Flooding in Europe

Assessment of Risk, Vulnerability, and Adaptation Measures

This is a more “sciencey” post about Flooding in Europe. If you’re interested, keep reading. If you’re not, that’s okay, I made a more reader-friendly version in an OP-ED intended for a general audience.

Photo Credit: Michael Probst (2021)

The other Lead Authors: Lisa Dalklint (Sweden), Sophie Lahey (USA)

Review Editors: Xiaoyan Kong (China,) Matti Myllynen (Finland)

EXECUTIVE SUMMARY 

Climate change has deeply impacted the hydrological cycle and is predicted to further impact the frequency, distribution, and intensity of precipitation events, resulting in more flooding in certain regions (high confidence). Due to differing flood drivers and regional exposure, there is medium confidence and medium agreement in the general flood attribution to climate change. {2.1, 2.2, 2.3, 2.4} 

Agriculture and urban infrastructure are among the most vulnerable sectors impacted by flooding (very high confidence). Agricultural processes are impacted by flooding, threatening crop yields through runoff, polluted water sources, and compromised soils; threatening human health and putting pressure on socioeconomic systems. Urban infrastructure is both a driver and an impact of flooding (medium confidence). Urban sprawl increases the vulnerability of natural systems to manage storm surge, and urban infrastructure can subsequently be damaged by flooding. {2.1, 2.2, 2.3, 3.1, 3.2, 3.3} 

Flooding poses cascading risks to environmental, economic, social, and governmental systems necessitating socio-political attention in Europe. (high confidence). Flood risk and damage threaten the lives of people, particularly in coastal and low-lying regions. Therefore, adaptation and mitigation measures of governments worldwide are of high priority. Governing bodies in Europe can continue to evaluate and address the cascading environmental, economic, social, and governmental systems involved in the preparedness and implementation of flood management. {2.1, 2.2, 2.3, 2.4, 3.1, 3.2, 3.3, 3.4, 3.5} 

Vulnerability to flooding in Europe varies between locales  (high confidence) based on sensitivity and risk of environmental circumstances, physical geography, and socioeconomic factors. (high confidence) Both urban and rural areas are susceptible to floods and experience different challenges in terms of adaptability. {3.1, 3.2, 3.3, 3.4, 4.2, 4.3} 

Successful adaptation requires mixed methods, including a mix of gray, blue, and green infrastructure (high confidence). Adaptation planning and implementation should be swift and ongoing to mitigate future risks (high confidence). {4.1, 4.2, 4.3, 4.4, 4.5}

Continued research and development of hydrological modeling and technological solutions will support overall adaptation efforts (high confidence). Hydrological modeling can help European cities, towns, and states better adapt to climate change-induced flooding by assessing effective measures and solutions at the local scale (high confidence). Utilizing historical local knowledge of extreme weather events helps communities implement appropriate adaptation measures (medium confidence). {4.3, 4.4, 4.5} 

Nature-based flood adaptation measures should be urgently implemented across multiscalar and multidimensional domains (high confidence). Nature-based measures are effective for medium and smaller flood events (medium confidence, high agreement) with uncertainty regarding how they can help cities adapt to larger flood events (medium confidence, low agreement). {4.1, 4.2, 4.3, 4.4, 4.5} 

Flood adaptation measures require multi-level governance with national oversight and regional planning and implementation (medium confidence). Flood adaptation requires governance and participation from various levels and stakeholders — from national governments to local officials and the public. {4.1, 4.2, 4.3, 4.4, 4.5} 

INTRODUCTION 

1.1 Point of Departure 

This chapter is part of Working Group II (WGII) contribution to the Seventh Assessment Report (AR7) of ‘Impacts, Adaptation, and Vulnerability’ of the Intergovernmental Panel on Climate Change. This chapter outlines the current landscape of flooding in Europe with a particular focus on climate change and floods in Europe covering peer-reviewed papers published between 2019 and September 2023. More detailed methodology is outlined in Appendix B. While further outlined in WGI, there is high agreement and medium-high evidence that human-induced climate change and coupled events of sea level rise, increase in precipitation, and extreme weather events result in more frequent and higher flooding impact in certain regions of Europe (IPCC, 2022). Hydrological and climatic assessments have documented global and regional flooding impacts attributed to climate change, including flood/storm-induced damages inland and in coastal areas. However, attributing flooding to changes in precipitation because of anthropogenic climate change is a limited approach because precipitation is among many factors that can lead to flooding (IPCC, 2022). Such events damage cities and infrastructure, as well as rural areas and agriculture, impacting the health and well-being of people. The first section of this chapter provides relevant definitions and outlines the relationship between climate change and flooding. The second section documents the observed and projected impacts and risks of floods in Europe, including relevant information from previous reports as well as the most pertinent publications from the state-of-the-art literature review on Flooding in Europe and the search strings ‘impact’ and ‘adaptation’. The third section outlines the exposure and vulnerability of communities in Europe with a specific focus on urban infrastructure and socioeconomic aspects as the literature review revealed a scientific focus on both topics. Refer to Appendix B for rationale and justification around the scope of this report and included domains. The fourth section considers adaptation measures and enabling conditions. Europe is a diverse continent geographically and sociopolitically, therefore the continent has been divided into four sub-geographical categories Northern Europe (NEU,) Eastern Europe (EEU,) Western and Central Europe (WCE,) and Southern Europe (SEU,) consistent with the methodology used in earlier IPCC Reports (IPCC, 2022). 

1.2 Relevant Definitions 

Given the multiscalar challenges of measuring flood areas, changes in precipitation and flow often serve as proxies for understanding and linking flooding to natural and artificial systems (IPCC, 2021). This report is a synthesis of a variety of multiscalar, multimodal flood types to capture the variety of flood that exists in Europe. AR6 WGI defined floods as the “inundation of normally dry land, which can be classified into types eg. pluvial flood, flash floods, river floods, groundwater floods, surge floods, coastal floods. These types depend on the space, time scales, and the major factors and processes involved” (IPCC, 2021). 

1.3 Flooding and Climate Change 

Climate change coupled with land use change increases the vulnerability of flooding events and an overall increase in exposure and risk to flooding-related events (IPCC, 2021). Present observations reflect an increase in atmospheric and sea temperatures as outlined by WGI and continued urbanization, intensification of land use, and high fossil fuel emissions further exacerbate climate-change-related hazards, including flooding. When the temperature of the atmosphere rises, it holds up to 10% more water vapor, increasing the intensity and frequency of extreme rainfall events (Angra & Sapountzaki, 2022; IPCC, 2021). For example, over the past 50 years, high-intensity precipitation has increased on the Spanish Mediterranean coast at the same time the area has seen rapid urbanization in flood-prone land (Ribas et al., 2020). Anthropogenic climate change will continue to threaten human-ecological systems unless urgent and widespread mitigation occurs (IPCC, 2021). Strategic adaptation of  pre-existing structures should include future-oriented and nature-based flood adaptation measures (Badura et al., 2021). 

