Climate change is making extremely wet winters in the UK 25 per cent more likely, study concludes
- 30 Apr 2014, 16:00
- Roz Pidcock
Rambling0n Flickr Creative Commons
In the UK, the probability of seeing an extremely wet winter
like we did this year is 25 per cent higher than it was before
humans started influencing the climate, scientists announced at the
European Geosciences Union conference today.
The study's conclusion isn't the only noteworthy thing about it,
however - the research was done almost entirely with the help of
members of the public.
Just two months after the flood waters began to subside, an
Oxford University project
assessing global warming's effect on the odds of very wet winters
has produced its first results.
The scientists found greenhouse gases in the atmosphere as a
result of human activity have increased the risk of extreme
rainfall in the southern part of the country by about 25 per
Total rainfall (mm) for January in southern England from
records going back to 1910.
Official Met Office
figures show this year saw the wettest January and wettest
winter in England and Wales in at least 248 years, when records
In January, parts of the southern England received more than 200
per cent of the average rainfall for the month - shown in dark blue
in the maps above.
The weather@home project, supported by
The Guardian, is an example of what's known as 'citizen
science'. That's where members of the public dedicate some time and
resources to collecting or processing scientific data.
More than 60,000 volunteers offered spare capacity on their home
computers for scientists to run model simulations. The simulations
compared rainfall projections in a world influenced by past
greenhouse gas emissions with a hypothetical world with no human
influence on the climate.
Comparing the number of extremely wet winters between the model
simulations allowed an estimate of how much more likely an event
like we saw this winter has become due to greenhouse gas
One in 80-year event
The scientists found an extreme rainfall event that would
normally happen once every 100 years (i.e. there's a one per cent
risk of it occurring in any given year) is now happening more like
once in 80 years (or a 1.25 per cent risk). In other words, the
risk of a very wet winter has increased by 25 per cent.
The graph below of seasonal rainfall in mm shows the difference
between the dark blue "winter as observed" and the dark green
"winter in the world that might have been". The difference is
"small but statistically significant", say the researchers.
In total, the team ran more than 33,000 model simulations -
something project leader Myles Allen says they simply wouldn't have
been able to do without enlisting the help of the public.
The scientists point out they used a range of different climate
models and not all gave the same result. In some cases, models
showed no change in risk or even a reduction. But overall, the
simulations showed a small but significant increase in likelihood
of extremely heavy rain events for the south of England.
Coming just two months after heavy rainfall and flooding hit the
UK, these results have been produced in next to real-time. That's a
remarkable achievement and testament to the ability of this type of
crowdsourcing work, Allen told a press conference at the EGU
And these are still just early days for the project. In the next
few months, it's hoped the results can feed into impact models to
put an estimate on the likely material and economic damage from
such extreme events, Allen tells Carbon Brief.
Dr Friedereke Otto, a researcher at Oxford University who was
involved with the weather@home project explains:
"Total winter rainfall, although useful
as a benchmark, is not the direct cause of flood damage, so we are
working with collaborators, such as the Centre for Ecology and
Hydrology, to explore the implications of our results for river
flows, flooding and ultimately property damage."
Loading the dice
Last September, the UN Intergovernmental Panel on Climate Change
(IPCC) released a
bumper assessment of how and why the climate is changing. It
concluded that Europe and the UK is "very likely" to see more heavy
rainfall events by the end of the century.
Heavy rainfall and flooding can disrupt important transport
links, something we saw a lot of in the UK the this winter.
As temperatures rise, basic physics dictates an increase in the
amount of atmospheric moisture, which is the fuel for heavy
rainfall events. That means whenever we have heavy (and prolonged)
rainfall events in the future, we can expect them to be
Otto said greenhouse gas emissions have "loaded the weather
dice", so the probability of extremely wet winters has slightly
increased. Otto adds:
"It will never be possible to say that
any specific flood was caused by human-induced climate change. We
have shown, however, that the odds of getting an extremely wet
winter are changing due to man-made climate change."
Heavier rainfall plus
sea level rise - which make storm surges bigger and more likely
to breach coastal defences - has scientists warning of a greater flood
risk in the UK as the climate warms.