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

===== 13.2.1.2.1 Riverine and pluvial flooding =====

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Precipitation has raised river flood hazards in WCE and the UK by 11% per decade from 1960 to 2010 and decreased in EEU and SEU by 23% per decade ( [[#Douville--2021|Douville et al., 2021]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). The most recent three decades had the highest number of floods in the past 500 years with increases in summer ( [[#Blöschl--2020|Blöschl et al., 2020]] ). Economic flood damages increased strongly, reflecting increasing exposure of people and assets ( [[#Visser--2014|Visser et al., 2014]] ; [[#Hoegh-Guldberg--2018|Hoegh-Guldberg et al., 2018]] ; [[#Merz--2021|Merz et al., 2021]] ).

Projections indicate a continuation of the observed trends of river flood hazards in WCE ( ''high confidence'' ) of 10% at 2°C GWL and 18% at 4.4°C GWL, and a decrease in NEU and SEU ( ''medium confidence'' ) with, respectively, 5 and 11% in NEU and SEU for a 100-year peak flow, making Europe one of the regions with the largest projected increase in flood risk ( [[#Di%20Sante--2021|Di Sante et al., 2021]] ; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). While there is disagreement on the magnitude of economic losses and people affected, there is ''high agreement'' on direction of change, particularly in WCE ( [[#Alfieri--2018|Alfieri et al., 2018]] ). New research increases confidence in AR5 statements that without adaptation measures, increases in extreme rainfall will substantially increase direct flood damages (e.g., [[#Madsen--2014|Madsen et al., 2014]] ; [[#Alfieri--2015a|Alfieri et al., 2015a]] ; [[#Alfieri--2015b|Alfieri et al., 2015b]] ; [[#Blöschl--2017|Blöschl et al., 2017]] ; [[#Dottori--2020|Dottori et al., 2020]] ; [[#Mentaschi--2020|Mentaschi et al., 2020]] ). With low adaptation, damages from river flooding are projected to be three times higher at 1.5°C GWL, four times at 2°C GWL and six times at 3°C GWL ( [[#Alfieri--2018|Alfieri et al., 2018]] ; [[#Dottori--2020|Dottori et al., 2020]] ). At 2°C GWL, the incidence of summer floods is expected to decrease across the whole alpine region, whereas winter and spring floods will increase due to extreme precipitation ( [[#Gobiet--2014|Gobiet et al., 2014]] ) and snowmelt-driven runoff ( [[#Coppola--2018|Coppola et al., 2018]] ).

Pluvial flooding and flash floods due to intense rainfall constitute most flood events in SEU and a substantial risk in other European regions (Cross-Chapter Paper 4; [[#Llasat--2016|Llasat et al., 2016]] ; [[#Rudd--2020|Rudd et al., 2020]] ). The majority (56%) of flood events between 1860 and 2016 were flash floods ( [[#Paprotny--2018a|Paprotny et al., 2018a]] ). These floods had considerable impacts including danger to human lives, for example, causing total economic damage of 1 billion USD in Copenhagen (Denmark) in 2011 ( [[#Wójcik--2013|Wójcik et al., 2013]] ), damage to private households of more than 70 million EUR in Münster (Germany) in 2014 ( [[#Spekkers--2017|Spekkers et al., 2017]] ) and during the 2021 floods in Belgium, Germany and the Netherlands over 200 deaths, damage to thousands of homes and disrupted water and electricity supply ( [[#Kreienkamp--2021|Kreienkamp et al., 2021]] ). The intensity and frequency of heavy rainfall events is projected to increase ( ''high confidence'' ) (Figure 13.3; [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ). Combined with increasing urbanisation, the risk of pluvial flooding is projected to increase ( [[#Westra--2014|Westra et al., 2014]] ; [[#Rosenzweig--2018|Rosenzweig et al., 2018]] ; [[#Papalexiou--2019|Papalexiou and Montanari, 2019]] ). Small catchments, steep river channels and cities are particularly vulnerable due to large areas of impermeable surfaces where water cannot penetrate ( [[#13.6|Section 13.6]] ).

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