Skip to content

How much has urbanisation affected United Kingdom temperatures?

May 6, 2019

By Paul Homewood



A study was published a couple of months ago, concerning the effect of urbanisation on UK temperatures:




This study aims to estimate the affect of urbanisation on daily maximum and minimum temperatures in the United Kingdom. Urban fractions were calculated for 10 km × 10 km areas surrounding meteorological weather stations. Using robust regression a linear relationship between urban fraction and temperature difference between station measurements and ERA‐Interim reanalysis temperatures was estimated. For an urban fraction of 1.0, the daily minimum 2‐m temperature was estimated to increase by 1.90 ± 0.88 K while the daily maximum temperature was not significantly affected by urbanisation. This result was then applied to the whole United Kingdom with a maximum T min urban heat island intensity (UHII) of about 1.7K in London and with many UK cities having T min UHIIs above one degree.

This paper finds through the method of observation minus reanalysis that urbanisation has significantly increased the daily minimum 2‐m temperature in the United Kingdom by up to 1.70 K.


As ever, the real issue with UHI is the change in the effect over time. Has, for instance, the effect of UHI increased in London and other cities increased over the last century, or was it just as great in 1919?

What we do know is that, generally speaking, towns and cities have both expanded over time, and seen increasing development in terms of roads, buildings, traffic and economic activity.

Indeed, these same tendencies also apply in small towns and what may appear to be relatively rural sites.

We also know that many of the sites used by the Met Office in their UK temperature series are urban and airport locations.


I have analysed temperature trends at Heathrow and Oxford since 1948 (when Heathrow’s data starts). As they are only 40 miles apart, there should be little difference in trend.

Significantly though, we find that the trend at Heathrow is much greater than at Oxford, 0.028C v 0.021C a year. In other words, Heathrow is warming faster than Oxford, at a rate of 0.7C per century.




This discrepancy can only be due to the increasing local effect of the airport. Over the years, Heathrow and most other airports around the world have transformed from being little more than grass fields to highly developed infrastructures with buildings, car parks, tarmac runways and, of course, jet planes forever taxiing around.

It may of course also be the case that urbanisation has also been pushing up temperatures at Oxford as well, and therefore that the airport effect is even greater than 0.7C.

What is clear is that the Met Office should stop using any sites where urbanisation or airport effect is a factor.

Globally the issue is also a major one, given the predominance of urban and airport sites.

  1. quaesoveritas permalink
    May 6, 2019 11:08 am

    In July 2018, when a “record” temperature was recorded at Heathrow, I did a comparison of Heathrow July temperatures with CET since 1948, which showed a 1c rise at Heathrow, compared with CET.
    I posted the results on the Google “weather and climate” group:!msg/weatherandclimate/a7x_o1v3Jtg/hFyTXPk4CAAJ
    I came to the same conclusion as you, that Heathrow was an unreliable site.
    I thought I contacted the UKMO about this but at the moment I can’t find the correspondence.

    • quaesoveritas permalink
      May 6, 2019 11:32 am

      I actually contacted the UKMO in 2015, about the earlier record.
      This is the reply I received:

      Thank you for your email enquiry in connection with the temperatures recorded at Heathrow.

      As with all our sites, our weather station at Heathrow conforms to World Meteorological Organisation (WMO) guidelines in relation to site and specific sensor locations to ensure relativity across sites and for historical comparisons. Details of these guidelines may be of interest to you and can be found at and ensure that a site is representative of the local area. While it isn’t possible to have an “ideal” or “normal” site this ensures that external factors are limited and to have continuity. All our sites are routinely visited by specialists and engineers to maintain high standards of recording and exposure of instrumentation along with accurate quality checks of observational data.

      The links below may be of interest to you and expand in further detail the points mentioned above.

      Discusses the heat wave and compares with other heat waves in the historical record

      Discusses record at Heathrow and compares with other stations in the area

      Heat wave more widely across Europe.

