Five things to know about flooding and climate change
- 27 Nov 2012, 15:00
- Freya Roberts and Roz Pidcock
Heavy rainfall continues to batter the UK this week, causing widespread
disruption. The Environment Agency has issued hundreds of
flood warnings and evacuated many from their homes. Is this
unpredictable weather normal, or is there a link between flooding
events like this and climate change?
Here's five things you should know about linking climate change
1. A warmer atmosphere holds more
According to the Intergovernmental Panel on Climate Change (
IPCC), the atmosphere is about 0.75
degrees warmer than it was at the start of the century, which
means it can hold 5-6 per
cent more moisture.
That doesn't automatically mean more heavy rainfall for the UK
because complex weather patterns govern the amount, timing and
distribution of rainfall. But it does mean that with more
water in the atmosphere, the volume of rainfall may increase
when it does pour.
This isn't the end of it though, because climate change
may affect atmospheric circulations like the
Jet Stream, which control the movement of weather systems over
the UK. Research on this is still fairly new, however, and the link
remains less than certain for now. But it's another reason why the
climate change link to flooding is complicated.
2. Evidence of heavier rainfall in the past is limited,
Extreme events are rare, and detecting trends outside natural
variability requires decades of continuous observations. So even
though there's a theoretical link between climate change and
rainfall, it's hard to find clear evidence yet because the record
of measurements is short and doesn't cover all parts of the
Globally, that makes it hard to distinguish any trend in the
intensity or frequency of flooding due to climate change, as the
IPCC concluded in its
Special Report on Extreme Events. But in Europe, where more
data on rainfall exists, there's some evidence for a trend towards
recent study finds greenhouse gas emissions contributed to
observations of more intense precipitation over two thirds of the
northern hemisphere between 1950-2000. Finding trends like this is
difficult with a small data set on rainfall, but should become
clearer as more extreme events occur over time.
3. Attributing specific events to climate change is
tricky, and flooding is no exception
In general, scientists are wary of attributing specific extreme
events to climate change because it's impossible to say whether an
event would have happened if global temperatures weren't
increasing. It's more helpful to consider how climate change may
have contributed to the frequency or severity of such events.
A recent study found although the precise human contribution to
widespread flooding in England and Wales in 2000 is difficult
to pinpoint, global greenhouse gas emissions increased the risk of
up to 90 per cent. Such careful analysis of the data takes time
and linking the current flooding in the UK to climate change is not
4. Scientists predict that heavy rainfall will increase in
Flooding occurs in a number of ways, and each may be affected by
change. Surface water flooding occurs where heavy rainfall
can't absorb into the ground or drain away. River flooding, closely
linked to surface flooding, occurs when streams burst their banks.
Coastal flooding results from high tides, storm surges and sea
Rising sea levels present a clear threat to flood coastal areas.
less certainty in projections of surface water and river
flooding. That's mainly down to uncertainty in modelling, and
difficulty simulating how weather patterns may change.
Based on physical reasoning, however, many studies - including
a government study on climate change risks - predict the UK
will experience more intense rainfall and more frequent high river
flows in the future, particularly during the winter. A recent
report from the
European Environment Agency (EEA) echoes this, predicting
increases in both river and coastal flooding in the UK.
5. Flooding isn't just about rainfall; other human factors
Flooding and extreme precipitation go hand in hand, but they
aren't the same thing. While climate change may directly alter
precipitation in the UK, flooding is a consequence of heavy
rainfall which also has a human component.
The rising cost of damages associated with flooding is a perfect
example of this. The rise could be down to a number of factors,
not simply the amount of rain that falls. People are getting better
at reporting damages, but human activities have a major impact
Changes in land use, such as building houses on flood plains and
paving over natural surfaces, are making people more vulnerable to
flooding. According to the
EEA report, climate change could contribute more in the future,
but for now, land use changes are the reason behind rising damage
costs in the UK.
So in summary, it's pretty difficult to assess the effect climate
change has on flooding. While in theory warmer temperatures may
lead to more rain, the climate system is pretty complicated in
practice. It looks likely that the UK will experience more surface,
river and coastal flooding in the future, but it's hard to be more
specific than that