UGA study ranks US cities based on the urban heat island effect on temperatures
From the UNIVERSITY OF GEORGIA
Highlights
- Urban heat island (UHI) intensities were estimated for the fifty most populous cities in the USA using PRISM climate data.
- The urban morphologies of the cities were quantified using spatial metrics and the NLCD 2006 land use/land cover dataset.
- The statistical analyses suggested that highly contiguous dense and sprawling urban development both enhance the UHI effect.
- City contiguity should be considered when devising strategies for UHI intensity mitigation.
- More discontiguous city configurations, especially if achieved by introducing urban green spaces, will likely reduce UHIs.
Athens, Ga. – Inner cities as well as suburbs show distinctly warmer temperatures–known as the urban heat island effect–than rural areas as a result of land use and human activities, which can affect rainfall, air quality and public health.
A University of Georgia study using a new method for calculating urban heat island intensities clarifies the conflict on whether urban density or sprawl amplify these effects more. It also provides a ranking of the top urban heat island cities among the 50 largest metropolitan statistical areas.
The urban heat island effect describes how the spatial configuration of cities, the materials in them (such as asphalt), lack of vegetation and waste heat can modify temperature.
The study, published in the journal Computers, Environment and Urban Systems, identifies Salt Lake City, Miami and Louisville as the top three urban heat island cities in the U.S.
Urban morphology–the patterns of a city’s physical configuration and the process of its development–has long been associated with the formation of urban heat islands. By examining the UHI intensities of 50 cities with various urban morphologies, the researchers evaluated the degree to which city configuration influences the UHI effect.
“The overall goal of our study was to clarify which urban form–sprawl or more-dense development–is most appropriate for UHI mitigation,” said the study’s lead author Neil Debbage, doctoral student in the Franklin College of Arts and Sciences’ department of geography.
The study establishes a method for estimating UHI intensities using PRISM–Parameter-elevation Relationships on Independent Slopes Model–climate data, an analytical model that creates gridded estimates by incorporating climatic variables (temperature and precipitation), expert knowledge of climatic events (rain shadows, temperature inversions and coastal regimes) and digital elevation.
The use of spatially gridded temperature data, rather than urban versus rural point comparisons, represents a new method for calculating a city’s canopy heat island intensity. The results identify the spatial contiguity of developed areas as a significant factor influencing the magnitude of the heat island effect.
“Not just whether cities have high-density development, but how the built infrastructure is connected–and disconnected by green spaces–has a great impact on heat island intensity,” said study co-author Marshall Shepherd, the UGA Athletic Association Distinguished Professor of Geography and Atmospheric Sciences.
“We found that more contiguous sprawling and dense urban development both enhanced UHI intensities. In other words, it does not appear to be a simplistic either-or situation regarding sprawl or density,” Debbage said.
The researchers hope the results can help influence local governments and city planners in the formulation of effective codes and policies to mitigate the urban heat island effect.
“It’s crucial to work toward a better understanding of the complex processes at the intersection of urbanization, climate and human health,” Shepherd said. “Current and future cities will be modified or designed with weather and climate in mind, and research at UGA will play a key role.
###
The study on “The Urban Heat Island Effect and City Contiguity” is available at http://www.sciencedirect.com/science/article/pii/S0198971515300089.
Abstract
The spatial configuration of cities can affect how urban environments alter local energy balances. Previous studies have reached the paradoxical conclusions that both sprawling and high-density urban development can amplify urban heat island intensities, which has prevented consensus on how best to mitigate the urban heat island effect via urban planning. To investigate this apparent dichotomy, we estimated the urban heat island intensities of the 50 most populous cities in the United States using gridded minimum temperature datasets and quantified each city’s urban morphology with spatial metrics. The results indicated that the spatial contiguity of urban development, regardless of its density or degree of sprawl, was a critical factor that influenced the magnitude of the urban heat island effect. A ten percentage point increase in urban spatial contiguity was predicted to enhance the minimum temperature annual average urban heat island intensity by between 0.3 and 0.4 °C. Therefore, city contiguity should be considered when devising strategies for urban heat island mitigation, with more discontiguous development likely to ameliorate the urban heat island effect. Unraveling how urban morphology influences urban heat island intensity is paramount given the human health consequences associated with the continued growth of urban populations in the future.
