Why is Heathrow so hot?

[danm]

Interesting article from the BBC and something that is a topic of debate on this forum. 

Heathrow often records the highest temperatures and the debate is whether it is artificially high due to being close to the north runway. The article below disputes that theory. 

Personally I think the reason it often records the highest temperatures is because (out of the official Met Office approved weather stations) it is one of the most inland stations within Greater London. So you have the combination of it being in the SE of England, traditionally the warmest area of the country in summer, being within Greater London so has the UHI effect, and is also as far away from the coast or the Thames Estuary that you could probably get in London. 

As the article also states below, there is actually very little difference between Heathrow and Kew (another centrally located London weather station), and has very similar readings to Northolt (which is just up the road) and St James's Park in the heart of London. 

Do people agree with the article or are Heathrow's temperatures slightly higher due to being by the runway?

Quote

 

https://www.bbc.co.uk/news/uk-44980493

Heatwave: Why is Heathrow so hot?

By Tom Edgington

BBC News

It's Europe's busiest airport, and as well as attracting millions of passengers could Heathrow also be a magnet for the sizzling heat?

Heathrow holds the UK record for July's hottest day ever. Three years ago it reached a sweltering 36.7C.

It also briefly recorded 2018's highest temperature of 35C, before being pipped by Faversham (35.3C) in Kent last Thursday.

And last year the thermometer peaked at 34.5C at - you guessed it - Heathrow.

So what's causing Heathrow to rise to the top of the temperature charts?

How is temperature measured?

To get a standardised temperature, a weather station, known as a Stevenson Screen, is used.

These white boxes, which contain a thermometer, are installed 4ft (1.25m) above the ground and are dotted all around the UK.

The weather station at Heathrow is located very close to the northern runway, so with aeroplanes constantly landing and taking off, does it make a difference to the temperature?

Not according to Paul Williams, Professor of Atmospheric Science at the University of Reading.

Heathrow's Stevenson Screen (the white box) is used to measure the temperature

"Planes make a negligible difference," says Professor Williams.

"Every time you use energy - whether it's from a plane's engine, or even just switching on a light bulb or taking a shower - it's eventually turned into heat.

"But all of that is a minor influence compared to the effect of the urban heat island."

The urban heat island is, Prof Williams explains, the process where buildings absorb more sunlight than open fields.

Cities tend to hang on to the heat for longer, which can push up temperatures by a few degrees, he says.

Heathrow's weather station is located close to the northern runway

 

Heathrow - with its large black asphalt runways and airport buildings - will naturally absorb more heat.

But London is very built-up, meaning surrounding areas should also be affected in a similar way.

This can be shown by comparing the average monthly temperature of Heathrow to nearby Kew, eight miles away.

The temperature graph above shows there is hardly any difference between Heathrow and Kew - but both areas are hotter, on average, than the rest of the UK.

That suggests that it is the buildings, rather than planes, contributing to the higher average temperatures.

But what about CO2 gas levels expelled by the planes?

Prof Williams says CO2 is a greenhouse gas and it does trap heat but, because it mixes very quickly with the air, it warms the entire climate, not just Heathrow.

"If you measure the CO2 levels above Heathrow they wouldn't be any higher than other parts of the UK because it spreads so quickly," he says.

The Met Office told us that their weather stations are built to very specific standards and any biases that could affect temperature records are taken into account when taking down readings.

The Met Office also pointed out that Heathrow is many miles from the sea, which means it does not benefit from a cooling effect that many coastal areas receive.

It says if you look at overall temperature records, there is a pattern between high temperature and the distance from the sea.

And even the soil can be a factor, according to Gareth Harvey from the BBC Weather Centre.

"Take, another very warm spot, like Wisley - located in the Surrey heathland and typified by sandy soils," he says.

"Sand is a natural insulator and so the heating effect of sunshine is stored in the top layer only, which gets very hot and then warms the air."

In summary, the overall temperature of any particular weather station is likely to be affected by several factors - such as the geographic features, the wind and the soil.

