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

=== 6.2.1 Risk Creation in Cities, Settlements and Infrastructure ===

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In addition to direct climate impacts, interactions among changing urban form, exposure and vulnerability can create climate change-induced risks and losses for cities and settlements. Climate change already interacts with ongoing global trends in urbanisation to create regionally specific impacts and risk profiles. Through demographic change and encroachment into natural and agricultural lands and coastal zones, rapidly expanding urban settlements can place new physical assets and people in locations with high exposure (Tessler et al., 2015; [[#Arnell--2016|Arnell and Gosling, 2016]] ; Kundzewicz et al., 2014). Increasing rates of global urbanisation will pose additional challenges to areas that have high levels of poverty, unemployment, informality, and housing and service backlogs ( [[#Jiang--2017|Jiang and O’Neill, 2017]] ; Williams et al., 2019). There is some evidence to suggest that climate change impacts themselves are increasing urbanisation rates, generating a challenging feedback loop. In sub-Saharan Africa, for example, manufacturing towns have experienced growth because of population movement following droughts in agricultural hinterlands (Henderson, Storeygard and Deichmann, 2017). The rapid rate of urbanisation therefore presents a time-limited opportunity to work toward risk reduction and transformational adaptation in towns and cities. The following sections explore these dynamic interactions between urban systems and climate change, and how these shape risk for people and for key infrastructures.

Examining projected climate change impacts and resulting risks in cities, settlements and key infrastructures requires the prerequisite development of scenarios which are plausible descriptions of how the future may develop based on a coherent and internally consistent set of assumptions about key driving forces, (e.g., rate of technological change, prices and relationships) and pathways or the temporal evolution of natural and/or human systems, such as demographic and urban land cover change, toward a future state or states ( [[#Gao--2020|Gao and O’Neill, 2020]] ; [[#Gao--2019|Gao and O’Neill, 2019]] ; see also [[#6.1.5|Section 6.1.5]] ).

Climate change research creates scenarios integrating emissions and development pathways dimensions (Ebi et al., 2014; van Vuuren et al., 2017b; van Vuuren et al., 2017a) and Representative Concentration Pathways (RCPs) (Riahi et al., 2017). For risk reduction at regional scales, scenarios require urban-relevant climate projections, for example, downscaling from global and regional climate models of variables such as temperature, precipitation, air pollutants and sea level rise that are analysed usually for mid- or end-21st Century timeframes (e.g., Mika et al., 2018; Kusaka et al., 2016; Masson et al., 2014b). These data are needed to ascertain likely ranges of climate change impacts within city and settlement boundaries, and to quantify physical exposure when developing pathways for risk reduction. Consideration of current and projected future growth pathways of multiple urban sectors and key infrastructure, for example, transport, energy and buildings, are also needed to estimate probabilities of risk outcomes and damages within and across urban systems (O’Neill et al., 2015)(WGIII AR6 Section 8).

The challenges of managing these risks are amplified by the complex interactions between climate and urban scenarios, owing to the smaller spatial–temporal scales of urban areas in climate change modelling relative to global climate models (GCM) and shared socioeconomic pathways (SSP); geographical or geomorphological variations in city location; uncertainties arising from incomplete assumptions about socio-economic pathways at urban scales affecting urban demographics, for example, fertility rates and life expectancies or increased rural–urban migration; and challenges in modelling the urban climate and in developing urban climate observational networks in cities (WGI Box 10.3; Kamei, Hanaki and Kurisu, 2016; Yu, Jiang and Zhai, 2016; [[#Jiang--2017|Jiang and O’Neill, 2017]] ; Baklanov et al., 2018). Additionally, carbon-intensive economic growth, increasing inequalities, global pandemics, and uncontrolled or unmanaged urbanisation will exacerbate the exposure and vulnerability of urban systems modelled in existing climate scenarios and pathways ( ''high confidence'' ) (Phillips et al., 2020; [[#Jackson--2021|Jackson, 2021]] ; [[#Raworth--2017|Raworth, 2017]] ; Moraci et al., 2020). Mitigating these outcomes requires new forms of urban governance for climate adaptation, disaster risk reduction and building resilience (see [[#6.4|Section 6.4]] ).

Strong connections exist between climate change scenarios and urban climate-related risks. In some cases, the linkage is direct as climate change is associated with more frequent and more intense extreme weather and climate events, as assessed in [[#6.2.3|Section 6.2.3]] . In other contexts, the connection is mediated by urban developmental pathways arising from local-scale environmental stresses and degradation, and access to adaptation options, as reviewed in [[#6.2.4|Section 6.2.4]] .

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