Floods

Extreme flooding events occur time and again, causing extensive flooding with considerable damage. This topic page provides an overview of the causes as well as adaptation and management options.

What is a flood?

A flood is when the volume of water in a stream or river exceeds the capacity of the stream or river bed. This results in temporary flooding of land that is not normally covered by water. This can cause considerable damage to infrastructure, the environment and private property, as well as loss of life. The severity of a flood essentially depends on significant, prolonged rainfall and/or snowmelt in the low mountain ranges in the entire catchment area of a stream or river (UBA 2011). In principle, floods are natural events. However, humans have a considerable influence on natural runoff events. Added to this is climate change, which influences the distribution towards a greater rainfall intensity with the consequence of an increase in winter runoff over the course of the year (LfU Bayern).

Natural runoff and human influence

The discharge of a stream fluctuates naturally over the course of the year. In Germany, natural runoff is mainly determined by rainfall and snowmelt in the Alps in summer. Evaporation also plays a role in summer. On average, high runoff occurs in winter and spring, as the snow falls as rain due to the higher temperatures and the snow melts in the low mountain ranges due to the higher temperatures. In late summer and fall, on the other hand, runoff is lower (UBA 2023; UBA 2011).

Extreme flood events are caused by certain weather constellations. In winter, continuous rainfall lasting several days to weeks, sometimes in combination with thawing and melting snow in the low mountain ranges, is usually responsible for flooding. In summer, it is often a case of rainfall lasting several days, which can occur in combination with heavy rainfall (DKKV-Topic Heavy Rain). In contrast to river floods, floods induced by heavy rainfall cause small rivers and streams in particular to rise quickly and also occur away from bodies of water (UBA 2023). Besides the amount of rainfall, it is crucial how much water reaches the river in an ‘effective runoff’ form. Depending on the vegetation, soil and terrain conditions, water runs off at different rates, is temporarily stored or seeps away. Soil that is already saturated as well as very dry soil can also absorb less water (LfU Bayern).

Over the past centuries, humans have intervened massively in the natural flow patterns of streams and rivers. Natural floodplains close to rivers have been developed for commercial or residential purposes, floodplains have been drained and converted into agricultural land (UBA 2011). Dike construction and river straightening mean that rivers are less branched and water flows away faster, which favors more intense flood waves. At the same time, more damage is caused when a flood wave hits a settlement or industrial site (UBA 2022).

Figure 1: Straightening of the Rhine since 1825 (BMUV)

Figure 2: Waterfront development at the Deutsches Eck in Koblenz (Wikipedia | Holger Weinandt)

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DKKV flood platform on flooding and flood events in Germany

The DKKV flood platform offers the opportunity to exchange information on the topic of floods and flooding in Germany. The platform serves as a source of information for pooling data on historical and current flood events, discussing measures and networking those affected, experts and interested parties. Through a combination of scientific publications, news updates and practical recommendations for action, the platform contributes to strengthening society’s resilience to flood disasters and flooding, promoting the exchange of knowledge and avoiding duplication of research.

To the DKKV Flood Platform

Past flood events

Figure 3: Flood in Passau in June 2013 (Wikipedia)

Floods in southern Germany 2024

Persistent heavy rainfall combined with a very wet spring led to flooding on the Danube, Neckar and Rhine rivers and their tributaries between May 30 and June 3, 2024, particularly in Bavaria and Baden-Wuerttemberg. In just five days, some places received more than twice as much rain as usual in the entire month of May. The event was classified as having the intensity of a 100-year event. The flood event in southern Germany was intensified by regional heavy rainfall events, which triggered flash floods in some places (DWD 2024). In Bavaria, a state of disaster was declared in 15 districts and three independent cities. The devastating consequences included dike breaches, restrictions in the drinking water supply, power outages and the evacuation of more than 6,600 people. The flood claimed at least six lives (CEDIM 2024, DWD 2024). You can read a DKKV statement on the flood disaster in southern Germany in 2024 here (DKKV Statement “Hochwasser Süddeutschland 2024” ist veröffentlicht | DKKV).

