Researchers emphasize evaluation of tradeoffs in battling urban heat island
Urbanization will increase average temperatures in Arizona’s Sun Corridor and white roofs can combat that, but not without consequences for the region’s hydroclimate
TEMPE, Ariz. – A team of researchers from Arizona State University have found that warming resulting from megapolitan expansion is seasonally dependent, with greatest warming occurring during summer and least during winter. Among the most practical ways to combat urbanization-induced warming – the painting of building’s roofs white – was found to disrupt regional hydroclimate, highlighting the need for evaluation of tradeoffs associated with combating urban heat islands (UHI).
“We found that raising the reflectivity of buildings by painting their roofs white is an effective way of reducing higher average temperatures caused by urban expansion,” said Matei Georgescu, an assistant professor in ASU’s School of Geographical Sciences and Urban Planning. “However, increased reflectivity also modifies hydroclimatic processes and, in the case of the ‘Sun Corridor,’ can lead to a significant reduction of rainfall.
Our maximum Sun Corridor expansion scenario leads to a 12% reduction in rainfall, averaged across the entire state. Painting roofs white leads to an additional 4% reduction in rainfall.”
The research is presented in the paper, “Seasonal hydroclimatic impacts of Sun Corridor expansion,” published in the Sept. 7, 2012 issue of Environmental Research Letters. Georgescu, the lead author of the paper, is joined by Alex Mahalov, The Wilhoit Foundation Dean’s Distinguished Professor in the School of Mathematical and Statistical Sciences at ASU, and Mohamed Moustaoui, an associate professor in ASU’s School of Mathematical and Statistical Sciences.
The paper focuses on Arizona’s Sun Corridor, the most rapidly growing megapolitan area in the United States. Located in a semi-arid environment, the Sun Corridor is composed of four metropolitan areas: Phoenix, Tucson, Prescott and Nogales. With a population projection expected to exceed 9 million people by 2040, the rapidly expanding megapolitan offers the opportunity to identify tradeoffs focused on sustainable expansion of the built environment.
The authors utilized 2050 projections of Sun Corridor growth developed by the Maricopa Association of Governments (MAG), the regional agency for metropolitan Phoenix that provides long-range and sustainably oriented planning. They conducted continuous multi-year, multi-member, continental scale numerical experiments for several 2050 Sun Corridor growth and adaptation scenarios and compared results with a modern day Sun Corridor representation.
“For a maximum expansion scenario, we find greatest warming to occur during summer, in excess of 1 degree C (1.8 degrees F) when averaged over the entire state of Arizona. Warming remains considerable during both spring and fall seasons, approaching 0.9 C. For a minimum expansion scenario, the consistent theme of maximum warming during summer with reduced, although still significant, warming during spring and fall seasons persists,” Georgescu added.
Whereas previous research has documented the contribution of cool roofs as an effective UHI mitigation approach, this work emphasizes the need to broadly evaluate impacts by exploring consequences that extend to hydrology and rainfall.
“Truly sustainable development will have to consider impacts extending beyond average temperature,” Georgescu explained. “A crucial step in that approach is to identify potential adaptation and mitigation strategies and assess tradeoffs, to ensure that we make smart decisions with minimum damaging consequences.”
All three co-authors are affiliated with ASU’s College of Liberal Arts and Sciences and the Global Institute of Sustainability.
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Is this article about the climate inside these buildings?Or,is it about the climate downwind of their UHI’s?Does the air move in there models?…1 degree?…WUWT?
Thanks for all the interesting articles and comments
*their
First, we need to ascertain just how stable temperature is supposed to be. Then we need to know what raising it in limited areas does. Iowans were delighted when the wind turbines warmed crop lands as they protected against freezing for short time into the fall. So in this case, we are happy to make things warmer….
Second, if we paint roofing white in New Hampshire, we may avoid urban heat sinks, but we raise the cost of heating during the 9 or so months of winter. So we keep the city cool, but use up more energy to do so. This entire piece does indeed point out how unintended consequences arise when people look at only one or two variables in a situation that has hundreds, then declare that their variable is what needs addressed.
Hydroclimate? Megapolitan? Don’t we have enough jargon and bafflegab already? Half of high school graduates think f**k-en is a language.
“… combating urban heat islands …”
Hmmm?, I don’t get it. The alarmists keep saying that UHI doesn’t exist. So why the “combat” ?
To me quite hard to believe it could have any such a significant effect … and it is even harder for me to believe they could have any certainty at all about their ability to calculate the magnitude of this effect with any degree of accuracy.
And it also seems to imply that surface warming (via UHI) would result in more rainfall – usually a plus in most situations.
The solution: “Just add water”
Not always an option (speaking as one who has lost trees these last two summers in Tejas) due to scarcity of water (we were on a once-a-week watering regimen in DFW area last year owing to drought and other factors).
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It’s too cold here in Michigan… maybe everyone should paint all the roofs black and it would suddenly become like Florida. Smh, what stupidity.
