Study: UHI affects the urban growing season

Urban Heat Island profile Image from Lawrence Berkeley Labs

Urban Heat Island profile Image from Lawrence Berkeley Labs


Spring comes sooner to urban heat islands, with potential consequences for wildlife

MADISON, Wis. — With spring now fully sprung, a new study by University of Wisconsin-Madison researchers shows that buds burst earlier in dense urban areas than in their suburban and rural surroundings. This may be music to urban gardeners’ ears, but that tune could be alarming to some native and migratory birds and bugs.

Urban-dwelling plants around the globe typically get a head start on the growing season compared to their rural counterparts because of the urban heat island effect, the phenomenon in which cities tend to be warmer than nonurban areas due to their plethora of built surfaces — made of concrete, asphalt and more — and scarcity of vegetation.

But according to the study, published this week in Environmental Research Letters, the urban heat island doesn’t lengthen the growing season uniformly across a city. Within the study site (Madison, Wisconsin) the researchers found that while the growing season lasted up to a week longer in the city’s densest areas, its parks subdued the warming effect and thus helped to normalize the growing season length.

“With a better understanding of the impacts of urbanization on vegetation, we can create more sustainable cities that behave more similarly to the natural areas they have replaced,” says lead author Samuel Zipper, who recently completed his Ph.D. in freshwater and marine sciences and is part of the UW-Madison Water Sustainability and Climate Project, a program funded by the National Science Foundation. “Every little bit of greenness counts within a city.”

The spring green-up underpins many important natural processes, like the budding of flowers and release of pollen. Throwing off the timing of this cycle can have cascading effects on urban ecosystems that may be harmful to birds, butterflies and other wildlife in search of food and habitat. The study shows that urban parks can provide them “cool island” refuges, with natural conditions to which they are better accustomed.

The study is the first of its kind to examine how variations in urban development impact the length of plant growing seasons at fine scales within a city. The research team relied on a uniquely dense network of temperature sensors scattered in and around Madison to get such a detailed look.

The sensors measured on-the-ground temperatures, which indicated when the potential growing season started and ended, and the team compared these measurements with satellite imagery that showed when vegetation actually turned green and brown.

The sensor data revealed that unless researchers are accounting for the types of plants they are observing, satellite data may not be the best way to tease out the temperature-based effects of urbanization on plants. The satellite-based method is commonly used to assess the start and end of growing seasons, but it may be sensing changes unrelated to the urban heat island, the team’s methods suggest.

For instance, grassy lawns in the suburbs greened up more quickly than urban trees despite higher air temperatures in the city. This is because once the snow melts, grass typically greens up sooner than trees, Zipper says.

“The degree to which the potential growing season gets longer is related to urban density, but the actual growing season depends on what is growing on the ground,” he explains.

The study is a step toward better understanding how urban development can impact not just growing seasons but also other natural cycles, like those of water and carbon. It could also help make cities more resilient to climate change.

The urban heat island effect is expected to increase as the climate warms, Zipper says, adding, “The fine-scale decisions we make in cities will be important.”


104 thoughts on “Study: UHI affects the urban growing season

    • Thank you, Bruce… for a minute i thought i was losing my mind. (did i accidently log onto hotwopper?)

    • what’s whacko about the UHI.
      The figures in the graph (UHI ~ 4˚C) tally with research about Melbourne which assigns a UHI of 5˚C.
      The whacko bit is how the reality deniers ‘krige’ the UHI into the fudged global surface temprerature data creating a) an unrepresentative weighting to UHI affected data and b) thereby introducing a bias over time. Its not CO2 wots dunnit, its concrete!

      • That was exactly my first reaction when I read this. What is the effect on temperature measurements?

    • Wacko indeed. “may be harmful to birds, butterflies and other wildlife in search of food and habitat“. Why do these eco-freaks always have to see everything as a negative. The birds, bees and butterflies can start getting food earlier in the city, and later on gett food further out, thus extending their feeding season. And they might even be able to extend the season even more with a final visit to the city. Just count it in with all the other positives that the eco-freaks resolutely refuse to see – like greater food production in Canada and Russia if the globe warms.

  1. Do I foresee another episode of “The Tales of Mr. Obvious” … how about “Mr. Obvious goes to Madison”

      • “You usually don’t get doctorates for stating the obvious.”
        If that is the case, 99.7% of the Doctorates in the world need to be revoked.

        • If you mean a well-written dissertation drawing conclusions on novel research so that it looks like one is “stating the obvious” you might have a high percentage, but nowhere near 99.7%. If you mean anything else, I challenge you do provide some some evidence.

