Climate-driven Changes in German Floods

Severe flooding has occurred in Germany over the last few decades, causing loss of life, displacement of people and livestock and heavy financial losses. For example, severe damage was caused in the Rhine river basin in 1993 and 1995, the Odra basin in 1997, the Danube basin in 1999, 2002 and 2006 and the Elbe basin in 2002. There is growing concern that climate change is to blame for increased flooding.

The researchers studied water flow measurements for the period 1951-2002 from 145 gauge stations across Germany to detect trends in the number and size of floods. The study used eight flood indicators, including annual, winter and summer maximum discharges and flood peak measurements, particularly in the large catchments of the Danube, Rhine, Elbe and Weser rivers.

Significant changes and trends in flood behaviour were found for the major catchment areas, suggesting that flood hazards have increased for large parts over the last 50 years. Findings include:

• Most indicator measurements had increased over time in western, southern and central areas (Danube, Rhine, Weser river basins) of Germany, particularly annual maximum discharges

• Smaller changes occurred in the northeast of the country (Elbe basin)

• Winter floods dominate the Rhine and Weser catchments

• More sites are affected by summer flooding in the Danube catchment than the Rhine and Weser catchments

• A cluster of gauges showing decreasing summer floods was detected in the Elbe and Weser basins

• The frequency of floods increased, especially along the River Danube

The clustering of flood sites and seasonal floods suggest that the changes have been driven by the climate. The researchers compared their results with other studies that have looked at changes in climate, particularly in the circulation patterns in the atmosphere. Such patterns appear to be related to flooding in Germany. The frequency and duration of atmospheric circulation patterns above Europe is suspected to be linked to floods.

For example, during the winter, increasing westerly circulation patterns have caused greater rainfall and for longer periods. This can cause saturation of the ground over a large scale with subsequent faster run-off. Moreover, winter temperatures have risen over the last 100 years. These climate change findings are consistent with, for example, the upward trends of the maximum discharges detected in the Elbe and Weser catchments in the winter. The researchers suggest the milder winters and intensified rainfall may have increased flooding.

In summary, flooding behaviour has increased in Germany over the last five decades. The pattern of flood changes varies significantly on a regional scale although this appears to be driven by wider-scale climate change.