Are you talking savings in HVAC costs ?
The article would seem to be addressing albedo (diffusely ‘reflecting’ incoming solar energy; but I cannot vouch for that ATTM.)
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Amen. Similar/same effect noted here when driving in from the outskirts of the city (suburbia) back into denser civilization, and the change is from prairie (rather than marshland) to ‘city’ …
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Maybe you can help me here, but, my experience is that steel roofs (*) run physically quite hot; is there some sort of surface treatment that is required?
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(* Contrast this with say a lush, green lawn which actually feels cool when one’s hand is placed upon it during mid-day even.)
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squid2112 – nobody says that UHI doesn’t exist just that its existence has been taken into account when looking at temperature anomalies.
It’s models all the way up to the rain clouds.
I’m not buying this unless the aggregate albedo is raised above the natural background albedo. Assume no buildings there. There is some natural albedo. Now you build a lot of black parking lots, roofs and highways and the aggregate albedo of the area drops. Now you start painting some roofs white. Until you get the aggregate albedo of the city above what it was naturally, which I suspect would require painting quite a lot of roofs to compensate for the unpainted roofs, streets, and parking lots, you aren’t going to have a negative impact on convection (which is probably the rainfall impact).
Thanks for reminding us: that untested models and purely statistically derived findings are irrelevant UNTIL reality checked. Lab conditions don’t exist in nature. Winds, tree leaf fall, mineral accretions, mold, UV molecular chopping, temperature variations, etc has ruined so many beautiful lab experiments… sometimes with great disaster! Yet academia continues to over-reach conclusions based on narrow scientific findings. Society seems to becoming increasingly insulated from base reality, by our impressive technology. It will always dog the elite. GK
“We found that raising the reflectivity of buildings by painting their roofs white is an effective way of reducing higher average temperatures caused by urban expansion,” said Matei Georgescu,
Lying sack of $#!^.
Matei Georgescu, you didn’t find anything. You ran a model. A model is a hypothesis, not a finding.
Notice how they now refer to their modeling:
They conducted continuous multi-year, multi-member, continental scale numerical experiments …
Now, models are called “experiments”.
No. A model is a hypothesis. An experiment would be what you would do to test your model. Your “numerical experiments” tell you nothing about the world. They only tell you how the model you created behaves.
Lying sack of $#!^.
Jim,
I was referring DX (direct expansion) AC units on roofs. Cooler roof = cooler condenser coil = more energy efficient operation of the AC.
Not necessarily, a good conclusion in my view. What if you had a black roof, with good foam thermal insulation under it. So the blacktop can get nice and hot without frying the building, and then it can radiate much better at that higher T^5 Temperature shifted peak, and also heat the air by conduction, which leads to convective cooling.
Well lotsa ways to skin a cat.
And to go along with Louise; UHIs are good for cooling the earth faster; but you have to get out of that Hansen habit of measuring the TEMPErature, of an Arizona Parking lot thermometer, and using it as the TEMPErature of some place 1200 km away from there, and claiming thw whole area is hot.
Wow there’a thing!
White buildings warm up less in the sun- Genius.
4% reduction in rainfall?
More like random noise.
Just like listening to the authors.
Maybe what is needed is a few less smart decisions.
When I lived in Puerto Rico (1968-1971) we white washed our flat roofs every dry season, i.e., the winter. No problem with rainfall there. Ever.
@richardscourtney
“And I did laugh. Thankyou.”
Don’t mention it. “Well, you’ve got to laugh, haven’t you…” was an old Blitz expression and, as far as I can see, science is in much the same mess now..
P.S. http://www.art.co.uk/products/p12362949-sa-i1734214/posters.htm
GP Hanner:
Thankyou for your post at September 8, 2012 at 11:58 am which says
People would not spend the time, money and effort painting the roofs each year if that were not necessary. It gives real-world confirmation to our experimental findings in the 1980s which I report in my above post at September 8, 2012 at 2:19 am. Clearly, we could have saved much effort if we had known what you and your neighbours knew.
And it seems the authors of the above model exercise reported in the above article still don’t know it.
Richard
Maybe you can help me here, but, my experience is that steel roofs (*) run physically quite hot; is there some sort of surface treatment that is required?
Whether the roof gets hot or not isn’t really relevant. Its the energy flows that matter. The most important in hot areas is reflectance (albedo). The second factor is emissivity. These 2 factors determine how much heat energy gets past the steel roof and hence into the house.
Here is an industry pamphlet which covers the basics.
http://www.coolmetalroofing.org/elements/downloads/CMR_Brochure.pdf
The person who invents a roofing material that changes from low to high albedo (reflectance) when temperatures warm past about 25C is going to make a fortune.
And, the reason vegetated areas and swamps are cooler is higher humidity, even though because of lower albedo they have more heat energy than urban surfaces. Which is why temperature is a meaningless metric when comparing the heating of urban versus non-urban areas.
Albedo plus humidity determines climate at all scales (IMO).