Graph of the Day: Large floods in Europe, 1985-2009

27 October 2013 (Norwegian Meteorological Institute) – A universal increase in flood maxima is not evident in Europe. Individual river gauges in Europe provide no conclusive and general proof as to how climate change has affected flood risk so far. There is evidence, however, that the number of large floods has increased.

The key causal factor, however, has shown an increase. Globally, over the past 50 years, heavy precipitation events have been on the rise for most extra-tropical regions, corresponding to a warmer Earth surface and lower troposphere. This includes widespread increases in the contribution to total annual precipitation from very wet days, days on which precipitation amounts exceed the 95th percentile value, in many land regions.

A similar trend is seen in Europe; according to observations, heavy precipitation has been on the rise in a warming climate over much of the region. However, intense precipitation in Europe exhibits complex variability and a lack of a robust spatial pattern. The principal seasonal effect is the increase in extreme precipitation in winter with heavy precipitation events becoming more frequent, even in regions with decreasing total precipitation amounts.

There is an increasing body of evidence showing unequivocal warming of the atmosphere, at all spatial scales. Corresponding precipitation changes have been less regular, but increases over land north of 30° N over the period 1901–2005 and decreases over land between 10° S and 30° N after the 1970s have been observed.

The rainfall statistics in Europe are strongly influenced by inter-annual and inter-decadal variability. Seasonality and structure of precipitation is subject to change as global warming affects the hydrological cycle. Winter precipitation has increased over much of Europe, in particular in the north, while summer precipitation has decreased, particularly in the south. Short and temporally isolated rain events have been regrouped into prolonged wet spells.

However, there are problems with availability of precipitation data, in general, and also with data homogeneity and accuracy, in particular in less developed countries, worldwide. These problems with data are particularly severe for heavy precipitation.

Despite the ambivalence of the precipitation data, flood damage has strongly increased due to a wide range of factors, and floods are an increasingly acute problem. Flood risk and vulnerability have had a tendency to increase over many areas in Europe, due to a range of climatic and non-climatic impacts whose relative importance is site-specific. Material damage caused by floods has been rising and the death toll continues to be high. Even if the most destructive floods occur elsewhere, Europe is not immune.

Extreme Weather Events in Europe: preparing for climate change adaptation [pdf]