Summer storms warning as climate change bites

The UK has been warned that climate change is set to see ever hotter and wetter summers with flash flooding events such as witnessed in London and across Europe becoming ever more common.

As Mayor of London Sadiq Khan called an emergency meeting of advisers to look at how the UK capital can better prepare to combat the floods, climate experts warned that global warming will have an effect on the future threat.

Dr Harvey Rodda, UCL Hazard Centre, Department of Earth Sciences, UCL, said: “The thunderstorms and intense rainfall which affected London over the weekend were not unseasonal or particularly severe. The rainfall totals (listed as around 40mm in 24 hours on some news sites) are also not particularly extreme when looking at rainfall records over the past 150 years in the UK as a whole and also compared the 24-hour totals of up to 150mm which led to the severe flooding in Belgium and Germany on 15-16 July.”

He added: “What is apparent however is the increasing frequency of these events with similar flooding occurring earlier in the summer, and also in recent years, interspersed with warm periods of maximum temperatures above 30 degrees Celsius.

“The drainage infrastructure in London also has a part to play in surface water flooding.  Many surface water sewers are old, have not been designed based on any hydrological studies, and are under-capacity.  Furthermore, local authorities are still accepting drainage designs for new developments which have been based on outdated data and methods from the 1970s rather than following the latest guidelines.”

“Without a specific attribution study it isn’t possible to know whether this event is linked to climate change,” added Dr Nikos Christidis, Senior Climate Scientist at the Met Office. “We know a warmer atmosphere can hold more moisture and that therefore rainfall events can become more extreme.  However, natural variations in rainfall mean that this event could be an example of a weather extreme that could have been feasible in the pre-industrial climate that was not affected by human greenhouse gas emissions.”

Another expert said that it was difficult for home and business owners to understand their exposure to the threat given the complexity of the UK’s system for monitoring extreme weather events. Dr Liz Stephens, hydrologist and associate professor of climate resilience, University of Reading, said:

“Despite improvements after the summer 2007 floods, when two-thirds of the 57,000 flooded properties were affected by surface water flooding, the UK still has a complicated set of roles and responsibilities for surface water flooding risk,” said Dr Liz Stephens, hydrologist and associate professor of climate resilience, University of Reading, said.  “Lead Local Flood Authorities take responsibility for managing it, the Environment Agency for mapping it, and the Met Office for providing early warning.  This makes it difficult for the public to have a good understanding of their own risk and what can be done.

“A landmark study in 2014 found that the intensity of summer rainfall events in the UK was expected to increase as a result of climate change, but the surface water flood hazard maps for the UK have not been improved since 2013.  These urgently need updating.

“The current accuracy of surface water flood maps reflects an investment choice and not what is possible with the state-of-the-art science.  It is deeply concerning that hospital emergency departments have had to close as a result of this flooding, and I hope that this is the wake-up call that the government needs to take this risk of climate change seriously.

“The precise location of the most intense rainfall, and consequently largest water depths, is difficult to forecast far in advance, and this uncertainty is reflected by the weather warnings covering such a large area – such as the Met Office’s amber weather warning covering most of south-east England on Sunday.

“It is difficult to help people prepare for surface water flooding if they don’t know they are at risk, and if they don’t receive precise warnings of the likely impacts when heavy rain is forecast.”

Dr Jess Neumann, Hydrologist, University of Reading, added: “Summer thunderstorms are not a new occurrence, but it is becoming ever clearer that the worsening impacts of flooding from intense rainfall are having devastating effects here in the UK and across Europe.

“Although it is not possible to attribute a single event to climate change, what we do know is that a warming atmosphere can hold more moisture and we are seeing an increasing number of storm events leading to flooding, with rainfall records being broken time and time again.  The severity and frequency of flooding is a stark warning that we are not prepared to deal with climate change.

“Parts of London have been flooded for the second time in less than a month, affecting people’s property, livelihoods and businesses but also critical infrastructure such hospitals and transport links.  Flash floods can rise quickly with devasting consequences.

“Flooding from intense summer rainfall is going happen more frequently.  No city, town or village is immune to flooding and we all need to take hard action right now if we are to prevent impacts from getting worse in the future.  There needs to be a complete shift away from all use of fossil fuels to renewable energy sources.  Planning and development need to consider flood risk from all sources (river, groundwater and flash floods) and adapt accordingly – it is not acceptable to keep paving over the land and expect the public to deal with the water when it comes into their homes.”

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