The last 30 years have been the worst in history in terms of flooding; in Spain, they are on the rise in autumn since 1940.

Images of the floods suffered by Los Alcázares in the DANAS in September and December and the storm Gloria in January.

A study with the participation of scientists from the CSIC, the University of Barcelona (UB) and the University of Almería (UAL) shows that the current higher frequency of floods is exceptional in comparison with the last 500 years.

The work, which appears published in the magazine Nature, shows that the last three decades (between 1990 and 2016) is it so among the most abundant periods in number of floods, being also the second largest in spatial extension with almost two million square kilometers affected in Europe.

In total, they have been collected 9,576 floods obtained from historical documents based on chronicles, annals, administrative and legal records, newspapers and private and official correspondence, as well as data on sediments deposited by past floods.

“With this volume and extent of flood data at daily resolution, it was obtained that the recent period is among the most abundant in the number of floods, being the second largest in spatial extent (almost two million square kilometers) and the third largest in spatial temporal extent, which means that Not only did it cover a large part of Europe, but it has also had a significant duration in time“, Emphasizes Gerardo Benito, CSIC researcher at the National Museum of Natural Sciences (MNCN-CSIC).

Scientists have also identified changes in the seasons of the year when floods occur. For example, 40% of historical floods in central Europe occurred in summer, while these have currently increased up to 55%. In Spain, floods have increased particularly in autumn, a change that began in the 1940s. Periods abundant in floods were those between 1760 and 1800, and between 1840 and 1870.

“In most of Europe, previous flood-heavy periods occurred during colder than usual phases; but nevertheless, the current period has been much warmer“, Highlights this researcher.

Climate change as a driver

The work confirms that climate crisis alters floods because it produces changes in atmospheric circulation. “Currently there is concern that climate change is altering the frequency and magnitude of floods in an unprecedented way. However, up to now it has been difficult to verify this because the flow measurement records in rivers are relatively short ”, explains Benito.

It also shows that while flood management is currently based on the analysis of systematic data over the past decades, extending the time interval to past centuries would greatly strengthen the analysisas they can provide a more comprehensive guide to possible future flood hazard changes.

“This would allow the creation of predictive tools that can improve adaptive capacity on a global and local scale. Undoubtedly, this work demonstrates the potential of documentary data and geological records from the past to contribute to this work ”, adds the CSIC researcher.

The finding that the past 30 years are separated from past flood-rich periods by a time gap of about 90 years may explain why recent floods have surprised public agencies so much in charge of managing risks.