One more reason to say asphalt affects local weather

Paved surfaces can foster build-up of polluted air

From the National Center for Atmospheric Research

BOULDER—New research focusing on the Houston area suggests that widespread urban development alters weather patterns in a way that can make it easier for pollutants to accumulate during warm summer weather instead of being blown out to sea.

The international study, led by the National Center for Atmospheric Research (NCAR), could have implications for the air quality of fast-growing coastal cities in the United States and other midlatitude regions overseas. The reason: the proliferation of strip malls, subdivisions, and other paved areas may interfere with breezes needed to clear away smog and other pollution.

Houston graphic

Paved surfaces in the Houston area keep the city warmer than more natural surfaces. As a result, overnight temperatures are often similar between the city and nearby offshore areas, which weakens summertime breezes and enables air pollution to build up. The stagnant conditions also persist during the day because of larger-scale wind patterns. (©UCAR, Illustration by Lex Ivy. This image is freely available for media use. For more information, see Media & nonprofit use.*)

The research team combined extensive atmospheric measurements with computer simulations to examine the impact of pavement on breezes in Houston. They found that, because pavement soaks up heat and keeps land areas relatively warm overnight, the contrast between land and sea temperatures is reduced during the summer. This in turn causes a reduction in nighttime winds.

In addition, built structures interfere with local winds and contribute to relatively stagnant afternoon weather conditions.

“The developed area of Houston has a major impact on local air pollution,” says NCAR scientist Fei Chen, lead author of the new study. “If the city continues to expand, it’s going to make the winds even weaker in the summertime, and that will make air pollution much worse.”

While cautioning that more work is needed to better understand the impact of urban development on wind patterns, Chen says the research can eventually help forecasters improve projections of major pollution events. Policymakers might also consider new approaches to development as cities work to clean up unhealthy air.

The article will be published this month in the Journal of Geophysical Research–Atmospheres, a publication of the American Geophysical Union. The research was funded by the U.S. Air Force Weather Agency, the U.S. Defense Threat Reduction Agency, and the National Science Foundation, NCAR’s sponsor. In addition to NCAR, the authors are affiliated with the China Meteorological Administration, the U.S. National Oceanic and Atmospheric Administration, and the University of Tsukuba in Japan. The research built on a number of previous studies into the influence of urban areas on air pollution.

Cleansing the air with more parks and lakes?

Houston, known for its mix of petrochemical facilities, sprawling suburbs, and traffic jams that stretch for miles, has some of the highest levels of ground-level ozone and other air pollutants in the United States.

Fei Chen

Fei Chen. (©UCAR, Photo by Carlye Calvin. This image is freely available for media use. For more information, see Media & nonprofit use.*)

State and federal officials have long worked to regulate emissions from factories and motor vehicles in an effort to improve air quality.

The new study suggests that focusing on the city’s development patterns and adding to its already extensive park system could provide air quality benefits as well.

“If you made the city greener and created lakes and ponds, then you probably would have less air pollution even if emissions stayed the same,” Chen explains. “The nighttime temperatures over the city would be lower and winds would become stronger, blowing the pollution out to the Gulf of Mexico.”

Chen adds that more research is needed to determine whether paved areas are having a similar effect in other cities in the midlatitudes, where sea breezes are strongest. Coastal cities from Los Angeles to Shanghai are striving to reduce air pollution levels. However, because each city’s topography and climatology is different, it remains uncertain whether expanses of pavement are significantly affecting wind patterns elsewhere.

Nine days of pollution

For the Houston study, Chen and his colleagues focused on the onset of a nine-day period of unusually hot weather, stagnant winds, and high pollution in the Houston-Galveston area that began on August 30, 2000. They chose that date partly because they could draw on extensive atmospheric measurements taken during that summer by researchers participating in a field project known as the Texas Air Quality Study 2000. That campaign was conducted by the National Oceanic and Atmospheric Administration, the U.S. Department of Energy, universities, and the Texas Natural Resource Conservation Commission.

In addition to the real-world measurements, the study team created a series of computer simulations with a cutting-edge software tool, NCAR’s Advanced Weather Research and Forecasting model.

Fei and his colleagues focused on wind patterns, which are driven by temperature contrasts between land and sea. If Houston were covered with cropland instead of pavement, as in one of the computer simulations, inland air would heat up more than marine air during summer days and cause a sea breeze to blow onshore in the afternoon. Conversely, as the inland air became cooler than marine air overnight, a land breeze would blow offshore—potentially blowing away pollution.

