Publication: Changing climate is affecting the flood regime

Seine flooding in Paris - January 2018 © Irstea / G. Thirel
Seine flooding in Paris - January 2018 © Irstea / G. Thirel

For the first time, an international study published in Nature, has demonstrated significant changes to high water flows across Europe over the last 50 years. Irstea contributed to the study by sharing its knowledge of hydrometric stations and of the impact of climate change on river regimes.

River floods cause considerable damage. Globally, it is estimated that the annual cost of this damage exceeds 100 billion dollars, and this sum continues to grow. How is climate change affecting flood intensity? Until now, existing studies have been unable to identify consistent continental-scale trends, particularly due to the limited spatial coverage of hydrometric stations.1

This study involving 35 European research groups provides a database containing flood peaks recorded at more than 3,700 hydrometric stations, more than 200 of which were in France. Results showed that the changes observed in Europe over recent decades are partly due to climate change. However, their impact is felt differently across the various European regions. Researchers noted an increase in flooding in northwestern Europe alongside a decrease in flooding in southern and eastern Europe.

 

Climate change - the deciding factor

Previous research has already shown that climate change is affecting the flood season. The aim of this study was to identify whether climate change was also having an impact on flood intensity. Researchers evaluated data from 3,738 hydrometric stations across Europe over a period of 50 years (1960-2010).

Flood changes in Europe
Changes to regional flood trends in Europe (1960-2010) © G. Bloeschl et al., Changing climate both increases and decreases European river floods, Nature

In France, the north of the country (up to the Loire river basin) is partly affected by the trend for increased flooding noted across northwestern Europe. However, the south of the country (excluding the Alps) is more affected by decreased flooding. Nevertheless, floods in small rivers and the risk of floods from surface runoff may be more significant because of an increase in storms.

 

Variations in flood flows

The extent of the changes to flood flows is significant. In the five decades studied, observations went from a drop in flood levels of up to 24% to an increase of up to 11% across Europe. If these trends continue into the future, they will have a significant impact on the flood risk of many European regions, and risk attribution (zoning, prevention and protection measures) will have to be adapted to this new reality.

 

Further information