      Therefore based upon the points covered, the increase in temperatures over the records at Heathrow can be considered an accurate and reliable representation of the local area, suitable for comparison against other sites and historical records.

      • Ray Sanders permalink
        May 6, 2019 6:59 pm

        I find the line in your reply from the met office “All our sites are routinely visited by specialists and engineers to maintain high standards of recording and exposure of instrumentation along with accurate quality checks of observational data.” rather interesting.
        In htis 2004 report the Royal Meteorolgical Society found the Stevenson Screen at Kew set at the wrong height!

      • Mack permalink
        May 6, 2019 11:28 pm

        Em, I notice that the Met Office justify record temps at Heathrow as being authentic because their site at Kew Gardens, a few miles away, is almost as hot. Both sit in urban locations surrounded by acres of concrete, asphalt and vehicle emissions. Whilst Kew has a few more trees and bushes, but acres of wonderfully reflective and incubating glass greenhouses and outbuildings in the middle of a suburban sprawl, it does lack the occasional 747 running down the rose beds every 90 seconds just to tip the thermometers over the edge. And the Met Office thinks that, because the temps between the two sites are broadly similar, they don’t have any temperature station sighting issues. Really? I mean, really?

      • paul weldon permalink
        May 7, 2019 10:25 am

        If you read through the paper Paul referred to, you will see that It is generally accepted that it is Tmin rather than Tmax that is affected by UHI. It is therefore difficult to argue your case. It is simply the case that some sites are more sensitive to UHI than others to particular weather conditions, and I would assume that both of the sites have a similar response to sunny conditions with little or no wind,

      • Gerry, England permalink
        May 7, 2019 1:47 pm

        I have seen a difference between the edge of Gatwick airport and my house 8 miles away of 4 degrees one evening in winter. More of land around the area is like where I like than Gatwick so that is not a representative place to measure. And that is no doubt the case elsewhere. NOAA have released – a bit surprising given what it shows – a report on the effect of measurement location backing up the problems Anthony Watts and the surface stations project found.

  2. Pancho Plail permalink
    May 6, 2019 11:11 am

    I know it is only anecdotal but it is nevertheless a consistent observation. I live in rural north Cheshire and drive regularly into my local small town and into the Manchester/Stockport conurbation. This is all based on my car’s external temperature gauge, so I don’t claim great precision, however I see a regular difference of 1K between my village and the local town only 3 miles away, and 3K between home and central Manchester. This is pretty much independent of the time of year and the only model involved is that of my car.

    • Neil Wilkinson permalink
      May 6, 2019 11:20 am

      As other commenters have pointed out, the BBC weather forecast frequently refer to rural areas being colder than urban, 🙂

      • Roy permalink
        May 6, 2019 4:41 pm

        And it’s been known for a BBC weather forecaster to refer to this as the ‘rural chill effect’! Err… don’t you mean the ‘real’ temperature. Honestly, can they try any harder to avoid stating the obvious?

  3. jack broughton permalink
    May 6, 2019 11:24 am

    The allowances used by the Met office and NOAA for UHI are apparently too small as many people have said over the years. However, I understand that the number of stations used has decreased substantially (both UK an worldwide) over the years and modern stations are highly automatic and mainly near urban centres: a double-whammy,

    The UHI effect is also very apparent on and near motorways where typically a 2 deg K temperature rise occurs. Modern car thermocouples are very accurate indeed provided that the car has not been static for long.

  4. Joan Gibson permalink
    May 6, 2019 12:07 pm

    You have to take the overall topography into account. Also effects of urban areas on temperatures tend to be local and not regional.

  5. Tony Budd permalink
    May 6, 2019 12:51 pm

    This is all very relevant to the whole debate, and should encourage somebody to work out exactly how much heat has been – and continues to be at an increasing rate – put into the atmosphere by the total combustion of all the coal, oil and gas removed over the last two centuries. Never mind greenhouse gases: surely this is a real effect? Just think of the result if all of those products had been collected together and then burnt at once! But the cumulative effect over time must be much the same.