Winter flood 2023/24

Between December 19, 2023 and January 5, 2024, flooding occurred in large parts of central and northern Germany, triggered by persistent rainfall from a series of consecutive low-pressure systems. The federal states of Lower Saxony, North Rhine-Westphalia and Saxony-Anhalt were particularly affected (DWD 2024). Winter floods of this intensity are typical for Germany. However, the event is characterized by the long-lasting precipitation of a total of 18 days with few interruptions in a relatively large affected region (NLWKN). The damage caused mainly affected infrastructure such as roads and bridges, while residential buildings were hardly affected. A more detailed overview and expert opinions on the winter floods can be found in the DKKV newsletter “Winter Floods 2023/24” (DKKV-Newsletter Winterhochwasser 2023/24).

Summer flood 2013

Due to several surface low-pressure systems in Central Europe, May 2013 was significantly too wet on a nationwide average, with 178 % of the long-term precipitation totals. This resulted in very high soil moisture levels in large parts of Germany (DKKV 2013). Heavy rainfall with local rainfall of over 400 mm in the Bavarian Alps then triggered severe flooding in large river basins in Germany between May 18 and July 4, 2013 (DKKV 2013). The federal states of Brandenburg, Baden-Württemberg, Bavaria, Hesse, Mecklenburg-Western Pomerania, Lower Saxony, Rhineland-Palatinate, Schleswig-Holstein, Saxony, Saxony-Anhalt and Thuringia were affected. A total of 56 local authorities in eight federal states were declared in a state of disaster (BMI 2013). The floods caused 14 fatalities and damage amounting to around 8 billion euros (DKKV 2013). A detailed report on the 2013 summer floods was published in the 53rd DKKV publication series “Das Hochwasser im Juni 2013: Bewährungsprobe für das Hochwasserrisikomanagement” (DKKV-Schriftenreihe Nr. 53 | DKKV).

Climate Change

Climate change has a significant impact on the frequency and intensity of flood events. From 1881 to 2022, the average air temperature in Germany rose by 1.7 °C, which is changing previous precipitation patterns (UBA 2023). While summer rainfall has remained largely unchanged, winter rainfall has increased by around 26 % (UBA 2023, LfU Bayern). Rising temperatures also mean that air can absorb more water vapor – 7% for every 1 °C rise in temperature. In combination with increased evaporation above the sea surface, this can lead to more intensive rainfall (DWD 2024) (DKKV Topic Heavy Rain). Following the summer floods in June 2024, an attribution study by the German Weather Service (DWD) investigated the extent to which the events are linked to climate change. The study shows that the probability of comparable rain events has already increased by a factor of 1.4 compared to a world that is 1.2 °C colder – i.e. 40 % more likely (DWD 2024).

In addition, higher temperatures reduce snow cover in winter, as less precipitation falls as snow and instead as rain, which runs off directly. This increases runoff in winter. At the same time, there is less snowmelt in summer, which reduces runoff in summer and favors low water situations. In general, however, few significant trends can be identified so far, as most situations that trigger floods depend on the respective weather constellation (UBA 2023).

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The return period of a flood

The probability of a flood occurring is described in “return periods”, which are determined from statistical evaluations of observation data. Statistically speaking, a 100-year flood occurs once every hundred years – this is also referred to as a flood of the century. However, return periods are often misleadingly communicated and can convey a false sense of security. A once-in-a-century flood does not occur every 100 years, but only provides an indication of the intensity of occurrence. In Cologne, for example, there was a 50-year event in both 1993 and 1995. This therefore only shows the intensity of a flood event. In addition, the probability of recurrence is changing significantly, partly due to hydraulic engineering measures and partly due to climate change. This is because today’s world is changing much faster than the world at the beginning and middle of the 20th century (GERICS 2013, UBA 2011).

Measures for natural and technical flood protection

Technical flood protection is an integral part of comprehensive flood risk management in order to protect people and infrastructure from flooding. This includes, for example, dikes, flood protection walls and mobile flood barriers, as well as artificial retention basins, dams and controllable and uncontrollable retention areas. In the city, the proper operation of the sewer network and pumping and sewage treatment plants is also crucial. In Cologne, for example, this is ensured by monitoring in discharge control centers. Furthermore, 900 slide gates can be installed in the canal network to protect it from incoming floodwater from the Rhine (SteB).