OBSERVED AND PROJECTED IMPACTS AND RISKS

2.1 Observed Increases in Floods 

Observed records show an increase in the frequency and intensity of flooding events in Europe due to climate-related impacts (medium agreement) (Angra et al., 2022; Mourand et al., 2022; Senko et al. 2022; Venvik et al. 2020; Laino et al. 2023). Rising global temperatures have intensified the water cycle, causing more intense rainfall events, prolonged periods of heavy rainfall, and increased snowmelt during winter months (Lastrada et al, 2021; Sassi et al., 2019). Exposure to riverine flash flood and pluvial diffused floods have likely increased especially in WCE and SEU (Paprotny et al., 2018). While the direct cause of floods is not universally attributed to anthropogenic climate change, global trends illustrate an increase in flooding that can be attributed to climate-related factors (Angra et al. 2022; Broderick et al. 2019; Lane et al., 2021). The risk and severity of flooding are geographically dependent on ice, soil character, wetness, urbanization, drainage infrastructure (such as dikes, dams, reservoirs, and stormwater retention), and overall socioeconomic capacities (IPCC, 2022). While there is low confidence about peak flow trends over the past decades on the global scale, there are regions experiencing increases, including north-western Europe, and regions experiencing decreases including parts of the Mediterranean (IPCC, 2021). River flood hazards in WCE and the UK have increased by 11% per decade from 1960 to 2010 and continue to rise today (IPCC, 2021). Flooding can have direct human and ecological impacts through infrastructure damage, drowning, hypothermia, electrocution, and the risk of getting hit by floating objects (Mourand et al., 2022). Additionally, flooding can have indirect threats like transporting contaminated water and transmission of disease, threatening public health (Nimac et al., 2022; Paterson et al., 2018). Human infrastructure development and rerouting of natural waterways are both drivers and exacerbators of flood impact (Angra et al. 2022; Essenfelder et al; Fitobar et al. 2022; Zuccaro et al. 2021). The combination of land-use changes, and an increase in the frequency and intensity of precipitation events lead to flooding vulnerabilities. 

2.2 Predicted Models and Risks 

Hydrological and atmospheric models seek to increase the strength of evidence in predicting hydrological flow and the developments in such technologies can support mitigation and adaptation measures. Of the n=66 articles examined for this chapter n=25 were models that mapped a variety of hydrological and climate models. The structural and methodological diversity of the models and simulations assessed in this chapter yield cascading uncertainties and levels of confidence (IPCC, 2021). With an effort to reduce vulnerability, increase mitigation efforts, and adaptive management, models can serve as a tool for understanding future scenarios. Hydrological models can be coupled with emissions scenarios to give an idea of the potential impacts and disturbances floods may have at regional levels (Jeantet et al. 2022; Mentaschi et al., 2020; Olefs et al. 2021; Nigussie et al. 2019). Projected changes in the hydrological cycle make societies more vulnerable to catastrophes (Essenfelder, et al., 2022 ; Rosbjerg et al., 2022). These changes will increase flood risk in some countries, depending on the area’s vulnerability (Le Floch et al., 2022; Angra & Sapountzaki, 2022). Climate change will also follow different sub-regional patterns, for instance, there are regions within Greece that will experience more drought, but others that will experience more rainfall (Angra & Sapountzaki, 2022). With high agreement and medium evidence, it is understood that limiting warming to 1.5 ℃  would limit risks of increases in heavy precipitation events on a global scale and in several regions compared to conditions at 2 ℃ global warming (IPCC, 2018). Direct damages from coastal flooding using economic risk models are projected to cost 13-39 billion EUR by 2050 between 2℃ and 2.5 ℃ GWL and 93-960 billion EUR by 2100 with a 2.5 ℃ to 4.5 ℃  GWL (IPCC, 2021). According to Statista and a report conducted by the European Commission and the Joint Research Center, a 3℃ warming scenario and no adaptation would put 482 thousand people in Europe at risk of river floods, costing upwards of 48 billion dollars in flood damage annually. In contrast, a best-case scenario under a 1.5 ℃ warming scenario and moderate mitigation would put 92 thousand people in Europe at risk of river floods and cost 8.6 billion dollars in flood damage annually (Statista 2023).

2.3 Infrastructure and Agriculture 

Urban infrastructure development is both a driver of flooding and a vulnerability to flooding-related events (medium confidence). Increased urbanization, construction of seawalls, and diverting of natural hydrologic infrastructure stresses hydraulic retention systems and can lead to high flow surges and flood hazards (Broderick, 2019; Kumar et al., 2020; Le Floch, 2022). Changes in the hydrological cycle and flooding events may disrupt water access (Lastrada et al., 2021). Calculating and planning water access can be increasingly difficult. Local vulnerabilities include different access to water. In Spain, the demand might be bigger than the supply in spring and summer, and the opposite during winter (Lastrada et al., 2021). Dry and hot summers and wet winters create difficulties in planning access to water (Lastrada et al., 2021). For example, flooding caused by climate change is projected to increase in Denmark, which could cause an increase in groundwater levels, creating instability in infrastructure and groundwater infiltration in city sewer systems (Rasmussen et al., 2023). Furthermore, current agricultural processes are sensitive to climate-change, and related hazards of flooding further exacerbate agricultural vulnerabilities. Intense rainfall events can damage crops and subsequent flooding and runoff flows can reduce crop yields and result in substantial economic losses (high confidence) (Peltonen et al., 2021; Senko et al.. 2022; Zhlinmma et al., 2022). Indirect and telecoupled agricultural impacts are further exacerbated by flood hazards (Epting et al., 2021; Liu et al., 2022). Widespread adaptation to flood-resistant crops and nature-based stormwater retention is needed to safeguard agricultural systems. 

2.4 Socio-Economic Impact  

Flooding also poses myriad socioeconomic risks (high confidence) as both acute and chronic floods can impact the economy, health, and livelihoods of people (Sassi et al., 2019; Statista, 2023). Flooding can lead to loss of employment, lack of access to childcare and school services, and increased domestic violence (Mason et al., 2021). Damaged infrastructure and transportation systems can freeze economic activity, such as in areas that rely on tourist activities (Marta et al., 2020). Flooding poses a direct threat to public health and both direct and indirect health implications impact the most vulnerable groups (Henriksen et al., 2022; Linares et al., 2020; Ribas et al., 2020). Furthermore, flooding and subsequent stormwater damage can introduce disease and spread disease through contaminated water (Statista, 2023). Stagnant waters can become breeding grounds for viral and parasitic diseases, threatening the livelihoods of people who rely on the water for consumption and sanitation. The river flash flood in Germany in 2021 resulted in almost 200 casualties and tens of thousands of properties damaged (Essenfelder et al., 2022). Flooding can result in a variety of cascading public health implications, including mental health challenges associated with the stress of flood-related events (Statista, 2023). Annual economic losses related to flooding are expected to increase in the future (Sassi et al. 2019). The tourism industry in particular experiences a direct hit from flooding, which can be an important source of income for many Europeans, especially in coastal and alpine areas. Facing economic risks can create discomfort and decreased health for the local populations (Statista, 2023). Even with installed adaptation measures, risks will remain large and costly. In a scenario of zero adaptation measures by 2080 and with 3 ° C warming, the average annual loss will be 17 times bigger than today (Sassi et al., 2019). With adaptation measures, it would still be 10 times larger. Annual economic losses in Europe would be much greater in 2080 than in 1970. (Sassi et al., 2019). Property damage might become a common problem (Nigussie & Altunkaynak, 2019). 

