Wet and dry: Is the UK’s weather going to get more extreme with climate change?
- 05 Mar 2013, 16:10
- Roz Pidcock
2012 was a year of extremes. Although it ended up being the UK's
second wettest year on record, the country also experienced
significant drought periods, according to new figures from the
Environment Agency (EA). We look at the science underpinning the
EA's announcement - and what it means for the UK's resilience to
extreme weather.
From extreme to extreme
According to the new EA figures,
released yesterday, over 20 million people in the UK were affected
by a hosepipe ban in early spring. But by the end of the year, more
than 6,000 flood warnings had been issued and 7,950 properties were
flooded.
Parts of the Tyne near Newcastle and the Ouse in Sussex went
from their lowest to highest average monthly flows in the space of
four months, the new figures show.
In total, 75 days last year saw flooding - equivalent to one in
every five days. But there was even more drought - 95 days
experienced drought conditions, or one in every four days.
Britain must build its resilience to be better prepared as the
risk of damage to UK lives and livelihoods continues to grow under
climate change, warned Environment Agency Chairman Lord Smith in
the EA's press
release yesterday. He said:
"The extremes of weather that we saw
last year highlight the urgent need to plan for a changing
climate."
The global climate is
warmer and generally wetter than it was at the start of the
century, according to a
recent analysis by the Met Office and a global team of
experts.
But attributing specific weather events to climate change
is difficult as there has always been extreme weather. Instead,
scientists talk about how climate change might be increasing the
likelihood of events reaching extreme proportions.
Drought days
Yesterday's press
release from the EA cited Met Office research from 2010
suggesting droughts as severe as the one the UK suffered in 1976
could occur
once every ten years by the end of the century.
But that might not tell the whole story. Factors other than
temperature and rainfall affect drought - like wind speed and
vegetation cover - which mean there is still a lot of uncertainty
in climate models about how the UK could be affected.
The once-every-ten-year figure from the press release is
actually the upper end of quite a large uncertainty range using
several versions of the same Met Office climate model (all
plausible) that treat drought in slightly different ways. At the
other end of the scale is a frequency of once every 50 or 100 years
- which is not too different from now.
What's more, the Met Office's research
wasn't intended to indicate which end of the scale is more
likely. Instead, it demonstrated just how much uncertainty
exists.
Another
paper from the Met Office later in 2010 says that although UK
climate projections "hint at an increase in the severity of
drought" in the second half of the 21st century:
"it is not yet possible to robustly
predict changes in UK meteorological droughts arising from
increased greenhouse gases".
This isn't to say the UK shouldn't be prepared for more frequent
droughts, just that predicting how severe they could be and which
parts of the UK will be hardest hit is far from an exact science
yet.
One problem is a lack of data. As lead author of both Met Office
papers, Dr Eleanor Burke, told Carbon Brief today:
"Since droughts by definition are rare
events, both model and observational data are really limiting when
it comes to trying to evaluate the impact climate change is having
on drought."
Flooding
Unlike drought, research suggests it might be
easier to link heavy rainfall events with climate change. The
Intergovernmental Panel on Climate Change (IPCC) concluded in its
Special Report on Extreme Events in 2012:
"[T]here is medium confidence that
anthropogenic influences have contributed to intensification of
extreme precipitation at the global scale".
A
recent study suggests greenhouse gas emissions contributed to
more intense precipitation over two thirds of the northern
hemisphere between 1950-2000. This is in part because rising
temperatures mean the atmosphere can hold more
moisture now than at the start of the century. Basic physics
suggests that more water in the atmosphere means that when it
rains, the volume of rainfall may
increase.
That doesn't automatically mean more heavy rainfall for the UK
because
complex weather patterns govern the amount, timing and
distribution of rainfall. But many studies - including
a government study on climate change risks - predict the UK
will experience more intense rainfall in the future, particularly
during the winter.
One complicating factor is
there's more to flooding than heavy rainfall - building houses
on flood plains and paving over natural surfaces make people more
vulnerable. The Met Office contributed to a study last year
predicting damages from river flooding could
double or triple across Europe by 2100.
Building resilience
So Britain needs to work on how to improve water supply during
periods of drought, while at the same time improving the UKs flood
defences for when heavy rain hits, Lord Smith explained in
yesterday's press release:
"More of this extreme weather will
exacerbate many of the problems that we already deal with including
flooding and water scarcity, so taking action today to prepare and
adapt homes, businesses, agricultural practices and infrastructure
is vital."
It's not just the UK talking about building resilience. This
week is the catchily-titled National
Severe Weather Preparedness Week in the US. The Climate
Commission in Australia also released a report today entitled "Angry
Summer", highlighting the influence of climate change on the
country's extreme summer - which saw temperature and rainfall
records tumble.
As ever, it's important to be careful when talking about the
role of human activity in extreme events and the same rules don't
necessarily apply to flooding and droughts. Throw the UK's
complicated weather systems into the mix and it's an even tougher
job. But the EA's figures do reflect a growing body of research
pointing to the fact that countries - including the UK - need to be
better prepared for extreme weather in the future.