Law of unintended consequences bites the 'white roof UHI solution' – causes reduced rainfall

From Arizona State University

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

painting white roofs

A construction crew works on a white roof in Washington, D.C. (©American Geophysical Union, photo by Maria-José Viñas. Reproduction permitted with credit.)

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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Nylo

This study looks pretty weak to me. I couldn’t understand very well the methodology, but I don’t see how they can reach that conclusion. Was it through experimental data or through modelling? In the first case, correlation is not causation. In the second, well, we have learnt already a number of things about climate models reliability, haven’t we.

kadaka (KD Knoebel)

New UHI solution: Install geothermal heatpumps everywhere.
Cover the roofs in heat collectors. You can incorporate them into the backs of solar photovoltaic panels.
Store the summer heat deep underground, use it for heating when needed around winter and for heating water year round.
Makes more sense than fighting the warmth by pumping CO₂ underground.
What’s the worse that could happen? In warmer sunnier places like the Sun Corridor, so much heat will get pumped underground that the deep stores will generate steam, that could drive a turbine and generate electricity?

michaeljmcfadden

OK, I have not read the research in question, but this figure seems out of line to me. Taking any significant geographical micro-climate type area (as in 500 square miles plus) even in an “urban” area in Arizona (which isn’t exactly = to the five boroughs of NYC) it’s hard to imagine that total roof area would be more than 25% or so to begin with at most. A lot of those roofs are already more gray than black (with a certain percentage already white I’m guessing as well), and the painted white wouldn’t stay nearly 100% reflective for very long, so I’m purely guessing that we’re talking about a reflectivity change of about 50% for that less-than-25% area — or a reflectivity change of 12.5% for the total area. Is rain production really 1/3 dependent purely upon reflectivity input into the microclimate (which is what would be needed for that “4%” final result)? Heh, and of course there’s the energy angle: the reduced rain would lead to increased air-conditioning, while the white roofs would lead to decreased air-conditioning! And white roofs might be more (or less) energy-expensive to produce/maintain.
If we were talking about the entire state of Arizona being urbanized to NYC level standards it would be something else, but given the reality of the situation I have a hard time believing any effect would be significant enough to really worry about. It *is* an interesting concept though! And if other costs were commensurate it would certainly be worth considering this sort of calculation if they were deciding about blacktop vs. whitetop road material etc.
– MJM

Rabe

… or increase. Or maybe not.

dp

Maybe they should paint the roofs green. Works for Brazil.

Wucash

It is a rather good idea on paper at least to combat UHI. What’s needed though is a surface that can change light reflectivity but remain cheap. For example a photoreactive paint, where it gets brighter with more light would be preferable, but I’m not sure if such a thing would have to be invented first.
An easier, but perhaps a more expensive solution would be to install a Venitian blinds-style electronic roof covers, that turns itself on when it’s needed.
P.S. If all the tarmac in a urban environment was coloured green for example, would that have an effect on the local temperature too? Would it have the same consequences as the white roof?

Richard T. Fowler

Kadaka, the problem with your idea is that it does not provide cover for any capping or taxing of CO2, nor for declaring CO2 to be a pollutant so it can be “regulated”.
RTF

Terry

Roger Pielke Snr will be smiling

gringojay

California naturally showed everyone The Way when director of general services in 2009 ordered “white as the default color on the state’s light-duty vehicle contracts”. Science now unsettling with unintended consequences worth calculating, since Ca. total state fleet is over 50,000 ( not all are light-duty vehicles). Seems impossible though to calculate the total surface area of Ca. commercial buildings (since 2006) with a flat roof being obliged to be white or light (reflective) shade.

Rik

What on earth is a “numerical experiment”? Is that equal to running a model several times?

kadaka (KD Knoebel)

From Richard T. Fowler on September 8, 2012 at 12:22 am:

Kadaka, the problem with your idea is that it does not provide cover for any capping or taxing of CO2, nor for declaring CO2 to be a pollutant so it can be “regulated”.

