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

=== 13.10.2 Key Risks Assessment for Europe ===

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Key risks (KRs) are defined as a subset of climate risks that can potentially become, or are already, severe ( [[IPCC:Wg2:Chapter:Chapter-16#16.5|Section 16.5]] ). The selection process included a review of KRs already identified in AR5 Chapter 23 ( [[#Kovats--2014|Kovats et al., 2014]] ) and a review of the large body of new evidence on projected risks presented in Sections 13.2–13.9. Key risks are reinforced by evidence from the detection and attribution assessment ( [[#13.10.1|Section 13.10.1]] ) and new evidence from WGI AR6 Chapters 11 and 12 on regional climatic impact drivers and extremes ( [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ; [[#Seneviratne--2021|Seneviratne et al., 2021]] ). Several expert opinion workshops of lead and contributing authors led to further refinements, adjustment and consensus building around the characteristics of KRs, which ultimately guided the construction of the burning embers (Figures 13.28–13.32; SM13.10). There is ''high confidence'' that under low or medium adaptation, high to very high risks are projected at 3°GWL (Figure 13.28; Sections 13.10.2.1–13.10.2.4). Most risks are assessed as moderate up to 1.5°GWL (Figure 13.28).

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[[File:1855ccaf5e0eae6b0b4e704e2d368e42 IPCC_AR6_WGII_Figure_13_028.png]]

'''Figure 13.28 |''' '''Burning ember diagrams for low to medium adaptation.''' (More details on each burning ember are provided in Sections 13.10.2.1–13.10.2.4 and SM13.10. Some burning embers are shown again in Figures 13.29–13.34 alongside burning embers with high adaptation.)

This section also includes an assessment of the solution space using illustrative adaptation pathways which show alternative sequences of options to reduce risks as climate changes (SM13.10). Low-effectiveness measures are followed by measures of higher effectiveness, while accounting for path dependency of decisions ( [[#Toreti--2019b|Toreti et al., 2019b]] ; [[#Haasnoot--2020a|Haasnoot et al., 2020a]] ). The process to derive the pathways draws on evidence from the feasibility and effectiveness assessments (Sections 13.2, 13.5–13.7).

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==== 13.10.2.1 KR1: Risks of Human Mortality and Heat Stress, and of Ecosystem Disruptions Due to Heat Extremes and Increases in Average Temperatures ====

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Key risk 1 has cut across humans and ecosystems, and severe consequences are mainly driven by an increasing frequency, intensity and duration of heat extremes and increasing average temperatures ( ''high confidence'' ) ( [[#Urban--2015|Urban, 2015]] ; [[#Forzieri--2017|Forzieri et al., 2017]] ; [[#Feyen--2020|Feyen et al., 2020]] ; [[#Naumann--2020|Naumann et al., 2020]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). The risk of human heat stress and mortality is largely influenced by underlying socioeconomic pathways, with consequences being more severe under SSP3, SSP4 and SSP5 scenarios than SSP1 ( ''very high confidence'' ) (Figure 13.22; Sections 13.6.1.5.2, 13.7.1.1; [[#Hunt--2017|Hunt et al., 2017]] ; [[#Kendrovski--2017|Kendrovski et al., 2017]] ; [[#Rohat--2019|Rohat et al., 2019]] ; [[#Casanueva--2020|Casanueva et al., 2020]] ). The SSPs impact natural systems as well but are not yet well studied. The impact of warming in marine systems are often synergistic with SLR in coastal systems and ocean acidification driven by the rise in CO 2 , while habitat fragmentation and land use have important synergies in terrestrial systems ( ''high confidence'' ) (Sections 13.3.1.2, 13.4.1.2). More intense heatwaves on land and in the ocean, particularly in Mediterranean Europe ( [[#13.4|Section 13.4]] ; Cross-Chapter Paper 4; [[#Darmaraki--2019b|Darmaraki et al., 2019b]] ; [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ), are expected to cause mass mortalities of vulnerable species, and species extinction, altering the provision of important ecosystem goods and services ( [[#Marbà--2010|Marbà and Duarte, 2010]] ).

