Study: city street & building layout determine intensity of the Urban Heat Island effect

How cities heat up
The way streets and buildings are arranged makes a big difference in how heat builds up, study shows

CAMBRIDGE, Mass. – The arrangement of a city’s streets and buildings plays a crucial role in the local urban heat island effect, which causes cities to be hotter than their surroundings, researchers have found. The new finding could provide city planners and officials with new ways to influence those effects.

Some cities, such as New York and Chicago, are laid out on a precise grid, like the atoms in a crystal, while others such as Boston or London are arranged more chaotically, like the disordered atoms in a liquid or glass. The researchers found that the “crystalline” cities had a far greater buildup of heat compared to their surroundings than did the “glass-like” ones.

A new study found that cities with an orderly pattern, like the street grid seen in most of this map, have a much greater urban heat island effect than those with a more disorderly pattern, such as areas in the upper right. Courtesy of the researchers

The study, published today in the journal Physical Review Letters, found these differences in city patterns, which they call “texture,” was the most important determinant of a city’s heat island effect. The research was carried out by MIT and National Center for Scientific Research senior research scientist Roland Pellenq, who is also director of a joint MIT/ CNRS/Aix-Marseille University laboratory called <MSE>2 (MultiScale Material Science for Energy and Environment); professor of civil and environmental engineering Franz-Josef Ulm; research assistant Jacob Sobstyl; <MSE>2 senior research scientist T. Emig; and M.J. Abdolhosseini Qomi, assistant professor of civil and environmental engineering at the University of California at Irvine.

The heat island effect has been known for decades. It essentially results from the fact that urban building materials, such as concrete and asphalt, can absorb heat during the day and radiate it back at night, much more than areas covered with vegetation do. The effect can be quite dramatic, adding as much as 10 degrees Farenheit to night-time temperatures in places such as Phoenix, Arizona. In such places this effect can significantly increase health problems and energy use during hot weather, so a better understanding of what produces it will be important in an era when ever more people are living in cities.

The team found that using mathematical models that were developed to analyze atomic structures in materials provides a useful tool, leading to a straightforward formula to describe the way a city’s design would influence its heat-island effect, Pellenq says.

“We use tools of classical statistical physics,” he explains. The researchers adapted formulas initially devised to describe how individual atoms in a material are affected by forces from the other atoms, and they reduced these complex sets of relationships to much simpler statistical descriptions of the relative distances of nearby buildings to each other. They then applied them to patterns of buildings determined from satellite images of 47 cities in the U.S. and other countries, ultimately ending up with a single index number for each — called the local order parameter — ranging between 0 (total disorder) and 1 (perfect crystalline structure), to provide a statistical description of the cluster of nearest neighbors of any given building.

For each city, they had to collect reliable temperature data, which came from one station within the city and another outside it but nearby, and then determine the difference.

To calculate this local order parameter, physicists typically have to use methods such as bombarding materials with neutrons to locate the positions of atoms within them. But for this project, Pellenq says, “to get the building positions we don’t use neutrons, just Google maps.” Using algorithms they developed to determine the parameter from the city maps, they found that the cities varied from 0.5 to 0.9.

The differences in the heating effect seem to result from the way buildings reradiate heat that can then be reabsorbed by other buildings that face them directly, the team determined.

Especially for places such as China where new cities are rapidly being built, and other regions where existing cities are expanding rapidly, the information could be important to have, he says. In hot locations, cities could be designed to minimize the extra heating, but in colder places the effect might actually be an advantage, and cities could be designed accordingly.

“If you’re planning a new section of Phoenix,” Pellenq says, “you don’t want to build on a grid, since it’s already a very hot place. But somewhere in Canada, a mayor may say no, we’ll choose to use the grid, to keep the city warmer.”

The effects are significant, he says. The team evaluated all the states individually and found, for example, that in the state of Florida alone urban heat island effects cause an estimated $400 million in excess costs for air conditioning. “This gives a strategy for urban planners,” he says. While in general it’s simpler to follow a grid pattern, in terms of placing utility lines, sewer and water pipes, and transportation systems, in places where heat can be a serious issue, it can be well worth the extra complications for a less linear layout.