I am not going to spend $42 to get the report.
It sounds like yet another computer game, and computer games are not real science.
The primary problem with the climate change cult is they try to predict the future, and the secondary problem is they do so with computer games that have no predictive ability.
However, based only on my internal BS detector while reading this post, I believe after reading this “study” I would have determined it to be as valuable as a steaming pile of farm animal digestive waste products.
Just like all climate computer games.
To add some value to this post:
I noticed the “Urban Heat Island” effect as a child on my bicycle:
I grew up in a small village with a population of less than 1,000 people, and a small downtown with
about a dozen stores.
In the summer friends and I always noticed it was hotter “downtown” surrounded by cement, bricks, asphalt, parked cars, etc.
We’d bicycle “downtown” on hot days to buy ice cream, and often started eating it while standing in front of the store on the hot asphalt or cement.
Soon someone would say it was too hot to stand there, so lets get back on our bicycles, and finish the ice cream while riding our bikes out of “downtown”.
So we noticed the UHI effect during the day in a tiny village (even though I believe it affects the nighttime temperature even more than the daytime temperature (as the cement, bricks, asphalt, etc. give up the heat they absorbed during the day).
If there was an easy to notice UHI effect in a tiny village of fewer than 1,000 people, it would seem that a large percentage of surface weather stations would be affected by UHI effect — not just “urban” stations
What percentage of weather stations are properly sited, surrounded by grass and trees, in an area never changed by economic growth?
Probably not many, based on work Mr Watts has led in the past at www. surfacestations.org — real climate science, not the usual scary climate model BS predictions of gloom and doom.
Probably none of this UHI effect really matters — NOAA is going to “adjust” the surface data until it eventually matches the confuser models anyway (heh, heh).
The link is the full paper without a paywall.
I see someone else has just found the paper online and posted a dropbox link. I got it through ResearchGate. Here’s an explanation for the negative effects:
In contrast to the intense UHIs of Salt Lake City,Miami and Louisville,
the negative values in Fig. 4 indicate that a city was actually cooler than
its natural surroundings. Riverside and Las Vegas exhibited the strongest
urban cool islands (UCIs) of −1.37 and −0.76 °C, respectively.
This “oasis effect” is largely due to the increased presence of moisture
and heightened potential for evaporative cooling within the cities
relative to the surrounding desert landscapes (Brazel, Selover, Vose, &
Heisler, 2000). The Riverside UCI was a particularly extreme case that
was partially influenced by the seasonality of aridity (Fig. 5), as the summertime
UCI peak occurred during a phase of extremely arid conditions
according to the De Martonne index.
The regions are SMSA’s, not counties, I think (from a quick overview).
Seeing Boston as negative tells me this “study” is laughable. You can FEEL the difference in the summer, it’s many degrees warmer in Boston than in suburbs only 15 miles away in any direction, especially in the early evening. The only time there is not much difference is in the spring time when there’s a strong sea breeze. But NEGATIVE??? No way.
Just looking at Blue Hills versus Boston data from 1940 -2015 using “Climate at a Glance” shows Boston ~3 degrees warmer on average despite being right on the water.
Not to defend the study, but are the “suburbs only 15 miles away” part of the SMSA? I haven’t dug into the nuts and bolts of the study (don’t intend to, either), but SMSA’s are pretty broad (as are the colored blotches on the map) and probably average out a lot of variation in local climate, though I’m sure there is some effort to control for this. Whether valid or not I couldn’t say. But any criticism that is easy to make has a strong likelihood of having been considered somehow.
Those “counties” surrounding every major city in the plot are each 40 – 60 miles across.