The burning embers on risks for humans (Figure 13.29a) differentiate between present and medium adaptation conditions, drawing on SSP2 and SSP4 (and to a lesser extent SSP3), and high adaptation conditions, drawing on SSP1 and papers using various temperature adjustment methods (Table SM13.25). There is ''high confidence'' that the risk is already moderate now because it has been detected and attributed with ''high confidence'' ( [[#13.10.1|Section 13.10.1]] ). The transition from moderate to high risk for human health is assessed to happen after 1.5°C GWL in a scenario with present to medium adaptation and implies a two- to threefold increase (compared with moderate risk levels) in magnitude of consequences such as mortality, morbidity, heat stress and thermal discomfort ( [[#Rohat--2019|Rohat et al., 2019]] ; [[#Casanueva--2020|Casanueva et al., 2020]] ; [[#Naumann--2020|Naumann et al., 2020]] ). At this level, the risk will also become more persistent across the continent due to increase in heat events exceeding critical thresholds for health ( ''high confidence'' on the direction of change and temperature transition, but ''medium confidence'' on the magnitude) ( [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ).

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[[File:de8802a592beec068512efcbf70150b1 IPCC_AR6_WGII_Figure_13_029.png]]

'''Figure 13.29 |''' '''Burning embers and illustrative adaptation pathways for risks to human health from heat (Key Risk 1)'''

'''(a)''' Burning ember diagrams for the risk to human health from heat are shown. The low to medium adaptation scenario corresponds to present, SSP2 and SSP4 socioeconomic conditions. The high adaptation includes SSP1 and adaptation needed to maintain current risk levels.

'''(b,c)''' Illustrative adaptation pathways for NEU (top) and SEU (bottom), and key messages based on the feasibility and effectiveness assessment in Figures 13.20 and 13.24. Grey shading means long lead time and dotted lines signal reduced effectiveness. The circles imply transfer to another measure and the bars imply that the measure has reached a tipping point (Tables SM13.24, SM13.25).

The burning embers on risk for terrestrial and marine ecosystems, and some of their services, are shown in Figure 13.28 (second and third ember from the left) (Tables SM13.26, SM13.27). The transition to moderate risk is currently happening as warming already results in changes in timing of development, species migration northward and upwards, and desynchronisation of species interactions, especially at the range limits, with cascading and cumulative impacts through ecosystems and food webs ( ''high confidence'' ) (Sections 13.3, 13.4; Figures 13.8, 13.12). While some terrestrial ecosystems are already impacted today, such as Alpine, cryosphere and peatlands, the impacts are not widespread and severe yet across a wide range of terrestrial systems. Around 2°C GWL, losses accelerate in marine ecosystem and appear across systems, including habitat losses especially in coastal wetlands ( [[#Roebeling--2013|Roebeling et al., 2013]] ; [[#Clark--2020|Clark et al., 2020]] ), biodiversity and biomass losses ( [[#Bryndum-Buchholz--2019|Bryndum-Buchholz et al., 2019]] ; [[#Lotze--2019|Lotze et al., 2019]] ) and ecosystem services such as fishing ( ''high confidence'' on the direction of change, but ''medium confidence'' on the local and regional magnitude) ( [[#Raybaud--2017|Raybaud et al., 2017]] ). The transition is happening at slightly higher warming in terrestrial systems due to a higher number of thermal refugia in terrestrial systems causing relocation but not already severe impacts ( ''medium confidence'' ) (Chapter 2).

