From the Royal Meteorological Society. (h/t to reader NJSnowFan)
How much has urbanisation affected United Kingdom temperatures?
Ian L. M. Goddard, Simon F. B. Tett
Abstract
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.
1 INTRODUCTION
The urban heat island intensity (UHII), which describes increased temperatures in urban areas, has long been known and attempts have been made to quantify it for many years (Mitchell, 1961; Oke, 1982). The urban heat island (UHI) develops through changes to the surface energy balance due to anthropogenic modifications to the land surface. The importance of understanding how these changes will affect the global climate and the potential bias to land temperature records arising from urbanisation has piqued interest in this area of research. Further, due to the consequences of increasing temperatures in urban areas, such as increasing air pollution and mortality rates (Johnson et al., 2005; Stedman, 2004), many studies have attempted to quantify how temperatures in highly urbanised areas will be affected by increasing urbanisation.
Previous studies have generally concluded that urban warming has had a negligible effect on global scale temperature series (Peterson et al., 1999; Parker, 2004). For example, Jones et al.(1990) showed that the urban warming effect corresponds to no more than 0.1 K over the last century. However on regional scales, the affect of urbanisation on temperature may be significant. Specifically in China, where there has been large expansion of urban areas, a significant effect has been estimated. Yan et al. (2010) concluded a large impact of urbanisation up to 0.54 K/decade on local temperature series in Beijing. Whilst Zhou et al.(2004) showed a smaller urban effect of about 0.05 K/decade in south east China.
This effect is not exclusive to Asia, several studies have found similar effects in Europe and parts of the United Kingdom (Emmanuel and Krüger, 2012; Grawe et al., 2013; Trusilova et al., 2008; Chrysanthou et al., 2014). To quantify the UHII, Trusilova et al. 2008 and Grawe et al. (2013) both used atmospheric models to estimate the effect of urbanisation on temperatures in mainland Europe and the greater London area respectively. In Europe, Trusilova et al. (2008) quantified an average increase in the daily minimum temperature (equation/asl2896-math-0001.png) of 1.53 ± 0.49 K and observed that the maximum daily temperature (equation/asl2896-math-0002.png) may increase or decrease depending on local climate. They reported that in cooler climates equation/asl2896-math-0003.png increased due to urbanisation. In the greater London area Grawe et al. (2013) found an average increase in (equation/asl2896-math-0004.png) and (equation/asl2896-math-0005.png) of 1.31 ± 0.30 and 0.57 ± 0.19 K respectively. Further, through the comparison of recorded minimum and maximum daily temperatures between urban and rural sites, Emmanuel and Krüger (2012) found for Glasgow, consistent with other studies, an average increase of 1.6 ± 1.2 and 0.8 ± 2.1 K in equation/asl2896-math-0006.png and equation/asl2896-math-0007.png respectively. The aim of this study is to estimate the impact of urbanisation across the entire United Kingdom.
Previous studies have used varying methods to quantify the impact of urbanisation on temperature. Yan et al. (2010) measured the significance of urbanisation by comparing temperature time series for urban and rural weather stations, observing a greater warming at urban sites. However, it is difficult to classify weather stations as either urban or rural. In their study Yan et al. (2010) used population density as a marker for urbanisation. However, this data is often out of date and can be hard to obtain for rural areas (Wang and Chen, 2016). Satellite data has also been used to asses the urbanisation of an area. Hansen et al.(2001) used satellite measurements of night‐time light emissions to classify weather stations as either urban, semiurban or rural; where a station classed as urban was located in a bright area, a semiurban station was located in a dimly lit area and a rural station in an unlit area. However, a problem with this method is that stations classed as urban may be located inside well lit city parks, where the UHII is reduced by the park cool island (PCI) effect (Cao et al.,2010). The PCI effect, caused by radiative exchanges with vegetation and its surroundings, partially mitigates the development of the UHI (Oliveira et al., 2011). Hence, using night‐time light emission data to characterise stations as urban or nonurban may lead to inaccurately characterising the effects of urban material on temperature. This study aims to deal with the problem of PCI mitigation of the UHI and the issues of urban/rural classification by determining the degree of urbanisation of a given weather station, rather than having discrete classes. This is done through the use of a land cover/land use dataset derived from satellite images to asses the fraction of urban material around weather stations (termed urban fraction).