VULNERABILITY

3.1 Exposure to Floods

Numerous European countries experience varying degrees of vulnerability to flood hazards, with a complex interplay of factors affecting the severity of impacts, particularly in regions with higher socioeconomic challenges (Fronzek et al., 2019; Żmudzka et al., 2019). Physical exposure to flooding varies geographically in temporal and spatial distribution (high confidence) (Linares et al., 2020; Ribas et al., 2020). Regions characterized by higher socioeconomic vulnerability are disproportionately affected by flooding, especially in combination with physical exposure (Linares et al. 2020; Ribas et al., 2020). Regional disparity highlights that low-lying cities, coastal regions, and highly urbanized regions with nonpermeable infrastructure are the most impacted by flooding (IPCC, 2022). 50 million Europeans live in low-elevation coastal zones within 10 m above mean sea level where risk is high (IPCC, 2022). Moreover, in mid-and high latitudes, such as in Greenland, Iceland, and the Alps, precipitation is predicted to increase, which will yield an increasing risk of flash flooding and urban flooding casualties (IPCC, 2007). The Mediterranean is particularly vulnerable to climate change due to its rapid urbanization, and myriad coupled climate vulnerabilities such as heat waves, droughts, and torrential rain events (Angra & Sapountzaki, 2022; Linares et al., 2020; Sassi et al., 2019; Zitties et al., 2022; Ribas et al. 2020). Mediterranean coastal areas (SEU) are especially vulnerable to extreme rainfall and flooding, partially due to the water vapor of the Mediterranean Sea (Angra & Sapountzaki, 2022). The geography of the Mediterranean makes the region particularly susceptible to flooding especially in the winter months (Angra & Sapountzaki, 2022). Varying climatic, environmental, and socioeconomic conditions determine the impact resilience of flood-prone regions. Stochastic rainfall models under various climate scenarios reflect an increase in fluvial and pluvial flooding with annual temporal alterations in traditional hydrological patterns. Already vulnerable areas, such as coastal areas, will be further affected by increasing climate-related impacts (Laino & Iglesias, 2023). 

3.2 Urban Flooding Vulnerability 

Rapid urbanization, which is expected to continue, drives an increasing vulnerability to European cities due to its effects on flood exposure of infrastructure (high confidence) (Axelsson et al., 2021; Essenfelder, et al., 2022; Nimac et al., 2022). More than 70% of Europeans live in urban areas (Essenfelder, et al., 2022). With intensified urbanization, many densely populated areas, particularly cities in low-lying areas, become increasingly vulnerable to flooding events (Axelsson et al., 2021; Essenfelder, et al., 2022; Nimac et al., 2022). Human changes in land use have increased the vulnerability to floods in most areas compared to the nineteenth century (Ribas et al. 2020). In urban areas, populations rely on existing infrastructure which is usually not well adapted to climate change and flooding events, as seen in examples from previous floods in Warsaw and Zagreb (Axelsson et al. 2021; Nimac et al., 2022; Żmudzka et al., 2019). Continued rapid and widespread urbanization makes flood-prone areas increasingly vulnerable (Ribas et al., 2020). Densification of urban areas entails increasing amounts of hard surfaces. As a result, cities become extremely vulnerable to especially flash floods that come with dramatic societal impacts such as loss of life (Fitobór et al., 2022; Ribas et al. 2020; Zitties et al., 2022). 

Urban development, infrastructure, and physical properties of urban areas play a role in the vulnerability to flood risk. The increase in non-permeable surfaces, closed basins, and transportation-related infrastructure matter in a city’s susceptibility to floods, as well as natural characteristics such as soil type and topography (Żmudzka et al., 2019). Furthermore, cities with old and poorly adapted stormwater and drainage systems are more vulnerable to flooding than others, since they were built for lower water flow (Nimac et al. 2022; Żmudzka et al., 2019). Coastal areas, such as in Spain, experienced rapid urbanization in the last two decades indicating an increased vulnerability (Ribas et al., 2020). Beach areas will be strongly affected by coastal flooding, increasing the vulnerabilities of these areas (Laino & Iglesias, 2023). Lastly, further research and data is needed in order to make secure vulnerability assessments that lay the groundwork for adaptive measures (Żmudzka et al., 2019). Socioeconomic aspects could be further investigated in research to examine the density and vulnerability of certain regions and vulnerable populations (Żmudzka et al., 2019). 

3.3 Vulnerable Populations 

Climate change-related hazards exacerbate the vulnerability of certain population groups, in particular socioeconomically disadvantaged groups and those living in high-risk regions (high confidence) (IPCC 2022; Laino & Iglesias, 2023; Ribas et al., 2020). As of 2020, 70-90% of losses from flooding in Europe are linked to socioeconomic development (Ribas et al., 2020). Vulnerability cannot be reduced only to the measurement of monetary damages, it is also manifested unequally between different intersectional aspects such as class, ethnicity, and gender (Ribas et al., 2020). Coastal communities are highlighted as among the most vulnerable to climate-induced flooding hazards in Europe (Laino & Iglesias, 2023). Coastal flooding poses a major threat to communities and their livelihoods, particularly UNESCO World Heritage sites (Angra & Sapountzaki, 2022; Le Floch et al., 2022). Greece is a Mediterranean country rich in historical and cultural sights, where these face risks due to extreme weather events (Mentzafou & Dimitriou, 2022). Archaeological sites are especially vulnerable to flooding, and these sites are usually less frequently monitored for flood management purposes (Mentzafou & Dimitriou, 2022). From earlier catastrophes, general knowledge of the risk facing cultural sights has risen (Mentzafou & Dimitriou, 2022). 

The population of the Mediterranean area is among Europe’s most vulnerable (high confidence). Vulnerable sectors of the region are those living in coastal areas, elderly, individuals with chronic diseases, and those in poor socioeconomic situations (Ribas et al., 2020). These groups are more susceptible to the effects of extreme weather events such as flooding (Linares et al., 2020; Ribas et al. 2020). Furthermore, the vulnerability of human health in the Mediterranean region increases with hydrological changes (Linares et al., 2020). Increased precipitation in warm areas such as SEU, can lead to an increased risk of diseases spreading, such as the West Nile Virus (Linares et al., 2020). Refugees are among the groups with the worst socioeconomic situations (Linares et al., 2020). They are especially vulnerable to flooding, as they are often placed in centers badly adapted to severe weather events and heavy precipitation, often in SEU. In these areas, diseases spread fast and these groups suffer from poor access to healthcare. Certain countries in the Mediterranean region can provide healthcare for migrants, although other healthcare systems might not be prepared for increased climate migration (Linares et al., 2020). 

3.4 Vulnerability in Agriculture

Agriculture is increasingly vulnerable to flooding due to coupled weather-related events such as droughts and diseases (high confidence) (Peltonen-Sainio et al., 2021; Senko et al., 2022; Zhllima et al., 2022). Vulnerability of crops to water depends on geographical conditions (Peltonen-Sainio et al., 2021; Zhllima et al., 2022). Some crops in low-land areas are projected to be negatively affected by more precipitation, while others are estimated to benefit from more water (Zhllima et al., 2022). The effects of increased precipitation have cascading effects on food security, the economy, and the  livelihoods of people (Henriksen et al., 2022; Zhllima et al., 2022). For instance, increased soil moisture during winter can lead to soil compaction which decreases the drainage capacity, making it more susceptible to flooding (Henriksen et al., 2022). Data from a case study in Croatia indicate that floods most often occur in the plant germination phase, meaning that the seeds get damaged in an early stage, which could mean a severe reduction in yields (Senko et al., 2022). Around 80% of the farmers experience flooding due to excessive rain events, especially those who are situated close to the Danube River (Senko et al., 2022). Agricultural practices and geographic vulnerabilities directly linked to flooding need strategic and widespread mitigation and adaptation strategies. 

