Editing IPCC:AR6/WGII/Chapter-14 (section)

==== 14.5.5.2 Projected Impacts and Risks ====

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Evidence since the AR5 highlights increased risk to quality of life in cities and rural communities as a result of exposure to intensifying climate-change hazards, and the compounding and interacting effects of climate and non-climate factors ( ''medium confidence'' ).

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===== 14.5.5.2.1 Rising temperatures and extreme heat =====

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Extreme heat events are projected to increase in frequency and intensity across North America in the coming decades ( [[#14.2.2|Section 14.2.2]] ; Figure 14.2F,G). Inland urban areas in the southern and eastern USA are susceptible to urban heat island effects, particularly the Midwest/Great Lakes regions ( [[#Krayenhoff--2018|Krayenhoff et al., 2018]] ) and also Mexico City and many other cities in Mexico ( [[#Vargas--2020|Vargas and Magaña, 2020]] ). Climate change (RCP8.5) interacting with urban form, development and systemic racism ( [[#Schell--2020|Schell et al., 2020]] ; [[#Hsu--2021|Hsu et al., 2021]] ) could worsen risks from extreme heat in North American cities, especially where there is limited adaptation ( ''high confidence'' ) ( [[#Krayenhoff--2018|Krayenhoff et al., 2018]] ). Impacts from extreme heat will be exacerbated when multiple hazards occur simultaneously (e.g., heatwaves concurrent with droughts) ( [[#Mora--2018|Mora et al., 2018]] ; [[#Zscheischler--2018|Zscheischler et al., 2018]] ). Extreme heat events increase energy demand for space cooling in buildings, especially during peak demand periods and heatwaves ( [[#IEA--2018a|IEA, 2018a]] ). This can decrease cooling efficiency, increase emissions of GHG from electricity generation, increase refrigerant loads and associated emissions, and negatively affect air quality ( [[#IEA--2018a|IEA, 2018a]] ). Major electrical grid failure (i.e., blackouts) have increased across the USA and will continue to be particularly dangerous for human health when they coincide with extreme heat events ( [[#Stone--2021|Stone et al., 2021]] ). Efforts to increase resilience of the infrastructure that cities rely on are increasing ( [[#Climate-Safe%20Infrastructure%20Working%20Group--2018|Climate-Safe Infrastructure Working Group, 2018]] ).

Warmer and/or drier conditions may reduce water supply reliability for cities and small communities that rely on surface water sources fed by rain or snowmelt runoff, for example, Victoria and Vancouver, Canada (CA-BC) ( [[#Metro%20Vancouver--2016|Metro Vancouver, 2016]] ; [[#Vadeboncoeur--2016|Vadeboncoeur, 2016]] ; [[#Islam--2017|Islam et al., 2017]] ); San Pedro, Hermosillo and Los Pargas, Aguascalientes, México (MX-NW, MX-CE) ( [[#Vadeboncoeur--2016|Vadeboncoeur, 2016]] ; [[#Soto-Montes-de-Oca--2019|Soto-Montes-de-Oca and Alfie-Cohen, 2019]] ); New York City (US-NE) (NYC Department of Environmental Protection, 2014); and Washington State (US-NW) ( [[#14.5.3.2|Section 14.5.3.2]] ; [[#Fosu--2017|Fosu et al., 2017]] ).

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===== 14.5.5.2.2 Storms and flooding =====

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Annual and winter precipitation is expected to increase for most of Canada ( [[#14.2|Section 14.2]] ; Figure 14.2D,E) and will increase flooding in cities and settlements ( ''high confidence'' ) ( [[#Bonsal--2019|Bonsal et al., 2019]] ). Although there is more geographic variation across the continental USA (e.g., between high-latitude and subtropical zones), extreme precipitation events are projected to increase in frequency and intensity with impacts on flood hazards ( [[#14.5.3.2|Section 14.5.3.2]] ; [[#Easterling--2017|Easterling et al., 2017]] ). Winter (snow and ice) storms are expected to increase in northern North America and decrease in southern North America under RCP8.5 ( [[#Jeong--2018b|Jeong and Sushama, 2018b]] ). Projected increases in wind-driven rain exposure is an emerging consideration for moisture-resilient design and management of buildings, especially in western and northern Canada ( [[#Jeong--2020|Jeong and Cannon, 2020]] ).

