie--2016|Brodie and Pearson, 2016]] ).

Some caveats are warranted. First, locating a specific city or settlement in a particular archetype does not account for future reclassification due to growth or shifts in development trajectories. Second, significant socioeconomic, political and governance variations exist within many C&amp;S, such as impoverished informal settlements alongside wealthy neighbourhoods in cities like Cape Town and São Paulo (also see Table SMCCP2.1). Third, this archetype framework does not explicitly reveal important interconnections between coastal C&amp;S and their hinterlands, or between particular C&amp;S through maritime trade or other economic, sociocultural and geopolitical interdependencies. Notwithstanding these caveats, these archetypes reveal differentiated physical impacts and socioeconomic conditions, as well as the variable challenges and opportunities arising when addressing climate change impacts and projected risk, which, depending on coastal type, C&amp;S size and resource availability, help to inform efforts to adapt and chart CRD for each archetype ( [[#Sánchez-Arcilla--2016|Sánchez-Arcilla et al., 2016]] ; [[#Rocle--2020|Rocle et al., 2020]] ; [[#Sterzel--2020|Sterzel et al., 2020]] ).

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