Editing IPCC:AR6/WGII/Chapter-13 (section)

==== 13.6.1.5 Built Environment, Settlements and Communities ====

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The expected shift of European residents to large cities and coastal areas will increase assets at risk ( [[#13.2|Section 13.2]] ). The share of urban population in Europe is projected to increase from 74% in 2015 to 84% in 2050, corresponding to 77 million new urban residents ( [[#UN/DESA--2018|UN/DESA, 2018]] ), with most of this increase in SEU and WCE (particularly in Turkey and France). In the EU-28, urban residents in 2100 may increase by about 30 million under SSP1 and SSP5, and decrease by 90–110 million under SSP3 and SSP4 ( [[#Terama--2019|Terama et al., 2019]] ).

About 32% of 571 European cities in the GISCO Urban Audit 2014 dataset show a medium to high or relatively high vulnerability against heatwaves, droughts and floods ( [[#Tapia--2017|Tapia et al., 2017]] ). Under current vulnerabilities, future climate hazards will augment climate risks for several cities, particularly beyond 3°C GWL (Figure 13.17). In many NEU cities, a high increase in pluvial flooding risk by the end of the century is possible, while in WCE cities may face a high increase in pluvial flooding risks, moderate to very high increase in extreme heat risk, and to some extent moderate to high increase in drought risk. Many SEU cities could face a high to very high increase in risks from extreme heat and meteorological drought.

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[[File:a700d10b7ca868732196d99c1f10cbe4 IPCC_AR6_WGII_Figure_13_017.png]]

'''Figure 13.17 |''' '''Projected changes in pluvial flooding, extreme heat and meteorological drought risks for the 65 largest cities in EU-28 plus Norway and Switzerland for''' '''2.''' '''5°C and 4.4°C GWL compared with the baseline (1995–2014) ( [[#Tapia--2017|Tapia et al., 2017]] ).''' Exposure is expressed in terms of current population. Values of climatic impact drivers are derived from the Euro-CORDEX regional climate model ensemble.

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===== 13.6.1.5.1. Risks from coastal, river and pluvial flooding =====

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New studies increase confidence in AR5 statements that flood damages will increase in coastal areas due to SLR and changing social and economic conditions ( [[#13.2.1.1|Section 13.2.1.1]] ). Except for areas affected by land uplift, it is projected that further adaptation will be required to maintain risks at the present level for most coastal cities and settlements ( [[#Haasnoot--2013|Haasnoot et al., 2013]] ; [[#Ranger--2013|Ranger et al., 2013]] ; [[#Malinin--2018|Malinin et al., 2018]] ; [[#Hinkel--2019|Hinkel et al., 2019]] ; [[#Umgiesser--2020|Umgiesser, 2020]] ).

In many cities, the sewer system is older than 40 years, potentially reducing their capacity to deal with more intense pluvial flooding ( [[#EEA--2020b|EEA, 2020b]] ). Apart from climate change, urbanisation is an important driver for increases in flooding risks as it results in growth of impervious surfaces. Flash floods are particularly challenging, causing the overburdening of drainage systems ( [[#Dale--2018|Dale et al., 2018]] ), urban transport disruptions, and health and pollution impacts due to untreated sewage discharges ( [[#Kourtis--2021|Kourtis and Tsihrintzis, 2021]] ).

More than 25% of the population in nearly 13% of EU cities live within potential river floodplains. In many of these places (e.g., 50% of UK cities), a significant increase in the 10-year high river flow is possible beyond 2°C GWL under a high-impact scenario (i.e., 90th percentile of projections) ( [[#Guerreiro--2018|Guerreiro et al., 2018]] ; [[#EEA--2020b|EEA, 2020b]] ).