And, even in the densest plots (Pittsburgh, NJ, Atlanta, San Francisco, etc) there are many miles of greenery and low density (non-urban) “City and suburb” spanning much more than that 15 mile distance they used.
But any criticism that is easy to make has a strong likelihood of having been considered somehow.
____
let’s try:
there’s literally tons of papers showing UHI when one simply combines ev’rydays records of weather stations,
distinguished city/rural.
Why do a paywalled studie, running a never proofed computer model, noone asks neither pays for –
could it be that
there is ‘a strong likelihood of having been considered somehow’
that operating time on climate modelling super computers has drastically fallen in price lastly and and hosts beg for use.
____
Just asking – Hans
servus mod, servus WordPress,
thx for coping with my dinglish.
On my small millenium gadget aka cell phone emerges a hyperventilating
‘that operating time on climate modelling super computers has drastically fallen in price lastly and and hosts beg for use.’
Not rare on this blog.
and and – sure Your’e working on it.
Regards – Hans
[??? .mod]
And yet UHI adjustments make the “data” hotter rather than cooler. No wonder these algorithms were kept secret for so long.
From an earlier WUWT post: http://wattsupwiththat.com/2014/08/03/something-detroit-has-in-abundance-uhi/
According to the authors, in Vegas in December (and most of the rest of the year except for the spring) it is 1°C cooler in town than it is in the desert outside town.
Anyone believe that?
Preposterous.
When I was in Vegas in July of last year, it was 113 F on the Strip at nine at night. The desert had to be cooler.
Yes, the desert cools rapidly at night. I grew up in the Arizona deserts. The city of Tucson was always much hotter at night in summer than at our ranch.
All the swamp coolers have increased the average humidity noticeably in the city, which dramatically slows down the rate of cooling at night.
I’m waiting to hear that the difference between the models and global average temperature is the blue areas and that therefore the models are correct.
They have invented or discovered something that nobody has ever suspected. A negative UHI effect. I wonder if they know how badly their new discovery conflicts with all known physics.
On a more positive note:
An organic chemist told me (many times) “Any theory which contradicts prior observation is Dead On Arrival”.
We do not need to worry about it, we do not need to refute it, we do not need to argue about it, we do not need to disprove it. If an idea contradicts established observations, it is wrong.
As we said in Chemistry, “Not faulty, Not flawed, Just Plain Wrong”. So much for Political Correctness.
Any notion that the UHI of Boston is negative is DOA.
We have been treated to many stupid/preposterous/fund grubbing papers recently at WUWT, leading up to the Paris COP, no doubt. This one just leaves me speechless.
Boston UHI is negative, speechless. DOA.
It is sad that students are no longer taught to check if their answer makes sense. These “researchers” clearly did not. It used to be, if you did a long, complicated mathematical calculation, the first thing you were taught to do in checking the answer was to look at it and see if it made general sense. Looking at the negative UHI for the Boston area would fail that check. Anyone living in the area knows that outside of the city itself it is cooler near the coast in the summer and fall by large amounts, and only marginally warmer in the winters. That’s why you travel to the coast in the summer. Boston itself is definitelyy warmer/hotter in the city than surrounding. But of course they could have based their Boston measurements on a location at the airport which is essentially IN Boston harbor. It would be a nice trick – use the downtown thermometers for global surface temperature, but then do this study using boston harbor with the cooling seabreeze for measuring UHI. I don’t know if that is what they did, but clearly the blue fails the test of whether the answer makes any sense. Next step after failing the sanity check should have been to go find their mistakes instead of publishing whatever their calculations spit out because they liked the answer.
The Channel Islands National Park has an UHI. Okay. Tells anyone what they need to know about quality control.
“…The study establishes a method for estimating UHI intensities using PRISM–Parameter-elevation Relationships on Independent Slopes Model–climate data, an analytical model that creates gridded estimates by incorporating climatic variables (temperature and precipitation), expert knowledge of climatic events (rain shadows, temperature inversions and coastal regimes) and digital elevation…”
Well there you go…a model which includes “expert knowledge of climatic events.” How is that programmed in? lol.