There is ''medium confidence'' that high adaptation or conditions posing low challenges for adaptation (e.g., SSP1) in the context of human health can delay the transition from moderate to high risk ( [[#Åström--2017|Åström et al., 2017]] ; [[#Ebi--2021|Ebi et al., 2021]] ). The illustrative adaptation pathways in Figure 13.29b,c show the sequencing of options to a high adaptation future for NEU and SEU. Whether or not adaptation measures are effective to reduce risk severity for people’s health depends on local context ( ''high confidence'' ) (Figure 13.29; Sections 13.6.2, 13.7.2). Some adaptation options are found to be highly effective across Europe irrespective of warming levels, including air conditioning and urban planning ( ''high confidence'' ) (Sections 13.6.2, 13.7.2; [[#Jenkins--2014b|Jenkins et al., 2014b]] ; [[#Donner--2015|Donner et al., 2015]] ; [[#Dodoo--2016|Dodoo and Gustavsson, 2016]] ; [[#Åström--2017|Åström et al., 2017]] ; [[#Dino--2019|Dino and Meral Akgül, 2019]] ; [[#Venter--2020|Venter et al., 2020]] ), although air conditioning increasingly faces some feasibility constraints (Figure 13.20). Building interventions alone have low to medium effectiveness independent of the region. Many behavioural changes, such as personal and home heat protection, have already been implemented in SEU ( [[#13.7.2|Section 13.7.2]] ; [[#Martinez--2019|Martinez et al., 2019]] ). To reach high adaptation, a combination of low, medium and high effectiveness measures in different sectors and sub-regions is needed, many of which entail systems’ transformations (e.g., heat-proof land management) (Chapter 16) and remain effective at higher warming levels ( ''medium confidence'' ) ( [[#Díaz--2019|Díaz et al., 2019]] ). These transformations have long lead times, thereby requiring timely start of implementation including regions that are not yet experiencing high heat stress (e.g., NEU) ( ''high agreement, medium evidence'' ).

Autonomous adaptation of species via migration in response to climate change is well documented in contemporary, historical and geological records (Chapter 2; Cross-Chapter Box PALEO in Chapter 1); however, the projected rate of climate change can exceed migration potential, leading to evolutionary adaptation or increased extinction risk (Chapters 2, 3; Sections 13.3, 13.4). A reduction of non-climatic stressors, such as nutrient loads, resource extraction, habitat fragmentation or pesticides on land, are considered important adaptation options to increase the resilience to climate-change impacts ( ''high confidence'' ) (Sections 13.3, 13.4; [[#Ramírez--2018|Ramírez et al., 2018]] ). A major governance tool to reduce climatic and non-climatic impacts is the establishment of networks of protected areas (Sections 13.3.2, 13.4.2) especially when aggregated, zoned or linked with corridors for migration ( ''high confidence'' ), as well as a cost-effective adaptation strategy with multiple additional co-benefits ( [[#Berry--2015|Berry et al., 2015]] ; [[#Roberts--2017|Roberts et al., 2017]] ). Reforestation, rewilding and habitat restoration are long-term strategies for reducing risk for biodiversity loss supported by assisted migration and evolution ( [[#13.3.2|Section 13.3.2]] , 13.4), though current laws and regulations do not include species migration ( ''high confidence'' ) ( [[#Prober--2019|Prober et al., 2019]] ; [[#Fernandez-Anez--2021|Fernandez-Anez et al., 2021]] ).

Very high risks are expected beyond 3°C GWL due to the magnitude and increased likelihood of serious consequences, as well as to the limited ability of humans and ecosystems to cope with these impacts. There is ''high confidence'' that even under high adaptation scenarios for human systems or autonomous adaptation of natural systems, the risk will still be high at 3°C GWL and beyond ( [[#13.7.2|Section 13.7.2]] ; [[#Hanna--2015|Hanna and Tait, 2015]] ; [[#Spencer--2016|Spencer et al., 2016]] ) with ''medium confidence'' on the temperature range of the transition. Projected SLR will strongly impact coastal ecosystems ( ''high confidence'' ), minimising their contribution to shoreline protection ( [[#13.10.2.4|Section 13.10.2.4]] ).