So, there's more to Heathrow's hot spot than its proximity to roaring jet engines and all that tarmac.

 

Edited August 2, 2018 by danm

[4wd]

It's partly the runways but much of the greater London area is one big heat island, in particular these built up areas retain heat overnight and start from a higher minimum each day.
Anyone who cycles or rides motorbikes will have noticed that any significant town is much warmer after sunset than rural areas.
Sometimes you can feel waves of heat coming up from the road and surfaces are literally warm to the touch for hours - just like a storage radiator with bricks inside.

[NTC]

Probably the same reason the weather forecasters use FInningley and seem to get the highest temperatures in Yorkshire, set up your weather station near an airport and it seems you get higher values.

[johnholmes]

This has always been a problem and inceases as more and more concrete is poured over the land at airports.

[danm]

2 minutes ago, johnholmes said:

This has always been a problem and inceases as more and more concrete is poured over the land at airports.

Do you think Heathrow's temperature recordings are "artificially" high sometimes due to planes taking off and landing, or is it just often on top because it's in a built up area? Which would be the case for many urban locations.

[johnholmes]

As the article quoted suggests, planes taking off and landing probably have very little, if any effect, on the temperature readings. The vast areas of concrete, runways, taxi-ways, parking areas, car parks, terminal areas etc, along with it being within the London heat island area anyway will be the main reasons. As he also suggested it apparently shows little difference from was it Kew he mentioned?

 

[mb018538]

Heat from planes etc would disperse quickly as the article says. It just happens to be in the overall warmest part of the entire UK - areas around the west of London are often the warmest spots.

[Aphelion369]

I’m not sure I find this convincing, tbh:

Quote

 

“Heathrow - with its large black asphalt runways and airport buildings - will naturally absorb more heat.

But London is very built-up, meaning surrounding areas should also be affected in a similar way.

This can be shown by comparing the average monthly temperature of Heathrow to nearby Kew, eight miles away.“

 

Surely if UHI is the key factor, they should have compared Heathrow with St James’s Park, right at the heart of London, and not another suburban station like Kew Gardens.

Also, my understanding is that the main concern about Heathrow is not so much the average monthly means but rather maximum temperatures in the summer, particularly during heatwaves such as in the recent summers, where Heathrow appears to “overperform” compared to other nearby stations. But the article evades this but instead focuses on average monthly means to prove an (all too easy) point that Heathrow and Kew indeed have very similar means year round. 

Even during this summer (2021), despite the absence of extreme heat so far, Heathrow has regularly and consistently recorded higher maxes than either SJP and Northolt, and if the rainfall stats are to be believed, has also mysteriously largely escaped the downpours which have plagued much of the southeast.

[cheeky_monkey]

On 05/08/2021 at 14:33, Aphelion369 said:

I’m not sure I find this convincing, tbh:

Surely if UHI is the key factor, they should have compared Heathrow with St James’s Park, right at the heart of London, and not another suburban station like Kew Gardens.

Also, my understanding is that the main concern about Heathrow is not so much the average monthly means but rather maximum temperatures in the summer, particularly during heatwaves such as in the recent summers, where Heathrow appears to “overperform” compared to other nearby stations. But the article evades this but instead focuses on average monthly means to prove an (all too easy) point that Heathrow and Kew indeed have very similar means year round. 

Even during this summer (2021), despite the absence of extreme heat so far, Heathrow has regularly and consistently recorded higher maxes than either SJP and Northolt, and if the rainfall stats are to be believed, has also mysteriously largely escaped the downpours which have plagued much of the southeast.

Heathrow should be compared to Northolt because both are located in similar surroundings and are not far apart...i used to live in Ruislip which is close to both Heathrow and Northolt..although Northolt is an RAF base and not a commercial airport both are surrounded by built up areas and located next to a major motorway.. being the M25 (Heathrow) and M40/A40 (Northolt)..therefore both should record very similar temperatures..if Heathrow is always warmer then i would put that down to the sheer amount of aviation traffic and nothing else.