However, technical measures alone are not enough to protect against flooding. Settlement along the river and the technical protection structures built centuries ago have had a massive impact on the flow of the river or stream (BMUV 2017). Concrete measures for a nature-based solution include alluvial forests, the creation of grassland, reforestation, unsealing and conservation tillage in agriculture (UBA 2011). Technical measures must be supplemented and in some cases replaced by such nature-based solutions and, above all, precautionary measures (land, building, behavioral and risk prevention) must be implemented and strengthened. In order to keep the damage potential as low as possible, more space should be given to the river and, if possible, no building land should be designated in flood-prone areas (SteB, UBA 2017). Strict regulations are required for flood-adapted construction and use where construction is permitted despite a legally defined floodplain (BezReg Köln). Particularly in the case of headwaters and tributaries, natural retention areas already hold water decentrally within the catchment area. In addition, behavioral and risk prevention are important building blocks for raising the population’s flood awareness and mobilizing them to take precautions themselves (DKKV Topic Risk Communication, Eigenvorsorge gegen Hochwasser). This includes the provision of information on hazards, such as hazard maps and water levels, as well as forecasts and warnings. In addition, there are private property protection measures (DKKV Topic Constructional Civil Protection) and financial instruments such as natural hazard insurance (DKKV Topic Insurance in Risk Management).

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Flood risk management in Germany

Flood risk management in Germany is regulated by the Federal Water Act (in German “Wasserhaushaltsgesetz”), which implements the European Flood Risk Management Directive. This includes, for example, regulations on the reclamation of retention areas, the conversion of grassland into farmland and building development, as well as the creation of hazard and risk maps (UBA). The regulations are supplemented by the water legislation of the federal states, which are responsible for implementing flood protection. Specific projects are in turn mainly the responsibility of municipalities and water boards (BMUV 2017). For flood risk management to be successful, however, it must be organized along catchment areas and not be tied to administrative boundaries (UBA 2011). In the wake of the 2013 floods, supra-regional flood protection measures were therefore combined in the National Flood Protection Program (NHWSP), which is funded by the federal government (BMUV 2017). In addition, flood protection requires the combined thinking of various disciplines, in particular water management, urban and regional planning, nature conservation, agriculture and forestry and disaster control (BMUV 2017).

Figure 4: Dike along the Rhine (DKKV)

Tips for personal precautions and what to do in the event of flooding

Pay attention to weather and flood warnings. Use warning apps such as NINA or KATWARN.
Follow the instructions of emergency services and pay attention to barriers and warning signs.
Do not enter any bank areas. There is a risk of undercutting or breaking off.
Avoid driving on flooded roads. Keep roads clear for emergency vehicles.
Vehicles should be removed from flood-prone areas in good time. Caution: Underground garages are life-threatening in the event of flooding or heavy rain!
Seal windows and doors as well as drainage openings (backflow protection).
Avoid cellars and lower-lying rooms.
Switch off burners, boilers and electrical appliances in rooms at risk of flooding in time.
Hazardous substances such as used oil, chemicals, paints, etc. should not be stored in rooms at risk of flooding and should otherwise be removed in time.
Pay attention to sick people, people in need of care and children and it is best to move them to safety in advance.

General precautionary measures and tips on how to behave in the event of a disaster are compiled by the BBK here: BBK Rategeber für Notfallvorsorge und richtiges Handeln in Notsituation and on the BBK Website.

Warning apps

Further tips on what to do in the event of flooding

Tips on precautionary measures

Created: December 2024

Current Information

Research on Damage, Recovery and Adaptation of Railway Infrastructure after the 2021 Flood

Feb 18, 2025

Jie Liu (Erasmus University Rotterdam, IHS) has been investigating the damage, recovery and adaptation of railway infrastructure following the 2021 flood events. The research focuses on affected regions in Rhineland-Palatinate and North Rhine–Westphalia. The study...