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==== 13.10.2.2 KR2: Risk of Losses in Crop Production, Due to Compound Heat and Dry Conditions, and Extreme Weather ====

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Key risk 2 encompasses agriculture productivity (Figure 13.30a). It is mainly driven by the increase in the likelihood of compound heat and dry conditions and extreme weather, and their impact on crops. There is ''high confidence'' that climate change will increase the likelihood of concurrent extremely dry (Table SM13.28) and hot warm seasons with higher risks for WCE, EEU (particularly northwest Russia) and SEU leading to enhanced risk of crop failure and decrease in pasture quality ( [[#13.5.1|Section 13.5.1]] ; [[#Zscheischler--2017|Zscheischler and Seneviratne, 2017]] ; [[#Sedlmeier--2018|Sedlmeier et al., 2018]] ; [[#Seneviratne--2021|Seneviratne et al., 2021]] ). The risk is already moderately severe due to multiple crop failures in the past decade in WCE and Russia ( [[#13.5.1|Section 13.5.1]] ; [[#Hao--2018|Hao et al., 2018]] ; [[#Pfleiderer--2019|Pfleiderer et al., 2019]] ; [[#Vogel--2019|Vogel et al., 2019]] ). Under high-end scenarios, heat and drought extremes are projected to become more frequent and widespread as early as mid-century ( [[#Toreti--2019a|Toreti et al., 2019a]] ). For present to moderate adaptation and at least up to 2.5°GWL, negative consequences are mostly in SEU ( [[#Bird--2016|Bird et al., 2016]] ; [[#EEA--2019c|EEA, 2019c]] ; [[#Moretti--2019|Moretti et al., 2019]] ; [[#Feyen--2020|Feyen et al., 2020]] ). The transition from moderate to high risk is projected to happen around 2.7°C GWL when hazards and risk will become more persistent and widespread in other regions ( [[#13.1|Section 13.1]] ; [[#Deryng--2014|Deryng et al., 2014]] ; [[#Donatelli--2015|Donatelli et al., 2015]] ; [[#Webber--2018|Webber et al., 2018]] ; [[#Ceglar--2019|Ceglar et al., 2019]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ; [[#Seneviratne--2021|Seneviratne et al., 2021]] ). This temperature increase will trigger shifts in agricultural zones, onset of early heat stress, losses in maize yield of up to 28% across EU-28 and regional disparity in losses and gains in wheat, which are not able to offset losses across the continent ( [[#Deryng--2014|Deryng et al., 2014]] ; [[#Szewczyk--2018|Szewczyk et al., 2018]] ; [[#Ceglar--2019|Ceglar et al., 2019]] ). There will be also broader adverse impacts such as reduction of grassland biomass production for fodder, increases in weeds and reduction in pollination ( ''medium confidence'' ) ( [[#Castellanos-Frias--2016|Castellanos-Frias et al., 2016]] ; [[#Nielsen--2017|Nielsen et al., 2017]] ; [[#Brás--2019|Brás et al., 2019]] ). Combined with socioeconomic development, increased heat and drought stress, and reduced irrigation water availability, in SEU are projected to lead to abandonment of farmland ( [[#Holman--2017|Holman et al., 2017]] ). Around 4°C GWL, the risk is very high due to persistent heat and dry conditions ( [[#Ben-Ari--2018|Ben-Ari et al., 2018]] ) and the emergence of losses also in NEU which would be much higher without the assumed CO 2 fertilisation ( [[#Deryng--2014|Deryng et al., 2014]] ; [[#Szewczyk--2018|Szewczyk et al., 2018]] ; [[#Harrison--2019|Harrison et al., 2019]] ).

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[[File:01670741c9f0a6dbc42530cf416b1e2d IPCC_AR6_WGII_Figure_13_030.png]]

'''Figure 13.30 |''' '''Burning embers and illustrative adaptation pathways for losses in crop production (Key Risk 2)'''

'''(a)''' Burning ember diagrams for losses in crop production with present or medium adaptation conditions, and with high adaptation, are shown.