In contrast, the actual paved surfaces of Houston absorb more heat during the day and are warmer overnight. This results in stagnation for three reasons:

  • At night, the city’s temperatures are similar to those offshore. The lack of a sharp temperature gradient has the effect of reducing winds.
  • During the day, the hot paved urban areas tend to draw in air from offshore. However, this air is offset by prevailing wind patterns that blow toward the water, resulting in relatively little net movement in the atmosphere over the city.
  • Buildings and other structures break up local winds far more than does the relatively smooth surface of croplands or a natural surface like grasslands. This tends to further reduce breezes.

“The very existence of the Houston area favors stagnation,” the article states.

The study also found that drought conditions can worsen air pollution. This is because dry soil tends to heat up more quickly than wet soil during the day. It releases more of that heat overnight, reducing the temperature contrast between land and water and thereby reducing nighttime breezes.

By comparing observations taken in 2000 with computer simulations of Houston-area winds and temperatures, the researchers were able to confirm that the Advanced Weather Research and Forecasting model was accurately capturing local meteorological conditions.

About the article

Title: A numerical study of interactions between surface forcing and sea-breeze circulations and their effects on stagnation in the greater Houston area

Authors: Fei Chen, Shiguang Miao, Mukul Tewari, Jian-Wen Bao, and Hiroyuki Kusaka

Publication: Journal of Geophysical Research–Atmospheres

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33 thoughts on “One more reason to say asphalt affects local weather

  1. I lived in Houston for about 25 years. It was always a pleasure to cycle after work, and it was almost always breezy. I thought it was the tradewinds as felt along the coastlines. When I moved to the Woodlands about 25 miles north of downtown Houston those breezes were gone and it was much less pleasant.

    Tom Bakewell

  2. Then we need to ask how extensive this effect is around towns and cities? Does it also impact on adjacent rural climate stations?

  3. Makes sense to me. You can smell asphalt on a hot day. Interesting side note, the reporter in NYC for NBC in discussing the current heat wave, noted that because of the asphalt and heat retention by concrete, the city would be up to 15 degrees warmer than ambient air. These are the same people that see AGW at every turn. It never occurred to them that the global temperature might not be as high if measured outside of UHE areas.

  4. Get a copy of Helmut E Landsberg – “The Urban Climate” –
    I think all this was basically known 30 years ago.
    Except for Houston specific things, what is new in the Chen study ?
    Now if I can be allowed a little rant – the UHI is the most IGNORED geophysical feature on the planet – and yet most of us live in one.

  5. I’m confused. First they say that warm natural landscapes warm up & create a sea breeze during the day, then cool down quickly producing a land breeze at night, which is correct. Next, they say that urban pavements warm up & “tend” to create a daytime sea breeze, which opposes the prevailing wind & results in stagnant air. This does not compute. Finally they say that during droughts, dry soil cools quickly at night, reducing the temperature contrast with the ocean, resulting in less wind. Again, this does not compute. Dry air holds no heat, same with dry soil, so the temperature contrast would be increased, not decreased.

  6. Looks to me like they got the circulation backwards – but Iana climate scientist.

  7. Ray:
    We were taught in a sailing course that I took many years ago that sailing on the west coast is better than on the east coast because the prevailing westerlies are in the same direction as the daytime sea breeze. The explanation is that the land heats up more quickly than the sea in daytime as you say. This creates an updraft, hence the wind from the west on the west coast. At night the reverse occurs with land cooling more rapidly than the ocean with the land breeze tending to be from the east. So, whether any land breeze counteracts the “prevailing” breeze depends on which coast one is on.

  8. The temperature differential makes sense, but I’m not going to believe that buildings make any impact on wind forces.

    A building may be what? 200 to 400 metres in height. And to what height is the air is affected by the temperature differential between land and sea? I don’t know, but I’m not going accept is makes any overall difference, a little slower at the surface interface yes, but nothing in toto.

    Sleepalot makes a good point. Where I live on the coast, the night breezes are “always” on shore at night.

  9. It might affect local weather, but it does have an effect on global warming climate statistics.

  10. What a bunch of dip dongs, it increases in the winter and keeps things warmer…………….

    Did anyone really expect the National Center for Atmospheric Research to give up a pay check?

  11. Um,
    I receive a free magazine (CE NEWS), it’s for civil engineers (way past my pay grade).
    It is interesting as far as I can follow it, and highlights the hoops engineers are forced to jump through to comply with ever changing “green” regulations.
    My only question is, who pays for all this engineering ?

