The Outlook for Europe: More Intense and Unusual Rainstorms
A hard rain’s a-gonna fall
European rainfall is often determined by the location and characteristics of the jet stream. This varies over time and is driven by cool air masses drifting down from the Arctic meeting moisture-laden warm air flowing up from the tropics. This year, the jet stream worked itself into an “Omega block” pattern. For people living in Western Europe, this development was unfortunate.
The result was an exceptionally moist low-pressure system that lingered over Western Europe for several weeks. The system spawned a series of destructive weather events including two named storms, Elvira and Friederike.
In Paris, the Seine reached its highest level in 30 years. In parts of southwestern Germany, up to 10 cm of rain fell in two hours; more rain than the region typically experiences in several weeks. Red weather warnings were issued for the Seine-et-Marne department in France as well as four states in central and northwestern Germany; these rare warnings are only issued when people need to “take action to protect themselves and their properties.”
In addition to bringing heavy rain, intense thunderstorms with lightning and hail formed along the boundary between the cold, dry air from the north and the warm moist air from the south and east. Southern Bavaria, for example, was pounded with hail up to 5 cm in diameter.
The riverine floods, flash floods, hailstorms and lightning strikes produced by these storms caused considerable damage, especially in Germany and France.
Tragically, 16 people were killed, and fatalities were recorded in Germany, France, Romania, Belgium and Poland. A lightning strike on a football pitch in southwestern Germany injured about 35 people, including many children. Another in Paris struck 11 people, including eight children.
Insured losses are estimated at EUR 1.2 billion in Germany and around EUR 2 billion in France. Overall economic losses in the countries affected are expected to total about EUR 4 billion.
Here to stay?
The Loire and Seine are susceptible to flooding during the winter when excess water builds up over several months. This year, they flooded in May-June. Perhaps disturbingly, the historical record shows only two instances in which these river basins experienced flooding outside the months of December-March. Those were in July 1659 and June 1856.
Elvira and Friederike were preceded by Desmond, Eva and Frank, three major storms that belted the UK and Ireland last December.
This troika of storms caused widespread flooding and made December the wettest calendar month in the UK since recordkeeping began in 1910. During Desmond, 341.4mm of rain fell in 24 hours at Honister Pass in northern England, setting a new national record for rainfall accumulation over a 24-hour period.
It was also the warmest December on record in the UK with an average temperature of 7.9C, 4.1C greater than the long-term average.
What role, if any, did climate change play in these episodes of extreme and unusual rainfall?
That’s the topic some climate scientists are investigating in the expanding subfield known as “attribution” research. Armed with more data and more sophisticated models, these researchers are probing the relationship between extreme weather and global climate change.
These scientists stress that the objective of attribution research is to investigate the relative contribution of global warming to severe weather events. As Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology, put it, “We cannot and should not say that a particular (event) is caused by global warming. But we can say that the probability of such an event is different today than in the pre-industrial era.”
Attribution modeling of these and other recent weather episodes found that climate change is contributing to the increasing frequency of intense and unusual rainstorms in Europe.
A team of researchers affiliated with the World Weather Attribution (WWA) partnership, for example, analyzed Desmond using three different climate models. Each produced a similar result: “the team found that an event like this is now roughly 40 percent more likely due to climate change than it was in the past.”
The WWA also analyzed the recent torrential rains in France and Germany. (Some of the same researchers participated in both efforts.) The analysis concluded:
“By comparing recent 3-day precipitation extremes in April-June with the historical record and climate model simulations, the team found that an event like this is now expected to occur roughly 80 percent more often due to climate change than it was in the past for the Seine River Basin. For the Loire River Basin, the team found that an event like this is now expected roughly 90 percent more often due to climate change than it was in the past .... The results for Germany are inconclusive.”
A multidimensional threat
These recent episodes also underscore the challenges involved in preparing for and responding to extreme weather events.
Of all the dangers posed by these types of rainstorms, riverine flooding is perhaps the most manageable – although it can still be immensely damaging. Floodplains are well mapped, and there are structural and non-structural measures that can be taken to minimize the impacts.
Also, riverine floods can often be predicted up to several days in advance so that local communities have time to prepare. (Click here to read more about the European Flood Awareness System.)
As Elvira and Friederike showed, however, there are other, harder-to-tackle threats in addition to riverine flooding.
Lightning, for example, is volatile and unpredictable. While measures can be taken to minimize damages to buildings, the only option people have is to take cover in a safe place.
Similarly, it's hard to predict where and when locally powerful hailstorms will occur, and hailstones can quickly cause substantial damage, especially to crops and automobiles.
Flash floods also develop quickly, and people in the path of a fast-moving wall of water often have only mere minutes to get out of the way. And the scope of the devastation left behind can grow rapidly as a flash flood gathers force and accumulates more and more debris.
Preparation is vital
For companies doing business in Europe, the varied threats posed by damaging and unusual weather require multifaceted responses. Perhaps most importantly, risk managers need to be aware that the threats are pervasive, and it’s not just structures located in known flood-prone areas that are in danger.
Which means that disaster planning is critical.
Property risk engineers can help companies develop emergency plans based on their particular circumstances, and that include measures for lessening the impact of a strong storm as well as for speeding the path to recovery. The latter is especially important given that lost revenues, damaged customer relationships and related financial impacts often exceed the property damage costs.
As the risk landscape changes, driven in part by climate change, companies should also assess the adequacy of their Property insurance policies to mitigate the risks associated with volatile and intense rainstorms.
Many climate scientists believe that “a hard rain’s a-gonna fall” is increasingly likely in Western Europe. That’s an unfortunate prospect, but one that companies would be advised not to underestimate.
Deutsche Welle, Climate change is making our summers more extreme, 30.06.2016
New Scientist, Understanding climate change’s role in the UK’s recent floods, 06.01.2016