    • Good one Mark. There must be way too much much money floating around for grants to anyone who fills out the paperwork and follows the bureaucratic maze and the bureaucratic dictates of global warming theory. It hurts three ways, our higher taxes, out higher borrowing and deficits, and mostly in the ways in which we stifle creativity and real scientific contributions–a great opportunity loss.

      • I almost said that another way such funding hurts us is by diverting potentially productive minds into the pursuit of meaningless trivia.
        Then I re-read the study and concluded that the mind involved never had a chance of being productive in the first place.

      • This is straight outta the rules of a bureaucracy.
        Rewarding those few that support your position, and distribute the cost broadly to those who do not.

  2. UHI = micro climate
    Micro climate = well-known to gardeners regardless of where they live…

      • Okay, okay… let’s not kick ’em when they’re down. How about Washington, D.C. instead?

      • I was thinking of LA, NY, SF, Boston, and Chicago actually. These cities deserve a surcharge on top of the punitive UHI tax for giving us nutters like Joseph Kennedy, Edward Markey, and too many California nutters to mention beyond Waxman, Boxer, Brown, and Pelosi.

      • Actually, let’s base it upon housing density. Any place with more than 8 homes/apartments per square acre is too “dense” and would create a high UHI. So those urban centers are going to pay for it pretty steeply!

  3. Urban trees and shrubs also tend to be non-native species with an earlier time of budding than the native species. Bud-breaking is related to both temperature and day length.

    • not necessarily i had an urban roof terrace with native shrubs and trees. I moved now to a rural village. Result: now these shrubs bud and grow early april or in short “as normal”, whilest in the big town of brussels they did bud early March. On the part that was oriented to the south with a big north and eastern wall they even did bud mid february.
      the walls of the building were protecting the shrubs from the nasty cold winds. on the other roof with full sun only mediterranian plants did do well as the roof was really hot.
      so yes urban regions do have lots of microclimates. Even a big building of a brewery has thus zones with different “climates”.
      so flanked by experience and observation i can say that in big cities they do bud easily almost 3-4 weeks earlier then in rural zones, depending on which species.
      to give an idea: sometimes here in belgium if the airmass comes from the south we can have a few days with 10-13 degrees, and in brussels that made my elderberry shrubs to bud while here in the rural village they don’t move.
      says enough for me

    • It seems to me that people in cities are already living with a level of warming that is supposed to mean the end of mankind. Why aren’t they all dead? This AGW pseudo- science is just laughable.

  4. gotta love the circular logic. UHI increases the measured average temps , which is used to claim global warming (er) climate change. And then climate change will increase with the effects of UHI…. The stupid is strong with these people.

  5. This is just amazing, incredible research! Who could possibly have come to these conclusions (eg growing seasons a bit longer in cities due to raised temperature!). This man deserves more than a PhD – he should get a Nobel Peace Prize. He’ll be telling us that more people live in cities next. Now that would be a revelation.

  6. So I guess the main finding is that CO2 causes cities and UHI which causes climate change. Further research needs to look into the mental health in a lot of these cities too. It’s a serious problem that needs a connection.

  7. So … let me make sure I understand.
    UHI is known and proven phenomena. This study shows that it affects the growing seasons on trees; growing season is longer in the densest part of a city. Weather stations that many years ago where located in rural areas are now in dense cities due to urbanization. Which means that weather stations read warmer than rural stations. Despite all that, it is the past temperatures that are in error, they were the ones that were too warm. Not the temperatures which have an UHI effect, nope they are pristine. Makes sense. (rolls eyes.)

      • I thought they did make adjustments. Since the urban records were less likely to have gaps in them, they adjusted the “poor” rural records to match the “better” urban records.

  8. Funny, my farm is 50 miles north of Downtown St. Louis MO in the Illinois river bluffs and my thermometers near the house often read very close to the official temp at Lambert International Airport. I see variations of 2-3 deg. F at different places on my 30 acres of timber, pastures and row crops.

      • Summer brings a prevailing southerly wind, so often it is cooler south of STL but warmer and higher in emissions to the north and NE. Air quality overall has improved immensely around here since the 60’s.
        During my career of providing HVAC services to a large college campus I saw large differences between the reported exterior temps of the core buildings on the BAS readouts, with temps usually several degrees cooler at the remote central chilling plant. The campus is a 3K acre suburban tract of bluffland.
        With so many microcosms created by pavement and structures, it is possible to cherry-pick much higher than average temperatures (as exist in the wooded expanses or open fields on campus).

    • It seems to me that people in cities are already living with a level of warming that is supposed to mean the end of mankind. Why aren’t they all dead? This AGW pseudo- science is just laughable.