3.5 Economic Vulnerability Related to Flooding

Certain areas in Europe are more economically vulnerable to flooding events, particularly those places where economies are dependent on coastal activities such as tourism or agriculture (high confidence)  (Linares et.al. 2020; Ribas et al., 2020). Future economic loss depends on the success of adaptation measures and socioeconomic impacts, and losses differ vastly between regions (Sassi et al. 2019). Areas where tourism is a big part of the local economy, such as coastal cities in Spain and Portugal, and recreational regions in Austria risk high economic and cultural loss due to flooding events (Laino & Iglesias, 2023; Nigussie & Altunkaynak, 2019; Pröbstl-Haider et al., 2021). Industrial areas near the coastlines or riverbanks also risk being damaged (Laino & Iglesias, 2023). Less snow in the winter and earlier glacier melt in the spring changes the timing for the peak runoff, impacting water availability and accessibility for agriculture and human use (Laino & Iglesias, 2023; Lastrada et al., 2021). Changes in the hydrological cycles of European mountainous regions have cascading effects on the vulnerability of the regions that depend on them for water access (Fuso et al. 2021; Lastrada et al., 2021). The hydrological changes of alpine rivers affect for instance lakes that serve multipurposes, such as Lake Como in Italy where water has to be lowered to prevent flood risk (Fuso et al., 2021). This adaptation measurement has socioeconomic consequences related to irrigation for agriculture, hydropower, and catchment purposes (Fuso et al., 2021). Competing interests clash in the face of vulnerability, illustrating an important need for collaborative, multi-governance adaptation measures (Fuso et al., 2021). 

ADAPTATION MEASURES AND ENABLING CONDITIONS 

4.1 Current Adaptation 

Current adaptation measures in Europe are insufficient to address the growing flood risks that regions face (high confidence) (Kourtis et al., 2021; Kumar et al., 2020). Existing measures in Europe focus on gray infrastructure and include a mix of green-blue-gray infrastructure, based on cases provided by the reviewed literature. Gray infrastructure is traditional flooding management, including measures such as drainage pipes and sewer networks (Rasmussen et al., 2023, Fitobór et al., 2022). Green and blue infrastructure are a part of nature-based solutions that include ecosystem restoration and local infrastructure including green roofs, permeable surfaces, and rain gardens, and are starting to be more widely adopted (Kourtis et al., 2021; Rasmussen et al., 2023). Nature-based solutions (NBS), a holistic adaptation approach, utilize both engineering and ecosystem components (Kumar et al., 2020). Gray infrastructure such as urban drainage is already widely used in cities across the world, but the ability of gray infrastructure to help European cities adapt to current flooding challenges is not strong enough (high confidence, medium agreement) (Fitobór et al., 2022; Kumar et al., 2020; Żmudzka et al., 2019). Gray adaptation such as traditional stormwater management and drainage pipes are insufficient to address larger-scale challenges (Fitobór et al., 2022). Studies indicate strong evidence that combining different approaches such as gray adaptation with green can better equip cities to adapt to floods (Kourtis et al., 2021; Pugliese et al., 2022).

4.2 Future Adaptation Options and Their Feasibility

Nature-based-solutions such as the expansion of green and blue infrastructure have the potential to provide measures Europe needs to manage flood risk, such as a 38% reduction in runoff when utilizing green roofs, rain gardens, and porous pavements (Rosenberger et al., 2021). There is strong evidence that NBS, coupled with hydrological and weather modeling, can help European regions adapt to flooding (high confidence) (Fitobór et al., 2022; Mourad et al., 2022). Nature-based measures exist as a wide variety of adaptations, as seen in Figure 1 in Appendix E. Urban areas would benefit from the addition of nature-based solutions such as green roofs, flood-tolerant flora, and rain gardens in both public and private spaces (Badura et al., 2021). Other factors such as urban densification also affect the mix of solutions (Rosenberger et al., 2021). NBS are considered cost-effective (high confidence) as opposed to traditional gray infrastructure, as NBS require fewer infrastructure and management costs while saving the public long-term through the adaptation measures (Axelsson et al., 2021; Mentzafou & Dimitriou, 2022). There is public value to nature-based solutions, based on experience with current climate change extremes and preference over business-as-usual (Badura et al., 2021). Additionally, an early warning system is an adaptation measure that alerts the local community of extreme flood events (Laino & Iglesias, 2023). Though these measures currently exist for some cities or regions, they could be improved to better transmit the warnings to the population through more effective means, as seen by the 2018 flood in Majorca, Spain, where a flash flood event caused 13 deaths and €17.5 million in damages despite warning systems (Ribas et al., 2020). For warning measures to be effective, warnings need to be targeted and locally implemented (Olefs et al., 2021). 

Hydrological modeling both assists with understanding the state of flooding, and which adaptation measures can be most effective in that area (Kourtis et al., 2021; Rasmussen et al., 2023). These models can assist diverse stakeholders such as policymakers, researchers, and urban planners to implement the best flooding adaptation measures for the region. Creating climate information for local levels while engaging users across levels allows for the information to be understood by a wider audience (Kumar et al., 2020). Utilizing both NBS and hydrological modeling is seen in the case of Słupsk in Northwestern Poland in WCE. Słupsk has a combined sewage system, meaning in extreme rainfall, a mixture of sewage and rainwater is released into the river due to an overloaded system (Fitobór et al., 2022). Researchers examined not only how hydrological modeling would indicate the increase of flooding, but also how to utilize modeling to see what solutions work best for the region, including NBS such as rain gardens (Fitobór et al., 2022). 

From an agricultural perspective, irrigation and drainage infrastructure improvements are needed to adapt to flooding and other climate change impacts (Senko et al., 2022; Zhllima et al., 2022).  Prioritizing drainage infrastructure also positively contributes to soil health (Peltonen-Sainio et al., 2021). Planting crops that are more tolerant of flooding is another adaptation measure available for farmers (Senko et al., 2022). Insurance programs in case of crop failure, coupled with these other measures should also be considered (Zhllima et al., 2022). 