This study also suggests that research on construction materials may offer a way forward to properly manage heat interaction between buildings in cities’ historical downtown areas.


The work was partly supported by the Concrete Sustainability Hub at MIT, sponsored by the Portland Cement Association and the Ready-Mixed Concrete Research and Education Foundation.


61 thoughts on “Study: city street & building layout determine intensity of the Urban Heat Island effect

  1. I wonder if rotating the building’s footprint on the site and shifting the spacing so buildings on opposite sides of the street weren’t facing each other would be just as effective?

    • “I wonder if rotating the building’s footprint on the site and shifting the spacing so buildings on opposite sides of the street weren’t facing each other would be just as effective?”
      Yes. Not only because it diffuses the energy, but also because it might reduce otherwise solid barriers to cooling airflow. As a long-time practitioner of CRD (climate responsive design) I thought this might be yet another rediscovery of the bleedin’ obvious, but this modelling of “local order parameter” might actually be something useful, provided of course, that it is used as a criterion to be explored as part of an iterative design process rather than a “Rule”. Adds something to Christopher Alexander’s “A City is not a Tree” semi-lattice principle.
      High thermal capacity structures eg concrete and masonry will absorb and re-radiate heat, such that in some tropical environments, there will be structures that do not cool down for seven months or more. One solution has been to construct with or apply reflective finishes. Some urban building codes have actually attempted to rule against reflectivity of surfaces, thereby contradicting measures designed to promote energy efficiency.

      • The problem with reflective surfaces on the side of buildings is that it reflects sunlight down onto the street and can actually make the streets hotter.

      • In my book “VASTU: A Practical Guide”, published in 1997 [both in English & Telugu, which was reviewed by major Indian daily news papers. On page 68 I presented a cartoon [around 10 cartoons were given to show different relating vastu mis-conceptions] showing the building on turner, to change the building direction with a caption “This arrangement is to suit every vastu pundit’s suggestions!”

        Dr. S. Jeevananda Reddy

      • I would think that having streets go straight through the city would provide better opportunities for wind to push air through the city.

    • I saw no mention of heat transfer from buildings by ways other than radiation, such as natural convection and wind. I think this is a major flaw, if these were in fact not considered. I see the width of the streets as another important factor. For example, many of Philadelphia’s streets between large buildings have only three lanes including the parking lane and some are even narrower, while Chicago has wider streets intended to prevent a repeat of their 1871 Great Fire. Chicago’s wide streets are a major factor for Chicago being the Windy City.

      • Painting is a bad idea – makes the road slippery and as it wears you’ll be leaching paint chips into the local waterways. However just switching from bitumen to to concrete roads made with a white sand would make a huge difference.

    • I did an ad hoc measurement on a large patch of asphalt (maybe 50 sqyards) that had been painted white for a very large crosswalk combined with a boulevard. I was actually surprised how the center of the white painted asphalt was nearly 25 F cooler than a similar patch of black asphalt 100 yards away, on a day that was 95 degree F. at high noon. I could have cooked an egg on the black ashphalt but I don’t think it would have cooked on the white painted asphalt. Didn’t carry the test that far since it was past breakfast…

      But I personally think there is much, much more to UHI effect globally than what is currently reported. For starters, these are highly built up concentrated population areas and the UHI is what it is. But nobody talks about the thermal heat coming out the tailpipe of millions of car, trucks, buses etc which is more inefficiency wasted as thermal heat than actual work done by said IC Engine, which at the end of the day is actually more heat rolling resistance, brakes, air drag etc. All thermal heat added to the UHI which actually isn’t even discussed much as contributing to additional heat, with albedo and thermal mass getting most of the ‘credit’. Then we don’t even consider the additional water vapor being generated by said millions of ICE vehicles from the exhaust. This must add local water vapor to local clouds which makes it rain more locally. Or the additional water vapour slows more AGW radiative transfer from said city & suburbs keeping it warmer longer.

