August 23, 2021

expert reaction to analysis of climate change and July’s flooding in Europe

A report issued by World Weather Attribution looks at climate change and the heavy rainfall events that lead to severe flooding in Western Europe during July 2021.

Prof Hannah Cloke, a natural hazards researcher at the University of Reading, said:

“The report by the World Weather Attribution Group provides a useful analysis of the link between climate change and these floods. It also highlights the difficultly in attributing specific flood events to climate change. Flood disasters are complex events that are caused by a combination of weather, the conditions of rivers, soils and vegetation, and where people are and how they respond. The authors have decided to focus on the key natural factor in these floods, the extreme rainfall.

“They conclude that climate change has made extreme rainfall events of this type more likely in this region. The range of this increased likelihood is wide – somewhere between 20% and 800% more likely. Patterns of rainfall are linked to a complex set of climatic influences, such as winds and moisture levels in the air and on land, which are themselves influenced by other factors. It’s therefore hard to exactly pinpoint how rainfall levels have changed as a result of climate change.

“They also show that when extreme rainfall events do happen, they can be more extreme, dumping more rain than would have fallen in a world without warming.

“It is crucial to highlight how climate change makes floods and other impacts on people more likely, but it is important that we do not use climate change as an excuse for inaction. Individuals, local authorities and governments still have the power to make specific, local changes that can save lives and protect property from the worst impacts of floods. Blaming others far away, or long ago, for these problems just shirks responsibility.

“We must tackle climate change, or these problems will only get worse in the future. We have to do more to adapt ourselves to deal with the natural hazards that we face now, whether they are made worse by climate change or not.”

Dr Linda Speight, a hydrologist at the University of Reading, said:

“The results from this attribution study are robust assessment of the meteorological conditions that contributed to the floods in Germany. They use well established methods and comprehensively assess both the data and climate models available for use in the study.

“The study openly acknowledges that climate attribution for events like we saw in Germany, which are very extreme (above any of the previous gauged records) and are driven by localised convective rainfall processes, is challenging. In response to this the confidence bounds given seem reasonable. It is disappointing,  but unsurprising, that the study was only able to focus on the meteorological aspects due to the lack of both event and historical observed river levels over long enough time periods. As such I think that they are right to only focus on the rainfall.

“There is an important acknowledgment that damage from floods is not only driven by the rainfall but by catchment conditions, in this case existing wet catchment acted to increase river levels, and that flood impacts depend on where people and property and located as well as their vulnerability.

“The message I take away from this is that when floods occur they are getting more extreme, and if the earth continues to warm they will continue to do so. Events like this must promote action to improve flood resilience across all aspects of flood risk management. However the challenges that the authors had in terms of being able to understand the hydrology of the event given the limited available data (and the fact that the event was so extreme a lot of the potential gauged records were unreliable) and the difficulties of representing small scale convective rainfall events in climate models.

“Whist scientists are continuing to work to develop methods to address these challenges, there is no time to wait for science to catch up with the urgent need for action. The headline findings, which are based on robust and well documented science, that that climate change has made extreme rainfall events between 1.2 and 9 times more likely must be a call to action.”

‘Rapid attribution of heavy rainfall events leading to the severe flooding in Western Europe during July 2021’ by Frank Kreienkamp et al. is issued by World Weather Attribution on Monday 23 August.

Declared interests

None received.