Could the UK be facing never-ending rain?

Fed up of the endless spring showers – or more accurately, floods?

It has felt relentless, with the country pummelled by rain since the autumn and on first name terms with more than a dozen storms. Remember Babet, Ciarán and Jocelyn?

Well, there’s bad news on that front. Not only is there more rain forecast for the Bank Holiday weekend, but the UK is set to face more and more rain as the planet continues to warm, coupled with more frequent and more intense storms.

Those are the findings of a new report from World Weather Attribution (WWA), which found the seemingly endless rain throughout autumn, winter and spring was ten times more likely to happen again due to climate change. It was also 20% wetter, which most of us won’t have trouble believing.

But, as many an annoying relative or climate change denier have asked, why isn’t global warming making Britain hotter and drier? Where is all the rain coming from – and more importantly, will it ever end?

Well the key is actually in the warming, and what that really means for Britain’s weather.

Why do warmer temperatures mean more rain?

At its most basic, the warmer the atmosphere, the more moisture it holds. For every one degree of warming, the air around us can hold 7% more water.

Meteorologist and author Jim Dale breaks it down.

‘This isn’t something that’s just come about in the last few days or weeks, it’s been well-known [for years],’ he says.

‘It’s basic physics to be honest. The warmer the air, the more it expands, the more capacity it has to hold moisture – it’s a space issue.

‘Now seven per cent might not sound like a big figure, but remember that’s the average.’

So some places will get more rain (hello UK) and others less.

‘The wet winter/spring we’ve just had is a direct result of exactly what we’re talking about – the air holding more water,’ adds Jim.

Will wet winters become more common?

The WWA report found that October 2023 to March 2024 was the second-wettest autumn to spring period in almost 200 years of records. You might think things like that are going to happen, and you can cope with one miserable winter a century. That should be us done for a while.

However, as temperatures rise, the times are changing.

With global temperatures already 1.2C above pre-industrial levels, the extreme rain and number of storms can now be expected to hit once every five years, according to the report.

If temperatures increase by 2C, they can be expected once every three years, and will be 4% more intense.

Putting storms to one side, total rainfall is also expected to increase.

Met Office spokesperson Oliver Claydon says: ‘Climate change also had a strong influence on autumn and winter total rainfall. In a pre-industrial climate, wet periods such as the 2023-24 October-March season had an estimated return period of one in every 80 years. But in today’s climate, they have become at least four times more likely, expected to occur about once every 20 years. 

‘The scientists estimate that climate change contributed to increasing the amount of total rainfall by about 15%. If global warming reaches 2C, similar periods of rainfall that can saturate soils and cause large agricultural losses will become much more common, expected to occur about once every 13 years.’

As seen this week, alongside flooding, excessive rain also destabilises the ground the ground, leading to mudslides. In Yorkshire, ten-year-old Leah Harrison was killed by a mudslide while on a school trip, while in Sumatra, Indonesia, dozens of people died when flash floods triggered cold lava mudflows.

Stormy times ahead

It felt like barely a week went by over winter that the UK wasn’t buffered by a new storm, including one, Storm Isha, which left two people dead and thousands without power.

‘There are more storms because of the heat,’ says Jim. ‘It’s the same scenario – and warming up the ocean is where it all starts. It’s the same as if you put a pan of water and you turn up the dial, suddenly your water starts boiling.

‘When the ocean heats up it transfers [more energy and water] into the atmosphere, which means bigger and bigger storms.’

There are other factors too, because air can be moist, but not rain. Rain forms in three different ways – frontal, orographic and convective.

Orographic rain is caused by the landscape, when hills and mountains push air up and over them. This cools it down, causing the water vapour to condense and fall as rain. 

Convective rain typically produces lighter showers, resulting from the Sun warming the ground and heating the air above it. As this warmer air rises, it again cools and condenses..

But frontal rain is the big one, where warm and cold air meet. The UK is perfectly placed for this to happen, with the mid-Atlantic current and jet stream sending in an almost constant supply of warm, wet air. 

This means when the UK is hit by low pressure – which brings colder air and is common over winter – the warm air rises above it, cools, and drops its water vapour as rain or snow.

This winter, Jim describes the country as being ‘locked in’ to low pressure, meaning little relief from the rain.

‘If we’re constantly in low pressure, say between autumn and spring, that’s a long period,’ he says. ‘That’s autumn, winter and spring, or three-quarters of the year.’

What is happening to the jet stream?

The northern hemisphere jet stream is a core of strong winds about five to seven miles above the Earth’s surface running west to east. 

It brings warm air from above the Atlantic, keeping the UK much warmer than other areas on a similar latitude (think of New York’s harsh winters, despite being further south) and can even speed up flights if they surf it just right.

However, as the atmosphere warms, it too is getting stronger.

‘For every degree rise in temperature, there’s a commensurate increase in speed of about two per cent,’ says Jim.

‘Again, that sounds small, the same as with CO2 when you’re talking parts per million, but if we were talking about four and a half parts per million of arsenic in your coffee, you’d know about it!’

A stronger jet stream will also lead to increased turbulence which, as seen in the Singapore Airlines tragedy this week, can be deadly. 

Climate change is leading to more and more turbulence, but not all turbulence is due to climate change.

‘We can’t blame every single event on climate change, or a faster jet stream,’ says Jim. ‘Weather happens.

‘But in all the cases we’ve spoken about, it’s “weather plus”, so in other words it’s adding to what you would have had, but increasing it, whether that’s the jet stream, turbulence, rainfall, and it all comes down to energy.’

In his books, Jim uses two choice terms to help describe what’s going on.

‘I use the words “big weather” and “chaos”,’ he says. ‘These mean we’re unsure of what’s going to happen, because we’ve never been here before.’