It’s late, I’m exhausted, and barely have enough remaining brainwaves to stumble to my bed.
But I can assure you this would be marketed as fair and equitable, as the costs would be borne by taxes on the hated “black burners” who insist on destroying the biosphere by continuing to use fossil fuel-derived energy.
And if that term sounds “racial”, don’t worry because they won’t worry about it as they gladly promote the implication that anyone who isn’t willing to do anything possible to combat climate change must obviously be of that political persuasion who’d want to do that as well. “Drill Alaskan oil, Kill African baby” and similar protestor-sign slogans will, of course, be expected.

Anopheles

I’ve done Phoenix and Tucson in the summer. I don’t see another one degree making a whole lot of difference. And there is one awful lot of desert and mountains in that ‘corridor’ which will overwhelm any effort of roof-painters.

Tony B (another one)

Oh No! Its the What Ifs, they are worse than we thought!!!
The following text tells us all we need to know…
“All three co-authors are affiliated with ASU’s College of Liberal Arts and Sciences and the Global Institute of Sustainability.”
What if they actually got real jobs? Did real work?

Mike McMillan

I vaguely recall that green (dark) was nearly as good as black for solar water heater panels. I had an old Chevy that was forest green, and it got too hot to touch sitting in the sun. Of course, correlation doesn’t mean causation.

oldseadog

More warming in summer and less in winter?
Well, who’d a thunk it.

Golden

So if everyone painted their roofs white, where would all that unrained rain go?

Friends:
Long ago the UK’s Coal Research Establishment (CRE) developed a range of roofing materials. One of these had an aluminium coating (like baking foil) for thermal reflectivity and low thermal emissivity
As anticipated, the reflectance of the coating rapidly reduced due to oxidation (the silver colour tuned to grey), but the remaining reflectance was (as had been calculated) a sufficient benefit over a tarred roof for the coating to have merit.
However, the reflectance continued to degrade as a result of dirt, bird droppings, algae, etc. accumulating on the surface. It was clear that similar accumulation would occur on tarred roofs. Hence, within about a year following installation there would be surprisingly little difference between the reflectance of a flat roof covered with a ‘traditional’ tarred roofing felt and and a flat roof with the aluminium-coated roofing material. And the ‘traditional’ roofing felt was cheaper.
So, on the basis of existing experimental data (which I helped to acquire) I think the effect of painting the roofs would be much less than the reported model study suggests.
Also, the anticipated reduction to rainfall is only indicated by use of a model. Were anybody willing to provide me with sufficient funds then I would be willing to conduct a model study which indicates the painted roofs would increase rainfall (i.e. give me the money, tell me what you want, and I can give you a model which provides what you want).
Richard

David Wright

The rain will still fall somewhere, it won’t stay up there forever!

Gary Hladik

Haven’t read it, but…
If white roofs tend to lower the temp toward its “natural” level, and that reduces rainfall, does that mean that urbanization has actually increased rainfall??? Plausible, I suppose, since urban areas use more water, and a lot of it evaporates, and evaporation presumably increases with temperature.

DirkH

“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.”

Liberal use of the word experiment.
Let me rephrase that:
They conducted continuous multi-year, massively multiplayer, continental scale role playing games for several 2050 Sun Corridor growth and adaptation levels. After they ran out of doritos, lead researcher Matei Georgescu, an assistant professor in ASU’s School of Geographical Sciences and Urban Planning, uploaded the recorded gameplay to youtube, declaring a record.
No remaining funding could be retrieved.

mfo

Wiki has a ‘cool roof’ article:
http://en.wikipedia.org/wiki/Cool_roof
“While it is true that cool roofs are mostly associated with white roofs, they come in a variety of colors and materials and are available for both commercial and residential buildings. Note that today’s “cool roof” pigments allow metal roofing products to be EnergyStar rated in dark colors, even black. They aren’t as reflective as whites or light colors, but can still save energy over other paints.
“A 2011 study by researchers at Stanford University suggested that although reflective roofs decrease temperatures in buildings and mitigate the “urban heat island effect,” they may actually increase global temperature. The study noted that it did not account for the reduction in greenhouse gas emissions that results from building energy conservation (annual cooling energy savings less annual heating energy penalty) associated with cool roofs.
” A response paper titled “Cool Roofs and Global Cooling,” by researchers in the Heat Island Group at Lawrence Berkeley National Laboratory, raised additional concerns about the validity of these findings, citing the uncertainty acknowledged by the authors, statistically insignificant numerical results, and insufficient granularity in analysis of local contributions to global feedbacks.”