We next detail the data and methodology used to determine both the degree of urbanisation of weather stations in the United Kingdom and the corresponding urbanisation effect. The results of the analysis are then reported before some discussion of the results and conclusions are given. This study finds there is no significant urban effect on the daily maximum 2‐m temperature but does find a significant increase in the daily minimum 2‐m temperature due to urbanisation.
…
3 RESULTS
We generally find weak and statistically insignificant relationships between monthly, seasonally or annually averaged ΔT max and urban fraction (Figure 3). When ΔT max is averaged annually, the linear relationship between this and urban fraction is insignificant (at a 97.7% confidence level) at 0.25 ± 0.42 K. The strongest relationships are observed in the winter months with December having an urbanisation effect of 0.67 ± 0.34 K. However, this relationship is insignificant for February through to October. The results suggest that urbanisation has had no significant impact on daily maximum temperature across most of the annual cycle.
Figure 3 Robust linear regression between ΔT max (red) and ΔT min (blue), and urban fraction. The y‐axis is the regression coefficient of ΔT max or ΔT min against urban fraction which we denote as the UHII. The x‐axis shows the period over which ΔT max or ΔT min was averaged. The black dashed line shows zero regression coefficient. Uncertainty estimates (vertical lines) are 2σ errors. The solid black vertical line separates the months from the seasonal and annual results
…
A significant increase in monthly, seasonally and annually averaged ΔT min is observed in areas of higher urban fraction. For annual average ΔT min, an urbanisation effect of 1.90 ± 0.88 K is found (Figure 3). Stronger relationships are found for ΔT min in the summer months where the maximum UHII reaches 2.17 ± 0.78 K in May.
…
We have used our results to generate a map of the change in T min due to urban material in the United Kingdom at the 10 km × 10 km scale (Figure 5). We define the UHII as the maximum change in temperature due to urbanisation within the city boundaries and we observe the largest UHII in central London with considerable UHIIs in many other cities. Refer to the Supporting Information for a table of the calculated UHIs of several major cities in the United Kingdom (Table S2).
Figure 5 Map showing the change in T min due to the urbanisation at the 10 km × 10 km scale over the United Kingdom and Ireland. The colour bar shows the magnitude of the temperature change in K
4 DISCUSSION AND CONCLUSIONS
The observed increase in T min can be attributed to an increased intensity of the UHI during the hours after sunset and into the night. Many studies have previously shown that UHII is maximised during the night (Arifwidodo and Tanaka, 2015; Montávez et al., 2000; Ripley et al., 1996). The intensity is maximised during these hours, as heat absorbed by urban structures will be re‐radiated back into the atmosphere at a slower rate, due to smaller sky views, than natural structures. Further, the increase in impervious surface in an urban area causes a reduction of the latent heat flux and a rise in the sensible heat flux (Zhou et al.,2014). This leads to a difference between the rates at which the urban and natural area will cool during the night, with urban areas sustaining a higher temperature into the night. With minimum temperatures often occurring at night, the slowed rate of cooling in urban areas results in an increase of the observed minimum temperature.
The reduced effect seen in T max may be the result of partial shading (reduced sky‐view factor) in urban areas. If less short wave radiation is absorbed in an urban area than in rural areas, we expect that during the daytime the UHII will be smaller than at night and in some cases has been shown to be negative (Trusilova et al., 2008). Further, the reduced effect may be attributed to higher storage in the day time energy budget of the urban over rural areas. Increased storage leads to less day time sensible heat flux in the urban area causing a reduced increase in temperature. Hence, we observe a smaller difference between the urban and rural temperatures and thus a lower UHII.
The results indicate some seasonal variability in the magnitude of the increase in both T minand T max. Our results for T min agree with previous literature, showing that the UHII is larger in summer than in winter (Kłysik and Fortuniak, 1999; Philandras et al., 1999). This may be due to increased wind and cloud cover in the colder seasons resulting in more mixing of the atmospheric boundary layer and less available short wave radiation. Both of these factors would act to reduce the magnitude of the UHII. Further we observe a significant effect on Tmax only in winter (Figure 3), possibly due to anthropogenic heating leading to a warmer climate in urban areas.
Unlike the studies performed by Wang et al. (2017); Yan et al. (2010); Zhou et al. (2004); Chrysanthou et al. (2014); who performed studies on the rate of warming against urbanisation rate, this study looked only at differences in recorded and reanalysis temperature data and not the rate at which they are changing with respect to one another. Analysis of older land use data sets (CLC 2000, CLC 2006) found no urbanisation changes in the regions around the weather stations used in the study suggesting that there has been no significant urbanisation changes in the United Kingdom since 2000.
In this study, relationships between the urban fraction around weather stations in the United Kingdom and temperature differences between observed and reanalysis values were examined. A small and statistically insignificant relationship was observed for T max. After performing several sensitivity tests, it was found that in almost all cases the result remained insignificant and even when significant, the effect was very weak. This is in contrast to the results for T min where urbanisation has caused significant warming. The results indicate that if an area is 100% urbanised, annual averge T min would have increased by 1.90 ± 0.88 K. The results of the sensitivity tests suggest that whilst this value may be a slight under‐estimate, the significance of the result is robust in most cases. We observe that when considering an area of 400 km2 over 100 km2 the effect may be increased, suggesting that a larger area may influence the UHII more than originally proposed in this study. The relationship found for Tmin in this study is in agreement with the results found by Trusilova et al. (2008) and shows a slightly stronger relationship than that found by Grawe et al. (2013). However, the results from this study show a slight, and largely insignificant, increase in T max due to urbanisation. Whilst the results are likely dependent on the ERA‐interim data used for the analysis, we see that the results are consistent with previous literature, where a weaker relationship between urbanisation and T max than in T min is found (Wang et al., 2017; Trusilova et al., 2008). Albeit, our study does not capture as large an effect in T max as the cited literature.
The full paper: (open access)
https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/asl.896
This is not unlike what our surfacestations project has found in the USA:
NEW STUDY OF NOAA’S U.S. CLIMATE NETWORK SHOWS A LOWER 30-YEAR TEMPERATURE TREND WHEN HIGH QUALITY TEMPERATURE STATIONS UNPERTURBED BY URBANIZATION ARE CONSIDERED
Figure 4 – Comparisons of 30 year trend for compliant Class 1,2 USHCN stations to non-compliant, Class 3,4,5 USHCN stations to NOAA final adjusted V2.5 USHCN data in the Continental United States
From the article: “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.”
Urbanisation increases the daily minimum within urban areas, not the entire United Kindom.
Concrete and buildings and pavement absorb a lot of heat during the day and radiate it during the night.
“Concrete and buildings and pavement absorb a lot of heat during the day and radiate it during the night.”
yup. This can also leads to UCI.. urban cool islands during the day.
But if you get a radiative canyon, then Tmax can be increased
“This can also leads to UCI.. urban cool islands during the day.”
Well, there’s something I never heard of. Would you mind expanding on that, Steven?
You learn something new every day on this website. 🙂
I live in a rural area about 40 miles from a city of 400,000, and when the winds settle down and no weather fronts are coming through, it is always several degrees warmer in the big city than in my area.
Yup.
UHI is worse in certain synoptic conditions. good thing these conditions dont happen every day.
I have had many occasions to drive through Oklahoma City or Tulsa, OK and then back in fairly short time intervals. Compared to the surrounding countryside, the central parts of the cities are generally warmer when traversed in either direction and the effect is just as pronounced in mid afternoon as at night. I find it hard to believe that daytime maximum temperatures are not similarly higher in urban areas of England.
“I find it hard to believe that daytime maximum temperatures are not similarly higher in urban areas of England.”
They have a sample of 34.
You have a sample of 2 or 3.
Yet you find it hard to believe. That’s weird.
In GENERAL UHI will hit Tmin and not impact Tmax. In their paper they give some of the reasons
why this is so. HOWEVER, you can find areas in SOME cities where tmax is ALSO impacted. you can even find cities that are cooler than the rural suroundings, it all depends on the city. but in general, what they found is accurate
Every city is different. Some have cool zones ( urban cool islands) but NONE is the same temperature
in every location. One location may show a 1C diference with the rural surroundings and 1km away
the difference may be 3C, or -1C.
Urbanization is not, however, responsible for the increase in extreme weather in the UK in recent decades… that’s down to climate change.
“Urbanization is not, however, responsible for the increase in extreme weather in the UK in recent decades”
I agree that UHI does not cause extreme weather, but I see no evidence of extreme weather in the UK in recent decades attributable to CO2, either. That was what you were implying, wasn’t it?
Wrong again Griff.
Actually, urbanization can be responsible. An increase in particulate matter (traditional pollution), combined with heat islands increasing convection helps create more powerful thunderstorms downwind of city centers.
https://wattsupwiththat.com/2010/03/17/another-uhi-effect-thunderstorms-lightning/
No CO2 needed.
Increase in extreme weather. Hilarious. You want to just read a little bit of English history of the last 700 years and then come back and suggest with a straight face that there is an increase in extreme weather in England. I can’t speak with much conviction for the wider UK, but I think you’ll find at least Scotland is similar…
TYPO in the first paragraph of the Abstract—change “and” to “an”:
“… and ERA‐Interim reanalysis temperatures was estimated.”
????
I can’t change their abstract.
Urbanisation is also tied to airports.
There used to be four stations that make up the CET, and one used to be at Ringway and the other at Squires Gate. Ringway is Manchester international airports, and Squires Gate is Blackpool airport. The Ringway recording site was in the middle of the taxiways, opposite the jet engine runnup bay, and the Squires Gate site was right next to the runway.
So a large part of the recent rise in CET temps, was recording the huge rise in air traffic at Manchester, from small turboprops to vast 777s and 747s, combined with a six-fold increase in movements.
The Manch temp site was moved from Manch to a rural location at Stonyhurst in 2005. But the new site was calibrated to the old site, and so still includes the huge rise in air-traffic from the 70s to the 00s. I also read a report that the new site at Stoneyhurst has some siting problems, but I did not find out what those were.
But you can see how deceitful these climate people are. Here is a paper on all the possible errors in the CET, yet it never mentions ‘airport’ or ‘aircraft’ once. How on earth can any honest person investigate CET temperature accuracy, without mentioning Manchester International airport?
https://www.metoffice.gov.uk/hadobs/hadcet/ParkerHorton_CET_IJOC_2005.pdf
Ralph
Gosh! A map that shows Norwich- quite a rarity! I wonder how much of our hot-spot is centred on the concrete monstrosity of the UEA : all those computers blazing away in the CRU must contribute something.
Most of the man made warming comes from one small round building: the Climatic Research Unit.
Isn’t that the truth! 🙂
More likely UEA is an outstanding centre of creative writing and the least successful ones we transferred to climate studies when their work became so fanciful as to be implausible to all but those in the creative arts rather than mainstream public.
Readers here might like to revisit the fairly long but reference-rich essay I wrote about UHI with some Australian examples, just before Christmas last year (not a good date for serious work releases).
It remains unexplained by all so far, how daily maximum UHI effect temperatures up to 8 deg C above surroundings have been measured for several major cities, yet the present paper under discussion here says little Tmax effect is observed by them in UK. It gives a possible interpretation that UHI can be severe, but it can also be short-lasting over a given day or week or so, and not happen many times a year. I do not support that impression because it is getting too like special pleading rather than strict observation.
Geoff
https://wattsupwiththat.com/2018/12/20/the-science-of-the-urban-heat-island-effect-is-pathetic-and-misleading/
Geoff Sherrington
I read your excellent WUWT head post last Dec (and also your fair communication with St. Mosher in the comment thread).
If I pull up the Met Office temps (https://www.metoffice.gov.uk/climate/uk/summaries/datasets) and average them over the past 20 years for the UK, starting 1999 in the wake of the 1998 climate shift …
Max C
Winter 1999-2008 7.32C
Winter 2009-2018 6.69C
Down 0.63C
Spring 1999-2008 12.24C
Spring 2009-2018 12.25C
up 0.01C
Summer 1999-2008 18.92C
Summer 2009-2018 18.91C
Down 0.01C
Autumn 1999-2008 13.43C
Autumn 2009-2018 13.31C
Down 0.12C
Annuals 1999-2008 12.99C
Annuals 2009-2018 12.84C
Down 0.15C
Min C
Winter 1999-2008 1.56C
Winter 2009-2018 1.01C
Down 0.55C
Spring 1999-2008 4.27C
Spring 2009-2018 4.03C
Down 0.24C
Summer 1999-2008 10.55C
Summer 2009-2018 10.41C
Down 0.14C
Autumn 1999-2008 6.66C
Autumn 2009-2018 6.56
Down 0.10C
Annuals 1999-2008 5.76C
Annuals 2009-2018 5.55C
Down 0.21C
Maybe UHI has plateaued and a cooling climate, particularly in winter, is making the UK even chillier. It seems a bit weird that all those UK school kids protesting a couple of weeks ago about the warming climate did so in a cooler climate than when they were born.
Going outside to protest Global warming, dear?
Make sure to dress warm.
Chris Gillham
“It seems a bit weird that all those UK school kids protesting a couple of weeks ago about the warming climate did so in a cooler climate than when they were born.”
https://drive.google.com/file/d/1szN7r90gAuiPfelY0wrnvnXvFmJPM9_C/view
What would you have told us within the big drop from 1960 till 1965, as you saw that the UK estimate for 1938-1965 would go below -0.2 °C / decade?
Do you have an idea about Norway’s estimate for 2000-2018? They won’t need Gran Canaria anymore if it continues there that way 🙂
And by how much did the Clean Air Act raise UK Temperature?
ralfellis and the airport heat syndrome
Regularly, this commenter writes about the same stuff concerning Jumbojet heat effects at Manchester Airport station in the UK.
Here is, for the period 1979-2018, a comparison of
– the average of all available GHCN daily UK stations
with
– the GHCN daily ‘RINGWAY’ station (within Manchester International Airport).
Trends in °C / decade for 1979-2018
– UK average: 0.22 ± 0.04
– RINGWAY: 0.13 ± 0.05
Trends for 1979-2004
– UK average: 0.47 ± 0.07
– RINGWAY: 0.45 ± 0.1
What does ralfellis mean here?
Maybe I should spend a full day in obtaining all these highly suspect weather stations worldwide located within big airports, and compare their average with that for the Globe??
You are not giving us the full information here – your figures are post-adjustments.
These temperatures were given a negative 0.5 degree c adjustment, due to UHI, between 1960 and 1980. And many of those adjustments were said in the report to be ‘arbitary’. Unfortunately, I cannot find the UHI adjustments for Ringway post 1980.
But this gives us a problem – if the UHI adjustments are of the magnitude of 0.25 degrees c per decade, then the adjustments are greater than the proposed warming. So what are we measuring here – global warming, or a meteorologists guestimate about UHI adjustments?
And do note that the Ringway site was moved to Stonyhurst because of the unreliability of Ringway. So there WAS a problem with Ringway (ie with having a temperature monitoring station in the middle of Manchester International Airport). But as you know – those problems will remain forever, hidden in the middle of the CET dataset. (Unless they can find a better rural dataset, and go back through the CET and replace all the Ringway records with the alternate records.)
Ralph
Looking at the CET dataset – perhaps they simply stopped making UHI adjustments in 1980. In which case that huge rise in CET since 1980 may be predominantly UHI. Do you have the adjustment record, post-1980?
R
ralfellis
Oh Noes! This is no more than typical pseudoskeptic nonsense. The less some know, the more they manage to guess, claim and pretend.
Here is the data about which you pretend it has been adjusted:
https://drive.google.com/file/d/17rZtMUSMc-bE5LH5p6VAjEVOEt9UDvy8/view
It is again a comparison between Manchester Airport data I found for 1951-2004, and the whole UK average for the same period. (Manchester data begins with January 1794, but is highly incomplete.)
*
Look at your wonderful ‘negative 0.5 °C UHI adjustements’… This is so ridiculous that I can’t even laugh about it.
You obviously don’t understand how these datasets are derived.
This is a graph of the adjustments that are made to the raw data, before those neat graphs you displayed are created. Look at the magnitude of the adjustments being made to the raw data……
Ralph
ralfellis
“You obviously don’t understand how these datasets are derived.”
I very obviously understand that you publish here an anonymous, nonsensical graph made by hand, and relying on no valuable, reproducible source at all.
Your behavior is typical for people who lack any experience, and thus believe in anything what fits to their narrative, no matter how wrong it is.
What I published can be reproduced using correct data, originating from verified datasets you would never be able to contradict or falsify other than with such unscientific methods.
Anonymous graph..? If you had bothered to look I have already published a link to it. It was published by Parker et al, in their 2005 paper…
UNCERTAINTIES IN CENTRAL ENGLAND TEMPERATURE 1878–2003 AND SOME IMPROVEMENTS TO THE MAXIMUM AND MINIMUM SERIES.
https://www.metoffice.gov.uk/hadobs/hadcet/ParkerHorton_CET_IJOC_2005.pdf
But I see you know absolutely nothing about how these ‘tamperature’ datasets are created, and the many (often unjustifuable) adjustments that are applied to them.
And I ask you again – if the adjustments have a greater amplitude than the actual tamperature variations, then what are we measuring – temperature or tamperature….?
Ralph
Doesn’t look very good when the last cited attempt to quantify it was in 1982. Perhaps they were just too busy running after carbon dioxide.
I´m sorry, but I have to ask few very stupid questions.
Is all warming on this planet manmade? If it warms 1C, what part of it is manmade? Is there not natural warming anymore?
Thank you, and sorry.
F1nn
I go with Roy Spencer (UAH). He is very pragmatic and tells us: 50% natural, 50% man-made.
Those who reject his view are in my mind either warmistas, or… coolistas.
The urban heat island intensity (UHII), which describes increased temperatures in urban areas, has long been known and attempts have been made to quantify it for many years (Mitchell, 1961; Oke, 1982).
I would dispute the claim that attempts have been made to quantify it. My daughter and I have both in widely different industrial and commercial firms both met ex climate scientists who were denied any grants after attempting to put projects in place to quantify this effect. This is in the UK but I know for certain this has also occurred in two European countries , Australia and the US.
In both cases the UK cases grants were refused as being liable to undermine other more major projects of the universities concerned.
D Cage
I propose a careful reading of e.g. this guest post:
https://wattsupwiththat.com/2018/12/20/the-science-of-the-urban-heat-island-effect-is-pathetic-and-misleading/
It helps!
Someone should analyze the connection between the strength of empirical findings on UHI and the volume of Mosher’s disparaging comments. The persistently high correlation would be revealing.
The considerable difference between urban and rural temperatures as in
such countries as the UK, reminds me of Stalin’s famous comment about
voting. “It does not matter how many people vote, but it does matter who
counts the votes.”
So of course it does matter just where the devices measuring the temperature
are situated.
I strongly suspect that just about all of the apparent increase in the
measured temperatures are due to the Heat Island Effect and not on CO2
levels. And I am sure that the Warmers lobby are well aware of this fact.
MJE VK5ELL