From the “department of limiting UHI” and NASA/GODDARD SPACE FLIGHT CENTER
Cities are well known hot spots – literally. The urban heat island effect has long been observed to raise the temperature of big cities by 1 to 3°C (1.8 to 5.4°F), a rise that is due to the presence of asphalt, concrete, buildings, and other so-called impervious surfaces disrupting the natural cooling effect provided by vegetation. According to a new NASA study that makes the first assessment of urbanization impacts for the entire continental United States, the presence of vegetation is an essential factor in limiting urban heating.
Impervious surfaces’ biggest effect is causing a difference in surface temperature between an urban area and surrounding vegetation. The researchers, who used multiple satellites’ observations of urban areas and their surroundings combined into a model, found that averaged over the continental United States, areas covered in part by impervious surfaces, be they downtowns, suburbs, or interstate roads, had a summer temperature 1.9°C higher than surrounding rural areas. In winter, the temperature difference was 1.5 °C higher in urban areas.
“This has nothing to do with greenhouse gas emissions. It’s in addition to the greenhouse gas effect. This is the land use component only,” said Lahouari Bounoua, research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study.
The study, published this month in Environmental Research Letters, also quantifies how plants within existing urban areas, along roads, in parks and in wooded neighborhoods, for example, regulate the urban heat effect.
“Everybody thinks, ‘urban heat island, things heat up.’ But it’s not as simple as that. The amount and type of vegetation plays a big role in how much the urbanization changes the temperature,” said research scientist and co-author Kurtis Thome of Goddard.
The urban heat island effect occurs primarily during the day when urban impervious surfaces absorb more solar radiation than the surrounding vegetated areas, resulting in a few degrees temperature difference. The urban area has also lost the trees and vegetation that naturally cool the air. As a by-product of photosynthesis, leaves release water back into to the atmosphere in a process called evapotranspiration, which cools the local surface temperature the same way that sweat evaporating off a person’s skin cools them off. Trees with broad leaves, like those found in many deciduous forests on the East coast, have more pores to exchange water than trees with needles, and so have more of a cooling effect.
Impervious surface and vegetation data from NASA/U.S. Geologic Survey’s Landsat 7 Enhanced Thematic Mapper Plus (EMT+) sensor and NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on the Terra and Aqua satellites were combined with NASA’s Simple Biosphere model to recreate the interaction between vegetation, urbanization and the atmosphere at five-kilometer resolution and at half-hour time steps across the continental United States for the year 2001. The temperatures associated with urban heat islands range within a couple degrees, even within a city, with temperatures peaking in the central, often tree-free downtown and tapering out over tree-rich neighborhoods often found in the suburbs.
The northeast I-95 corridor, Baltimore-Washington, Atlanta and the I-85 corridor in the southeast, and the major cities and roads of the Midwest and West Coast show the highest urban temperatures relative to their surrounding rural areas. Smaller cities have less pronounced increases in temperature compared to the surrounding areas. In cities like Phoenix built in the desert, the urban area actually has a cooling effect because of irrigated lawns and trees that wouldn’t be there without the city.
“Anywhere in the U.S. small cities generate less heat than mega-cities,” said Bounoua. The reason is the effect vegetation has on keeping a lid on rising temperatures.
Bounoua and his colleagues used the model environment to simulate what the temperature would be for a city if all the impervious surfaces were replaced with vegetation. Then slowly they began reintroducing the urban impervious surfaces one percentage point at a time, to see how the temperature rose as vegetation decreased and impervious surfaces expanded.
What they found was unexpected. When the impervious surfaces were at one percent the corresponding rise in temperature was about 1.3°C. That temperature difference then held steady at about 1.3°C as impervious surfaces increased to 35 percent. As soon as the urban impervious surfaces surpassed 35 percent of the city’s land area, then temperature began increasing as the area of urban surfaces increased, reaching 1.6°C warmer by 65 percent urbanization.
At the human level, a rise of 1°C can raise energy demands for air conditioning in the summer from 5 to 20 percent in the United States, according the Environmental Protection Agency. So even though 0.3°C may seem like a small difference, it still may have impact on energy use, said Bounoua, especially when urban heat island effects are exacerbated by global temperature rises due to climate change.
Understanding the tradeoffs between urban surfaces and vegetation may help city planners in the future mitigate some of the heating effects, said Thome.