'''(b)''' Illustrative adaptation pathways and key messages based on the feasibility and effectiveness assessment in Figure 13.14. Grey shading means long lead time and dotted lines signal reduced effectiveness. The circles imply transfer to another measure and the bars imply that the measure has reached a tipping point (Table SM13.28).

Farmers have historically adapted to environmental changes, and such autonomous adaptation will continue. Higher CO 2 levels have a fertilisation effect on plants that is considered to decrease crop production risks ( [[#Deryng--2014|Deryng et al., 2014]] ). Adaptation solutions to heat and drought risks include changes in sowing and harvest dates, increased irrigation, changes in crop varieties, the use of cover crops and mixed agricultural practices ( [[#13.5.2|Section 13.5.2]] ; Figures 13.14, Figure 13.30b). Under high adaptation, the use of irrigation can substantially reduce risk by both reducing canopy temperature and drought impacts ( ''high confidence'' ) ( [[#13.5.2|Section 13.5.2]] ; [[#Webber--2018|Webber et al., 2018]] ). Some reductions of maize yields in SEU are still possible, but are balanced by gains in other crops and regions ( [[#Deryng--2014|Deryng et al., 2014]] ; [[#Donatelli--2015|Donatelli et al., 2015]] ; [[#Webber--2018|Webber et al., 2018]] ; [[#Feyen--2020|Feyen et al., 2020]] ). At 3°C GWL and beyond, the adaptive capacity is reduced ( [[#Ruiz-Ramos--2018|Ruiz-Ramos et al., 2018]] ). Crop production is a major consumer of water in agriculture ( [[#Gerveni--2020|Gerveni et al., 2020]] ), yet a potentially scarcer supply of water in some regions must be distributed across many needs (KR3, [[#13.10.2.3|Section 13.10.2.3]] ), limiting availability to agriculture which is currently the main user of water in many regions of Europe ( ''high confidence'' ) ( [[#13.5.1|Section 13.5.1]] ). Where the ability to irrigate is limited by water availability, other adaptation options are insufficient to mitigate crop losses in some sub-regions, particularly at 3°C GWL and above, with an increase in risk from north to south and higher risk for late-season crops such as maize ( ''high confidence'' ). Under these conditions, land abandonment is projected ( ''low confidence'' ) ( [[#Holman--2017|Holman et al., 2017]] ).

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==== 13.10.2.3 KR3: Risk of Water Scarcity to Multiple Interconnected Sectors ====

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Risks related to water scarcity across multiple sectors can become severe in WCE and, to a much larger extent, in SEU based on projections of drought damage, population and sectors exposed, and they increase in water exploitation (Figure 13.31a; Table SM13.29). In EEU, uncertainty in hydrological drought projections and risk consequences is higher ( [[#Greve--2018|Greve et al., 2018]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ; [[#Seneviratne--2021|Seneviratne et al., 2021]] ) and the available number of publications is lower, not allowing a conclusion on how risk levels change with GWL. Yet, there is emerging evidence that drought-related risks increase with warming beyond 3°C GWL also in EEU (Seneviratne, 2021, for hydrological drought and 4°C GWL; Kattsov and Porfiriev, 2020). Evidence from the detected changes and attribution assessment suggests that the risk is already moderate in SEU (e.g., 48 million people exposed to moderate water scarcity between 1981 and 2010) ( ''high confidence'' ) ( [[#13.10.1|Section 13.10.1]] ; Figure 13.31a).

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[[File:a9e6cd50050d2ae16cae6474a0e6f027 IPCC_AR6_WGII_Figure_13_031.png]]

'''Figure 13.31 |''' '''Burning embers and illustrative adaptation pathways for risk of water scarcity to people (Key Risk 3)'''

'''(a)''' Burning ember diagrams for the risk of water scarcity with no or low adaptation, and with high adaptation for SEU and WCE, are shown.