  9. Brought this up before on here, there are species of plant that survive and flower in London because of UHI that otherwise would not because they require an extra 1c.

    • I live in Saskatchewan, zone 1 for gardeners. We can get zone 3 plants to grow just by planting close to the foundation on the South side of a house. No guarantees though, a winter like 2013 comes along and kills stuff that did fine since 1995 or even 1983. Climate didn’t change, just year to year variability.

    • There is a hall on the campus of the College of William and Mary (Williamsburg, Virginia) that has two palm trees growing right up against the outside wall. There is a massive heating vent that warms the area enough to allow the trees to flourish. Little mini heat island.
      I wonder if there are any whack jobs on campus who claim the trees’ survival is a sign of global warming.

  10. Didn’t Dr.Richard Muller determine that there is no urban heat island effect in his Berkeley Earth Surface Temperature project?

    • How did he conclude that cities dont warm up more than the surrounding countryside?

    • I believe he concluded that there has been no increase in UHI over the last 100 years.
      Apparently having small towns double and triple in size stopped making a difference around 1900. Perhaps due to better construction techniques and new ways of pouring concrete which caused it to no longer heat up.

    • “The Urban Heat Island effect is real. Berkeley’s analysis focused on the question of whether this effect biases the global land average. Our UHI paper analyzing this indicates that the urban heat island effect on our global estimate of land temperatures is indistinguishable from zero.”

      • So – the UHI is real. But it’s indistinguishable from land temps (being a 0 degree difference). If you cannot distinguish it, and it is no different from the regular land – then how can you say it’s real?

  11. Wouldn’t the existence of any DOUBT about the impact of localized WEATHER (which is frankly what UHI is) also be doubt about, oh, I don’t know, proxies like tree rings (which are built on the premise that localized weather–what the tree actually experiences–has an effect on a tree’s growth)?
    This is idiotic beyond idiotic. Anyone who’s ever traversed between urban and rural during the Spring season knows this. How much funding from the public trough did this get??? And this is from my home state of Wisconsin….I am going to drown myself in beer and cheese curds.

    Climate Change and
    Cherry Tree Blossom Festivals in Japan
    Richard Primack and Hiroyoshi Higuchi
    Page 8 of the PDF has a lovely contour map of dates of flowering.
    Page 6 has a 1000 year record of the dates (very compressed Y scale)

    Cherry trees were monitored for their flowering times in 1989 at numerous locations in Osaka, shown as black dots in this map. Isoclines are produced by a computer program to show the geographic pattern of flowering. Trees flower earliest on March 19 in the center of the city and progressively later at greater distances from the center. The latest flowering is along the coast to the west of the city, due to the moderating influence of the sea. A city park to the northeast of the city center also creates a small area of later flowering.

    • From the charts in the link, it looks like current global warming is approaching that of the MWP.
      Not surprising. And no acceleration. Just natural variability.

      • Yup! It’s the tilt towards the sun,
        The ways oceans run
        And clouds, in complexity forming.

    • Stephen;
      I think your link is more interesting than the article posted here, even with the UHI affecting the dates in Osaka there doesn’t appear to be any out of the ordinary events affecting the cherry blossoms. Considering UHI and our modern abilities to strengthen the gene poll of these trees you would expect a much earlier blossoming date even if CAGW didn’t exist, but there isn’t much out of the ordinary here form a quick eyeball inspection of the charts. It would be interesting to see these dates plotted against other temperature records and maybe sea rise records as well.

  13. “My only “head scratcher” was that next to last paragraph –
    The study is a step toward better understanding how urban development can impact not just growing seasons but also other natural cycles, like those of water and carbon. It could also help make cities more resilient to climate change.”
    I am not at all sure I can see a relationship between the study and natural carbon cycles, for example, but can anyone please explain how and why cities need “resilience” to climate change? After all, he doesn’t seem to talk much about the population of people, he seemed only concerned with the butterflies and migratory birds.

    • @Tom O Yes the second to last one is on the “newer” focus expanding climate change tentacles even wider than “climate” and the newly created position of Resilience officials in local governments initially funded by foundations and left planted permanently in the Urban Regulation Carpet.
      But note especially the last paragraph —
      The urban heat island effect is expected to increase as the climate warms, Zipper says,
      adding, “The fine-scale decisions we make in cities will be important.”
      thus the further regulation of every detail of life in future cities.