    • Steven Mosher permalink
      May 7, 2019 5:01 am

      Tiny amount. google anthropgenic heat flux

  6. Broadlands permalink
    May 6, 2019 1:07 pm

    Some thoughts from the past on the UHI:

    Climatologist, Dr. REID BRYSON, 1976…

    “Now we’re not yet at the point where we can calculate exactly what collective effect all our sprawling cities have on the larger climate. But it is quite possible that the growing megalopolis-type urban areas here in North America and the new concentrations of people in Europe and elsewhere are already slightly modifying the atmospheric circulation patterns of the whole hemisphere. In fact, since we already know that these metropolitan areas do alter the micro-climates around them, it would be hard to believe that they have no effect at all on the macroclimate.”

    “Back in the 70s it was calculated by Dr. Reid Bryson that if all of the waste heat from all of our power plants through the year 2000 were dispersed evenly in the oceans it would increase the average sea temperature by only .00001°C. If this is true then it seems folly to “correct” for the so-called UHI effect by arguing that these ‘artificially’ elevated temperatures are outliers that were measured too close the the ‘blast furnace’ and therefore don’t really exist? Yes, our collective added heat is quickly distributed vertically and horizontally but it is still there in the meantime and is simply being measured in the wrong place? Moving the thermometer out in the countryside or to the beach won’t make the urban heat go away, it just makes the triviality seem less trivial?.. and us feel more comfortable away from the city.”

  7. May 6, 2019 2:36 pm

    Oxford is maybe not the best reference because it is well known to have suffered substantial increases in UHI in the 20th century. Another point is that UHI has 2 components, one from very local effects, such as a nearby wall or shed, and one from general background warmth. The former is not related to being in a town, you could get it in the countryside, what NASA does with UHI (estimated via light emissions) is somewhat Mickey Mouse.

    • TinyCO2 permalink
      May 6, 2019 3:58 pm

      I agree. I took a number of UK stations, including Oxford and subtracted Stornaway as the most likely station the east affected by warming. All resultant plots showed warming with Oxford the greatest (didn’t try Heathrow).

    • paul weldon permalink
      May 7, 2019 10:47 am

      Your second point is extremely valid and often little appreciated when assessing station siting and adjustments.But the first point I would contest. I know the city well, and the area of the city has changed little over the last century (take a look at the age of the buildings). Certainly there has been an increase in traffic during the century, but that has changes little over the last 40 year or so as the city centre is virtually traffic free and the parking facilities n the city area limited. Most use the park and ride facility or local bus service form the outlying towns/villages. From my own investigation of UHI in the UK, Oxford has one of the lowest UHI effects over time. Interestingly, the Radcliffe Observatory website suggest that the difference in temperatures between the 19th century and the 20th century are mostly down to UHI, answering Pauls point..

  8. A C Osborn permalink
    May 6, 2019 2:55 pm

    I question this study.
    How for instance did they mearure London’s temperature? Or for that matter the other cities.
    In their list of data, from what I could see the closest they got to London was Heathrow.
    There just happens to be a weather station at Greenwich Observatory and anothe aat the London City Airport.

    • Steven Mosher permalink
      May 7, 2019 5:04 am

      Paul did an own goal here and Proved that adjustments for UHI are perfect

      Heathrow: adjusted down 1C

      Oxford is also adjusted down

      • May 7, 2019 10:03 am

        Trouble is that the Met Office don’t make any adjustment at all!

      • quaesoveritas permalink
        May 7, 2019 10:26 am

        As Paul says, the MO didn’t make any adjustment.
        Also, 1c is clearly not enough, since that figure is approximately the rate at which Heathrow is increasing, relative to CET, not the differential between Heathrow and CET.
        Otherwise the differential is accelerating at Heathrow.
        Why would that be the case?