'''(b)''' Illustrative adaptation pathways and key messages (see Figure 13.6). Grey shading means long lead time and dotted lines signal reduced effectiveness. The circles imply transfer to another measure and the bars imply that the measure has reached a tipping point (Table SM13.29).

Risk of water scarcity has a high potential to lead to cascading impacts well beyond the water sector. These materialize in a number of highly interconnected sectors from agriculture and livestock farming to energy (hydropower and cooling of thermal power plants) and industry (e.g., shipping) ( [[#Blauhut--2015|Blauhut et al., 2015]] ; [[#Stahl--2016|Stahl et al., 2016]] ; [[#Bisselink--2020|Bisselink et al., 2020]] ; [[#Cammalleri--2020|Cammalleri et al., 2020]] ). Extensive water extraction will augment pressures on water reserves, impacting the ecological status of rivers and ecosystems dependent on them ( [[#Grizzetti--2017|Grizzetti et al., 2017]] ). Socioeconomic conditions contributing to severe consequences are when more residents settle in drought-prone regions, or when the share of agriculture in GDP declines ( ''high confidence'' ). For Europe, risks of water scarcity will be higher under SSP5 and SSP3 than under SSP1 ( ''medium confidence'' ) ( [[#Byers--2018|Byers et al., 2018]] ; [[#Arnell--2019|Arnell et al., 2019]] ; [[#Harrison--2019|Harrison et al., 2019]] ). Transition to high risks is projected to occur below 2°C GWL in SEU and be associated with more persistent droughts ( [[#13.1.3|Section 13.1.3]] ), and at 2°C GWL to show a 54% increase of the population facing at least moderate levels of water shortage ( [[#Byers--2018|Byers et al., 2018]] ). This transition will happen at higher warming in WCE since risks are projected to increase less rapidly (transition between 2°C and 3°C GWL) ( ''medium confidence'' ) ( [[#13.2.1.2|Section 13.2.1.2]] ; [[#Byers--2018|Byers et al., 2018]] ). At 3°C GWL and beyond, water scarcity will become much more widespread and severe in already water-scarce areas in SEU ( ''high confidence'' ) and will expand to currently non-water-scarce regions in WCE ( ''medium confidence'' ) ( [[#13.2.1.2|Section 13.2.1.2]] ; [[#Bisselink--2018|Bisselink et al., 2018]] ; [[#Naumann--2018|Naumann et al., 2018]] ; [[#Harrison--2019|Harrison et al., 2019]] ; [[#Koutroulis--2019|Koutroulis et al., 2019]] ; [[#Cammalleri--2020|Cammalleri et al., 2020]] ; [[#Spinoni--2020|Spinoni et al., 2020]] ). Decrease in hydropower potential in SEU and WCE are expected beyond 3°GWL (Figure 13.16).

To reduce risk to water scarcity, adaptation measures, at both the supply and the demand side, have been suggested ( [[#13.2.2|Section 13.2.2]] ; Figures 13.6, 13.31b; [[#Garnier--2019|Garnier and Holman, 2019]] ; [[#Hagenlocher--2019|Hagenlocher et al., 2019]] ). Several measures are already in place showing high technical and institutional feasibility (Sections 13.2.2.2, 13.5.2.1). The effectiveness of options varies regionally (in particular between northern and southern regions). For example, in SEU many water reservoirs are already in place. Irrigation is used to support agriculture where rain-fed supplies are not sufficient ( [[#13.5.2|Section 13.5.2]] ). Their future extension depends on available precipitation. Also, wastewater reuse can only be effective if sufficient wastewater is available. Improvements in water efficiency and behavioural changes are very effective in SEU (&gt;25% of damages avoided) ( [[#13.2.2.2|Section 13.2.2.2]] ). Investments in large water infrastructures and advanced technologies (including storage), water transfer, water recycling and reuse, and desalination will allow to buy time and therefore to cope with additional warming ( [[#Papadaskalopoulou--2016|Papadaskalopoulou et al., 2016]] ; [[#Greve--2018|Greve et al., 2018]] ). Beyond 2.5°C GWL, transformational adaptation is needed to lower risk levels, such as planned relocation of industry, abandonment of farmland or the development of alternative livelihoods ( [[#Holman--2017|Holman et al., 2017]] ). In WCE, the solution space to water scarcity is expanding with considerable potential for investments in large water infrastructure and advanced technologies (including storage), for reducing risks above 3°C GWL ( [[#Greve--2018|Greve et al., 2018]] ). Under medium warming a larger portfolio of measures might be needed in SEU in particular, although it may not be able to completely avoid water shortages at high warming.

