Editing IPCC:AR6/WGII/Chapter-6 (section)

=== 6.1.3 Terminology and Definitions ===

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This chapter covers both ‘cities and settlements’ and ‘key infrastructure’.

Definitions of ‘urban’ have become more nuanced since the AR5 review with the publication of the OECD report ‘A new perspective on urbanisation’ ( [[#OECD%20and%20European%20Commission--2020|OECD and European Commission, 2020]] ). This report presents two new global definitions of urbanisation reflecting the degree of urbanisation on a continuum of cities, towns and semi-dense areas, and rural areas. The OECD estimates almost half the world’s population (48%) live in cities, while just 24% live in rural areas and 28% live in towns and semi-dense areas (28%). In addition, the OECD report defines metropolitan areas as functional urban areas together with their surrounding commuting zones ‘to capture the full extent’ of a city’s working population. Metropolitan areas account for 54% of total world population, with the OECD estimating that commuting zones representing 17% of the overall metropolitan population, rising to 31% in high-income countries. In the context of these global definitions, this chapter identifies ‘cities and settlements’ as concentrated human habitation centres (along a dynamic continuum from rural to urban) (Murali et al., 2019; [[#Ward--2016|Ward and Shackleton, 2016]] ) (Figure 6.1) that are fundamentally inter-connected to other urban centres and rural areas as nodes within broader networks.

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[[File:9463d3b3559028c57c12ae89b05e6272 IPCC_AR6_WGII_Figure_6_001.png]]

'''Figure 6.1 |''' '''Defining ‘urban’ and ‘rural’ in relation to cities and settlements'''

Key infrastructure is used here to refer to ‘critical nodes and arteries’ that comprise urban energy, food, water, sewerage, health, transport and communication systems ( [[#Steele--2017|Steele and Legacy, 2017]] ; Maxwell et al., 2018; Bassolas et al., 2019). Key or critical infrastructure provides much of the material basis of cities and settlements, as well as the mechanisms for enabling flows of people, goods, data, waste, energy (through urban metabolism processes of consumption and production) and capital, between urban regions and rural areas (Blay-Palmer et al., 2018; Dijst et al., 2018). An overview of this process of ‘planetary’ urbanisation is provided in Box 6.1. The balance of accumulated scientific knowledge on climate risks, impact and adaptation has been generated from studies in large and medium-sized cities of 1 million or more. While these larger cities continue to grow rapidly (UNDESA 2018), settlements of more than 5 million people contain less than a quarter of the world’s urban population, and more than half of the world’s urban residents live in settlements of 1 million or less (Table 6.1). There is a key gap in knowledge, especially concerning urban enabling environments and how smaller settlements can be supported to accelerate equitable and sustainable adaptation in the face of financial and governance constraints (Birkmann et al., 2016; Shi et al., 2016; [[#Dulal--2019|Dulal, 2019]] ; Rosenzweig et al., 2018b).

'''Table 6.1 |''' Proportion of the urban population in different size class urban areas (UN-DESA 2018). Each column indicates the percentage of urban residents in that region living in cities of that size class.

{| class="wikitable"
|-
! Proportion (by region) of urban population living in cities with population size

! Africa

! Asia

! Latin America and the Caribbean

! Europe

! Northern America

! Oceania

! World

|-
| 10 million +

| 8

| 15

| 17

| 4

| 10

| 0

| 13

|-
| 5–10 million

| 6

| 9

| 3

| 5

| 17

| 0

| 8

|-
| 1–5 million

| 22

| 22

| 25

| 16

| 30

| 60

| 22

|-
| 500,000–1 million

| 9

| 10

| 8

| 11

| 13

| 2

| 10

|-
| 300,000–500,000

| 6

| 6

| 6

| 8

| 7

| 11

| 6

|-
| Under 300,000

| 48

| 38

| 40

| 57

| 24

| 27

| 41

|}

This chapter takes a comprehensive approach to understanding ‘key infrastructure’ as expressed in social, nature-based and physical infrastructure. Social infrastructure includes the social, cultural, and financial activities and institutions, as well as associated property, buildings and artefacts and policy domains such as social protection, health and education that support well-being and public life (Frolova et al., 2016; [[#Latham--2019|Latham and Layton, 2019]] ). Nature-based infrastructure focuses on solutions to risk, applying natural assets such as trees or open water, physical infrastructure describes engineering approaches and grey/physical infrastructure refers to engineered assets that provide one or multiple services required by society, such as transportation or wastewater treatment ([IISD, N.D.]; see also Annex II: Glossary).