      • TinyCO2 permalink
        May 7, 2019 10:44 am

        Gosh, a whole degree! When my semi rural home is 2C cooler than the more urban area halfway to the centre of town, which is far less built up than Heathrow. The town centre is closer to 3C. If the location according to this BBC image

        is true, the prevailing wind blows the heat from the bulk of the airport across the station.

      • paul weldon permalink
        May 7, 2019 11:11 am

        I have tried over the last 6 months to get the met office to state by what amount do they adjust for UHI. They have to date avoided answering my question. The ‘own goal’ is disallowed, Paul refers to the lack of adjustment to met office data, not to that of Berkeley. I would suggest that Berkeley proves his point.

      • paul weldon permalink
        May 7, 2019 11:18 am

        With reference to CET: It is now being revamped by the met office because of problems with the change form using Malvern util 2004 when it closed, and replacing it with Pershore College. The met office says that Malvern was prone to excessive UHI during hot spells, which I have checked out, and although not as strong as they suggest, there was a definite increase in anomaly over the period, by around 0.7C between 1976 and 2004. There are aso queries among others about the use of Ringway in earlier years. CET is therefore not as reliable as previously thought.

  9. May 6, 2019 3:14 pm

    Reblogged this on WeatherAction News and commented:
    It’s seems as if much of the data we’ve been using is simply not fit for purpose.

  10. May 6, 2019 4:04 pm

    So, it has just begun to dawn on climatologists (a.k.a UHI-denialists) that UHI really is contaminating the surface temperature record?

    It should be obvious that is not the *current size* of the UHI that causes the artificial temperature increase, but the *rate* of expansion or intensification of the UHI. The rate of UHI increase is going to be higher in the rabidly-developing areas of a city or town. This is especially true around the outskirts.

    As you point out, the UHI at LHR has expanded/intensified enormously since it was just a grassy field alongside a lane called “Heath Row”.

    At Oxford on the other hand, for several centuries the temperatures have been recorded at the Ratcliff Observatory more-or-less in the heart of dreamy Oxford. It too lies well within an UHI, but unlike Heathrow, the observatory area has not been developing rapidly throughout the recording period.

    Well not until recently! The university has just built several new faculty buildings (complete with open-air car-parks) right next door to the observatory. So we can expect even Oxford’s hitherto stable record to show a UHI driven temperature increase.,-1.2619783,3a,75y,266.6h,89.05t/data=!3m6!1e1!3m4!1sOjulRCB3s8e8ig-cpeDa1A!2e0!7i13312!8i6656

    • Steven Mosher permalink
      May 7, 2019 5:06 am

      Not really , we adjust oxford down, from .71C to .39C

      • paul weldon permalink
        May 7, 2019 11:29 am

        From when until when? Is the same adjustment used for the whole period of the record? What is important to assess the change in temperature over time is the change in UHI over time. Certainly Oxford needs an adjustment of around 0.3C if it is used to represent the surrounding area. But without considering how the site has changed over time, the adjustment does nothing to address the issue of what is the correct to use temperature records to support/challenge climate change claims.

      • May 7, 2019 10:03 pm

        Just to clarify, that’s 0.71 °C / Century adjusted down to0.39 °C / Century .

  11. JimW permalink
    May 6, 2019 4:52 pm

    You will have read the attached
    If the likes of Mosher are keen to try to diminish the role of UHI you can bet its effect is large.

