Pioneering analysis projects extreme rainfall in UK may be more common and erratic over next century as impact of climate change intensifies
Press release issued: 7 March 2023
A new set of 100-year climate projections has been created to assess the likelihood of heavy rain downpours in the UK, which can cause flash flooding, over the coming years and decades.
Its findings, published in Nature Communications, showed that under a high greenhouse gas emissions scenario extreme rainfall events could be four times as frequent by 2080 compared to the 1980s. Previous less sophisticated models show a much lower increase of around two and a half times over the same period.
The higher-resolution Met Office model (with km-scale grid spacing), providing greater levels of detail and accuracy, also revealed likely increases were significantly greater in certain regions. For example, extreme rainfall events in Northwest Scotland could be almost 10 times more common, while they were found to be closer to three times more frequent in the south of the UK.
As the atmosphere warms it can hold more moisture, at a rate of 7% more moisture for every degree of warming. On a simple level, this explains why in many regions of the world projections show an increase in rainfall as a consequence of human-induced climate change.
This study has shown that during extreme rainfall events in the UK the intensity of downpours could increase by 5-15% per °C of regional warming. This change is also uneven across the UK, with the greatest shifts projected to occur in the Northwest of the UK and less change seen in the central and south regions.
Lead author Met Office Climate Scientist Lizzie Kendon, Professor of Climate Science at the University of Bristol Cabot Institute for the Environment, said: “Being able to look at our projected future climate in such detail has unlocked an incredible amount of information and has shown how expected increases in intense rainfall events will actually manifest at local scale and for the coming years. Having this level of detail is crucial to ensure that we’re prepared for the possible extremes of the future.
“The greater future increases in the number of extreme rainfall events in higher compared to lower resolution models shows the importance of having km-scale projections to enable society to adapt to climate change.”
Although there is a long-term increase in the number of extreme rainfall events in the UK over the next century, the number of events annually remains erratic much like the observational record. As the climate warms, it is notable how variable the number of events becomes year to year.
Professor Kendon said: “The observed rainfall record in the UK is fairly erratic with a large amount of variability, these latest projections show that this is likely to continue through the century. What we can see from the higher resolution output is an even more erratic frequency of extreme events each year, so this could mean we see clusters of record-breaking intense rainfall events, followed by a period when no records are broken. Despite the underlying trend, these pauses in the intensification of local rainfall extremes can last a surprisingly long time – even multiple decades.”
The research highlights the importance of meeting carbon emissions targets and also planning for increasingly prevalent extreme rainfall events, which look highly likely, to varying degrees of intensity, in all greenhouse gas emissions scenarios.
The tendency for extreme years to cluster poses key challenges for communities trying to adapt and risks infrastructure being unprepared, since climate information based on several decades of past observations may not be representative for the following decades.
This model therefore provides a vital tool for planners and policy makers preparing for a climate-resilient future.
Professor Kendon said: “Another concern is apparent sudden transitions to a much higher frequency of extreme events illustrated by the model output. This would suggest a sudden increase in the numbers of extreme rainfall events, outside of the experience of recent decades. If this scenario did happen it could lead to impacts where infrastructure was unprepared for such a change in our weather.”
'Variability conceals emerging trend in 100yr projections of UK local hourly rainfall extremes' by Kendon E.J et al. in Nature Communications