“Urbanization is a good thing,” said Bounoua. “It brings a lot of people together in a small area. Share the road, share the work, share the building. But we could probably do it a little bit better.”
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There is something else in play here. A lot of “urban” areas and even small towns have street lightning, this can also throw growing seasons for trees etc out of wack. By artificially lengthening the growing season for tree growth around street lamps ( and this could even kill them by being unprepared for winter) you can add even more variables to the mix. It may be a small point but seeing that every one’s knickers are in a knot about a few parts ppm’s of C02 I thought I’d throw this in.
Just to set you lot straight, here is the ‘truth’ about UHI from the horse’s mouth itself, the supposed wisdom of SkepticalScience – or maybe they just got it wrong yet again.
https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=11&cad=rja&uact=8&ved=0CFwQFjAKahUKEwj-2uWqhMbHAhVmOdsKHbkJAgU&url=https%3A%2F%2Fwww.skepticalscience.com%2Furban-heat-island-effect.htm&ei=AlHdVf7REuby7Aa5k4go&usg=AFQjCNFhJnZgZObsxQ81kpNRkffja-W8Rw
Perhaps not as obvious as it should be; here in South Africa, I live in a city called Johannesburg; Our mean temperature is lower, and the humidity higher, than the surrounding area called the Highveld. Perhaps not coincidentally, we were also at one stage the largest man-made forest in the world. This is largely made up of so-called invasive species, which were regularly tended and supplied with water by the inhabitants. These are also the plants that this article identifies as having the most cooling effect, as the most efficient “pumps” of water. We are now removing these plants in the name of water thrift, and replacing them with indigenous species, which are not efficient water “pumps”. I wonder what the local climate will be like in another 100 year’s time… I might not have to live that long to see a demonstration, though. A local wine farm won a “green” award for removing invasive species from it’s land, and proudly announced that after the last bluegum was removed, a stream started flowing that had not done so for a long time. The stream water did not miraculously just appear there, so it was most likely that it was being pumped into the atmosphere as water vapour by the “invasive” trees. I’m sure that this is bound to affect the local microclimate, to which wine grapes are supposed to be particularly sensitive. I will be following the news on this particular vineyard with great interest for the foreseeable future.
Interesting, Tony. Thanks.
Well, this is not a surprise, but yet one of the most useful studies by nasa. I am only a bit wondering why the author claims that this is an “addition” to the co2 warming. if I don’t mistake, it’s a source of warming which is already recorded by temperature stations in cities. therefore for those looking for the real impact of co2, uhi should be substracted from the raw temperature.
The alarming thing is that, in growing cities (over the course of decades), most of the warming measured is the consequence of a growing uhi. Yet the temperature record has been adjusted so that rural warming trends match city warming trends, whereas only about 3% of the planet is urbanised. It’s a scientifical non-sense.
Watch the “drift” of climate science papers as the presidential election approaches. If a republican president becomes more likely with the Congress remaining in “red” hands there will be more papers with an element of reality in them even from US government agencies. This could be a positioning paper as NASA have been under attack in the Senate for their spending on climate as opposed to rockets.
Around half the heat lost from the surface comes from evaporation from plants. It therefore also follows that plants are essential in reducing the amount of rain that finds its way into rivers.
Most “global warming” was never anything to do with CO2, but was instead a reduction in the level of plants in and around places where there were temperature sensors. Even a really basic knowledge of the atmospheric cooling tells us this is true, yet for political reasons certain academics and government organisations have been carrying out a campaign of hate against any who dared to suggest anything other than CO2.
London (UK) UHI case:
http://cimss.ssec.wisc.edu/climatechange/globalCC/lesson7/images/UHI_London.gif
credit wisc.edu
Narrative:
“The intensity of the heating varies across a city, with the highest temperatures found near the city core. For instance, under clear skies and light winds, temperatures in central London (see figure ‘above’) during the spring reached a minimum of 11° C (52° F), whereas in the suburbs they dropped to 5° C (41° F), a difference of 6° C (11° F).”
Beneficial aspect of the London’s UHI, considering large population and many old poorly insulated homes, is considerable saving on the winter heating bills. My energy consumption (kW, gas CH , both buildings of early 1960’s similar construction) fell by about 30% in the winter months, by moving some years ago from isotherm “6C” to the edge “11C” area.
vukcevic August 26, 2015 at 1:09 am That fits well with the weather forecasts, they always talk about at least 5 or 6 degrees colder in the county side compared to the Cities in the UK.