  12. Breaking news… NCAR discovers UHI, or one aspect/manifestation of it.
    Tune in tomorrow when NCAR discovers grass is green, water is wet, and wild animals are wild.

  13. Simulations aren’t science. This study could have become scientific if they’d measured wind in a nearby all-rural spot at a similar distance from the ocean, and compared that with downtown wind. Seems like the first thing you’d want to do, before forming or testing any theories.

  14. I agree with Warwick Hughes. We were doing similar UHI studies in Winnipeg in the late 1960s and early 1970s partly because it was an ideal location. It is a large isolated city on an essentially isotropic plain with extremely cold winters when the UHI is greatest. We also studied the variations between vegetated and paved surfaces, on particulate levels in the city on hourly, daily, and seasonal scales at the surface and above the city to determine the effect of fallout of the particulates. We were following earlier work done by Chandler as set out in his 1962 book The Climate of London that was based on his doctoral work of 1952. Oke among others was doing similar studies in Vancouver at the same time – an oceanside city similar to Houston. My doctoral thesis supervisor Bruce Atkinson did his doctoral thesis on the effect of a city (London ) on precipitation patterns.

    I was keynote speaker for the first conference on urban forests and the role of trees and vegetated areas in a city. Geiger had examined the role of vegetation and other factors in his classic work Climate near the Ground. I gave a public lecture on the role of trees and vegetation in Winnipeg and cities in general preceding a presentation by Jane Goodall, which allowed an opening line of reaching a peak in my career of being a warm up act for chimpanzees. I served on committees advising city leaders of the importance of vegetation in the city.

    As Warwick correctly points out none of this is new and seems to underscore today’s poor science that fails to do complete literature reviews. They seem to assume that if it is more than 10 years old it has no value.

    All this is further support for my argument that the IPCC and funding directed to proving their false hypothesis set climate research back 30 years. This theme is posted in an article on my web page under the title “Corruption of climate science has created 30 lost years.” There are also a couple of article on the UHI on the web site.

  15. As I understand GISS, if given a choice between measuring SST and projecting a land-based station reading onto the sea, GISS will use the projection route. Of course, this does not explain all the GISS increases, but it may be part of reason that GISS sometimes has higher temperature trends than other estimates of temperature trends.

  16. I have lived in Houston for 64 years. Our prevailing wind is mostly from the Gulf rather than towards it as the drawing suggests. That’s both day and night. It is generally stronger during the day than at night of course. How do I know that? I live about a mile north of the end of runway 17/35 at Hobby Airport. It’s the shortest runway thankfully so we only get smaller aircraft passing a bit west of us. When a cold front blows through, the planes are taking off in our direction. Most of the time, they are landing. That’s both day and night. I have lived in this particular area since around 1959. But even before that, as kids, we were aware of the onshore wind because my father would not let us take the boat out unless the wind was onshore. I remember him saying: “Boys, stay with the boat if something happens. If I don’t find you first, the wind will blow you ashore and you can walk home. Don’t ever try to swim it.”
    That’s not to suggest that the concrete isn’t influencing the local climate. And industry is the largest contributor to VOC air pollution (and prosperity) here. Automobiles and trees were about tied in VOC emissions the last time I checked. They said “If the city continues to expand, it’s going to make the winds even weaker in the summertime, and that will make air pollution much worse.” I doubt it. Winds from the Gulf would tend to dissipate the pollution that we have just as model created winds towards the Gulf would. Perhaps they should have spent more time observing the conditions in Houston and less time modeling. Or they could have checked Wikipedia. :)

    “Houston’s climate is classified as humid subtropical (Cfa in Köppen climate classification system). Spring supercell thunderstorms sometimes bring tornadoes to the area. Prevailing winds are from the south and southeast during most of the year, bringing heat across the continent from the deserts of Mexico and moisture from the Gulf of Mexico.[

  17. well – I have lived in the great city of Houston for the last four years. As posted above, there is often a strong onshore wind – in fact ths year it has been pretty constant at 10mph+ for the last three months solid.! When we get a cold front the wind switches round but after a few hours (or maybe a day or two) the flags all snap back t’other way.

    Of course , this is just weather….

  18. Tim Ball said @ June 9, 2011 at 6:53 pm

    “I agree with Warwick Hughes. We were doing similar UHI studies in Winnipeg in the late 1960s and early 1970s partly because it was an ideal location…”

    Some of us are even old enough to remember :-) Thanks for hanging in there Tim. You’re a champ!