      Just a few examples of stuff we never talk about, but it does have a value and when you add It up all locally, it has a local effect that adds to the global effect of a smidgion more heating. And if you follow me so far and agree that there maybe is a wee bit more heat to the UHI effect, and from sources that we don’t even think about much as just a few examples I point out, then how in Sam Hell does CO2 get the bad rap for all current planetary heating that is barely happening? Someone should write a more detailed post on this subject, because I personally think there is a lot more to this line of thinking that currently gets little mention. And it diminishes CO2 as the culprit for everything!

      • That was a very informative Earthling2. The Urban heat island (UHI) effect is hardly mentioned in my opinion.

      • And prior to advent of the CO2 climate change myopia, something called an inversion layer was often attributed to hot weather. Often times, i can remember getting a blow by blow update of what it was doing, and when the inversion layer was going to be blown away during heat snaps.

        Meteorology does not employ inversion layers any more since the advent of the said CO2 climate myopia.

      • I live less than a mile outside of a small 6,000 person town in the farmland of Ohio, and most days UHI is 0-3 degrees in that little town, but sometimes on very cold days in the morning it can be as much as 12 degrees Fahrenheit. How can they adjust for that? One day the UHI is 12 degrees, the next day 2, and the next day 6. Adjusting for UHI in a model is almost impossible because you have no clue what to adjust by unless you have another thermometer outside of town. And if you had another thermometer outside of town then shouldn’t you just use that one and not the one in town being effected by UHI?

      • They just proclaim that the increase in UHI is only a few hundredths of a degree over the last 100 years, so it can be ignored.

      • When I was a weather forecaster at NAS Fallon we were tasked with doing a study to determine what the air temperature was 2″ above the pavement. This study was done during June-August when the daytime temperatures were consistently 100-102F. The temperatures just above the pavement ranged from 120-125F. Even here in PDX I’m willing to bet the temperature above the blacktop is in that range on a hot day. Nothing compares to blacktop for heating up a city.

  2. Is this all that they do anymore is play with computers? No analysis of construction materials, building types, plant materials, kinds of streets, etc? I guess it’s too much trouble to actually go out and do a detailed field analysis.

    • Good point. It appears that they “only” looked at building placement relative to one another (griding). Nothing on the materials, building spacing, road widths, street furniture (or trees), clouds, humidity, rain, sun angle, building height, or wind. (that I can think of in this small space of time).

      • turbulent air flow V laminar airflow maybe?

        I’m thinking of Perth, Western Australia’s St Geoge’s Windtunnel Terrace. A straight run East West that cools pretty fast compared to some of the hodgepodge building layouts elsewhere around the city.

    • I think they were enamored with the idea of using a molecular scale model on a macro scale problem. And then only on the night time radiative part if UHI. But UHI is a daytime phenomena that is not just radiative, as well.

      But they do have a point that cities in warm climates may want to take steps (and grid irregularity is only one of many) to minimize the UHI effect, while cities in colder climates might want to maximize UHI in winter.

  3. I think this is important work because every little bit helps.
    Heat Island Effect is real, wind breaks work and white painted roofs are cooler. Thanks

  4. Models upon models upon models…

    But, but, it’s based on classical statistical physics…

    Then, instead of validation or verification, they run their model soups for all of USA’s states and cities…

    Delusional comes to mind.

  5. The solution was figured out thousands of years ago in the Middle East and Southern Europe: Narrow streets with multi storey buildings, arranged radially from a central plaza. The cool air is drawn along the narrow streets from the suburbs and escapes upward from the hot surface of the central plaza. A fountain may be added to increase the moisture content of the air so as to increase its buoyancy.

    • I thought the fountains were added to provide water for the population.
      That they also helped cool was serendipitous.

      • Sometimes the ancients discovered that something worked without knowing how. It is the same phenomena that cause thunderstorms along the Texas dry line. Moist warm air will rise up in advance of hot dry air. (I couldn’t understand it until I was forced to compute, in forecasting class, the density of moist air vs. hot, dry air, then I understood it)

  6. facepalm.
    p-hacking all the way down, yet another “most research find are false” study.
    They were bound to find some relationship, just out of random effect of the many factor influencing UHI (building height, population density, wealth, energy use, parks and plants, and water management, wind stregth, etc.). They decided beforehand to assign it to order, instead of working properly, that is, to run principal component analysis.