4.3 Local Data and Knowledge in Modeling to Avoid Maladaptation

Using local knowledge and differences for flooding adaptation can help prevent maladaptation by reducing overgeneralizations (Marta et al., 2020).  Local data is lacking in several regions of Europe, often in rural areas, and is an important part of adaptation planning (Angra & Sapountzaki, 2022; Laino & Iglesias, 2023; Żmudzka et al, 2019). An assessment of ten coastal cities in Europe shows that there is a large lack of data on past extreme events, which is needed to develop suitable adaptation programs (Laino & Iglesias, 2023). Systemized data gives clarity in planning for different contextual settings across national regions, such as microclimate and different hydrological patterns (Żmudzka et al, 2019). There is strong evidence that avoiding ineffective adaptation measures can be countered by modeling, which could help stakeholders find solutions that fit their specific region and area (high confidence) (Fitobór et al., 2022; Kumar et al., 2020). A study in Warsaw, Poland used meteorological measuring stations and interventions from the fire department to determine urban flood hazards, which can be used to help equip Warsaw city planners with the capacity to better adapt (Żmudzka et al, 2019). This study demonstrates the capacity of local stakeholders to acquire meteorological data from existing sources (Żmudzka et al, 2019). Analytical studies with local data can support how cities and regional municipalities can adapt most effectively to reduce their vulnerability (Angra & Sapountzaki, 2022). Furthermore, stakeholders can figure out how much and where green infrastructure is needed in cities using a dynamic planning method that includes extreme weather modeling (Fitobór et al., 2022). Data needs to be standardized to achieve effective modeling, though, so that future modeling can occur and data is accessible (Kumar et al., 2020). 

4.4 Limits to Adaptation

A one-size-fits-all approach to adaptation for flooding is not effective given the diverse and unique challenges across subregions of Europe (Axelsson et al., 2021; Marta et al., 2020; Ribas et al., 2020). Cities and regions need to adapt their measures and approaches rather than mimicking the solutions of another region (Axelsson et al., 2021). A local approach also needs to be considered at the national-local-regional level. Creating flood risk scores at the national level can result in regions over or under-adapting (Broderick et al., 2019). Though there is strong evidence that NBS provides adaptation for flooding events, there is disagreement about how the degree of flooding impacts the effectiveness of nature-based solutions and green infrastructure. NBS for an archeological site in SEU was effective for small and medium-sized flood events, but more susceptible to large events based on modeling (Mentzafou & Dimitriou, 2022). NBS will provide smaller adaptation impacts for larger flooding-induced rain events based on a study in WCE (Fitobór et al., 2022). Other studies showed that afforestation provides effective mitigation measures for flooding for moderate and extreme events based on hydrological modeling in NEU (Mourad et al., 2022). One limitation to agricultural adaptation is that many farmers lack the financial capacity to implement adaptation measures (Zhllima et al., 2022). Additionally, 37% of farmers surveyed in Albania indicated that they would implement adaptive measures, but do not have enough information or knowledge (Zhllima et al., 2022). Better financial support as well as more information regarding the costs and benefits of various adaptation measures is needed for more robust agricultural adaptation against flooding (Peltonen-Sainio et al., 2021). 

4.5 Enabling Conditions

Flood adaptation requires governance and participation from various levels and stakeholders - from national governments to local officials and civil engagement and support (Kumar et al., 2020). Central governments should be included in support and risk management due to risks and sector-wide exposures as well as the ability to provide resources to develop products for modeling and data management (Orr et al., 2021). Local officials can implement the solutions that work best for the area. Using historical local knowledge of extreme weather events such as floods and forest fires can help communities connect these extreme events to climate change, and further what adaptation measures would work (Angra & Sapountzaki, 2022). Local knowledge can then be utilized to create a collaborative process that includes expertise from the local area (Laino & Iglesias, 2023). A study from Prague suggests that NBS could be welcomed by the public if planners communicate the double-win for climate change and biodiversity (Badura et al., 2021). Individual cities can utilize different approaches and mixes of adaptation. Utilizing NBS requires a holistic approach with a mix of policy instruments. 

REFERENCES 

Angra, D., & Sapountzaki, K. (2022). Climate Change Affecting Forest Fire and Flood Risk—Facts, Predictions, and Perceptions in Central and South Greece. Sustainability, 14(20), 13395. https://doi.org/10.3390/su142013395

Axelsson, C., Soriani, S., Culligan, P., & Marcotullio, P. (2021). Urban policy adaptation toward managing increasing pluvial flooding events under climate change. Journal of Environmental Planning and Management, 64(8), 1408–1427. https://doi.org/10.1080/09640568.2020.1823346

Badura, T., Krkoška Lorencová, E., Ferrini, S., & Vačkářová, D. (2021). Public support for urban climate adaptation policy through nature-based solutions in Prague. Landscape and Urban Planning, 215, 104215. https://doi.org/10.1016/j.landurbplan.2021.104215

Broderick, C., Murphy, C., Wilby, R. L., Matthews, T., Prudhomme, C., & Adamson, M. (2019). Using a Scenario‐Neutral Framework to Avoid Potential Maladaptation to Future Flood Risk. Water Resources Research, 55(2), 1079–1104. https://doi.org/10.1029/2018WR023623

Christidis, N., & Stott, P. A. (2021). The influence of anthropogenic climate change on wet and dry summers in Europe. Science Bulletin, 66(8), 813–823. https://doi.org/10.1016/j.scib.2021.01.020

Díaz-Sanz, J., Robert, S., & Keller, C. (2020). Parameters influencing run-off on vegetated urban soils: A case study in Marseilles, France. Geoderma, 376, 114455. https://doi.org/10.1016/j.geoderma.2020.114455

Doroszkiewicz, J., Romanowicz, R., & Kiczko, A. (2018). The Influence of Flow Projection Errors on Flood Hazard Estimates in Future Climate Conditions. Water, 11(1), 49. https://doi.org/10.3390/w11010049

Epting, J., Michel, A., Affolter, A., & Huggenberger, P. (2021). Climate change effects on groundwater recharge and temperatures in Swiss alluvial aquifers. Journal of Hydrology X, 11, 100071. https://doi.org/10.1016/j.hydroa.2020.100071

Escalante, E. F., Sauto, J. S. S., & Gil, R. C. (2019). Sites and Indicators of MAR as a Successful Tool to Mitigate Climate Change Effects in Spain. Water, 11(9), 1943. https://doi.org/10.3390/w11091943

Essenfelder, A. H., Bagli, S., Mysiak, J., Pal, J. S., Mercogliano, P., Reder, A., Rianna, G., Mazzoli, P., Broccoli, D., & Luzzi, V. (2022). Probabilistic Assessment of Pluvial Flood Risk Across 20 European Cities: A Demonstrator of the Copernicus Disaster Risk Reduction Service for Pluvial Flood Risk in Urban Areas. Water Economics and Policy, 08(03), 2240007. https://doi.org/10.1142/S2382624X22400070

Faggian, P. (2021). Future Precipitation Scenarios over Italy. Water, 13(10), 1335. https://doi.org/10.3390/w13101335

Fitobór, K., Ulańczyk, R., Kołecka, K., Ramm, K., Włodarek, I., Zima, P., Kalinowska, D., Wielgat, P., Mikulska, M., Antończyk, D., Krzaczkowski, K., Łyszyk, R., & Gajewska, M. (2022). Extreme weather layer method for implementation of nature-based solutions for climate adaptation: Case study Słupsk. Science of The Total Environment, 842, 156751. https://doi.org/10.1016/j.scitotenv.2022.156751

Floren, A., Horchler, P. J., & Müller, T. (2022). The Impact of the Neophyte Tree Fraxinus pennsylvanica [Marshall] on Beetle Diversity under Climate Change. Sustainability, 14(3), 1914. https://doi.org/10.3390/su14031914

