The largest-scale study of its kind by a multinational research team has demonstrated the impact of climate change on the severity of flooding across Europe.
The study – published in the journal Nature – was led by the Vienna University of Technology and involved research institutions and academics in 24 European countries, including Dr Conor Murphy, of the Department of Geography and ICARUS at Maynooth University.
The study, which looked at river flow data from thousands of locations over a 50-year period, found that flood events are becoming increasingly severe in north-western Europe, including Ireland, but decreasing in size in southern and eastern Europe.
This ranges from an 11% increase in flood levels in northern England and southern Scotland to a 23% reduction in parts of Russia and eastern Europe, with the researchers saying their findings provide the clearest evidence yet, at the European scale, of the link between climate change and flooding.
Link to climate change
It had long been suspected that human-induced climate change was having an impact on the magnitude of floods because a warmer atmosphere can store more water, though this is not the only factor leading to flood changes in a warming world.
However, until now, the extent to which climate change affects the severity of floods across Europe had not been clear because previous studies have been on a smaller scale due to a lack of access to data from parts of the continent.
But, thanks to a large-scale European collaboration involving almost 50 scientists from 35 institutions in 24 countries, the new study has been able to draw upon a huge amount of data, with the researchers analysing records from 3,738 flood measurement stations across Europe from the period 1960 to 2010.
Dr Conor Murphy of Maynooth University‘s Irish Climate Analysis and Research Units (ICARUS), said: “This timely study adds to a growing body of evidence which shows that flood magnitude has increased in northwest Europe, including Ireland, over the last five decades.
“We show this is part of a continent-wide pattern of changes in flooding which is in line with what we may expect in a warming world. This highlights the importance of long-term hydrological monitoring and the benefits of data sharing and collaboration at a European scale in order to better understand the mechanisms behind observed changes in flooding.”
The lead author, Professor Günter Blöschl of the Vienna University of Technology, said: "We already knew that climate change is shifting the timing of floods in a year, but the key question had been, ‘Does climate change also control the magnitude of flood events?’. Our study finds there are consistent patterns of flood change across Europe and these are in line with predicted climate change impacts, such as a contrast between increasing flooding in the north and decreases in the south.”
The evaluation of data from the measurement stations over the 50-year period studied revealed growing trends in different regions of Europe.
In north-western Europe, floods are increasing because flood generating rainfall (annual maximum seven day rainfall totals), is increasing and soils are becoming wetter. The largest increases are evident for northern England and southern Scotland, but across Britain and Ireland as a whole flood magnitudes have been increasing at a rate of about 5% per decade since the 1960s.
In southern Europe, on the other hand, flood levels tend to decrease, as climate change results in declining precipitation and higher temperatures cause increased evaporation of water in the soil. However, for small Mediterranean rivers, floods may be becoming larger due to more frequent thunderstorms and land management changes such as deforestation.
In Eastern Europe, flood levels are also decreasing, which is due to shallower snow packs in winter associated with the higher temperatures.
If the trends in changing severity of flooding continue into the future, major increases in flood risk can be expected in many regions of Europe. With the total annual bill from flood damage – estimated to be $100 billion worldwide – continuing to rise, along with the devastating impact on communities, the researchers advised policymakers to include their findings in their flood management strategies.
Increasing flood discharges imply that, five decades ago the 100-year flood discharge – often used to design flood defences and critical infrastructure, is now likely to be exceeded on average more often than once in 100 years. In north-western Europe, what was the 100-year flood discharge in 1960 has now typically become a 50- to 80-year flood discharge, potentially making levels of protection offered by existing flood defense structures less safe.
Dr Murphy said: "Flood management must adapt to the realities of our changing climate and associated flood risk over the coming decades. Incorporating the evidence of increasing flood risk into engineering design and general flood management would ensure we are better prepared for future changes“.
The Nature publication will be available at https://www.nature.com/articles/s41586-019-1495-6 which will go live after the embargo expires.