Wet and dry: Is the UKs weather going to get more extreme with climate change?
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.