Study: Human Activity Increased Likelihood and Severity of July Floods in Western Europe

The con­ven­tional wis­dom has long been that it is dif­fi­cult to attribute any sin­gle event to cli­mate change. However, the sci­ence on extreme weather attri­bu­tion has advanced rapidly in the past half-decade.

A recent report from the World Weather Attribution Initiative has con­cluded that the extreme flood­ing events expe­ri­enced west­ern Europe from July 12 to 15 were made more likely as a result of cli­mate change.

Over the course of three days, heavy rain­fall asso­ci­ated with a cold, low-pres­sure weather sys­tem known as the Bernd led to severe flood­ing in west­ern Germany and its neigh­bors, caus­ing mil­lions of Euros of dam­age and killing 226 peo­ple.

Germany bore the brunt of the extreme weather event, but flood­ing also occurred in Belgium, Luxembourg, the Netherlands and Switzerland.

As extreme weather events con­tinue to dom­i­nate the news cycle, sci­en­tists have been rac­ing to find out how much cli­mate change is respon­si­ble for any sin­gu­lar event.

To deter­mine the role of cli­mate change in July’s floods, the WWA researchers focused on the hydro­log­i­cal fac­tors that trans­formed the heavy rain­fall into his­toric flood­ing.

The researchers found that the areas around the Erft and Ahr, Germany, as well as the Meuse region in Belgium, expe­ri­enced as much as 90 mil­lime­ters of rain­fall in 24 hours.

The researchers found that cli­mate change dri­ven by human activ­ity inten­si­fied the rain in this region by three to 19 per­cent. High tem­per­a­tures, which increase the abil­ity of the atmos­phere to hold mois­ture, also con­tributed to the down­pours and increased the like­li­hood of heavy rain­fall by a fac­tor of 1.2 to nine.

“We com­bined the knowl­edge of spe­cial­ists from sev­eral fields of study to under­stand the influ­ence of cli­mate change on the ter­ri­ble flood­ing [in July], and to make clear what we can and can not ana­lyze in this event,” said Sjoukje Philip, a cli­mate researcher with the Royal Dutch Meteorological Institute and part of the WWA team.

“It is dif­fi­cult to ana­lyze the cli­mate change influ­ence on heavy rain­fall at very local lev­els, but we were able to show that, in west­ern Europe, green­house gas emis­sions have made events like these more likely,” he added.

Along with the floods in west­ern Europe, the WWA also con­cluded that the record-break­ing heat­wave along the west­ern coast of North America ear­lier this sum­mer and the April cold snap across south­ern Europe were made more likely as a result of cli­mate change.

• World Weather Attribution Initiative
• BBC
• Reuters