  7. What is new, is actually old. As others here have pointed out.

    The home city of Marco Polo, Korcula, knew this 1000 years ago. The streets there are different widths and shapes, E-W and N-S. It is broadly fish boned shaped, off a central N/S street. The eastern side has curved streets which reduce the effect of the cold winter north and east winds. The other streets are designed to block sun in the summer, and increase the cooling of sea breezes.

  8. Sounds like a lot of modeling and effort, for what?

    How about just a little common sense and use the term ‘shade’. If cooling is the main cost then align buildings in an east-west direction whereas one utilizes the others shade in mid summer. If heating costs are the main concern then arrange orientation to utilize the sun when at a low angle in the southern sky in winter, assuming a northern hemisphere location. Country folks call it a shady or a sunny exposure. An HVAC engineer/designer would know this from any design book written within the past 50 years or older.

    One thing (among many) that Architects just can’t seem to grasp is to never consider ice and snow, not orientate commercial building entrances with a full northern exposure. Another fail is to put a bend in a strip mall that sets up a wind vortex that gathers leaves, trash, doors blowing open, etc. I won’t even start to further criticize some of their ideas/designs in structural truss type designs that can’t be fabricated or built. So many structural related issues to even begin to start. I must say that I have never met an architect whom I had respect for. Engineers can usually be reasoned with.

    Architects have my ire as they are most likely to be involved as planners. Unfortunately, engineers work for the architects thru contract. LEED was created to try to bring some sense to the architects.

  9. I would think the airflow in a gridded layout would be a lot better, due to the longer fetch and channeling effect compared to a chaotic layout where the wind is blocked in all directions.

    • There is more general smoothness in a chaotic systems and more roughness – with sharp edges – in systems with regular patterns, intervening with overall and varying flow as happens in nature.

      Although regular patterns enhance flow in the designed directions, say as with traffic, this control is limited to these targeted vectors, and most other – abundant – vectors are out-of-play.

      Regular systems always set a limited target: this is both their strength and their weakness, depending on the dynamics you need.

      This is my intuition here, not being an engineer, hope it makes sense.

  10. One tree in the yard can block exposure to the nighttime sky and greatly inhibit radiative losses. Anyone can see this when a yard has frost but the part of the yard near a tree does not. A forest of buildings would have the same effect. If the forest is gridded, rather than random, it would block the night sky view the most efficiently.

    I’ve been amazed by how full exposure to the nighttime sky can freeze things while just a little blockage at the horizons does not. Perhaps a square grid is the type of layout that minimizes the view of the horizon for most buildings.

    • Has anyone ever looked at how even a minor blockage of the night sky view at a particular ground location can affect nighttime emperatures? Trees or buildings several hundred yards away from a monitoring location can affect nighttime temperstures.

      • That’s why there is a requirement that there be no trees, bushes or buildings in the area of sensors.
        As to how much impact a distint tree or grove of trees could have, a lot would depend on whether they are uphill or downhill from the sensor.

      • One very calm morning around May we were on lake Superior heading northeast out of Marquette Mi to go fishing, near shore the west horizon was partially blocked by hills, when we got about 1 mile offshore we suddenly hit skim ice. Its deep the whole way, the only explanation was that those hills blocked enough clear night sky to prevent skim ice from forming until we got far enough away from them.

      • Perhaps it is shortsighted just to say no trees or buildings in the area of the sensor. Locations a distance away from the sensor could be blocked and become warmer at night due to less sky exposure. These could become additive and indirectly affect the sensor location.