A max UHI intensity of 1.49°C? That doesn’t pass the sniff test. Oh, it’s even the annual average, so the calculated UHI intensities for summer months are blended with the probably lower figures for other seasons. However, NASA is on record for finding that “Summer land surface temperature of cities in the Northeast were an average of 7 °C to 9 °C (13°F to 16 °F) warmer than surrounding rural areas over a three year period.”
http://wattsupwiththat.com/2010/12/14/image-the-urban-heat-islands-in-the-northeast/
Anthony measured a 10F° (5.5C°) difference in Reno at night in late October.
http://wattsupwiththat.com/2008/10/29/uhi-is-real-in-reno-at-least/
Incidentally, the press release of that NASA study says “Cities in desert regions, such as Las Vegas, in contrast, often have weak heat islands or are actually cooler than the surrounding rural area.” So there’s something to the negative UHI notion.
Katherine
No. They “claim” there is something to the negative UHI graphs that they worked to get published (prior to Paris). But UNLESS they are using a “daily average” that tries to combine those very cold non-UHI nights AROUND the desert cities with the very evident 3-5 degree C EVERYDAY temperature effects that actually are present in every city in the world – but in areas that vary with every county plotted in the map, their paper is falsified by Nature. (er, nature.)
Having lived in Las Vegas for a few years, I can assure you that it does not have a negative UHI.
I don’t see why Las Vegas should have a negative UHI effect when Phoenix has been shown by experimental data to have a positive UHI. See citations for Idsos and others. http://www.co2science.org/subject/u/summaries/phxurbanco2dome.php
Maybe it’s all the swimming pools at the hotels and the irrigation of the landscaping where normally there would only be desert? Plus the all high-rises probably cast long shadows. I suspect there’d be a lot more of those high-rise hotels in Las Vegas than Phoenix. But that’s speculation…assuming NASA’s claim is true.
Extensive evaporation might, and I repeat, MIGHT, be enough to counteract the effect of all that asphalt during the day, but at night, the resulting humidity will hold in the heat generated during the day.
Phoenix and surrounding areas still use flood and sprinkler irrigation which far outweigh the swimming pools (besides some areas of Phoenix have many swimming pools. The point, is it is easy to make hypotheses why Las Vegas has a negative UHI effect. But these hypotheses are easily to prove false when using observations and data as Idso and his colleagues did in Phoenix. Please go to the source linked above and see the value of observations and data.
I know San Diego has some UHI mitigation programs, but negative? About a decade ago, it as among the highest.
Atlanta was of the first UHIs to be studied I think. It as blamed for changing rain patterns…and this was back in the 60s or 70s. But it shows a mild with all that sprawl and concrete jungle since?
Deserts cool rapidly at night. Very rapidly. Unless it is a box canyon with few trees, these radiate heat for a long time.
Cities never cool quickly at night! Never! I know of no desert with miles of black asphalt, for example, not even in Death Valley and I grew up in the Southwest deserts and lived far from the cities much of the time including at Kitt Peak.
In the evening, desert temperature changes cause a wind to rise up [which] cools things even faster but in the cities, buildings block this wind, another reason it is hotter in cities there. And I assure everyone, having also lived in Death Valley once, at night it gets downright COLD. Even in summer except the salt flats and even these are cold by dawn.
Humidity also plays a significant role in urban/rural/desert rates of cooling during the evening. A number of studies have found cities are relatively more humid in the evening, even though they may be less humid during the day. This is attributed to more dewfall outside urban areas, which brings urban aerosols into the picture.
The wind you describe could be due to elevation differences. I haven’t experienced similar winds in the flat Australian deserts.
Winter in the Chicago area, the ground freezes solid.
Shovels don’t work against the frozen ground, so you pull out the pick and swing it as hard as you can (it helps to keep you warm ), and chip away at the frozen ground.
It gets cold enough that even the laziest workers want to swing the pick.