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==== 13.10.2.4 KR4: Risks to People, Economies and Infrastructures Due to Coastal and Inland Flooding ====

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Damages and losses from coastal and river floods are projected to increase substantially in Europe over the 21st century ( ''high confidence'' ) ( [[#13.2.1|Section 13.2.1]] ; SM13.10). Coastal areas have already started to be affected by SLR (see Box 13.1; [[#13.10.1|Section 13.10.1]] ) and human exposure to coastal hazards is projected to increase in the next decades ( ''high confidence'' ), but less under SSP1 (20%) than SSP5 (50%) by the end of the century ( ''medium confidence'' ) ( [[#Merkens--2016|Merkens et al., 2016]] ; [[#Reimann--2018a|Reimann et al., 2018a]] ). Under low adaptation (i.e., coastal defences are maintained but not further strengthened), severe consequences include an increase in expected annual damage by a factor of at least 20 for 1.5°C–2.1°C GWL (i.e., high risks) and by two to three orders of magnitude between 2°C and 3°C GWL in EU-28 (i.e., very high risk) ( ''medium confidence'' ) (Figures 13.28, 13.34c; [[#13.2.1.1|Section 13.2.1.1]] ; [[#Vousdoukas--2018b|Vousdoukas et al., 2018b]] ; [[#Haasnoot--2021b|Haasnoot et al., 2021b]] ). Under high adaptation (i.e., lowlands are protected where it is economically efficient), expected annual damages still increase by a factor of 5 above 2°C GWL ( [[#13.2|Section 13.2]] ; [[#Vousdoukas--2020|Vousdoukas et al., 2020]] ). Sea levels are committed to rise for centuries ( [[#Fox-Kemper--2021|Fox-Kemper et al., 2021]] ), submerging at least 10% of the territory in 12 countries in Europe if GWL exceed 1.5°C–2.5°C ( [[#Clark--2016|Clark et al., 2016]] ), and this represents a major threat for the European and Mediterranean cultural heritage (Figure 13.28; Cross-Chapter Box SLR in Chapter 3; Cross-Chapter Paper 4; [[#Marzeion--2014|Marzeion and Levermann, 2014]] ; [[#Reimann--2018b|Reimann et al., 2018b]] ).

Pluvial and riverine flood events in Europe have been attributed to climate change, but the associated damages and losses also depend on land-use planning and flood risk management practices ( ''medium confidence'' ) ( [[#13.10.1|Section 13.10.1]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). Exposure to urban flooding will increase with urbanisation ( [[#Jongman--2012|Jongman et al., 2012]] ; [[#Jones--2016|Jones and O’Neill, 2016]] ; [[#Dottori--2018|Dottori et al., 2018]] ; [[#Paprotny--2018b|Paprotny et al., 2018b]] ). Flooding is projected to rise with temperature in Europe with, for example, a doubling of damage costs and people affected from river flood for low adaptation above 3°C GWL ( [[#Alfieri--2018|Alfieri et al., 2018]] ). Inland flooding represents a KR for Europe due to the extent of settlements exposed, the frequency of the hazards, the risks to human lives associated with flash floods and the limited adaptation potential to pluvial flooding (e.g., difficulty to upgrade urban drainage systems) ( [[#Dale--2018|Dale et al., 2018]] ; [[#Dale--2021|Dale, 2021]] ); hence, risks can become very high from 3°C GWL (Figure 13.32a).