Fronzek, S., Carter, T. R., Pirttioja, N., Alkemade, R., Audsley, E., Bugmann, H., Flörke, M., Holman, I., Honda, Y., Ito, A., Janes-Bassett, V., Lafond, V., Leemans, R., Mokrech, M., Nunez, S., Sandars, D., Snell, R., Takahashi, K., Tanaka, A., … Yoshikawa, M. (2019). Determining sectoral and regional sensitivity to climate and socio-economic change in Europe using impact response surfaces. Regional Environmental Change, 19(3), 679–693. https://doi.org/10.1007/s10113-018-1421-8

Fuso, F., Casale, F., Giudici, F., & Bocchiola, D. (2021). Future Hydrology of the Cryospheric Driven Lake Como Catchment in Italy under Climate Change Scenarios. Climate, 9(1), 8. https://doi.org/10.3390/cli9010008

Gu, L., Chen, J., Yin, J., Slater, L. J., Wang, H., Guo, Q., Feng, M., Qin, H., & Zhao, T. (2022). Global Increases in Compound Flood‐Hot Extreme Hazards Under Climate Warming. Geophysical Research Letters, 49(8), e2022GL097726. https://doi.org/10.1029/2022GL097726

Hanlon, H. M., Bernie, D., Carigi, G., & Lowe, J. A. (2021). Future changes to high impact weather in the UK. Climatic Change, 166(3–4), 50. https://doi.org/10.1007/s10584-021-03100-5

Harvey, B., & Shaffrey, L. (2021). How will climate change impact North Atlantic storms? Weather, 76(10), 329–329. https://doi.org/10.1002/wea.4075

Henriksen, H., Schneider, R., Koch, J., Ondracek, M., Troldborg, L., Seidenfaden, I., Kragh, S., Bøgh, E., & Stisen, S. (2022). A New Digital Twin for Climate Change Adaptation, Water Management, and Disaster Risk Reduction (HIP Digital Twin). Water, 15(1), 25. https://doi.org/10.3390/w15010025

Iepema, G., Hoekstra, N. J., De Goede, R., Bloem, J., Brussaard, L., & Van Eekeren, N. (2022). Extending grassland age for climate change mitigation and adaptation on clay soils. European Journal of Soil Science, 73(1), e13134. https://doi.org/10.1111/ejss.13134

IPCC, 2007: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 996 pp.

IPCC, 2018: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I. Gomis, E. Lonnoy, T. Maycock, M. Tignor, and T. Waterfield (eds.)]. 

IPCC, 2021: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2391 pp. doi:10.1017/9781009157896.

IPCC, 2022: Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press. Cambridge University Press, Cambridge, UK and New York, NY, USA, 3056 pp., doi:10.1017/9781009325844.

Jeantet, A., Thirel, G., Jeliazkov, A., Martin, P., & Tournebize, J. (2022). Effects of Climate Change on Hydrological Indicators of Subsurface Drainage for a Representative French Drainage Site. Frontiers in Environmental Science, 10, 899226. https://doi.org/10.3389/fenvs.2022.899226

Kay, A. (2022). Differences in hydrological impacts using regional climate model and nested convection-permitting model data. Climatic Change, 173(1–2), 11. https://doi.org/10.1007/s10584-022-03405-z

Kay, A. L., Griffin, A., Rudd, A. C., Chapman, R. M., Bell, V. A., & Arnell, N. W. (2021). Climate change effects on indicators of high and low river flow across Great Britain. Advances in Water Resources, 151, 103909. https://doi.org/10.1016/j.advwatres.2021.103909

Kourtis, I. M., Bellos, V., Kopsiaftis, G., Psiloglou, B., & Tsihrintzis, V. A. (2021). Methodology for holistic assessment of grey-green flood mitigation measures for climate change adaptation in urban basins. Journal of Hydrology, 603, 126885. https://doi.org/10.1016/j.jhydrol.2021.126885

Kumar, P., Debele, S. E., Sahani, J., Aragão, L., Barisani, F., Basu, B., Bucchignani, E., Charizopoulos, N., Di Sabatino, S., Domeneghetti, A., Edo, A. S., Finér, L., Gallotti, G., Juch, S., Leo, L. S., Loupis, M., Mickovski, S. B., Panga, D., Pavlova, I., … Zieher, T. (2020). Towards an operationalisation of nature-based solutions for natural hazards. Science of The Total Environment, 731, 138855. https://doi.org/10.1016/j.scitotenv.2020.138855

Laino, E., & Iglesias, G. (2023). Extreme climate change hazards and impacts on European coastal cities: A review. Renewable and Sustainable Energy Reviews, 184, 113587. https://doi.org/10.1016/j.rser.2023.113587

Lane, R. A., Coxon, G., Freer, J., Seibert, J., & Wagener, T. (2022). A large-sample investigation into uncertain climate change impacts on high flows across Great Britain. Hydrology and Earth System Sciences, 26(21), 5535–5554. https://doi.org/10.5194/hess-26-5535-2022

Lane, R. A., & Kay, A. L. (2021). Climate Change Impact on the Magnitude and Timing of Hydrological Extremes Across Great Britain. Frontiers in Water, 3, 684982. https://doi.org/10.3389/frwa.2021.684982

Lastrada, E., Garzón-Roca, J., Cobos, G., & Torrijo, F. J. (2021). A Decrease in the Regulatory Effect of Snow-Related Phenomena in Spanish Mountain Areas Due to Climate Change. Water, 13(11), 1550. https://doi.org/10.3390/w13111550

Le Floch, N., Pons, V., Hassan Abdalla, E. M., & Alfredsen, K. (2022). Catchment scale effects of low impact development implementation scenarios at different urbanization densities. Journal of Hydrology, 612, 128178. https://doi.org/10.1016/j.jhydrol.2022.128178

Linares, C., Díaz, J., Negev, M., Martínez, G. S., Debono, R., & Paz, S. (2020). Impacts of climate change on the public health of the Mediterranean Basin population—Current situation, projections, preparedness and adaptation. Environmental Research, 182, 109107. https://doi.org/10.1016/j.envres.2019.109107

Liu, S., Pérez-Sánchez, J., Jimeno-Sáez, P., Alcalá, F. J., & Senent-Aparicio, J. (2022). A novel approach to assessing the impacts of dam construction on hydrologic and ecosystem alterations. Case study: Castril river basin, Spain. Ecohydrology & Hydrobiology, 22(4), 598–608. https://doi.org/10.1016/j.ecohyd.2022.08.004

Mastrandrea, M.D., C.B. Field, T.F. Stocker, O. Edenhofer, K.L. Ebi, D.J. Frame, H. Held, E. Kriegler, K.J. Mach, P.R. Matschoss, G.-K. Plattner, G.W. Yohe, and F.W. Zwiers, 2010: Guidance Note for Lead Authors of the IPCC Fifth Assessment Report on Consistent Treatment of Uncertainties. Intergovernmental Panel on Climate Change (IPCC). Available at <http://www.ipcc.ch>.

