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

===== 13.2.2.1.2 Riverine and pluvial flood risk management =====

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Structural flood protection (e.g., levees) is considered economically beneficial in densely populated areas ( [[#Alfieri--2016|Alfieri et al., 2016]] ; [[#Dottori--2020|Dottori et al., 2020]] ) and could reduce flood damage by ~45% as estimated under 1.5°C GWL and ~70% under 3°C GWL ( [[#Dottori--2020|Dottori et al., 2020]] ).

Providing more room for water through NbS is increasingly considered ( [[#Kreibich--2015|Kreibich et al., 2015]] ) as they can reduce risk effectively at lower costs, except in places with limited space or in areas with large protection. Such measures include (forest) restoration for upstream retention, restoration of river channels and widening riverbeds for natural flood retention ( [[#Kreibich--2015|Kreibich et al., 2015]] ; [[#Barth--2016|Barth and Döll, 2016]] ; [[#Wyżga--2018|Wyżga et al., 2018]] ). Natural retention areas are estimated to be the most effective option to reduce riverine flood risk across Europe in the 21st century, followed by protection ( ''low evidence'' ) ( [[#Dottori--2020|Dottori et al., 2020]] ).

Wet and dry proofing of buildings can be applied at household level. While measures taken at household level can reduce the risk of flooding, there is often insufficient investment ( ''medium confidence'' ) ( [[#Bamberg--2017|Bamberg et al., 2017]] ; [[#Aerts--2018|Aerts et al., 2018]] ). Reasons include low awareness or under-estimation of the risk ( [[#Kellens--2013|Kellens et al., 2013]] ), low perceived efficacy of adaptation measures ( [[#van%20Valkengoed--2019|van Valkengoed and Steg, 2019]] ) and lack of financial support ( [[#Kreibich--2011|Kreibich, 2011]] ). In the long term, risk reduction measures by governments are projected to outweigh floodproofing at household level, in particular in WCE, while for near-term household adaptation or regionally in SEU this could reduce risk more effectively ( [[#Haer--2019|Haer et al., 2019]] ). Relocation of households has occurred in response to river flood events (e.g., the 2013 flood events along the Danube River in Austria), with financial compensation playing a crucial role ( [[#Mayr--2020|Mayr et al., 2020]] ; [[#Thaler--2020|Thaler and Fuchs, 2020]] ; [[#Thaler--2021|Thaler, 2021]] ).

Urban drainage infrastructure is designed based on historical rainfall intensities, and thus may not have sufficient capacity for increased future intensities ( [[#Dale--2018|Dale et al., 2018]] ). Adaptation options to pluvial flooding include large retention ponds, local green spaces and green roofs within cities ( [[#Zölch--2017|Zölch et al., 2017]] ; [[#Maragno--2018|Maragno et al., 2018]] ; [[#Babovic--2019|Babovic and Mijic, 2019]] ; [[#Ribas--2020|Ribas et al., 2020]] ).

Early warning systems, insurance and behaviour change can complement protect and accommodate measures to limit residual risk ( ''high confidence'' ). Early warning systems have high monetary benefits ( [[#Pappenberger--2015|Pappenberger et al., 2015]] ). Behavioural adaptation to flooding relies on recognition of the threat and capacity to respond, both of which are often lacking ( [[#13.11.2.2|Section 13.11.2.2]] ; [[#Bamberg--2017|Bamberg et al., 2017]] ; [[#Haer--2019|Haer et al., 2019]] ). Flood risk insurance and compensation systems vary across European countries, ranging from post-disaster payments by governments and compulsory flood insurance, to public–private partnerships where the state acts as reinsurer ( [[#Keskitalo--2014|Keskitalo et al., 2014]] ; [[#Surminski--2015|Surminski et al., 2015]] ; [[#Hanger--2018|Hanger et al., 2018]] ). Risk-based insurance premiums can induce risk-averting behaviour but may become unaffordable to poor households and some households in high-risk zones ( [[#Hudson--2018|Hudson, 2018]] ; [[#Surminski--2018|Surminski, 2018]] ). Increasing future flood risks due to both climatic and socioeconomic change could overburden government budgets ( ''medium confidence'' ) ( [[#13.11.2|Section 13.11.2]] ; [[#Paudel--2015|Paudel et al., 2015]] ; [[#Mysiak--2016|Mysiak and Perez-Blanco, 2016]] ; [[#Schinko--2017|Schinko et al., 2017]] ; [[#Mochizuki--2018|Mochizuki et al., 2018]] ), resulting in unavailable or unaffordable insurance for private customers ( [[#13.8.3|Section 13.8.3]] ; [[#Hudson--2016|Hudson et al., 2016]] ; [[#Surminski--2018|Surminski, 2018]] ), and underfunding and insufficient solvency of insurance companies ( [[#13.6.2.5|Section 13.6.2.5]] ; [[#Lamond--2014|Lamond and Penning-Rowsell, 2014]] ). Local knowledge about disastrous flood events in the past can be lost across generations, leading to (re)-settlement in flood-prone areas ( [[#Fanta--2019|Fanta et al., 2019]] ).

Limits to adaptation to extremely high SLR scenarios have been identified for coastal defences, such as the Venice MoSE barrier (see Box 13.1), Thames Barrier in the UK ( [[#Ranger--2013|Ranger et al., 2013]] ) and the Maeslant Barrier in the Netherlands ( [[#Kwadijk--2010|Kwadijk et al., 2010]] ; [[#Haasnoot--2020b|Haasnoot et al., 2020b]] ). However, the scale and pace of adaptation required to face high-end SLR scenarios along all coasts of Europe has been poorly studied. Given the lead and long lifetime of large critical infrastructures, there is a growing need to look beyond 2100 to support the design of new infrastructures (Cross-Chapter Box SLR in Chapter 3).

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