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===== 13.6.1.5.2 Risks from heatwaves, cold waves and drought =====

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Heatwave days and number of long heatwaves increased in most capitals from 1998–2015 compared with 1980–1997 ( [[#Morabito--2017|Morabito et al., 2017]] ; [[#Seneviratne--2021|Seneviratne et al., 2021]] ). In the summer of 2018, many cities suffered from heatwaves attributed to climate change ( [[#Vogel--2019|Vogel et al., 2019]] ; [[#Undorf--2020|Undorf et al., 2020]] ). As a result, indoor overheating and reduced outdoor thermal comfort, often coupled with urban heat island (UHI) effect, have already impacted European cities (see also [[#13.7.1|Section 13.7.1]] ; [[#Di%20Napoli--2018|Di Napoli et al., 2018]] ; [[#EEA--2020b|EEA, 2020b]] ).

Heatwaves are ''likely'' to become a major threat, not only for SEU but also for WCE and EEU cities ( [[#Russo--2015|Russo et al., 2015]] ; [[#Guerreiro--2018|Guerreiro et al., 2018]] ; [[#Lorencova--2018|Lorencova et al., 2018]] ; [[#Smid--2019|Smid et al., 2019]] ). At 2°C GWL and SSP3, half of the European population will be under very high risk of heat stress in summer ( [[#Rohat--2019|Rohat et al., 2019]] ). The UHI effect will further increase urban temperatures ( [[#Estrada--2017|Estrada et al., 2017]] ). In many cities, hospitals and social housing tend to be located within the intense UHI, thus increasing exposure to vulnerable groups ( [[#EEA--2020b|EEA, 2020b]] ). There is ''high confidence'' that overheating during summer in buildings with insufficient ventilation and/or solar protection will increase strongly, with thermal comfort hours potentially decreasing by 74% in SEU at 3°C GWL ( [[#Jenkins--2014a|Jenkins et al., 2014a]] ; [[#Hamdy--2017|Hamdy et al., 2017]] ; [[#Heracleous--2018|Heracleous and Michael, 2018]] ; [[#Dino--2019|Dino and Meral Akgül, 2019]] ; [[#Shen--2020|Shen et al., 2020]] ). Highly insulated buildings, following present building standards, will be vulnerable to overheating, particularly under high GWL levels, unless adequate adaptation measures are applied ( [[#Williams--2013|Williams et al., 2013]] ; [[#Virk--2014|Virk et al., 2014]] ; [[#Mulville--2016|Mulville and Stravoravdis, 2016]] ; [[#Fosas--2018|Fosas et al., 2018]] ; [[#Ibrahim--2018|Ibrahim and Pelsmakers, 2018]] ; [[#Salem--2019|Salem et al., 2019]] ; [[#Tian--2020|Tian et al., 2020]] ). Cities in NEU and WCE are more vulnerable due to limited solar shading and fewer air conditioning installations ( [[#Ward--2016|Ward et al., 2016]] ; [[#Thomson--2019|Thomson et al., 2019]] ). Cooling energy demand in SEU buildings has been projected to increase by 81–104% by 2035 and 91–244% after 2065 compared with 1961–1990 depending on GWL ( [[#Cellura--2018|Cellura et al., 2018]] ). Increases of 31–73% by 2050 and 165–323% by 2100 compared with 1996–2005 were estimated for buildings in NEU ( [[#Dodoo--2016|Dodoo and Gustavsson, 2016]] ) with risks modified by adaptation ( [[#13.6.2|Section 13.6.2]] ; [[#Viguié--2020|Viguié et al., 2020]] ). Cold waves beyond 3°C GWL will not represent an effective threat for European cities at the end of the century, and only a marginal hazard under 2°C GWL ( [[#Smid--2019|Smid et al., 2019]] ).

