Climate change found to increase heavy rains like those of UK’s Storm Desmond
In the second real-time extreme weather attribution study in the context of the World Weather Attribution project the team found a 5-80% increase in the likelihood of heavy precipitation like those associated with storm Desmond to occur due to anthropogenic climate change.
The Atlantic Storm Desmond brought torrential rain and gale-force winds to parts of England, Scotland, and Ireland from early Friday, Dec. 4 to early Sunday, Dec. 6. The fourth named storm of the Autumn/Winter 2015 season, Desmond dumped so much rain in such a short period of time that the U.K. provisionally set a new all-time national record for the greatest 24-hour rainfall when 13.44 inches (341.1 mm) of rain fell on Honister, Cumbria between 6:30 p.m. Dec. 4 and 6:30 p.m. Dec. 5. The U.K. Met Office issued a rare red “take action” warning – the first since 12 February 2014 – for parts of Cumbria and the Scottish Borders as a result of this powerful storm. The excessive nature of this record rainfall event, which led to flooding of more than 5,000 homes and businesses, and left over 60,000 people without power has led many to question whether climate change played a role, especially since there have been several large floods over the last decades.
To assess the potential link between the U.K.’s record rainfall and man-made greenhouse gases in the atmosphere, the CPDN team together with the Royal Netherlands Meteorological Institute (KNMI), as part of the World Weather Attribution (WWA) partnership led by Climate Central conducted independent assessments using three peer-reviewed approaches. These approaches involve statistical analyses of the historical temperature record, the trend in a global coupled climate model, and the results of thousands of weather@home simulations. Applying multiple methods provides scientists with a means to assess confidence in the results.
Based on these three approaches – all of which are in agreement – we found that global warming increased the likelihood of the heavy precipitation associated with a storm like Desmond. The increase is small but robust. It should be noted that a positive attribution for an extreme rainfall event like Desmond is still somewhat rare. Evidence of this can be found in a summary of the events analysed as part of the annual BAMS Special Issue on Explaining Extreme Events from a Climate Perspective. Whereas the vast majority of heat events studied found a climate change signal, less than half of the papers looking at extreme rainfall events found a human influence.
By comparing recent extreme events with the historical record and climate model simulations, we found that an event like this is now roughly 40% more likely due to climate change than it was in the past, with an uncertainty range of 5% to 80%. It is important to note that this analysis only considers externally driven changes in precipitation. It does not take into account other factors that influenced the flooding. While our analysis provides evidence that climate change has aggravated the flood hazard in this part of the world, risk is also determined by trends in exposure and vulnerability. As events like this become more common in the U.K., it will be important to discuss both changing risks associated global warming and the overall adequacy of flood defences.
Following a press briefing of these findings by CPDN’s Friederike Otto and WWA colleague Maarten van Aalst during the climate conference in Paris, the research findings were widely covered in the British press. With the first article below being the title story of FT UK online on Friday 11th December.
http://www.ft.com/intl/cms/s/0/e1466920-9f81-11e5-8613-08e211ea5317.html#slide0
http://www.mirror.co.uk/news/uk-news/climate-change-blame-devastating-storm-6992177
At the same time of the press briefing a scientific paper with the details of the research has been submitted to the open review journal Hydrology and Earth System Sciences (HESS).
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