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===== 14.5.5.2.3 Sea level rise =====

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In the USA, many people are projected to be at risk of flooding from SLR ( ''high confidence'' ) (see Box 14.4). A projected SLR of 0.9 m by 2100 could place 4.2 million people at risk of inundation in US coastal counties, whereas a 1.8-m SLR exposes 13.1 million people ( [[#Hauer--2016|Hauer et al., 2016]] ). In California, under an extreme 2-m SLR by 2100, 150 billion USD (2010) of property or more than 6% of the state’s GDP and 600,000 people could be affected by flooding ( [[#Barnard--2019|Barnard et al., 2019]] ). A 1-m SLR would inundate 42% of the Albemarle-Pamlico Peninsula in North Carolina and incur property losses of up to 14 billion USD (considering the 2016 USD value) ( [[#Bhattachan--2018|Bhattachan et al., 2018]] ). In nine southeast US states, a 1-m SLR would result in the loss of more than13,000 recorded historical and archaeological sites with over 1000 eligible for inclusion in the National Register for Historic Places ( [[#Anderson--2017|Anderson et al., 2017]] ). This SLR raises groundwater levels by impeding drainage and enhancing runoff during rain events ( [[#Hoover--2017|Hoover et al., 2017]] ); coastal flooding enhances saltwater intrusion affecting drinking water supply in settlements (e.g., coast of Texas) ( [[#Anderson--2016|Anderson and Al-Thani, 2016]] ).

In Canada, SLR is expected to increase the frequency and magnitude of extreme high-water-level events ( [[#Greenan--2018|Greenan et al., 2018]] ) and to create widespread impacts on natural and human systems ( ''high confidence'' ) (see Box 14.4; [[#Lemmen--2016|Lemmen et al., 2016]] ). Although coastal sensitivity is high in the Arctic, Canada’s more populated regions are also sensitive to the impacts of SLR ( [[#Manson--2019|Manson et al., 2019]] ). The Mi’kmaq community of Lennox Island First Nation is exploring relocation options because of erosion from SLR (Savard et al., 2016).

In Mexico, crucial coastal tourism cities, such as Cancun, Isla Mujeres, Playa del Carmen, Puerto Morelos and Cozumel (MX-SE), are at risk of SLR with an estimated economic impact of 1.4–2.3 billion USD ( [[#14.5.7|Section 14.5.7]] ; [[#Ruiz-Ramírez--2019|Ruiz-Ramírez et al., 2019]] ). Negative effects of the ‘coastal squeeze’ phenomena (generated by SLR, land subsidence, sediment deficit and current urbanisation processes) have been documented on tourist destinations along the coasts of the Mexican Gulf of Mexico and Mexican Caribbean. Zoning, limiting urbanisation along the coastline and using NbS (see Box 14.7) are alternatives that could be applied to improve the adaptation of these destinations ( [[#Martínez--2014|Martínez et al., 2014]] ; Salgado and Luisa Martinez, 2017; [[#Lithgow--2019|Lithgow et al., 2019]] ).

Rural low-lying coastal areas are at risk from SLR where natural barriers or shoreline infrastructure are deteriorating and this interacts with remoteness, resource-dependent economies and socioeconomic challenges to adaptive capacity ( [[#Bhattachan--2018|Bhattachan et al., 2018]] ; [[#Manson--2019|Manson et al., 2019]] ). The Northeast Atlantic region of North America (CA-AT, US-NE) is exposed to high risk by combined effects of land subsidence and climate-driven SLR (see Box 14.4; [[#Lemmen--2016|Lemmen et al., 2016]] ; [[#Sweet--2017|Sweet et al., 2017]] ; [[#Fleming--2018|Fleming et al., 2018]] ; [[#Greenan--2018|Greenan et al., 2018]] ).

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