1 to 3 degrees is nowhere near enough and Berkely’s estimate is totally laughable.
The difference must be higher outside suburb / or in rural areas. How NASA found out the claim, I would like to know the science and also how vegetation can limit the heat absorbed by the concrete or black top roads. Main cause of CC is urbanization. Millions of Square KMS of land surface is covered by concretes and black topped roads transforming the soil surface into dry land that is worse than desert. Deserts can hold water and let ground water recharge but urban areas only drain water to sea and stops evaporation which is vital for rain cycle.
So, What they found was that if you have less solid, manmade material and more natural material you get less UHI. OMG; who’d a thunk it.
DA I could have told them that 40 years ago. Also ,”Obvious science”, they will fine higher humidity in city with large amount of vegetation. We live on a swamp cooler planet.
But this is one of the reasons you don’t want big trees in the city.
Also in winter.
http://archive.9news.com/images/640/360/2/assetpool/photogallery/251303/50ft%20pine%20tree%20fell%20onto%20house%20%20%20karl%20kirsch.jpg
I guess the tree got fat on top eating up all that excess CO2 and fell over 😰
With a saw cut stump matching the saw cut at the base of the tree, it wasn’t the tree’s fault; it was the yahoo who cut that tree.
Gravity teaches another wannabe lumberjack a lesson.
Some folks just can’t grasp observational physics.
That one looks more like you don’t want apprentice lumberjacks in the city! Hire a professional!
Now that they’ve gotten that 1.3°C to 1.6°C range nailed down, it’s a good bet those figures will be used to adjust rural temps upward so that they’re comparable to urban temps. It would be probably be too much to expect of NASA’s Goddard Space Flight Center to deduct the figure from urban temps to remove the UHI component. After all, if they did that, they might get cooling.
See vukcevic August 26, 2015 at 1:09 am for more realistic values.
Useless, taxpayer-funded model-driven garbage. NASA has become a joke, in large part thanks to Coal-Trains-of-Death climate clown Hansen.
Urbanization is generally a bad thing. It promotes economic disparity, which must be subsidized, and social strife, which must be suppressed. And, apparently, global warming. Every heat island counts.
It’s really not that simple and more trees won’t fix it. Thermal mass/specific heat of building materials concentrated in urban areas not only absorb more, they are also cool much slower than rural areas. Add to that heat released from building systems and automobiles, which is also absorbed by those same building materials. UHI effect on the climate is not going away. Even if populations completely dispersed the structures will still maintain a measure of heat island.
Well, well UHI strikes again, I wish someone would make up their minds. Twenty years ago an EPA presenter emphasized UHI and what we needed to do to mitigate it. Then five years ago articles were published indicating than UHI had no impact on warming statistics (they used a city with temperature records back to the 17th century to “prove” that UHI was not an issue).. Anxiously awaiting the next reversal.
Only way to keep land surface cool is by keeping moist all over as soil used to be before urbanization. The difference must be higher outside suburb / or in rural areas. How NASA found out the claim, I would like to know the science and also how vegetation can limit the heat absorbed by the concrete or black top roads. Main cause of CC is urbanization. Millions of Square KMS of land surface is covered by concretes and black topped roads transforming the soil surface into dry land that is worse than desert. Deserts can hold water and let ground water recharge but urban areas only drain water to sea and stops evaporation which is vital for rain cycle.
I’ M Right in the middle of one of their red spots sitting among several lakes with 100’s of acres of state forest in my back yard. The forest here is so thick satellite TV isn’t available and radio is spotty yet they show me in an UHI. FRAUD
…And CO2 is good for vegetation. Problem solved even before it started as they have been preaching how CO2 levels continue to rise.
Very odd that Western Illinois, AKA “Forgottonia,” shows so much dark red. I never realized those little towns like Bushnell, Colchester, La Harpe, and Oquawka were such powerful urban heat islands…or something.
Can anyone overlay this map with the distribution of contributing weather stations?