No mosquitoes though 🙂
The problem is they used PRISM data.
there isnt a person on the site ( except me I guess) who has any idea what prism data is and what its limitations are.
jeez guys… go look at the details before spouting off.
Mr. Mosher, I see you passed up the chance to display your unequaled brilliance by explaining in a few words what the PRISM data is.
But you certainly jumped at the chance to claim to be brighter, more dilligent, more thorough than anyone else, while at the same time providing ample evidence you haven’t even read all the comments here, from those whom you would so foolishly disparage.
Mosher does not read many comments. He does not need to, as he knows that of all WUWT readers, only he knows enough to understand climate related issues. 😉
Prior mentions of PRISM (a model) in comments before Mosher’s at 9:02 pm :
commieBob September 18, 2015 at 11:57 am
Michael Jankowski September 18, 2015 at 5:26 pm
He perhaps may not read the article summary, either, otherwise he’d have noticed PRISM was mentioned twice.
I do. I believe PRISM was developed about 20 years ago by that well known climate denier and debunked fired Oregon State Climatologist George Taylor.
I haven’t Googled to check on that… but that’s my memory.
The PRISM techniques do an excellent job of mapping climate data in physiographically complex areas. Taylor has always done excellent work and I found him to be a truly nice guy. Of course that was before the era of climate hatred.
Several points.
Urban aerosols can affect clouds, precipitation and hence temperatures up 200 km downwind. Hence any analysis needs to take account of wind direction.
Urban albedo affects daytime and nighttime temperatures differently. Where an urban area has a higher albedo (generally the case), more sunlight is reflected upward and with less heat absorbed at the surface and re-radiated at night, nights are cooler. However, albedo changes to ground surfaces, vertical surfaces and roofs will have different effects on temperatures measured a few feet above the ground.
All they seem to have found is that evapotranspiration of vegetated areas decreases temperatures, but paradoxically the increased humidity retains more heat near the surface due to the water vapour greenhouse effect, and it feels hotter to people, because as humidity increases, sweating becomes less effective at cooling us. Therefore their conclusions about mitigating UHI are wrong at a practical level. They need to take humidity into consideration.
The study tells us little about the interesting question, which is how much UHI has changed over time? (and hence the effect the changes have had on the surface temperature record). 3 effects, probably account for most of the changes over time; vegetation and irrigation changes, albedo changes and aerosol changes. Just one example, where I live in Perth, about 50% of houses now have high albedo steel roofs, whereas 50 years ago none would have. A rough calculation gives me 2% of total solar insolation, which would have previously been absorbed at the surface is now reflected upward.
Keep in mind that all this UHI debate is largely unnecessary if we rely on satellite temperature data which is consistent, comprehensive, and calibrated.
Surface thermometer data has so many localization and citing and consistency problems that the errors are almost as big as the signal and the adjustments are as big as the signals.
Philip. Have you ever walked in a city at night or used the concept of impervious areas? Have you felt the temperature of asphalt?
I cannot find by experience or data anything to support what you say: “Urban albedo affects daytime and nighttime temperatures differently. Where an urban area has a higher albedo (generally the case), more sunlight is reflected upward and with less heat absorbed at the surface and re-radiated at night, nights are cooler.”
The fact that there are negatives values greater than half a degree indicates the results have a built in understatement of about a degree. A very large number of lawns kept looking green in areas of drought can result in about a half degree cooling but even this is optimistic.
Slowly starting to shape up winter polar vortex. For now blocking it begins on the eastern Siberia. We can already see there in the stratosphere, ozone area of elevated temperature. I conclude from this that cold air from the north will now reach out to the west of North America. Let’s see how the situation develops.
The trees of the rural area always turn earlier than those of the urban areas in the fall.
“Athens, Ga. – Inner cities as well as suburbs show distinctly warmer temperatures–known as the urban heat island effect–than rural areas as a result of land use and human activities, which can affect rainfall, air quality and public health.”
