Three ways to reduce Europe’s flood risk
Paul Hudson, Leiden University
From the Czech Republic to Spain, Europe has been plagued by devastating floods this autumn.
Climate scientists agree that severe flooding was probably driven by climate change resulting in record-breaking rainfall. Warmer temperatures increase the amount of water vapour in the atmosphere, especially over warmer oceans, which increases the amount of rainfall. Europe is projected to experience a greater frequency of severe floods, potentially with dire consequences to economies and livelihoods.
It’s challenging to reduce flood risk in Europe because of the high density of population and economic activities within flood-prone lands, as well as substantial cultural heritage. Flood risk has increased in Europe largely because people have moved into protected areas that were formerly flood prone, referred to as the “levee effect”.
Implementing effective flood management is also difficult because not all floods are the same. Broadly, Europe is impacted by three main types of flood processes: fluvial, pluvial and coastal storm surge.
Fluvial flooding refers to excessive precipitation (both rain and melted snow) flowing into upstream river basins drives high run-off and downstream over-bank flooding. These floods are particularly severe in mountainous regions near the coast, like Valencia, Spain in 2024, because steep slopes accelerate runoff.
Pluvial flooding occurs when local rainfall is not adequately drained, fields in rural areas become saturated, while flash floods can occur in urban areas. Excessive local rainfall is especially a problem over lowland rivers and deltas during wet winter months, as saturated lands do not permit drainage of additional rainfall and run-off, leading to local flood problems.
Strong winds drive coastal storm surge events. This causes rivers to backup and overflow, flooding adjacent lands. Storm surge events are more common in winter months.
The most challenging floods to manage are caused by multiple flood processes. Last winter in the lower Rhine basin in Germany and the Netherlands, three flood processes combined to produce flooding (high water), saturating fields and substantially impacting agricultural activities for months.
For the first time since its construction in 1997, the huge Maeslant barrier at the mouth of the Rhine River near Hook of Holland, had to close to manage a storm surge.
Three key steps
Reducing flood risk in Europe will require massive investment that includes a basin-wide management approach, as recommended in the EU floods directive. In addition to greater focus on nature-based solutions, such as returning agricultural lands to natural vegetation, a unique combination of hard (structural) and soft (policy) measures are needed to reduce flood risk within a given river basin.
While flooding from extreme rainfall in Europe cannot be avoided, the risk and devastation can be reduced. In Valencia, Spain, people were not given enough advanced warning of floods. The first step must be to improve public early warning systems and raise awareness so that people take flood alerts seriously.
Upper river basin measures may include improved land-use planning, such as afforestation (planting trees where there were none before), to reduce run-off. Reservoirs can be used to either hold back water to reduce downstream transmission of floodwaters or to release reservoir water before arrival of the flood wave.
Lower basin approaches should include redesign of hydraulic infrastructure (such as dykes, groynes, bridges) downstream to accommodate both higher peak and longer-duration floods. Areas that are allowed to flood can be expanded. This is being done effectively in the Netherlands, as part of the Room for the River programme, which restores the floodplains.
The approach was shown to be successful during the devastating European floods of July 2021. The flooding overwhelmed centuries-old villages along Meuse (Maas) River basin headwaters in parts of northern Germany, Belgium, Luxembourg and France, and resulted in more than 200 fatalities.
But further downstream in the Netherlands, floodwaters caused much less damage thanks to the Dutch Room for the River scheme. While Maas River floodwaters attained high levels, they were contained and did not overtop the dykes, protecting riverside communities. Enhancing the natural buffering effect of floodplains can reduce the severity of downstream flooding.
While long-term strategies to improve flood management are expensive, the personal and financial cost of ineffective flood management is much higher. European nations need to be vigilant, forward-thinking and proactive about implementing effective flood management.
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Paul Hudson, Associate Professor of Physical Geography and Sustainability, Leiden University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
