#Europe; #ChangeInFloodPattern; #MostFloodRichPeriods; #MoreFloodsInSummer
Vienna (Austria), Jul 25 (Canadian-Media): The change in the flood pattern for the first time was found over the last decades in Europe compared to past centuries, according to an international research project coordinated by the Vienna University of Technology (TU Wien), with participation from researchers of the University of Barcelona, Spain. The study, published in the journal Nature, concludes we are in one of the most flood-rich periods in Europe from the last five hundred years.
Photograph of the Almanzora River in the town of Huércal-Overa (Almería) in the bridge of Santa Bárbara during the floods between October 18 and 19 in 1973. Photo provided by the Town Hall of Cuevas del Almanzora. Figure: structures still preserved from the bridge of Santa Bárbara built during the 19th century eighties. Image credit: Lothar Schulte/UB
The last three decades within the last half of the millennium, the study said, are among the most important periods regarding the frequency and magnitude of floods in Europe, the distribution of the floods, as well as the temperature of the air and flood seasonality have changed, with a higher percentage of floods in summer.
Whereas from 1500 to 1900, floods used to take place with higher frequency during cold climate phases, while after 1990, floods increased within the context of global warming.
Nine periods of floods that were more abundant and the associated regions were identified after analysis of the data., the most notable periods being 1560-1580 (western and central Europe), 1760-1800 (most part of Europe), 1840-1870 (western and southern Europe), and 1990-2016 (western and central Europe).
The analysis also highlighted that the current phase is the third most severe regarding floods.
Now, floods cause annual damages accounting for more than 100,000 million euros, and the general tendency of abundant floods is increasing.
Historical data from half a millennium
The international study, coordinated by Günter Blöschl, director of the Institute of Hydraulic Engineering and Water Resources Management in TU Wien with participation of thirty-four research groups from all over Europe, among which are also researchers of the National Museum of Natural Sciences (CSIC Madrid) and the University of Almería (UAL).
In the study, thousands of historical documents with direct and contemporary information on flood episodes in Europe from 1500 to 2016 were analysed by the researchers.
Historical data from Spain and a part of the series in Switzerland was provided by the research teams of the University of Barcelona, CSIC and the University of Almería, which possess detailed records in the European context.
"The special challenge of this study was to compare sources and texts that were very different from others from other centuries and cultural regions", said Mariano Barriendos, researcher at the Department of History and Archaeology of the UB, together with Andrea Kiss (TU Wien).
Those texts were studied in their historical context with deep attention to details and a cross-check between episodes of different kinds of documents, places and basins. For instance, the case of data in the Spanish Mediterranean watershed, this check included 4,500 flood cases.
Differences in current river floods
The result of the comparison with air temperature reconstructions in all Europe which verified that the most notable historical flood periods were colder than intermediate phases seemed to contradict the observation which states that in some areas, such as northern-eastern Europe, the recent warm weather is aligned with severe floods.
"The co-variability of temperatures and rainfall, and their modifications, as well as the intensification or weakness due to atmospheric dynamics, can be key aspects to understand those processes", said Fernando Sánchez Rodrigo, physicist at the University of Almería.
The seasonality of floods within the year has changed as well. Previously, the 41% of floods in central Europe took place in summer, compared to the nowadays' 55%. These shifts are related to changes in rainfall, evaporation and snowmelt, and are an important indicator to distinguish between the role of climate change and other control factors such as deforestation and river management.
These results have been obtained from a new database compiled by the authors of the study, which includes the exact dating of almost all flood episodes recorded in documentary and bibliographical sources.
Gerardo Benito, research professor of Earth Sciences of the CSIC, notes that this database provides direct proof of the level of floods during periods of climate crisis, with a high potential for risk studies.
The new study is the first to assess historical periods of floods for a whole continent with such detail during the last five hundred years.
Better data, better forecasts
Due to the change in flood generating mechanisms, use of tools, was advocated by Günter Blöschl, to study the risk of floods that capture the physical processes involved as well as management strategies to incorporate recent changes in the risk analysis.
It is highlighted by the team of authors that the adaptation of the management of floods should be done by keeping in mind new realities of the effects of this phenomenon during the coming decades.