      • Makes you wonder how urbanites made it through the mid ’30s without A/C or advanced regulation…

      • Well, in DC they slept outside on porch roofs and congressmen fled back home during August. (Never have heard what the politicians from the Deep South thought of the recess timing.) Now the congressmen still flee in August and WaPo alternates between claiming it is the HOTTEST SUMMER EVAH and running articles about people who eschew AC. I am not in those articles.

  14. while the growing season lasted up to a week longer in the city’s densest areas…
    No problem, they have already adjusted a degree for that….

  15. Oh, no ! Urban birds and bugs are not mobile ! They’re doomed !
    They can’t survive ! It’s all our fault !

    • I wouldn’t call it interesting, I would call it obvious and not worth wasting research time and funding on

    • Might as well do a study on how leaving the fridge door open affects the food inside

  16. No mention of the demon molecule?
    Why? Because the UHI warming effect is scale dependentof , and also depedent on land use, the type of construction material that predominate, and underlying use of air conditioning during the warmest months.
    Phoenix Arizona, with its frreways, urban center, with a large multi-runway airport smack in the center of the city, and lots and lots of AC running on hot summer nights is the UHI poster child.
    So where the quote by the investigator is:

    “The urban heat island effect is expected to increase as the climate warms, Zipper says, ..”

    Is misleading. UHI warms (retains heat through the night hours), regardless of whether the underlying regional climate is warming or cooling.

  17. I would be more interested to find what percentage of the recording stations for temperature used in order to determine global temperatures, are found in areas wherein UHI is a large factor. Why don’t they study that?

  18. Samuel Zipper is a prime example of an ivory-tower intellectual steeped in Greenie idiocy, devoid of either common sense or rational thought process. Cities are built for people, not bees and butterflies. And “green spaces” (parks) are nice places to have for people to visit as a respite from some of the drab, dreary and cacaphonous city environment. This is what a PHD buys nowadays?

  19. “Study: UHI affects the urban growing season”
    They needed a study to figure that out?

  20. “Spring comes sooner to urban heat islands, with potential consequences for wildlife”
    First thing we need to do is find some wildlife in urban cores.

      • Good point.
        We don’t give rats enough credit. If one mammal has done more to make the world safe for immigrant species, it would be humans. But rats should get special mention for their ability to wipe out native species, helping other migrants to flourish.
        And, my theory of dinosaur extinction depends on rats or their ancestors. Flightless birds are the nearest thing we have to dinosaurs, and as soon as the rats (or humans) show up, they are history.
        Let’s give credit where credit is due.

    • This squeaky new PhD is an academic. Probably noticed that the frat keggers tend to happen earlier on the city campus than on the rural ones. Ditto for the urban nightclub scene…
      Hence the UHI effect on urban wildlife.
      Sounds like a real party animal.

      • In order to be a party animal, doesn’t one first have to get invited to parties?
        This guy strikes me as the type who spent a lot of Friday and Saturday nights watching TV in the basement.

  21. From the article: “The urban heat island effect is expected to increase as the climate warms, Zipper says,”
    The urban heat island effect is expected to increase IF the climate warms. Don’t assume too much.

    • TA
      It will absolutely increase as the climate warms, but not because the climate warms.

  22. BTW, the jetstream is lining up in the right way, coming in from the southwest into the area where the cold and warm fronts meet, to make some big tornadoes over the next few days, in Tornado Alley. Most of the action will probably be north of Oklahoma tonight. That’s where everything converges.

  23. Self evident studies are being paid for government and this is being done by,… a PhD in freshwater and marine sciemces!!!
    I’m reminded of a Bob Newhart monologue where he’s taking a flight with the Acme Airline and Sash and Door Company.

    • That was my first thought – how is this study related to freshwater OR marine science? I hope this was not part of his dissertation, though it is still alarming to think that someone thought this was a good project for a newly minted freshwater/marine scientist. No one with expertise in botany or urban wildlife was available?

  24. “With a better understanding of the impacts of urbanization on vegetation, we can create more sustainable cities that behave more similarly to the natural areas they have replaced,”
    So what? Mama Nature can handle it.

  25. Anthony, this is an example of a dumb post that your blog can do without. If you eliminate posts like these, not only will the quality of your blog increase, but the workload (for you and your mods) will decrease. This is an easy, pragmatic answer to some of the woes that you’ve pointed out (in your posting over the weekend)…

    • IMHO exposing the weakness of the alarmists is beneficial……and therefore not dumb….

      • I believe UHI effect is the biggest single reason so many city dwellers think they’ve seen a change for much warmer in their world, possibly second to the constant “hottest year evah” refrain in the media.
        The same UHI will no doubt ease the effects of the Atlantic and Pacific oceans being in concurrent cold phases, but wo’s counting blessings nowadays?

