10 questions on flooding to Prof. Annegret Thieken (geoecologist at the University of Potsdam) & Prof. Bruno Merz (hydrologist at the GFZ Helmholtz Centre for Geosciences and the University of Potsdam)
- What are the driving factors behind flooding?
Flooding is mainly caused by heavy or prolonged rainfall, snowmelt and short periods of intense rainfall. The decisive factors are how much rain falls in a given period, how much water can seep into the ground and be retained in the landscape, and how quickly the rainwater reaches streams and rivers. Natural factors such as soil conditions and slope gradient also play a role. In addition, human interventions such as land sealing, river straightening and the loss of natural floodplains (floodplains) influence the extent of flooding, as they reduce the landscape's ability to absorb and store water.
- Will climate change cause flooding events in certain areas of Germany to occur more frequently or intensely?
The answer varies depending on the type of flooding. A distinction is made between large-scale river flooding and small-scale, very rapid flash floods. In addition, there are pluvial floods, which occur after intense heavy rainfall, especially in cities, even without streams or rivers overflowing their banks. Trend analyses show climate-related increases in flood runoff in many areas of central and north-western Europe in recent decades. With regard to flash floods and pluvial flooding, the increase in heavy rainfall is also expected to lead to a higher frequency of flood events.
- How are flood events changing as a result of climate change? Will we see more events in other seasons?
There is empirical evidence that climate change is altering the timing of flood events throughout the year. For example, in north-eastern Europe, floods are occurring earlier due to earlier snowmelt in spring, while winter and spring floods in north-western Europe are occurring later in the year. In addition, heavy rainfall and short-term events in summer are increasing, which is leading to greater risks.
- Should we expect more flooding in cities?
In cities, heavy rainfall, such as that which occurs during thunderstorms, leads to flooding particularly quickly due to the high proportion of sealed surfaces. Because climate change is increasing the frequency and intensity of such heavy rainfall events, cities must expect more flooding in the future. Urban planning and flood protection therefore face the important task of adapting to this growing risk.
- Can artificially created forests, floodplains, moors or similar systems provide sustainable protection against flooding?
Artificially created or near-natural systems such as forests, floodplains and moors can provide sustainable protection against flooding. These are also referred to as natural or nature-based solutions. Forests delay the runoff of precipitation by storing water in the soil and through evaporation, they stabilise the soil and reduce erosion. Floodplains and moors act as natural retention basins that mitigate flooding by temporarily storing water and releasing it slowly. However, their effectiveness depends heavily on site conditions. In the event of very heavy rainfall or saturated soils, their damping effects are limited. Such systems are therefore important but complementary components of flood protection.
- How do floods affect people's well-being?
Experiencing a flood first-hand has a significant impact on the well-being of those affected, often for a long time afterwards. Victims frequently suffer from anxiety, depression, sleep disorders and post-traumatic stress disorder, which can last for months or even years. The psychological stress is caused, among other things, by the loss of homes and possessions or even family members and friends, the experience of threat and loss, uncertainty and fear of further events. Those affected often feel left alone with the task of rebuilding. Targeted support, such as psychosocial services and therapies, is important for coping with these stresses.
- Is flood damage on the rise?
Flood damage is increasing significantly, particularly to infrastructure and buildings. The floods in July 2021 caused total damage of around €33 billion in Germany alone, of which around €5.5 billion was insured. The main causes of the increase are climate change and increased development and concentration of value in areas at risk of flooding, such as along rivers.
- What precautions must Germany take in the coming years to protect itself against flooding?
Germany has invested heavily in flood prevention in recent years. Nevertheless, there is room for improvement in several areas. One of these areas is the protection of critical infrastructure such as energy supply, health facilities and communication networks. Local flooding can lead to widespread network failures. Strategies are needed here to better prepare critical infrastructure for extreme events and make it more resilient.
- What measures can individuals take to effectively protect themselves and their property in the event of flooding?
Individuals can protect their property through various measures. These include structural modifications such as the installation of backflow valves and waterproof basement windows and doors. Mobile or stationary protective barriers can also prevent water from entering. It is also important to take out natural hazard insurance, as standard building insurance policies do not usually cover damage caused by flooding. It is equally important to find out about the risk of flooding at an early stage and to know how to respond appropriately. Only those who prepare in advance can act quickly and safely in an emergency to protect themselves and their property in the best possible way (https://www.starkregenvorsorge-flyer.de/).
- How effective are existing flood warning systems, and where is there room for improvement?
Flood warning systems in Germany are technically well developed. The flood forecasting centres of the federal states publish forecasts for hundreds of river gauges throughout the country. The federal government's Modular Warning System (MoWaS) bundles warnings from various sources and disseminates them via various channels such as warning apps (NINA, Katwarn), radio, sirens and cell broadcast. However, there is room for improvement in local implementation, for example in the rapid and comprehensive transmission of warnings to all those affected. In extreme situations, mobile network failures can make it difficult to disseminate warnings. It is also important that warnings are formulated in a way that is understandable, timely and tailored to the target group, and that the population is made more aware of emergencies. Recommendations for action that are appropriate to the severity and dynamics of the approaching event are an essential part of warnings.
Translated with DeepL.com (free version)