  19. I consulted the U of Minn website as usual this spring with questions about which Plant Hardiness Zone my garden is in. Look at this. The U sent me straight to the National Arboretum. They state that many large urban areas carry a warmer zone designation than the surrounding countryside. But they don’t say a thing about things getting warmer. Hmmm… a branch of the federal government untouched by NOAA??

  20. I learned about this in High School Science class more than 30 years ago.
    It’s as though the entire scientific community has developed altzheimers.
    Or maybe the copyright ran out on my old textbook and someone is looking to recycle the info for profit.

  21. So just how much of that kind of wind blockage pollution do you think will be generated by one of those massive wind “energy” farms that are deliberately set up to block as much wind as is possible ??

  22. Another model that assumes the whole planet is covered by concrete and asphalt. The lands around cities are usually green (somewhere out there anyway) so there should still be a good draft passing through the paved area.

  23. Pat wrote:

    Interesting side note, the reporter in NYC for NBC in discussing the current heat wave, noted that because of the asphalt and heat retention by concrete, the city would be up to 15 degrees warmer than ambient air. These are the same people that see AGW at every turn. It never occurred to them that the global temperature might not be as high if measured outside of UHE areas.

    See, you shouldn’t be surprised; the favorite refrain of warmists is that “correlation is not causation”. Unless the correlation supports their cause, in which case it is 100% linked.

  24. I don’t think this was really meant to be “climate science,” per se, although it sounds like the sort of thing Pielke, Sr is into. But look at who paid for this study:

    “The research was funded by the U.S. Air Force Weather Agency, the U.S. Defense Threat Reduction Agency, and the National Science Foundation…”

    In particular, according to DTRA:

    “Each day, DTRA is working to predict, understand, and address the effects of nuclear and radiological weapons. Using innovative science and technology, DTRA works with federal agencies and foreign governments to improve global preparedness and response capabilities.”

    A better understanding of how winds work around urban areas could be useful to someone interested in what happens with nuclear, chemical, biological or radiological weapons.

  25. The neglect of focusing on UHI is intentional. Find someone from the left and I will show you someone that believes we should all be living in dense, tightly-packed cities.

    The same could be said of black carbon, to a much lesser degree. Poor people (especially those outside of the Western world) rely the most on the burning of biomass to live. So, they routinely ignore the devestating effects of soot in favor of hyper-focusing on Co2. The rich man’s pollutant.

  26. In what might be a coincidence (or might indicate the run up to a big “scientific conference” somewhere), the BBC’s Richard Black is back peddling alarm on urban air quality:-

    Of course, I doubt that anyone on here will stick their chest out and say that air pollution is never a problem. And what Black reports and what Fei Chen and his co-authors say in their paper about Houston could be right. Or at least, more right than wrong.

    But it does occur to me that it would be interesting to know what air quality was like in either Houston or London, 5, 10, 20 or 50 years ago?

    How much “excess morbidity” was there then?

    How do they compare with (say) Berlin, Rome, Moscow, Beijing, Mumbai, Cairo, Rio, Jakarta?

    What “excess morbidity” is there in these cities?

    And are any of the reported deaths genuine or are they all cyber-people predicted by a computer model?

    It is inescapable that bad air quality gives people with asthma problems and may well increase the number of asthma sufferers.

    But, cynic that I am, I just wonder if these guys are just shills for BigElectricCar?

    Can’t be, surely…….

  27. The phrase “Urban Heat Island” is conspicuously absent from the report. Is NCAR afraid of using terminology that has become associated with ‘deniers?”.

  28. Like others, I have lived in the Houston area for many years, although closer to the coast (Clear Lake area). I would figure that the authors of this study would at least reference some historical data, such as this wind rose from the Texas Commission on Environmental Quality (this is for August, although the study did go from 8/30 through 9/9, one of the hottest times I remember here in Clear Lake)

    Seems to me the predominate wind is from…the coast.

  29. In short he suggests that Houston should stop being Houston and get with the program. Unless Houston went through a massive change, it was the largest city in the US that had no real zoning laws and the only way to achieve the level of change that is suggested is to change that which makes Houston great. Houston has expanded the way it has precisely because the government has very little to say on where a developer builds and what he builds. There are laws that prevent things such as bars being built within a certain distance of schools and what not, but zoning, nope. It is one of the last bastions of free market development, builders build where people want to be, not where the government says they are to be.

  30. Maybe there is another way of looking at this. Not that the asphalt of a city heats but that the soils, lawns, and tree canopies of rural areas cool. Do leaves on a tree ever get as hot as concrete pavement or sand on a beach? I assume that the water necessary to keep a plant alive also somehow cools it.

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