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UHI is alive and well
Watts Up With That?
Monday, February 1st, 2010
One of the most ridiculous claims recently related to Menne et al 2010 and my surfacestations project was a claim made by DeSmogBlog (and Huffington Post who carried the story also) is that the “Urban Heat Island Myth is Dead“.
To clarify for these folks: Elvis is dead, UHI is not.
For disbelievers, let’s look at a few cases showing UHI to be alive and well.
CASE 1: I’ve measured it myself, in the city of Reno for example:
The UHI signature of Reno, NV – Click for larger image
Read the story of how I created this graph here The procedure and raw data is there if you want to check my work.
I chose Reno for two reasons. It was close to me, and it is the centerpiece of a NOAA training manual on how to site weather stations to avoid UHI effects.
CASE 2: NOAA shows their own measurements that mesh well with mine:
To back that up, the NOAA National Weather Service includes the UHI factor in one of it’s training course ( NOAA Professional Competency Unit 6 ) using Reno, NV.
In the PCU6 they were also kind enough to provide a photo essay of their own as well as a graph. You can click the aerial photo to get a Google Earth interactive view of the area. The ASOS USHCN station is right between the runways.
This is NOAA’s graph showing the changes to the official climate record when they made station moves:
Source for 24a and 24b: NOAA Internal Training manual, 2004-2007
Oops, moving the station south caused a cooling. Fixed now, all better.
What is striking about this is that here we have NOAA documenting the effects of an “urban heat bubble” something that DeSmog Blog says ” is dead”, plus we have NOAA documenting a USHCN site with known issues, held up as a bad example for training the operational folks, being used in a case study for the new USHCN2 system.
So if NOAA trains for UHI placement, I’m comfortable in saying that DesmogBlog claims of UHI being “dead” are pure rubbish. But let’s not stop there.
CASE 3: From an embattled scientist.
A paper in JGR that slipped in 2007 without much notice (but known now thanks to Warwick Hughes) is one from Phil Jones, the “former” director of the Hadley Climate Center in the UK. The paper is titled: Urbanization effects in large-scale temperature records, with an emphasis on China
In it, Jones identifies an urban warming signal in China of 0.1 degrees C per decade. Or, if you prefer, 1 degree C per century. Not negligible by any means. Here is the abstract:
Global surface temperature trends, based on land and marine data, show warming of about 0.8°C over the last 100 years. This rate of warming is sometimes questioned because of the existence of well-known Urban Heat Islands (UHIs). We show examples of the UHIs at London and Vienna, where city center sites are warmer than surrounding rural locations. Both of these UHIs however do not contribute to warming trends over the 20th century because the influences of the cities on surface temperatures have not changed over this time. In the main part of the paper, for China, we compare a new homogenized station data set with gridded temperature products and attempt to assess possible urban influences using sea surface temperature (SST) data sets for the area east of the Chinese mainland. We show that all the land-based data sets for China agree exceptionally well and that their residual warming compared to the SST series since 1951 is relatively small compared to the large-scale warming. Urban-related warming over China is shown to be about 0.1°C decade−1 over the period 1951–2004, with true climatic warming accounting for 0.81°C over this period.
Even though Jones tries to minimize the UHI effect elsewhere, saying the UHI trends don’t contribute to warming in London and Vienna, what is notable about the paper is that Jones has been minimizing the UHI issues for years and now does an about face on China.
Jones may have tried to hide CRU data, but he’s right about China.
CASE 4: From “The Dog ate My Data” who writes:
The Australian Bureau of Meteorology (BOM) blames Melbourne’s equal warmest overnight temperature of 30.6 degrees, on January 12 on the heat island effect. The previous time the city was that hot overnight was February 1, 1902.
The Age newspaper cites a meteorologist at the bureau, Harvey Stern,
Melbourne recorded its equal warmest overnight temperature, 30.6 degrees, on January 12. The previous time the city was that hot overnight was February 1, 1902.
A meteorologist at the bureau, Harvey Stern, said that Melbourne suffered from a heat island effect, in which a city is warmer than the surrounding countryside.
This was the case especially at night, because of heat stored in bricks and concrete and trapped between close-packed buildings.
I am stunned if that is correct firstly because BOM isn’t blaming Global Warming and secondly that the urban heat island effect directly receives the blame. With faults in the 2007 IPCC’s AR4 now pouring out I guess it is not suprising that attributions of weather events are now, shall we say, possibly becoming more circumspect.
CASE 5: Heatzilla stomps Tokyo
From the website “science of doom” who writes:
New Research from Japan
Detection of urban warming in recent temperature trends in Japan by Fumiaki Fujibe was published in the International Journal of Climatology (2009). It is a very interesting paper which I’ll comment on in this post.
