Floods and drought: Two sides of the same coin

Flood is a major risk in Europe: The Central European floods of 2002 and 2013 are only the most recent reminders of the loss potential of this peril. Of course, floods have happened throughout history, and occasional anomalies are to be expected, but studies confirm that climate change has significantly expanded the seasonality, and increased the severity and frequency, of floods in Europe, with clear regional patterns emerging.

Higher temperatures increase flood risk in Central and North Western Europe

A 2019 analysis of historical flood data revealed both increasing and decreasing trends over the last five decades.1 In large parts of Central and North Western Europe, flood-related river discharge increased up to 11% per decade, while the Mediterranean area and Eastern Europe showed a significant reduction.

The severity of floods depends not only on precipitation levels and the extent to which paved surfaces increase runoff, but also on soil moisture, snowmelt, and persistent weather patterns, all of which are influenced by warming temperatures. Variations in annual peak flood discharges don’t directly impact tail risk, but they are correlated to extreme flood events.

The same study highlights how the recurrence of typical "100-year floods" has changed from the 1960s to today.2 What was considered a 100-year flood 60 years ago now can occur every few decades — or even more frequently — in many regions in Central and North Western Europe. At the same time, return periods have increased significantly in South and Eastern Europe.

Urbanisation and population growth drive flood risk

Socio-economic factors also contribute to flood risk. Changing land use for forest management, agriculture and water drainage have significant effects. Urbanisation also impacts the hydrological cycle, as more paved surfaces increase runoff, overwhelming rivers during heavy rainfall. This reduction of natural absorption zones amplifies the impact of smaller flood events, in particular. Figure 1 shows that urbanisation could lead to a tenfold increase in the number of small floods, and a doubling in size of a typical 100-year event.3

Southern and Eastern Europe will suffer from drought

On the other side of the coin, rising temperatures will lead to increased evaporation and a decrease in rainfall in southern and eastern regions, potentially resulting in drought. And with drought comes the risk of subsidence, or soil movement. Long and intense dry spells can lower the ground so much that fissures in the earth appear, damaging the foundations of houses, bridges, industrial sites and other structures. Then sinkholes start to appear, causing the collapse of entire buildings. All are areas of potential protection gap in property insurance.

Losses from drought-induced subsidence have been rising. A study from Swiss Re and the Swiss Federal Institute of Technology in close collaboration with the National Centres of Competence in Research shows that in France alone, economic losses from soil subsidence rose by more than 50% between 1990 and 2010.4

Both frequency and severity of incidents of soil subsidence are likely to increase with climate change, which will require a full understanding of current conditions and integration of risk into a broader adaptation policy.

The solution isn't what you may think

The most urgent question we need to ask isn't how to tackle climate change, but how we can best adapt to a changing climate in order to avert the most damaging consequences — in short, how to mitigate climate risk, and how to make our world more resilient.

References

1 G. Blöschl et al., "Changing Climate Both Increases and Decreases European River Floods", Nature, vol 573, 2019.
2 Ibid.
3 G.E. Hollis, ”The effect of urbanization on floods of different recurrence interval“, Water Resources Research, vol. 11, no. 3, 1975.
4 T. Corti et al. “Simulating past droughts and associated building damages in France“, Hydrology and Earth System Science, 2009.

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