In Brief

Alpine flooding

Flooding is a significant natural hazard that affects many people worldwide every year

Words by Stephen McHugh
16 May 2022

The European Alps are prone to flooding and this densely populated region is experiencing a high warming rate

Flooding is a significant natural hazard that affects many people worldwide every year. Understanding flood frequency and severity is critical to minimising the human and economic costs, but climate change is likely to alter flooding patterns, making risk management more complicated.

Bruno Wilhelm at the Université Grenoble Alpes, France and colleagues compiled and analysed palaeoflood and temperature records from the European Alps over the past 10,000 years to assess whether there is a relationship between changing temperature and the frequency and magnitude of floods. The team chose the European Alps because mountainous areas are particularly prone to flooding and this densely populated region is already experiencing a high warming rate that may be leading to more frequent heavy rainfall events.

Interestingly, the researchers find that past warming tended to coincide with a decrease in flood events

Interestingly, the researchers find that past warming tended to coincide with a decrease in flood events. Specifically, warming of 0.5 to 2 °C coincides with a 25–50% decrease in the frequency of large flood events (those that typically have a recurrence interval greater than ten years). The team suggest that floods are more frequent during colder periods because the soil moisture content is high and precipitation increases due to the prevailing westerly winds and incoming storm track. However, there is some evidence that past warming is linked to an increase in extreme flood events (those with a recurrence interval of greater than 100 years) in small alpine catchments, with these events triggered by localised but intense convective storms.

The work highlights the value of palaeoflood data and the need for records covering at least 200 years, so that robust flood patterns can be detected.

While the analysis is limited to the Alps, and research in different environments and locations is crucial to improve our understanding of flood risk, the results illustrate the complexities of flood responses to changing climate.