At 2°C GWL and beyond, cities in SEU and large parts of WCE would exceed the historical maximum 12-month Drought Severity index of the past 50 years (see [[#13.2|Section 13.2]] on drought risks) and 30% will have at least 30% probability of exceeding this maximum every month ( [[#Guerreiro--2018|Guerreiro et al., 2018]] ). This could adversely affect the operation of municipal water services ( [[#Kingsborough--2016|Kingsborough et al., 2016]] ). For example, under 2°C GWL, the reservoir storage volume is predicted to decrease for all of England and Wales catchments, resulting in a probability of years with water-use restrictions doubling by 2050 and quadrupling by 2100 compared with 1975–2004 ( [[#Dobson--2020|Dobson et al., 2020]] ). The combination of high temperatures, drought and extreme winds, potentially coupled with insufficient preparedness and adaptation, may amplify the damage of wildfires in peri-urban environments ( [[#13.3.1.3|Section 13.3.1.3]] ). High fuel load combined with proximity of the built environment to wildland highly increases fire risks ( [[#EEA--2020b|EEA, 2020b]] ).

Extreme heat and drought causes shrinking and swelling of clays, threatening the stability of small houses in peri-urban environments ( [[#Pritchard--2015|Pritchard et al., 2015]] ), with damage costs of 0.9–1 billion EUR during the 2003 heatwave ( [[#Corti--2011|Corti et al., 2011]] ). In WCE and SEU, mean annual damage costs could increase by 50% for 2°C GWL, and by a factor of 2 for 3°C GWL ( [[#Naumann--2021|Naumann et al., 2021]] ).

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===== 13.6.1.5.3 Risks from thaw of permafrost and mudflows =====

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Increasing temperatures in NEU and the Alps has led to accelerated degradation of permafrost, negatively affecting the stability of infrastructures ( [[#Stoffel--2014|Stoffel et al., 2014]] ; [[#Beniston--2018|Beniston et al., 2018]] ; [[#Duvillard--2019|Duvillard et al., 2019]] ). In the Caucasus, glacial mudflows due to permafrost degradation and modern tectonic processes pose a significant danger to the infrastructure ( [[#Vaskov--2016|Vaskov, 2016]] ). In the past 30 years, the permafrost temperature in the European part of the Russian Arctic has increased by 0.5–2°C, resulting in damage to buildings, roads and pipelines, and to significant expenditure for stabilising soils ( [[#Porfiriev--2017|Porfiriev et al., 2017]] ; [[#Konnova--2019|Konnova and Lvova, 2019]] ). Beyond 3° C GWL, the bearing capacity for infrastructure in the permafrost region of the European Russia could decrease by 32–75% by mid-century and by 95% by 2100, potentially affecting settlements in northern EEU ( [[#Shiklomanov--2017|Shiklomanov et al., 2017]] ; [[#Streletskiy--2019|Streletskiy et al., 2019]] ). The increasing number of cycles of freezing and thawing, observed in EEU, has led to accelerated ageing of building envelopes ( [[#13.8.1.4|Section 13.8.1.4]] ; [[#Frolov--2014|Frolov et al., 2014]] ). Permafrost degradation due to higher temperatures could increase the potential of debris flow detachment in Alpine locations ( [[#13.6.1.4|Section 13.6.1.4]] ; [[#Damm--2013|Damm and Felderer, 2013]] ).

Increased precipitation falling on local topography can increase landslide and mudflow risks, as seen in settlements at the Caucasus mountainous region ( [[#Marchenko--2017|Marchenko et al., 2017]] ; [[#Efremov--2018|Efremov and Shulyakov, 2018]] ; [[#Kerimov--2020|Kerimov et al., 2020]] ). At the Umbria region in Italy, landslide events could increase by 16–53% under 2°C GWL and by 24–107% beyond 3°C GWL, mostly during winter ( [[#Ciabatta--2016|Ciabatta et al., 2016]] ). Risks from shallow landslides are expected to increase in the Alps and Carpathians if no adequate risk mitigation measures are put in place ( [https://www.ipcc.ch/chapter/13#CCP5.3.2 CCP5.3.2] ; [[#Gariano--2016|Gariano and Guzzetti, 2016]] ).

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