The abstract reads:
The contribution of urban effects on recent temperature trends in Japan was analysed using data at 561 stations for 27 years (March 1979–February 2006). Stations were categorized according to the population density of surrounding few kilometres. There is a warming trend of 0.3–0.4 °C/decade even for stations with low population density (<100 people per square kilometre), indicating that the recent temperature increase is largely contributed by background climatic change. On the other hand, anomalous warming trend is detected for stations with larger population density. Even for only weakly populated sites with population density of 100–300/km2, there is an anomalous trend of 0.03–0.05 °C/decade. This fact suggests that urban warming is detectable not only at large cities but also at slightly urbanized sites in Japan. Copyright, 2008 Royal Meteorological Society.
Why the last 27 years?
The author first compares the temperature over 100 years as measured in Tokyo in the central business district with that in Hachijo Island, 300km south.
Tokyo – 3.1°C rise over 100 years (1906-2006)
Hachijo Island – 0.6°C over the same period
This certainly indicates a problem, but to do a thorough study over the last 100 years is impossible because most temperature stations with a long history are in urban areas.
However, at the end of the 1970’s, the Automated Meteorological Data Acquisition System (AMeDAS) was deployed around Japan providing hourly temperature data at 800 stations. The temperature data from these are the basis for the paper. The 27 years coincides with the large temperature rise (see above) of around 0.3-0.4°C globally.
And the IPCC (2007) summarized the northern hemisphere land-based temperature measurements from 1979- 2005 as 0.3°C per decade.
How was Urbanization measured?
The degree of urbanization around each site was calculated from grid data of population and land use, because city populations often used as an index of urban size (Oke, 1973; Karl et al., 1988; Fujibe, 1995) might not be representative of the thermal environment of a site located outside the central area of a city.
What were the Results?
Mean temperature anomaly vs population density, Japan
The x-axis, D3, is a measure of population density. T’mean is the change in the mean temperature per decade.
Tmean is the average of all of the hourly temperature measurements, it is not the average of Tmax and Tmin.
Notice the large scatter – this shows why having a large sample is necessary. However, in spite of that, there is a clear trend which demonstrates the UHI effect.
There is large scatter among stations, indicating the dominance of local factors’ characteristic to each station. Nevertheless, there is a positive correlation of 0.455 (Tmean = 0.071 logD3 + 0.262 °C), which is significant at the 1% level, between logD3 and Tmean.
Here’s the data summarized with T’mean as well as the T’max and T’min values. Note that D3 is population per km2 around the point of temperature measurement, and remember that the temperature values are changes per decade:
The effect of UHI demonstrated in various population densities
Note that, as observed by many researchers in other regions, especially Roger Pielke Sr, the Tmin values are the most problematic – demonstrating the largest UHI effect. Average temperatures for land-based stations globally are currently calculated from the average of Tmax and Tmin, and in many areas globally it is the Tmin which has shown the largest anomalies. But back to our topic under discussion..
And for those confused about how the Tmean can be lower than the Tmin value in each population category, it is because we are measuring anomalies from decade to decade.
And the graphs showing the temperature anomalies by category (population density):
Dependence of Tmean, Tmax and Tmin on population density for different regions in Japan
Quantifying the UHI value
Now the author carries out an interesting step:
As an index of net urban trend, the departure of T from its average for surrounding non-urban stations was used on the assumption that regional warming was locally uniform.
That is, he calculates the temperature deviation in each station in category 3-6 with the locally relevant category 1 and 2 (rural) stations. (There were not enough category 1 stations to do it with just category 1). The calculation takes into account how far away the “rural” stations are, so that more weight is given to closer stations.
Estimate of actual UHI by referencing the closest rural stations – again categorized by population density
And the relevant table:
Temperature delta from nearby rural areas vs population density
Conclusion
Here’s what the author has to say:
On the one hand, it indicates the presence of warming trend over 0.3 °C/decade in Japan, even at non-urban stations. This fact confirms that recent rapid warming at Japanese cities is largely attributable to background temperature rise on the large scale, rather than the development of urban heat islands.
..However, the analysis has also revealed the presence of significant urban anomaly. The anomalous trend for the category 6, with population density over 3000 km−2 or urban surface coverage over 50%, is about 0.1 °C/decade..
..This value may be small in comparison to the background warming trend in the last few decades, but they can have substantial magnitude when compared with the centennial global trend, which is estimated to be 0.74°C/century for 1906–2005 (IPCC, 2007). It therefore requires careful analysis to avoid urban influences in evaluating long-term temperature changes.
