Flash floods: a grim reminder that adaptation is as important as reducing emissions
Posted on 23 Jul 2021 in Commentary
Learning lessons from the devastating flooding in Western Europe and China – and raising awareness of the importance of flood risk reduction activities and the long-term consequences of inaction – should be seen as a necessary investment in our future, write Swenja Surminski and Viktor Rözer, as they draw out particular lessons for Germany.
The shocking pictures from the recent flash floods in Western Europe and China highlight once more that weather extremes are increasing in many parts of the world. Our new normal will mean higher frequency and intensity of weather extremes such has floods, heat and drought, as well as long-term shifts such as sea-level rise.
Politicians have been quick to point to climate change as the driving factor in the flooding and are once more promising more action to reduce emissions and fight climate change. While this is clearly of utmost importance, it is an illusion to believe that the increase in extreme weather we are already experiencing can be reversed by more ambitious climate action. The scale of the recent disasters is a reminder that adaptation to climate risks is as important as reducing greenhouse gas emissions. There is clearly no silver bullet solution; our preparedness, response and recovery – in short, our resilience – to such events needs to be adjusted to new risk levels.
Better integration of current and future flood risk in urban planning and land-use processes is needed to help avoid the creation of new risks when, for example, new property developments are built in areas that are likely to be affected by increases in flood frequency. And for some areas it will mean difficult choices, including managed retreat and resettlement.
Flash flooding – a familiar set of challenges
It is too early to draw any detailed conclusions from the recent events, but previous research points to several challenges we are now seeing repeatedly in regard to catastrophic flash floods:
- Intense rainstorms dropping the amount of rainfall usually expected over several weeks or months over smaller catchment areas means that flooding reaches areas that the public is either not aware are at risk or where people are not prepared for the speed and intensity of flash floods.
- Urban drainage systems become overwhelmed, turning streets into torrents, flooding low-lying structures such as underpasses or tunnels, frequently catching people by surprise, turning cars and basements into deadly traps.
- The high amount of rainfall cannot infiltrate quickly enough in narrow valleys – such as the heavily affected Ahr valley in Germany. This leads to direct surface water runoff which turns small creeks into raging rivers within a few hours, ripping through settlements in valley bottoms and overwhelming dams.
- Local flood risk managers and emergency responders are overwhelmed by the speed and intensity, mostly being trained to respond to and warn against slow onset floods with several days of lead time.
More focus needed on flash and surface water flooding in Germany
While the sheer amount of water, the devastation and the tragic loss of over 150 lives in Europe’s case might make such events appear unmanageable, our research of flood risk management systems has revealed a number of improvements that can help save lives and reduce losses.
The Grantham Research Institute is working on flood resilience with the cities of Cologne and Remscheid in Western Germany as part of the Zurich Flood Resilience Alliance to better understand resilience to flooding. Together with local partners we carry out the Flood Resilience Measurement for Communities (FRMC), which provides an in-depth analysis of a communities’ resilience flooding using 44 indicators ranging from the structural protection of urban infrastructure to risk communication and emergency response.
Research we conducted with the Geneva Association for a report on Flood Risk Management in Germany contains some particularly relevant observations. In analysing the current state of the flood risk management system in Germany and its 16 federal states, the report recognises a gradual shift towards a more anticipatory system focused on risk reduction, prompted by recent floods. But it also highlights the lack of strategic focus on how to achieve flood resilience, especially in regard to the emerging challenge of surface water and flash floods.
After the devasting floods along the Elbe and Danube rivers in 2002 and 2013, Germany and the affected federal states invested greatly in improving structural protection and overhauled their flood risk governance structure to include safety protocols, emergency response and building codes. Although successful in reducing damage (damage in 2013 was less than in 2002 despite equal magnitudes of the events) most of the efforts were targeted towards slow onset floods along the big rivers. Yet in recent years, a combination of increased surface water runoff from intensive agriculture in rural areas on often steep terrain, soil sealing in urban areas, outdated drainage infrastructure and in some parts increases in the rainfall intensity from climate change have led to an increase in flash and surface water floods in Germany – almost all parts of the country have experienced one or other of these hazards.
While flash and surface water floods are now seen as significant threats in Germany, complex (and often inefficient) governance structures and responsibilities spread across federal, state-level and local actors slow down necessary action.[i] Some individual cities and communities have taken steps – for example, launching risk maps for surface water flood risk to inform the general public about risk hot spots – but there is no concerted action. This means the majority of the general population is unaware of flash flood and surface water flood risk and therefore is also unlikely to respond to early warnings. This was also highlighted by the Zurich Risk Nexus report on the 2016 flash floods in Germany.
While this type of flood can be hard to predict, often being triggered by local, fast-moving convective rain storms, the floods we have seen this past week in Germany, Belgium and the Netherlands were predictable with current technology (and were predicted), with at least several hours’ lead time. The high death toll means that warnings either did not reach the affected areas or no clear information was given to emergency responders and/or to the public on how to stay safe. This is despite the fact that early warning and risk communication for these fast onset floods have been known issues in Germany for some time now.
A survey after three surface water flood events between 2005 and 2010, for example, showed that between only 7 and 12% received the severe weather warning. Another survey four years later after a surface water flood in Münster in 2014 still showed very similar results. There is an official German emergency warning app, NINA, but it currently has 8.8 million users which accounts for just 11% of the population – many vulnerable and older age groups are unlikely to be reached by this service.
Our recommendations for mitigating flash flood risk in Germany
Based on our work in Germany and elsewhere we suggest the following to help avoid such terrible scenes in the future:
- Flash flood and surface water maps for the entire country. Many areas, especially those far away from rivers or the sea, appear to be safe from flooding but can quickly flood during extreme rainfall events. Making those maps available and easily accessible can help people identify their risk and prepare for the worst.
- Improved dissemination of early warnings. Unlike slow onset floods with several days’ lead time, every minute counts when it comes to flash floods. Existing warning chains and technology appeared to be either too slow and/or ineffective in the latest flood events.
- Awareness raising and clear advice. Warnings need to be accessible and actionable with clear advice on how to respond. This can be done through increasing focus on participatory activities, such as campaigns, training, education events, and participatory decision-making processes for flood risk management policy and planning. This may also increase trust between residents and local leaders.
- Regular ‘climate checks’ of critical infrastructure and older buildings. Most buildings and critical infrastructure have not been designed with increasing impacts from climate change in mind. Regular checks can help to make sure that building standards and design are adjusted to increasing risk levels. This also includes urban drainage systems.
- Stronger planning regulation and building codes. Space must be made for water, using nature rather than blocking, concreting over, and destroying it.
- Improve absorption capacity through ‘sponge cities’ with blue-green infrastructure and changes in land-use practices in agriculture and forestry. The more rainfall that can be absorbed, the less water ends up in rivers or in urban drainage systems, causing floods.
- Improve the resilience of digital and communication infrastructure. Many affected areas are currently completely cut off without any connection via phone, mobile or internet. Emergency responders have reported that their communication was severely disrupted during the event, leading to uncoordinated actions.
Unfortunately, this will not be the last flash flood Germany will ever see, but hopefully it will be the last with such a terrible loss of life and livelihoods.
[i] See Box 3 of the Geneva Association report for details of the complex governance structure around surface water flood risk in Hanover, for example.