The weather is becoming more extreme, and that means Europe needs better coastal and river flood forecasting and smarter building design to help contain the cost of flooding.
At the start of 2014, floods forced people from their homes across the UK, while in 2013 rivers burst their banks and flooded large parts of the Czech Republic, Germany and Slovakia. It’s hard to forecast where the water will spill into streets and homes as it depends on where storms strike. However, extreme flooding is becoming more common across Europe, and smarter forecasting can help minimise the risk.
‘Extreme weather events are getting more frequent and more extreme. Rainfall can be more concentrated – when it rains, it rains more over a short period,’ said Professor Slobodan Djordjević of the University of Exeter in the UK, who leads the EU-funded CORFU project looking at flood resilience, a measure of a region’s ability to cope with flooding.
The four-year project brings together researchers from Europe and Asia so they can work together to identify which parts of a city are liable to flooding, and learn from each other ways of managing the threat of flooding, for example by allocating resources in the best way.
‘You cannot protect everyone from everything – the goal of adaptive flood risk management planning is to figure out how to use available financial resources in the best way possible to minimise damage over a period of time and thus reduce the overall risk,’ he said.
Flood forecasting for large areas – like cities or countries – relies partly on meteorological prediction models. Some of these operate using real-time information from sensors or weather observations and, combined with information about previous episodes of flooding, can be enough to give reliable short-term advance warning.
‘This can be useful in making informed decisions – requesting evacuations, bringing in temporary flood defences or portable pumping stations. But we are talking hours or days,’ said Prof. Djordjević.
However, the project looking at ways to identify and manage long-term flood risk in cities such as Dhaka, in Bangladesh, which is home to around 7 million people. ‘Flood maps are overlapped onto urban growth maps and on that basis we can identify certain areas where flood risk may increase and we can analyse effectiveness of various resilience measures,’ said Prof. Djordjević.
‘Extreme weather events are getting more frequent and more extreme. Rainfall can be more concentrated – when it rains, it rains more over a short period.’
Professor Slobodan Djordjević, Professor of Hydraulic Engineering, University of Exeter, UK
This information allows planners to minimise the risk of death from floods caused by damage to property and infrastructure, but it also has implications for public health. Several major rivers from upstream countries bring untreated wastewater to Bangladesh so when flooding occurs, disease outbreaks are common.
In Europe too, urban growth exacerbates flood risk. Cities have expanded into areas where the risk of flooding is high – like flood plains in coastal areas and near river banks.
In the countryside, rainwater can seep into the soil but in urban areas, it often has nowhere to go. Unable to permeate roads and rooftops, this run-off can wreak havoc by forming large pools of flood water.
‘Flooding is caused by different problems in different areas. The flash flooding we see in urban areas due to fast run-off from steep catchments can be very dangerous for people – it’s responsible for the images we’ve seen ... of cars being taken away by floodwater,’ said Prof. Djordjević.
Prevention cheaper than cure
Longer-term thinking is required when designing buildings and planning cities in order to minimise flood risk. Rather than having to spend hundreds of millions of euros on repairing damage, it would be wiser to invest time, thought and technology in making urban areas more flood resilient.
Take Hamburg in Germany, for example. Developing inner city areas on the banks of the River Elbe, which are prone to storm surges, required some ingenuity. Roads have been elevated and new buildings in the HafenCity area are built on eight-metre-high plinths.
Natasa Manojlovic from the Hamburg University of Technology, said these projects are about more than just the need to build in a flood-resistant way. ‘The elevation of the existing floodwall has been used as an opportunity to enhance the amenity of the area and make it more attractive for visitors,’ she said.
When waterproofing buildings in HafenCity, every effort has been made not to spoil the area’s identity. ‘And, in the case of a storm surge, the evacuation routes are planned and made transparent to the stakeholders. Residents are regularly informed about the flood situation in the area,’ said Manojlovic, who is also a partner in the CORFU project.
Such social aspects of flood defences are frequently overlooked, according to Dr Zoran Vojinović, from the UNESCO Institute for Water Education.
‘Flood risk governance is not only technological, but also significantly social, economic, organisational and political,’ he said.
Dr Vojinović is the coordinator of the EU-funded PEARL project, which started at the beginning of 2014 and brings together experts in hydro engineering and risk reduction to work out how communities and experts can collaborate to reduce the risks from floods.
‘There is a lack of interaction between social aspects and engineering in planning for resilience, and this creates a hindrance for solving some of the major flood-related problems,’ he said.
Communities directly affected by floods should be central to the decision-making processes rather than leave it solely to external experts. ‘They should be active participants in guiding the technical aspects of flood management projects. For example, they can help to define acceptable levels of risk and provide inputs into the design of engineering structures.’
The EU-funded RISC-KIT project is running 10 study sites covering every regional sea in Europe and is developing tools that will allow authorities to identify areas that are at high risk of flooding. This includes a rapid assessment tool for the identification of high-risk coastal areas. For these hotspots better early warning systems can be implemented.
‘The tools and software we are developing are either freeware or open source. This means that these tools are easily accessible and transparent for flood forecasting authorities in Europe and beyond,’ said Dr Ap van Dongeren, the project coordinator. The model system can also be used well before a storm to evaluate which prevention and mitigation measures work best to protect against floods, he explained.
Scientists believe Europe will flood more often in the future as the sea levels rise due to climate change and intense rainfall becomes more frequent.
‘These problems are to an ever-increasing extent directly attributable to the actions of human beings,’ Dr Vojinović from the PEARL project said. ‘The sooner we realise that these problems are not down to nature alone, the more likely we are to develop better solutions.’
In winter 2014, the UK was hit by severe storms and flooding, with the month of January being the wettest ever recorded.
It follows intense rainfall in 2013 over Central Europe which led to flooding in Germany, the Czech Republic, Austria, Hungary and Poland, causing rivers to burst their banks, and forcing thousands of people to evacuate their homes.
The extreme weather in the UK coincides with disruptions to the Pacific and North Atlantic jet streams, as well as an unusual displacement of the stratospheric vortex, which has also left parts of the US and Canada frozen, the UK Met Office said.
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