So, in this very thorough study, in Japan at least, the temperature rise that has been measured over the last few decades is a solid result. The temperature increase from 1979 – 2006 has been around 0.3°C/decade
However, in the larger cities the actual measurement will be overstated by 25%.
And in a time of lower temperature rise, the UHI may be swamping the real signal.
The degree of urbanization around each site was calculated from grid data of population and land use, because city populations often used as an index of urban size (Oke, 1973; Karl et al., 1988; Fujibe, 1995) might not be representative of the thermal environment of a site located outside the central area of a city.
Case 6: California Counties by population show a distinct UHI signature.
My friend Jim Goodridge, former California State Climatologist identified the statewide UHI signature issues way back in 1996. This graph had a profound effect on me, becuase it was the one that really made an impact on me, switching my views to being skeptical. Yes, I used to be a warmer, but that’s another story.
Goodridge, J.D. (1996) Comments on “Regional Simulations of Greenhouse Warming including Natural Variability” . Bull, Amer. Meteorological Society 77:1588-1599.
Goodrich (1996) showed the importance of urbanization to temperatures in his study of California counties in 1996. He found for counties with a million or more population the warming from 1910 to 1995 was 4F, for counties with 100,000 to 1 million it was 1F and for counties with less than 100,000 there was no change (0.1F).
He’s been quietly toiling away in his retirement on his computer for the last 15 years or so making all sort of data comparisons. One plot which he shared with me in 2003 is a 104 year plot map of California showing station trends after painstakingly hand entering data into an Excel spreadsheet and plotting slopes of the data to produce trend dots.
He used every good continuous piece of data he could get his hands on, no adjusted data like the climate modelers use, only raw from Cooperative Observing Stations, CDF stations, Weather Service Office’s and Municipal stations.
The results are quite interesting. Here it is:
I’ll have more interesting revelations from Jim Goodridge soon.
Case 7: NASA JPL’s climatologist says UHI is an issue
This press release from NASA Jet Propulsion Lab says that most of the increase in temperature has to do with ubanization:
[NASA's JPL Bill] Patzert says global warming due to increasing greenhouse gases is responsible for some of the overall heating observed in Los Angeles and the rest of California. Most of the increase in heat days and length of heat waves, however, is due to a phenomenon called the “urban heat island effect.”
Heat island-induced heat waves are a growing concern for urban and suburban dwellers worldwide. According to the U.S. Environmental Protection Agency, studies around the world have shown that this effect makes urban areas from 2 to 10 degrees Fahrenheit (1 to 6 degrees Celsius) warmer than their surrounding rural areas.
Patzert says this effect is steadily warming Southern California, though more modestly than some larger urban areas around the world. “Dramatic urbanization has resulted in an extreme makeover for Southern California, with more homes, lawns, shopping centers, traffic, freeways and agriculture, all absorbing and retaining solar radiation, making our megalopolis warmer,” Patzert said.
CASE 8: You can see it from space. NASA (not the GISS division) measures it. Here’s a report they presented at the last AGU meeting in December 2009. Gee, that curve below looks like Reno, NV, doesn’t it?
- A d v e r t i s e m e n t
The urban heat island effect can raise temperatures within cities as much as 5 C higher than the surrounding countryside. New data suggests that the effect is more or less pronounced depending on the type of landscape — forest or desert — the city replaced. Credit: NASA
› Larger image
NASA researchers studying urban landscapes have found that the intensity of the “heat island” created by a city depends on the ecosystem it replaced and on the regional climate. Urban areas developed in arid and semi-arid regions show far less heating compared with the surrounding countryside than cities built amid forested and temperate climates.
“The placement and structure of cities — and what was there before — really does matter,” said Marc Imhoff, biologist and remote sensing specialist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “The amount of the heat differential between the city and the surrounding environment depends on how much of the ground is covered by trees and vegetation. Understanding urban heating will be important for building new cities and retrofitting existing ones.”
Goddard researchers including Imhoff, Lahouari Bounoua, Ping Zhang, and Robert Wolfe presented their findings on Dec. 16 in San Francisco at the Fall Meeting of the American Geophysical Union.
Satellite imagery of suburban (top) and urban Atlanta shows the differences in daytime heating, as caused by the urban heat island effect. Credit: NASA Goddard’s Scientific Visualization Studio
› Larger image (suburban)
› Larger image (urban)
Yep, UHI is alive and well. Anybody with an automobile dashboard thermometer who drives a commute from country to city can easily measure UHI, and you don’t have to be a climate scientist to prove it to yourself.
UPDATE: For a primer on how UHI is not dealt with by NOAA and CRU, have a look at this Climate Audit post:
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