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

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

<div id="h3-43-siblings" class="h3-siblings"></div>

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).

<div id="_idContainer100" class="Figure"></div>

[[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]] ).

<div id="13.10.3" class="h2-container"></div>

<span id="consequences-of-multiple-climate-risks-for-europe"></span>