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[[File:b07d7660beafed2a9b8a4b5123ed4160 IPCC_AR6_WGII_Figure_13_032.png]]

'''Figure 13.32 |''' '''Burning embers and illustrative adaptation pathways for inland and coastal flooding (Key Risk 4)'''

'''(a)''' Burning ember diagrams for the risks from riverine and pluvial flooding, with and without adaptation, are shown.

'''(b)''' Illustrative adaptation pathways to riverine flooding risks.

'''(c)''' Burning ember diagrams for the risks from coastal flooding, with and without adaptation, are shown.

'''(d)''' Illustrative adaptation pathways to coastal flooding risks. Grey shading means long lead time and dotted lines signal reduced effectiveness. The circles imply transfer to another measure and the bars imply that the measure has reached a tipping point (Tables SM13.30, SM13.31).

A range of adaptation options to coastal flooding exists, and adaptation is possible in many European regions if started on time ( [[#13.2|Section 13.2]] ; Figure 13.32d). Continuing a protection pathway is cost-effective in urbanised regions for this century ( [[#Vousdoukas--2020|Vousdoukas et al., 2020]] ), but there is ''high agreement'' that it comes with residual risk if coastal defences fail during a storm. This residual risk can be reduced through early warning and evacuations, insurance and accommodate measures ( [[#13.2.2|Section 13.2.2]] ). Soft limits to protection have been identified under high GWL, in particular due to the rate of change and delayed impacts of long-term SLR ( ''medium confidence'' ) ( [[#Hinkel--2018|Hinkel et al., 2018]] ; [[#Haasnoot--2020a|Haasnoot et al., 2020a]] ). Ecosystem-based solutions, such as wetlands, can reduce waves’ propagation, provide co-benefits for the environment and climate mitigation, and reduce costs for flood defences ( ''medium confidence'' ) ( [[#13.2.2.1|Section 13.2.2.1]] ). At higher GWL, ecosystems are projected to experience reduced effectiveness due to temperature increases and an increased rate of SLR combined with a lack of sediment and human pressures (Cross-Chapter Box SLR in Chapter 3). Retention and diversion can be effective for compound flooding or for estuaries with a limited storm surge duration, but there is a lack of knowledge on their effectiveness (Sections 13.2.2).

In the case of river flooding, adaptation has the potential to contain damage and losses up to 3°C GWL (Figure 13.32b; [[#Jongman--2014|Jongman et al., 2014]] ; [[#Alfieri--2016|Alfieri et al., 2016]] ), provided they are implemented on time and that the technical, social and financial barriers are addressed (Sections 13.2.2, 13.6.2). Residual risks can be reduced through early warning and evacuations, insurance and accommodate measures ( [[#13.2.2|Section 13.2.2]] ; [[#Kreibich--2015|Kreibich et al., 2015]] ). Accommodation strategies, such as retention and ecosystem-based solutions, require space, which is not always available in cities. Both protection and flood retention are effective in reducing inland flooding risk across Europe, but with regional variation in the benefit-to-cost ratio ( ''medium confidence'' ) ( [[#Alfieri--2016|Alfieri et al., 2016]] ; [[#Dottori--2020|Dottori et al., 2020]] ). Furthermore, upgrading drainage systems to accommodate increase in pluvial flooding is costly, technically complex and requires time ( [[#Dale--2018|Dale et al., 2018]] ; [[#Dale--2021|Dale, 2021]] ).

Avoiding developments in risk-prone areas can reduce both coastal and inland flooding risks and can be followed by planned relocation, particularly in less populated areas. To align relocation with social goals and achieve positive outcomes, long lead times are needed ( [[#Haasnoot--2021a|Haasnoot et al., 2021a]] ).

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