The press release begins by describing UHI the way it is understood by all. Then they completely contradict themselves by reporting negative UHI. PRISM or no PRISM, this is sense-free. The green space in a city cannot make the city cooler than the countryside, as most of a city is not green space.
What sort of scam is this?
“The green space in a city cannot make the city cooler than the countryside, as most of a city is not green space.”
It can if the countryside is a desert like in Vegas. But overall, the net cooling added to the temp adjustments for UHI are crazy.
The important fact is whether or not a land weather station has been affected by a CHANGE in the environment near it by economic growth, paint changes on the box, equipment changes inside the box, movement to a different location (possibly more than once), no longer in use, missing readings “infilled” by smarmy bureaucrats, and the repeated “adjustments”, “re-adjustments” and “re-re-re-adjustments”.
I would suggest the “adjustments” are more important than the other factors — they show the obvious fact that smarmy data collectors have predicted the future climate, and have been repeatedly “adjusting” the data to make their (wild guess) predictions appear to be more accurate.
In addition, over 70% of the planet is water, and I believe the ever-changing methodologies for measuring the surface temperature above the water is haphazard, non-global, far from accurate, and worthy of being the subject of a twenty-minute Three Stooges short.
I have lived and predicted the weather day in, day out in Chicago, New York and San Diego and predicted the weather nationally for sixty years so my close up and prolonged encounter with the UHI is very real, more real than some computer model that seems to attempt to apply the same analysis to dramatically different geographic locations. In the flat plains where the dynamic weather pattern of fronts and pressure centers is powerfully in control, the UHI is very dramatic. Chicago, Omaha, Kansas City, Dallas, St Louis, etc have clear and well defined UHIs. In coastal locations where the the dynamic pattern has been altered by the Ocean waters and various mountain ranges that somewhat alter the wind flow, the UHI is still present but its pattern is dramatically altered by these geographic influences. New York, Boston and Philadelphia are examples of this sort of situation. On the west coast, there is very little dynamic weather, the Ocean and blocking of the Mountain ranges totally overwhelms the UHI. Seattle, San Francisco, Los Angles and San Diego are examples of this pattern.
In the classic UHI the cities island of heat is carried 100 miles or more downstream by the prevailing wind and the heating also increases downwind precipitation measurably. And up wind of the city, both the cooling and drier conditions are very clear. It is the most obvious and dramatic and easily measurable impact of mankind on his climate. But the effect is not serious and has only tiny impact on the overall and continuing climate of Earth.
I’ve read the all the comments up to this time and have not seen my understanding of the purpose of the paper expressed. The paper does not appear to be about understanding the UHI and how it affects regional, continental, and global temperatures. It appears to me to have a different purpose.
Here to me, is the money quote:
“ ‘We found that more contiguous sprawling and dense urban development both enhanced UHI intensities. In other words, it does not appear to be a simplistic either-or situation regarding sprawl or density,’ Debbage said.
The researchers hope the results can help influence local governments and city planners in the formulation of effective codes and policies to mitigate the urban heat island effect.”
Note that the purpose of the study is not to understand the magnitude of UHI temperatures so as to correct regional and planetary “average temperatures.” The purpose is influence “…codes and policies to mitigate the urban heat island effect” So they want to mitigate the UHI temperature effect. People often say they want to move away from warmer central city to the cooler countryside. Thus creating “urban sprawl” This study purports to show that there is no difference in UHI temperature between the urban core and the suburbs.
Academics hate “urban sprawl.” They want everyone to live in densely packed urban areas. No doubt the study was started in hopes of showing the densely packed urban areas had lower UHI effects than urban sprawl. Since that didn’t happen, they can at least say “ See packing people densely in the Urban Core doesn’t produce any higher UHI temperature effect than urban sprawl, so that is not a reason to oppose cramming people together in the urban core.
So the paper is not about temperature, it’s about city planning.
So it looks like ‘science to order’ then?
Academics hate urban sprawl; they need some ‘scientific’ evidence that it’s the same in the suburbs as in town so as to discourage suburban development. Hey presto, paper delivered.