Marta, E., Guglielmo, R., Giuliana, B., Alessandra, B., Veronica, V., & Paola, M. (2020). Past and future hydrogeological risk assessment under climate change conditions over urban settlements and infrastructure systems: The case of a sub-regional area of Piedmont, Italy. Natural Hazards, 102(1), 275–305. https://doi.org/10.1007/s11069-020-03925-w

Martínez-Gomariz, E., Locatelli, L., Guerrero, M., Russo, B., & Martínez, M. (2019). Socio-Economic Potential Impacts Due to Urban Pluvial Floods in Badalona (Spain) in a Context of Climate Change. Water, 11(12), 2658. https://doi.org/10.3390/w11122658

Mentaschi, L., Alfieri, L., Dottori, F., Cammalleri, C., Bisselink, B., Roo, A. D., & Feyen, L. (2020). Independence of Future Changes of River Runoff in Europe from the Pathway to Global Warming. Climate, 8(2), 22. https://doi.org/10.3390/cli8020022

Mentzafou, A., & Dimitriou, E. (2022). Hydrological Modeling for Flood Adaptation under Climate Change: The Case of the Ancient Messene Archaeological Site in Greece. Hydrology, 9(2), 19. https://doi.org/10.3390/hydrology9020019

Meresa, H., Donegan, S., Golian, S., & Murphy, C. (2022). Simulated Changes in Seasonal and Low Flows with Climate Change for Irish Catchments. Water, 14(10), 1556. https://doi.org/10.3390/w14101556

Meresa, H., Murphy, C., & Donegan, S. E. (2023). Propagation and Characteristics of Hydrometeorological Drought Under Changing Climate in Irish Catchments. Journal of Geophysical Research: Atmospheres, 128(10), e2022JD038025. https://doi.org/10.1029/2022JD038025

Meresa, H., Murphy, C., Fealy, R., & Golian, S. (2021). Uncertainties and their interaction in flood hazard assessment with climate change. Hydrology and Earth System Sciences, 25(9), 5237–5257. https://doi.org/10.5194/hess-25-5237-2021

Molina, J.-L., Zazo, S., & Martín, A.-M. (2019). Causal Reasoning: Towards Dynamic Predictive Models for Runoff Temporal Behavior of High Dependence Rivers. Water, 11(5), 877. https://doi.org/10.3390/w11050877

Mourad, K. A., Nordin, L., & Andersson-Sköld, Y. (2022). Assessing flooding and possible adaptation measures using remote sensing data and hydrological modeling in Sweden. Climate Risk Management, 38, 100464. https://doi.org/10.1016/j.crm.2022.100464

Nigussie, T. A., & Altunkaynak, A. (2019). Impacts of climate change on the trends of extreme rainfall indices and values of maximum precipitation at Olimpiyat Station, Istanbul, Turkey. Theoretical and Applied Climatology, 135(3–4), 1501–1515. https://doi.org/10.1007/s00704-018-2449-x

Nilsen, I. B., Hanssen-Bauer, I., Dyrrdal, A. V., Hisdal, H., Lawrence, D., Haddeland, I., & Wong, W. K. (2022). From Climate Model Output to Actionable Climate Information in Norway. Frontiers in Climate, 4, 866563. https://doi.org/10.3389/fclim.2022.866563

Nimac, I., Cindrić Kalin, K., Renko, T., Vujnović, T., & Horvath, K. (2022). The analysis of summer 2020 urban flood in Zagreb (Croatia) from hydro-meteorological point of view. Natural Hazards, 112(1), 873–897. https://doi.org/10.1007/s11069-022-05210-4

O’Briain, R. (2019). Climate change and European rivers: An eco‐hydromorphological perspective. Ecohydrology, 12(5), e2099. https://doi.org/10.1002/eco.2099

Olefs, M., Formayer, H., Gobiet, A., Marke, T., Schöner, W., & Revesz, M. (2021). Past and future changes of the Austrian climate – Importance for tourism. Journal of Outdoor Recreation and Tourism, 34, 100395. https://doi.org/10.1016/j.jort.2021.100395

Orr, H. G., Ekström, M., Charlton, M. B., Peat, K. L., & Fowler, H. J. (2021). Using high-resolution climate change information in water management: A decision-makers’ perspective. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 379(2195), 20200219. https://doi.org/10.1098/rsta.2020.0219

Paprotny, D., Sebastian, A., Morales-Nápoles, O., & Jonkman, S. N. (2018). Trends in flood losses in Europe over the past 150 years. Nature Communications, 9(1), 1985. https://doi.org/10.1038/s41467-018-04253-1

Paterson, D. L., Wright, H., & Harris, P. N. A. (2018). Health Risks of Flood Disasters. Clinical Infectious Diseases, 67(9), 1450–1454. https://doi.org/10.1093/cid/ciy227

Peltonen-Sainio, P., Sorvali, J., & Kaseva, J. (2021). Finnish farmers’ views towards fluctuating and changing precipitation patterns pave the way for the future. Agricultural Water Management, 255, 107011. https://doi.org/10.1016/j.agwat.2021.107011

Pimentel-Rodrigues, C., & Silva-Afonso, A. (2022). Rainwater Harvesting for Irrigation of Tennis Courts: A Case Study. Water, 14(5), 752. https://doi.org/10.3390/w14050752

Pröbstl-Haider, U., Hödl, C., Ginner, K., & Borgwardt, F. (2021). Climate change: Impacts on outdoor activities in the summer and shoulder seasons. Journal of Outdoor Recreation and Tourism, 34, 100344. https://doi.org/10.1016/j.jort.2020.100344

Pugliese, F., Gerundo, C., De Paola, F., Caroppi, G., & Giugni, M. (2022). Enhancing the Urban Resilience to Flood Risk Through a Decision Support Tool for the LID-BMPs Optimal Design. Water Resources Management, 36(14), 5633–5654. https://doi.org/10.1007/s11269-022-03322-x

Rasmussen, P., Kidmose, J., Kallesøe, A. J., Sandersen, P. B. E., Schneider, R., & Sonnenborg, T. O. (2023). Evaluation of adaptation measures to counteract rising groundwater levels in urban areas in response to climate change. Hydrogeology Journal, 31(1), 35–52. https://doi.org/10.1007/s10040-022-02573-7

Ribas, A., Olcina, J., & Sauri, D. (2020). More exposed but also more vulnerable? Climate change, high intensity precipitation events and flooding in Mediterranean Spain. Disaster Prevention and Management: An International Journal, 29(3), 229–248. https://doi.org/10.1108/DPM-05-2019-0149

Rosbjerg, D., Engeland, K., Førland, E., Haghighi, A. T., Mehr, A. D., & Olsson, J. (2022). Nordic contributions to stochastic methods in hydrology. Hydrology Research, 53(6), 840–866. https://doi.org/10.2166/nh.2022.137

Rosenberger, L., Leandro, J., Pauleit, S., & Erlwein, S. (2021). Sustainable stormwater management under the impact of climate change and urban densification. Journal of Hydrology, 596, 126137. https://doi.org/10.1016/j.jhydrol.2021.126137

Sapač, K., Medved, A., Rusjan, S., & Bezak, N. (2019). Investigation of Low- and High-Flow Characteristics of Karst Catchments under Climate Change. Water, 11(5), 925. https://doi.org/10.3390/w11050925

Sassi, M., Nicotina, L., Pall, P., Stone, D., Hilberts, A., Wehner, M., & Jewson, S. (2019). Impact of climate change on European winter and summer flood losses. Advances in Water Resources, 129, 165–177. https://doi.org/10.1016/j.advwatres.2019.05.014