This approach is based on a framing of cities and settlements as complex systems where social, ecological and physical processes interact in planned and unplanned ways. This chapter therefore builds on the AR5 [[IPCC:Wg2:Chapter:Chapter-10|Chapter 10]] ( [[#Arent--2014|Arent et al., 2014]] ) conception of key economic sectors and services (e.g., energy, water, transport, waste, sanitation and drainage) by positioning these within three major categories of infrastructure: social, nature based and physical (see [[#6.3|Section 6.3]] ). Where adaptation challenges can be responded to by more than one approach, sometimes working together, this is noted (see also Sections 17.2 and 17.4). This approach allows an understanding of adaptation that is not constrained to the administrative boundaries of cities and settlements, but that includes the networks and flows that connect peri-urban communities, metropolitan regions, suburban settlements and more rural places (see Box 6.1). Both formal provision of infrastructure services by government and informal provision by communities and individuals are considered at risk from climate change, as are existing adaptation pathways and actions.

Cities are complex entities where social, ecological and physical systems interact in planned and unplanned ways (Markolf et al., 2018). The complexity of cities, settlements and key infrastructure (Figure 6.2) where multiple functional systems continuously interact makes it difficult to distinguish risks (Box 6.1). The literature often resolves this by offering discrete assessments for specific sectors (see [[#6.3|Section 6.3]] ). This fragmented approach to understanding climate change associated impacts and risks is then reflected also in siloed approaches to risk management and adaptation financing (see [[#6.4|Section 6.4]] ). Recent literature notes that resilience planning has begun to overcome this tendency by presenting climate change impacts, losses and damages, and urban processes, as unfolding together in interacting and cascading pathways (Fraser et al., 2020; Eriksen et al., 2020) (Figure 6.2). The chapter reflects this change in the literature by presenting climate change impacts through a series of risk assessments, including by hazard type, through indirect impacts on health or food security, key infrastructure systems, land use and human mobility, water flows and on structural conditions, such as poverty and justice in the city (see Sections 6.3 and 6.4). In a departure from AR5 we also consider the consequential interactions of climate risks, impacts, adaptation and climate mitigation (see also Cross-Working Group Box URBAN in Chapter 6).

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[[File:11f21bcf861c8a31cd6bae4c55659355 IPCC_AR6_WGII_Figure_6_002.png]]

'''Figure 6.2 |''' '''The interconnected nature of cities, settlements and infrastructure'''

The IPCC 1.5°C Special Report commented that ‘The extent of risk depends on human vulnerability and the effectiveness of adaptation for regions (coastal and non-coastal), informal settlements, and infrastructure sectors (energy, water, and transport) ( ''high confidence'' )’ ( [[#IPCC--2018|IPCC, 2018]] ).We take this statement as a starting point for assessing the risks to cities, settlements and key infrastructure, with infrastructure extended as noted above. Risks from climate change are understood as the product of climate change associated hazards impacting on exposed and vulnerable people and assets (including biodiversity). Adaptation can, in some cases, reduce exposure and susceptibility and enable recovery and scope for transformation toward long-term equitable and sustainable development. Risks describe both present conditions and future prospects. Direct attribution of hazards to climate change remains limited to temperature extremes and sea level rise, though we consider all hydrometeorological hazards as systems associated with climate change processes.

This chapter also assesses conditions supporting incremental and transformative adaptation ( [[#6.4|Section 6.4]] ). Incremental and transformative adaptation are both important but serve distinct roles in the interaction of urban systems, climate risk and risk management, and in advancing social justice, just transitions and climate resilient development (see [[#6.4|Section 6.4]] ). Climate resilient development pathways are an emerging concept in the literature since the AR5 (Schipper et al., 2020). Climate resilient development is an iterative process of systemic change that integrates both mitigation and adaptation efforts (see Annex II: Glossary). Initial studies highlight the way rapid urbanisation and precarious urban housing and land tenure can undermine climate resilient development, while human settlements that are managed to protect housing tenancy and land tenure rights can advance land use planning and social learning while reducing inequalities and vulnerability and enhancing resilient development (Mitchell, Enemark and Van der Molen, 2015; [[#Bellinson--2019|Bellinson and Chu, 2019]] ; [[#Ürge-Vorsatz--2018|Ürge-Vorsatz et al., 2018]] ). The benefits of integrating decision making across scales for climate resilient development is also highlighted in [[#6.4|Section 6.4]] . How households engage with communities and neighbourhoods and larger units within cities, and how cities (both formal and informal) interact with sub-national and national actors is also discussed, as is the role of finance and community-based organisations (CBOs)/NGOs in the governance process.

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