An international study conducted by Günter Blöschl of the Technical University of Vienna explains how the last three decades have been among the richest flood periods in Europe in the past 500 years. The study also shows how these last three decades differ from other periods full of river floods in terms of duration, extension in space, air temperature and seasonality of floods.
Compared to the past, the present period is more extensive, the seasonality of the floods has varied and the relationship between floods and air temperature has reversed. In the past, alluvial phenomena occurred more frequently in decades characterized by low temperatures, while today global warming is one of the main factors of their increase.
Data analysis identified nine flood-rich periods and the regions associated with them. Among the most relevant periods, 1560–1580 in western and central Europe, 1760–1800 with most of Europe, 1840–1870 in western and southern Europe and 1990–2016 in western and central Europe stand out.
Günter Blöschl said: "Our study shows for the first time that the mechanisms have changed: while in the past floods have occurred more frequently in colder conditions, it is now the opposite. The hydrological conditions of the present are very different from those of the past.
Despite the efforts needed to mitigate climate change, we will still see the effects of these changes in the coming decades. Flood management must adapt to this new reality."
All the risks for Europe
Alberto Viglione of the Polytechnic University of Turin, said: "We had already detected the influence of climate change on floods in Europe in the past 50 years.
However, it is also important to understand if what has been seen in the last 50 years is a completely new situation or if it is only a repetition of something that has already happened in the past. Until now, the available data had not been sufficient to answer the question.
Thanks to the work done in this study we can now confidently say that yes, the characteristics of the floods of the recent decades are different from those of previous centuries." Andrea Kiss of the Technical University of Vienna, herself a researcher and historian, said: "The challenge of this study was to make comparable texts very different from each other in type, dating and areas of origin.
We managed to achieve this comparability by contextualizing all the texts in the relevant historical periods, with careful attention to detail. " These changes are related to changes in rainfall, evaporation and melting snow and are an important indicator for distinguishing the role of climate change from that of other causes such as deforestation and river regulation.
These discoveries were made possible thanks to the new database created by the authors of the study, which includes the exact dating of almost all the flood events reported by sources in the historical archives.