Senko, H., Pole, L., Mešić, A., Šamec, D., Petek, M., Pohajda, I., Rajnović, I., Udiković-Kolić, N., Brkljačić, L., Palijan, G., & Petrić, I. (2022). Farmers observations on the impact of excessive rain and flooding on agricultural land in Croatia. Journal of Central European Agriculture, 23(1), 125–137. https://doi.org/10.5513/JCEA01/23.1.3292

Statista (2023). Report on Floods in Europe. Politics and Society. European Commission, Joint Research Center. Accessed: 10-19-23. https://www.statista.com/study/110351/flooding-in-europe/ 

Venvik, G., Bang-Kittilsen, A., & Boogaard, F. C. (2020). Risk assessment for areas prone to flooding and subsidence: A case study from Bergen, Western Norway. Hydrology Research, 51(2), 322–338. https://doi.org/10.2166/nh.2019.030

Werg, J. L., Grothmann, T., & Löchtefeld, S. (2021). Fostering Self-Protection against Impacts of Heavy Rain at the Municipal Level. Sustainability, 13(13), 7019. https://doi.org/10.3390/su13137019

Zhllima, E., Imami, D., Nam, J., Shoshi, P., & Gjika, I. (2022). Awareness of Climate Change Impact and Adaptation in Agriculture – The Case of Albania. European Countryside, 14(4), 604–622. https://doi.org/10.2478/euco-2022-0030

Zhou, Su, Leng, & Peng. (2019). The Role of Hazard and Vulnerability in Modulating Economic Damages of Inland Floods in the United States Using a Survey-Based Dataset. Sustainability, 11(13), 3754. https://doi.org/10.3390/su11133754

Zittis, G., Almazroui, M., Alpert, P., Ciais, P., Cramer, W., Dahdal, Y., Fnais, M., Francis, D., Hadjinicolaou, P., Howari, F., Jrrar, A., Kaskaoutis, D. G., Kulmala, M., Lazoglou, G., Mihalopoulos, N., Lin, X., Rudich, Y., Sciare, J., Stenchikov, G., … Lelieveld, J. (2022). Climate Change and Weather Extremes in the Eastern Mediterranean and Middle East. Reviews of Geophysics, 60(3), e2021RG000762. https://doi.org/10.1029/2021RG000762

Żmudzka, E., Kulesza, K., Lenartowicz, M., Leziak, K., & Magnuszewski, A. (2019). Assessment of modern hydro‐meteorological hazards in a big city – identification for Warsaw. Meteorological Applications, 26(3), 500–510. https://doi.org/10.1002/met.1779

Zuccaro, G., & Leone, M. F. (2021). Climate Services to Support Disaster Risk Reduction and Climate Change Adaptation in Urban Areas: The CLARITY Project and the Napoli Case Study. Frontiers in Environmental Science, 9, 693319. https://doi.org/10.3389/fenvs.2021.693319

Note: Bolded items are literature from outside the systematic scientific review added to the report, such as IPCC and Europa reports. 

Appendix A. Not posted on Substack ;)

Appendix B. More substantiated Methods 

Scientific Review

This chapter documents the most recent findings regarding flooding in Europe and the relevant impacts and adaptation based on a literature review conducted through a search on Web of Science. Using Web of Science, and the boolean search string “climate change” AND “Flood” and “Europe” yielded 1775 articles. The results were then limited to articles published in English and then further limited by countries in the EU or considered part of the European continent, yielding 1561 articles. The search was further refined to publications in the last 5 years (2019, 2020, 2021, 2022, and 2023 until September) yielding 655 articles. The key terms “impact” and “adaptation,” were used to further refine the literature review, yielding 73 articles, which served as the basis for each key finding reported in this chapter. The number of articles was further reduced to 66 due to articles outside of geographic scope or focus of flooding, despite the search filters. To systematically review the literature, the article title, author, keywords, and abstract were included in an Excel sheet and other variables to research and categorize. These variables were determined from IPCC AR6 chapters on flooding, impact, and mitigation and class literature regarding impact, vulnerability and adaptation. Additional variables included whether articles focused on rural, urban, or both; current adaptation; future adaptation; type of study; country of focus; long-term risks; short-term risks; coupling of other hazards; and type of flooding. A systemized literature review was then conducted to identify this information for each article and confirm that the article fell within scope of the research, focusing on Europe and flooding. The articles were divided into thirds for review by each author, who communicated any questions or inconsistencies to determine how to systemize and categorize the variables. 

Headline Development

After screening the abstracts, the research team developed key headlines that encapsulated the most pertinent themes in the literature reviewed. The section headings and focus of the report mirror the headings of earlier WGII reports. However, given the substantial weight of articles in our literature review that address modeling of floods in Europe as well as particular case studies of adaptation measures, more weight is given to these sections. In the given time constraints of this chapter, some snowballing of literature drawn from the reference list occurred with an emphasis on filling research gaps of the key headlines. To avoid bias in the snowballing of literature, a focus was given to articles cited in previous IPCC reports. 

Agricultural / Urban Infrastructure Focus

When examining flooding in Europe, we limited the focus to looking at agricultural and urban infrastructure. Based on the systematic literature review, we found that 16 articles focused on urban flooding, 8 articles focused on rural flooding, and 4 articles focused on both urban/rural flooding. While both aspects are included in the report, it’s important to note that the literature heavily focuses on the urban and infrastructure perspective and thus the report may include more urban aspects than agricultural or rural aspects. 

Appendix C. Treatment of Uncertainties 

The treatment of uncertainties were based on the guidance note by lead authors of the IPCC fifth assessment report by Mastrandrea et al. 2010. The graphic below illustrates how we calibrated the confidence levels reported in our chapter. As a research team, we deemed confidence levels based on the following calibration: out of applicable articles we reviewed, if evidence was robust with widespread agreement, we assigned high or very high confidence. If evidence was robust but there was  disagreement among articles, we assigned medium confidence. Other variations were assessed according to the figure below. Because our literature review was a state-of-the art review and was limited to articles over the past 5 years, a further cross-reference of earlier IPCC reports to report the physical basis for floods in Europe and earlier reported confidence levels. Particular attention was given to the WGII AR6 Report and Chapter 13 on Europe for this cross-referencing. In addition to the level of confidence, when a bold statement of controversy was claimed, we made a specific note to include the level of evidence and agreement across the literature we examined.  

Figure A.1. Confidence Level

Source: Mastrandrea M. et al. 2010 Guidance note for lead authors of the IPCC fifth assessment report on consistent treatment of uncertainties Figure obtained from Olsson Slides MESS 51 2023. 

Appendix D. Classification of Subregions in Europe

Figure D.1 Regions of Europe used in this chapter 

Source: IPCC Figure 13.1 | Geographical subdivision of land (a,b,c,d) and ocean (i,ii,iii) regions of Europe. The overlay represents the WGI AR6 (IPCC, 2021) subdivisions for climate-change projections of land, while the colour coding indicates the European countries (or, in case of the Russian Federation, the European part of the country, EEU, used for this chapter). Note that in the WGI AR6 report, MED includes both Southern Europe and Northern Africa, while this chapter includes only the northern (European) part of the MED region. To distinguish between the two the region is called SEU here.

Appendix E: Nature-Based Solutions Figure 

Figure 1: examples of nature-based flood adaptation measures from (Badura et al., 2021)