  12. Ray Sanders permalink
    May 6, 2019 6:28 pm

    The Met office data is rather dodgy to say the least! Firstly why would the Royal Meteorological Society launch investigations into the accuracy of the Met Office data as per this report below.
    This report actually found the Kew Stevenson screen to be set at the wrong height which I find rather implausible to be an accidental mistake. Worse, however, is the issue relating to the alleged record temperature set at Brogdale Faversham.
    Here are the *facts of that “record” – through that summer of 2003 builders were developing the site (a tourist attraction and also home to the National Fruit collection.) They discovered that the area surrounding pallets of paving setts significantly warmed up in the sun…….so they rather rascally wheeled some palletts around the screen for the day and removed them later. (it was done “for a laugh”) The site is not automatic so it was not until some days later that the “record” was discovered. As the RMS report clearly states the reading was significantly out of step with those in the area and as access to the site was freely available, they could not rule out “actions by persons unknown”. In the report the photographs acyually show the building materials still in the vicinity.
    The Met Office in its eagerness to publicise itself (it is a profit making concern) simply accepted the totally unlikely reading and declared a record.
    That might sound crazy but consider the Scottish all time record at Greycrook which occurred on the same day. What sort of temperatures does that site record now? Well it was actually removed in 2004 less than a year later due to “unreliable” results. Furthermore the Brogdale record broke the same day highest at Broadness (jokingly referred to as “Gravesend” – it is not in Gravesend and not even in the Gravesham local authority area probably to make it impossible to find) and that station no longer exists. The Broadness station (Dartford) actually had the cooling vents from the Thames Navigation radar within metres of the screen and can anybody really accept a reading from a station downwind of one of the then UK’s largest power plants – LittleBrook D.

    *And for those who really want to know how I am so sure of the fact…….no I did not do it but was on the site at the time and dozens of people knew what was going on. To this day it is discussed with nod and a wink in the local hostelries!

  13. Michael permalink
    May 6, 2019 9:56 pm

    There was a big flap on Watts about 10 yrs ago about Darwin airport in Aus. In 1946 it was a dirt strip, now it’s 100+ hectares of concrete, yet the temp was being ‘adjusted’ up instead of down.

  14. Charles Pickles permalink
    May 7, 2019 7:27 am

    Over the many years of following this excellent blog site, I have yet to see any reference to the thousands of weather stations, both professional and amateur, which appear like a perpetual dose of measles across the world, in the Wunderground website that shows huge variance within quite small areas; and certainly the differences between urban and rural sites. Have these not been studied as another contribution to this particular debate?

  15. paul weldon permalink
    May 7, 2019 10:18 am

    Paul, I would disagree over your comment that the met office should stop using weather stations situated in areas prone to UHI. That would leave us with areas of the UK without a temperature record. With the majority of people living in urban areas, it is correct to inform them of the temperatures they encounter. Where the problems arise is that the same information is being used to assess the temperature over time, with regards to climate change. Here it needs to be made clear that UHI is having an effect on the data, and this needs to be made clear by the met office – how much and where. After a long correspondence with the met office over this issue, they are still unwilling to say how the raw data is adjusted, nor will they make available the full up to date data. They are certainly aware that their data is under-adjusted, but I would guess that it is not politically expedient for them to make any changes at present. Having said that, they are at present working on the CET data set as there are obviously errors in the way it is adjusted. I can let you have more details of my correspondence with them if you require.

    • May 7, 2019 10:39 am

      I agree Paul, but they should not be using such stations in their climate trends.

  16. John Medlock permalink
    May 7, 2019 10:33 am

    What is also not taken into consideration is the effect, similar to UHI, that has been happening in the countryside through change of land use. Cutting down forests and replacing with arable land considerably reducing the cooling effect of evaporation and evapotranspiration resulting therefore in an increase in temperature. We are told that 75% of the earth’s land surface has been altered by man through urbanisation and agriculture which has to have had some influence on global temperatures.
    This was well documented a few years ago now in the paper entitled “Water for the Recovery of the Climate – A New Water Paradigm” to be found at

  17. johnmclean7 permalink
    May 15, 2019 12:38 am

    Don’t forget that the adjustment of all previous data by a uniform amount ignores any non-meteorological gradually increasing influences on measured temperature. Such practices excessively lower earlier temperatures and no absolutely nothing to remove the trend caused by those non-meteorological factors.

Comments are closed.

%d bloggers like this: