External thermometer on modern car easily detects UHI

Brooks Hurd has sent in this set of observations of temperature changes while driving in and out of various Californian UHI’s in his Passat. Maybe some other readers could send in other data, good project for the kids to keep them occupied for a while.

This was taken with the
built in exterior thermometer on our Passat. I do not claim that it is
highly accurate. It rounds to the degree F, which is still more accurate
than the thermometer. It is, however, consistent enough for the data which I
took to be meaningful.

I drove from where I live in San Luis Obispo north through downtown and onto
101 to Newark, California (east side of San Francisco Bay). I left one hour
before sunrise so there was no effect from the sun. Sunrise was about the
time that I drove into King City. You can clearly see the temperature rise.
After Gonzales I quit taking data because of solar effects.

The towns which are en route are separated from each other by truly
rural areas, thus there is a good rural baseline. These towns, except for
San Luis Obispo, are located in the Monterey Valley.

The two step changes are where I drove over a ridge. The first ridge was the
Cuesta Grade. The second was in the Monterey Valley, just south of King

I took data when the temperature changed since this was less distracting
than taking data at constant time or mileage intervals. This compresses the
x axis, but clearly shows the UHI.

I was amazed that even the very small towns had a visible UHI. The spike in
San Luis Obispo up to 45 F was real. The temperature stayed at 45 until I
climbed most of the way up “The Cuesta Grade.” San Luis Obispo is at 50-70m
elevation. The top of the grade is ~500m.

I found problems in certain places. For example, Santa Barbara does not
provide useful data since it is located on the Pacific. The ocean overwhelms
the UHI. US Midwestern cities (located on plains), and cities located in
broad valleys (like the Monterey Valley) should provide good data since they
are not effected by nearby oceans or lakes.

I like valleys or plains, since these areas have a local climate which is
relatively consistent in the area surrounding the town/city of interest.

7 thoughts on “External thermometer on modern car easily detects UHI”

  1. Funnily enough I was going to mail a comment about my experiences last summer here in the UK. There were a number of occasions (at night) last July when I noticed temperature differences of several degrees over distances as small as 5 or 6 miles (and I don’t mean upwards). But a TV programme aired last night (Sunday) makes any further comment unneccessary.

    Here in the UK, we’ve just been ‘treated’ to yet another doom and gloom documentary on climate change by the BBC. Among the usual “mights”, “coulds”, “may bes” and “much worse than we previously thought” drivel, there was an interesting point raised by one of the presenters.

    Kate Humble, when discussing the potential impacts of future summer heat-waves, pointed out that during the hot summer of 2006, temperatures in London were up to 9 degrees C higher than they were in the surrounding countryside. Unfortunately, she seemed unable (or unwilling) to note the possible connection between increasing urbanisation and the rising temperature trend in the UK.

    The UK Met Office has declared 2006 to be the warmest year on record. That in itself isn’t particularly remarkable, but the relatively large margin of 0.2 deg C higher than the previous record is a bit surprising, so I checked a few UK ‘rural’ stations on the GISS site. For some stations (Valley and Leeming) 2006 wasn’t even the warmest year. For the Valentia Observatory (in Ireland) 2006 only ranks 11th warmest. Now I know Valentia is not part of the UK but it is only around 250 miles from the Central England region.

    I’m convinced that the UH effect is big factor in the 2006 record.


  2. Valentia and Armagh may be the only suitable sites in the UK that are useful for climate studies. All the other sites suffer from UHI’s and regional land cover changes that make them unsuitable.

    In 2004, Susan Mims used a car thermometer to measure changes in temperatures. She could detect the presence of a black road 500 feet from the road solely by looking at the thermometer and not looking out the window. Unfortunately, that study no longer seems to be on the web.

  3. John and Douglas,

    You pointed out another factor which I did not point out in my email to Warwick. Since my data was mostly taken before sunrise, it did not have much of an effect from solar adsorption and radiation in urban areas. These effects would be easier to see after sunset. Therefore, my UHI data could be considered to be the minimum between sunset and sunrise.

    Regarding Kate Humble finding a 9 deg C UHI for London last year, do you know if Phil Jones told her that she was wrong? Dr. Jones has told us that the UHI does not exist.

  4. I routinely witness a gradient which is the reverse of what “should be” according to the published climate zones. For example, when I drive at night in winter from where I live, which is in a marine influenced thermal belt (Zone 16 according the the Sunset Magazine Western Gardening Book’s scheme) into the northern Santa Clara Valley’s supposedly more extreme, supposedly colder-at-night, supposed receptor of cold air drainage from my neck of the woods are (Zone 15 – 17 boundary area) I actually see the temperature rise! There is only one reasonable explanation for that, given that there is only scattered residential and pastoral activity where I live, and residental, commercial and industrial activity in the Northern Santa Clara Valley. In other words, I am casually measuring the effects of anthropogenic energy flux in the first 300 meters above ground.

  5. We too have a thermometer readout in our Subaru Outback. This reads in Deg C. We take in interest in the temperature changes on our two hour journey from Cammeray (some 6km NNE of Sydney City) to Marulan some 170km to the SW where we have a place in the country.

    The elevation of our place in the country is 600m above sea level, and at Cammeray we are about 20 metres above sea level. Cammeray is on an arm of Sydney Harbour, and subject to afternoon sea breezes. The place at Marulan is quite a way inland.

    The first thing that we notice is just how widely the temperature can vary on a journey. The extreme can be when there is a frost in the country in say September (as there was last year). The temperature as measured by the car was -4 deg when we left the farm around 7:00 am. By the time we reached the outskirts of Sydney, the temperature had reached 25 degrees (don’t worry, we managed to survive the dramatic temperature difference). Driving past Sydney AIrport we notice that the temperature increases to around 28 deg C, then when we reach Cammeray, the temperature drops back to around 25 deg.

    We have noticed this UHI effect on pretty much every journey. Generally Sydney Airport is around 3 deg C higher in temperature than either Liverpool on the outskirts of Sydney or Cammeray. We drive alongside the CBD area of Sydney City, and it is evident that the UHI continues there, before it drops off again to Cammeray.

    It would be good to capture a trace of the temperature record for each journey. We travel down to the country and back, on average every two weeks. Our return journey nearly always starts at around 2 pm and we generally arrive back at Cammeray at 4 pm. Is there a low cost device that can capture time of day, lats/longs, and the temperature readout? If so, we could gather detailed information on the UHI effects on that journey.

    Appreciate any guidance.

  6. Ray

    Recording a profile would be somewhat tedius but an can GPS could track your position – and someone with a notebook writing down the car temp every 2 minutes versus time on the trip would be the only way you could record the data without buying some temperature logging gadget.

    Once finished you would then need to get the BOM data for the temp stations they monitor along or close to the route and fit a curve to that data.

    The scaling off, or in whatever graphing program you have, estimate the BOM temp over the day and subtract this from your data, reading per reading per unit of time.

    That should leave you with anomalies which can be interpreted.

    Be warned it will be a tedious job collecting the temperature data versus time.

    You also need a GPS program like Oziexplorer to dowmload the track data in terms of position. And interpolation between the track points will be necessary to link remp data to position.

    I am designing an experiment using professional temperature loggers, GPS track loggers and a temperature base station – and just having the hardware does not make it any easier.

    Warwick and I will have ago at it in a few weekends time.

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