I would bet a rather substantial amount that the great majority of weather stations (according to this map) should have between a 1 and 3 C UHI-linked warming that should be SUBTRACTED from the station data when trying to estimate the CO2 linked part of global warming. But I never grapped any of the maps that show the distribution of stations. I just remember them being denser in the urban areas and sparse in precisely the places where the urbanization is sparse. I wouldn’t be surprised if a lot of them live inside even the sparser network of red dots on the west-central part of the continent.
rgb
I can’t overlay them, but here are the stations (as long as sharing my map works).
https://www.google.com/maps/d/edit?mid=zFc6ZVuRjl0U.kyckeuzeYY54&usp=sharing
Sort of. My browser has issue with it. Then there is the resolution issue on the map above, too. Offhand they look like they have some overlap, but I’m not sure I can manage to screen scrape the two and construct a transparent overlay, at least not until I have a lot more time.
Sad, really — this would be an interesting way of checking GISS’s UHI correction that is quite independent of what they are using now.
rgb
I have KML files for all of the NCDC stations, but they are quite dense once read into google maps.
If you can figure out how to get the nasa data into google maps (or something that reads the KML file) I’ll gladly forward it, it might already be in sourceforge, but I generate them automatically. Put I haven’t segregated them by year, let alone which ones nasa used to create any particular temperature/UHI data set.
http://sourceforge.net/projects/gsod-rpts/files/Reports YearlyContinental_Ver_2.1.zip
rgbatduke
I understand Hansen’s NASA/GISS urban heat island “correction” uses each month’s “latest” NASA light survey index of all of the US (clouds and all?) to re-correct every year’s data of every temperature value based on the nighttime light value. Theory being, higher night time light values mean more electric use mean more “urbanization” mean more UHI to “correct for” – regardless of what the actual surface temperatures were then, are now, or will be in the future. Further, the “night index correction” means no single month’s value can be directly against ANY previous recorded value, since the whole temperature set is recalibrated every computer run based on an ever-changing “value” not related to the previous month, year, decade, or 30 year interval.
Thus, if flares from a gas field or a “highlight” or halo effect were present, then the temperature records themselves are changed based on the assumed amount of night light measured. So, a pristine surface temperature station is changed arbitrarily, while a downtown record (Central Park or the Detroit airport or the Philadelphia Airports or – to pick obvious examples) are compared against ever-darker urban settings.
Does this help?
http://wattsupwiththat.com/2014/03/25/study-many-us-weather-stations-show-cooling-maximum-temperatures-flat/#comment-1598548
Where to place a Stevenson Screen?
Lest us assume that there are 10,000 Stevenson Screens located on continental USA. Where would you place them if you had the chance to place them all?
1) Place them in a pattern where they would be equidistant from any others, (Triangular elements?) and cover the whole USA?
2) Ensure that 3% of them are located with UHI locations? Any on inland water bodies?
None next to restaurant stove exhausts, or emergency diesel exhaust pipes, etc.
As regards Phoenix, that is a figment of someone’s imagination.
?w=584
Most new developments around Phoenix don’t have grass lawns, and they have few trees. They have crushed rock “lawns” with drought-resistant plants and drip irrigation.
One notable exception in the Phoenix area is Arizona State University at Tempe. There’s plenty of irrigated foliage there, and it’s just south of Tempe Town Lake, a small replica of the now-dry Salt River that once had a ferry boat on it. Tempe Lake was created in 1999. North of the lake is the well-watered 125-acre Phoenix Zoo. Tempe ASU station temperatures began a decline in 2001.
Here’s a comparison of Jun-Jul-Aug mean minimum temperature trends at Phoenix Sky Harbor Airport and Casa Grande—a farming community 41 miles SSE of the airport that grew into a Phoenix suburb in the 2000s:
Do you see any “cooling effect” at either location?
More hogwash. Most of the summertime warming in Phoenix is in warmer nights. The city cools more slowly than the desert, and it isn’t due to CO2.
That is quite possible, but daily warming is approximately the same as that nightly cooling, remember in the spring the length of the day increases and the length of the nightly cooling decreases, until after the summer equinox where the night starts to lenghten, but there’s still a lot of stored heat to lose.
This the Day to day change in min temp for the northern hemisphere.
This
Is the IR temp of
Tsky
Grass
Concrete
Asphalt
The long slope is my concrete sidewalk cooling as the shadow increases on it
Wait… concrete and asphalt heat up when exposed to the sun and create different temps in a city than in a place with no concrete and asphalt?
Well, I guess I can finally apply for my own study on the topic “Water – Is it wet?”
In much the same way I can prove I do have a brain (I got pictures), too late I’ve got pictures!
8-14u
Tsky
Grass
Concrete (with increasing shadow)
Asphalt