    • We’re talking here about climate “science”. Show me where the dumb stops and I’ll be delighted to stop talking about it.

      • No, mark, you’re right… This isn’t about that. Anthony is looking for ways to better his blog. I’m just suggesting that if he’d cut out the stupid stuff then the folks would be happier and anthony & co. would have a needed reduction in their work load. Long time regulars have voiced the complaint that anthony has been posting at break neck speed of late. Some think that the content could use a little improvement as well. I’m just glad to get anthony’s attention for a pragmatic solution to some of his problems. (didn’t mean to be hurtful, just wanted to help…)

      • You might be happier, but given the number of posts on these articles, it really does look like most people do not agree with you.
        You really should refrain from assuming that everyone agrees with you, especially when the evidence runs the other way.

      • It’s not about me… There are grumblings from the folks that anthony is posting too much and too much questionable stuff these days. I just want to get it into his head that this is something he might want to consider. It’s up to him. He might think about it, then again he might dismiss it. The important thing is that he gets ideas about what he might do just to ponder them. That’s what he’s been asking for…

      • MarkW May 26, 2016 2:21 pm
        “Study: UHI affects the urban growing season”
        They needed a study to figure that out?
        Mark, nice to see that you were in agreement with me until you decided to disagree. dumb study = dumb post (QED…)

  26. The proportion of land, that is covered by cities?
    Apart from the way UHI effect biases the average high, the amount of the of “environment” effected by the studied effect?
    Does not seem to be defined by Sam Zipper, seems even the obvious eludes these clowns.

  27. Funny. I thought the weather stations that were affected by UHI’s were the cause of perceived global warming, but now I’m told that GW will make the UHI even worse. Pretty worthless study, actually. That being said, they do a neat thing here in Santiago where the driveways and some parking lots are a checkerboard concrete pattern with grass growing in between. They look much better than solid concrete and seem much cooler. Only problem is watering and mowing your driveway.

  28. I live near the mouth of a river that flows into the Chesapeake Bay. During the summer, the temperature can drop about 6 degrees when I approach and enter my community. In the winter, the temperature is usually a few degrees warmer. This year we have experienced a cooler, rainy April and May. It has finally started to warm up a bit, just in time for opening our community pool for Memorial Day. My azaleas, which usually bloom in April are just now starting to flower.

    • I saw a NOAA future weather forcast yesterday that shows the East and West coasts as warmer than normal, and the central part of the U.S. as cooler than normal, in the coming months.
      I’m not sure I have ever seen a weather pattern like that. The central U.S. is the hottest part of the country during the summer, once the heat really settles in, at least in my memory, which is fairly long.
      I am real curious to see a weather pattern that keeps the central U.S. cooler than the coasts during the heighth of the summer. I’ll also appreciate the cooler weather, if it happens. 🙂
      Usually, around here, it is about 105 degress or more sometime during the summer. It was up to 114 degrees in 2010. So we will take a little cool weather, if we can get it. Maybe *this* NOAA forecast will be accurate.

  29. The Berkeley study on UHI is broadly correct, I would think, in that given the very small percentage that urban areas represent of the total surface area of the earth, the likelihood is that the effect of UHI on overall surface temperatures is negligible. The problem is that it appears that a large minority, and in many places a small majority, of surface temperature data collection points are located in urban, built up or commercial/industrial areas. This means that artificially high temperatures due to UHI are being heavily relied upon thereby distorting the picture in surface temperature data sources, particularly when this involves (as it invariably does) the projection of this questionable temperature data, by “sparse data infilling” onto the vast areas of the earth’s surface not covered by temperature data stations.

    • Yeah, the surface temperature data is useless as a scientific tool. It says what its authors want it to say, not what the real world says, which makes it a propaganda tool.
      The satellite temperature record is the only uncontaminated temperature data we have. And fortunately, there are still a few honest people in the world, who will tell it like it is.

  30. Urban areas typically amount to only a few percent of the land areas in the US, and the plants cultivated therein are more often than not non-native species that would be of little interest to migratory fowl. Native plants to which the migratory fowl have become accustomed are more often than not considered to be ‘weeds’ by the denizens of these UHI areas, and are often systematically eradicated in these areas.

  31. If it were not for the corruption of climate science, a study like this might be of interest and of use. This would be a good study for a horticultural professional to do, the better to advise the cities of what sort of plants might be encouraged in their local environment. You know, practical knowledge to solve a problem. The Romans were good at that, but, hey, the Dark Ages and all. But, since climate science is corrupt, it will just be used for propaganda.

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