    • There was a study several decades ago that sought to discredit the notion of heat islands.
      The study looked at city temperatures and compared them to “windiness”, under the theory that UHI should be lower when there was wind compared to when there wasn’t.
      There were a number of problems with the study.
      The first being that most of the sensors chosen weren’t actually in the cities. (Well sited sensors are not supposed to be surrounded by buildings.)
      The second was the study made no effort to account for wind direction.
      That is, when a sensor is outside a city, a wind from one direction could cool, but a wind direction from another might actually end up warming.
      Another was treating all cities as if they were equal in size and layout.

      Basically it was just another climate science paper designed to find the results the author needed.

  11. I didn’t see a link. How did they control for the multitude of local factors that could influence heat island (persistence of winds, blocking mountains, etc.) and how where was this single temperature measurement taken (was it blocked from wind or shaded by buildings, sited at the airport, etc.). Is the physics software particularly appropriate for the use? I think the paper is tackling a serious question and I applaud the attention given urban design. I just don’t know if I can take it seriously.

  12. It might be interesting to examine the difference with a grid aligned N-S, getting the face of the buildings perpendicular to the sun to capture maximum sunlight, as opposed to one rotated 45° from the same. It might be worth looking at in a very hot locale to minimize UHI , and cooling expense.

    • Related, I’m wondering if there’s a strong correlation between a city following a regular grid and that grid being aligned with the cardinal compass points.

  13. Not buying this… This is like saying CO2 is responsible for most warming. While the Grid layout might be a component in the urban heat island effect, I am skeptical it is THE primary component. Here are some guesses at other co-contributors:

    Energy usage per land unit
    Number of parks
    Number of trees
    Materials used in streets and buildings, especially roofs
    Amount of air conditioning (related to energy used)
    Speed of natural wind flow
    Geography (if you build in a bowl shaped area, you can trap the pollution)
    Depth and volume and temperature of sewers

    Modern grid cities may consist of more or less of the above, and therefore while the layout is correlated, it isn’t the main cause.

    When I see a bunch of peer reviewed science that collaborates this finding, then I’ll believe it.

    • Water more than anything determines surface temperature on land. Dry means hot and moist means cool. Surface here means the actual solid surface – not surface air temperature.

      Warming due to CO2 is theory. Warming due to an urban heat island effect is an established and recognized fact.

  14. Because of the high concentration of over educated liberal idiots residing in our cities, I always believed that UHI (Urban Heat Island) effect would be far more responsible for reinforcing the warmists’ viewpoint than the falsification of the historic record.

    I must admit that the two items are fighting it out neck and neck in the race to the greatest cause of the alarmists’ misunderstanding.

  15. For what it is worth, that map is of Los Angeles, laid out NEast to SWest in the 1780’s, with the center of the dark blue circle positioned at the Univ. of Southern California. Due North East of the circle is Downtown Los Angeles, itself encircled by freeways on all sides. Large undeveloped areas are the hills the North of the city. Prevailing winds come from the Pacific Ocean to the West and SouthWest. The “old” NE/SW alignment of the city was facing the rising SE sun in winter to maximize warmth. After expansion, the City went on a direct North/South grid towards the South and West. As a collection of small towns, you can see other areas where alignment is entirely different.,-118.2832001,10052m/data=!3m2!1e3!4b1

  16. Gerry, England February 24, 2018 at 4:07 am
    Does it run downhill though? Perhaps we need a model?

    Back 50 years or so when the world was still sane, heavy summer rains in Central Florida which is not completely flat, flooded a new housing development in a low lying area.
    After several hours of heated Townhall debate endeavouring to allocate the blame, the Chair turned to board member ‘Candy’ Mullins, a confectionary salesman, who had hitherto remained silent, and asked: “Mr. Mullins do you have anything add?” After a pause while he scratched his crew-cut head, Candy Mullins replied in his southern drawl “ whaale, seems to me that when God made the world He made it so’s water run downhill, and they ain’t a damn thing we can do about it….” at which point the meeting was adjourned.

  17. I can remember when I got my first motorcycle 66 years ago (Triumph 650) and riding out of New Orleans on hwy 61 to Baton Rouge and feeling the difference in air temperature being so much cooler as I left the city. This was in summer time. I suggest all these scientists try it.

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