Current European flood-rich period exceptional compared with past 500 years


Overflowing rivers can cause enormous problems: Worldwide, the annual damage caused by river floods is estimated at over 100 billion dollars - and it continues to rise. To date it has been unclear whether Europe is currently in a flood-rich period from a long-term perspective. In addition to the many other historical places of this study, Augsburg can, despite various calamities in its over 2000 year old history, refer to a very good historical data situation. The importance of flowing water, at least since Roman times, is also reflected in Augsburg's designation as a UNESCO World Heritage Site.

A large international study involving scientists from the University of Augsburg as well as the TU Wien (Vienna) provides clear evidence that the past three decades were among the most flood-rich periods in Europe during the past 500 years, and that this period differs from others in terms of its extent, air temperatures and flood seasonality. Compared to the past, floods tend to be larger in many places, the timing has shifted and the relationship between flood occurrence and air temperatures has reversed. In the past, floods tended to occur more frequently in cold phases, while today, global warming is one of the main drivers of their increase. The results of the study have now been published in the Nature Research Journal.

Historical data from half a millennium

" According to the present study, we can state a change in the overall climatic conditions for the emergence of the last flood-rich phases (1990 - 2016) since the year 1500. Here, too, climate change is a driver towards more extensive and extreme damage events.," says Dr. Oliver Böhm from the Institute of Geography at the University of Augsburg, a co-author of this study. Blöschl states further: "For forecasts of the next decades, however, it is also important to understand whether this is a completely new situation or whether this is just a repetition of something that has already occurred. So far, the available data had not been sufficient to ascertain whether this is the case or not. We have examined this question in great detail and can now say with confidence: Yes, flooding characteristics in recent decades are unlike those of the previous centuries.” For the study, tens of thousands of historical documents containing contemporary flood reports from the period 1500 to 2016 were analysed. The TU Wien team has worked with historians from all over Europe. "The particular challenge of this study consisted in making the very different texts of the different centuries and different cultural regions comparable, explains Andrea Kiss from the Vienna University of Technology, researcher and historian herself, and one of the key authors of the publication. "We managed to achieve this comparability by putting all the texts in their respective historical contexts with painstaking attention to detail."

Formerly cold, now warm: River floods now function differently

The data analysis identified nine flood-rich periods and associated regions. Among the most notable periods were 1560–1580 (western and central Europe), 1760–1800 (most of Europe), 1840–1870 (western and southern Europe) and 1990–2016 (western and central Europe). Comparisons with air temperature reconstructions showed that these historical flood periods were substantially cooler than intervening phases. "This finding seems to contradict the observation that, in some areas such as in the northwest of Europe, the recent warmer climate is aligned with larger floods," says Blöschl. Prof. Buermann from the Institute of Geography at the University of Augsburg, who was not part of the study, says “These impressive results add to a body of growing evidence showing that the water cycle has fundamentally changed in recent decades”. The timing of the floods within the year has also changed. Previously, 41% of Central European floods occurred in the summer, compared to 55% today. These shifts are related to changes in precipitation, evaporation and snowmelt and are an important indicator for distinguishing the role of climate change from that of other controls such as deforestation and river management. This meta-analysis has been made possible with a new data base compiled by the study authors that includes the exact dating of almost all flood events reported by written historical sources. So far, one had to often rely on other, less precise sources of information, such as lake sediments. It is the first study worldwide to evaluate historical flood periods for an entire continent in such detail.

Better data - better forecasts

Because of the shift in the flood generating mechanisms, Günter Blöschl advocates the use of tools for flood-risk assessment that capture the physical processes involved, and management strategies that can incorporate the recent changes in risk. "Regardless of the necessary efforts of climate change mitigation, we will see the effects of these changes in the coming decades," says Blöschl. "Flood management must adapt to these new realities."

Original publication

Blöschl G. et al., Current European flood-rich period exceptional compared with past 500 years, Nature 583, 560-566 (2020).

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Head of chair
Physical Geography and Climate Science

Univ.Prof. Dipl.-Ing. Dr.techn. Günter Blöschl

Institute of Hydraulic Engineering and Water Resources Management
TU Wien

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