Lewis P Buckingham

They could consider planting desert adapted trees in the house shaded part of the garden. Any waste water placed in the subsoil would help sustain tree shade and evaporative cooling by the leaves.

mwhite

“Trees and other plants help cool the environment, making vegetation a simple and effective way to reduce urban heat islands.”
http://www.epa.gov/hiri/mitigation/trees.htm
“Trees and vegetation lower surface and air temperatures by providing shade and through evapotranspiration. Shaded surfaces, for example, may be 20–45°F (11–25°C) cooler than the peak temperatures of unshaded materials.1 Evapotranspiration, alone or in combination with shading, can help reduce peak summer temperatures by 2–9°F (1–5°C).2, 3
Trees and vegetation are most useful as a mitigation strategy when planted in strategic locations around buildings or to shade pavement in parking lots and on streets. Researchers have found that planting deciduous trees or vines to the west is typically most effective for cooling a building, especially if they shade windows and part of the building’s roof.”
Much better don’t you think?
Check the references, this has been know for years

The easiest way to compensate for the lack of rain induced locally by these white rooftops is to hold dances on the rooftops daily. The researchers from Arizona State University should have access to a talent pool capable of teaching the student to perform the traditional rain dance.
/sarc

Steel roofs are a better option as they reflect solar energy outside the visible spectrum as well as the visible spectrum. Take a look at where I live, south of the river, Perth, on Google Earth. More than 2 out of 3 roofs look white, but in fact they are steel.
As for ‘Sun Corridor expansion scenario leads to a 12% reduction in rainfall’, I don’t know what assumptions were made to reach this conclusion, but Roy Spencer found in the USA southwest urban temperatures decreased with urban density. He suggests and I agree, that the cause is decreased vegetation (and irrigation) and hence reduced humidity.
So the 2 rainfall reductions are due to different causes. One due to fewer plants (and irrigation0, hence reduced humidity. The other due to reduced temperatures (from white roofs) and reduced thermal convection.

Tom in Florida

According to weather.com the average annual rainfall for Tempe is 9.37 inches. A 4% reduction would be .37 of an inch. Red flags should go up when percentage is used instead of actual numbers. As they say, figures lie and liars figure.
http://www.weather.com/weather/wxclimatology/monthly/85281

The other unintended consequence … thanks to the law of consumer gravity, everything, especially including mass quantity suppliers inevitably run a race to the bottom. Billions of gallons of white paint will necessarily be supplied by the lowest bidder using the cheapest labor and the loosest standards.
So just imagine white roofs all over the world leeching particles of white paint made in China into the local ground water tables. Yeah, that’s a great idea. Eco-Nazis or Eco-Frauds? We report, you decide.

Tom in Florida

Looks like I was a little too hasty in my comment (early in the AM). Noting that the area in question is not Tempe but rather Phoenix/Tuscon/Prescott/Nogales. However using the link just change the city and you can see the precipitation for all those cities. The same basis of my post still holds, 4% of very little is very little.

How do these people know that the reduced rain was because of white roofs and not because of a double La Nina?

Mike M
Brian Johnson uk

Another bunkum conjecture to capture AGW Grant money

Doug Huffman

Unintended consequences are prevented by their – their! – Precautionary Principle.
Sod roof coverings are a cultural tradition here, and now at the crux of a business conflict. The grasses are cropped by goats but their use has been ‘trademarked’ and successfully protected in local courts.
Meanwhile, locally, phragmities are burned and poisoned even though reed is the traditional thatching of choice. Phragmities thatched roofs last hundreds of years with little maintenance, and have a significant insulating ‘R’ value, and sequester carbon at almost tonne for tonne.

H.R. (back from Jamaica)

What about all that white stuff that covers roofs and everyhing else during the N.H. winter? Whole regions of the U.S., N. Europe, Canada, etc. are white and it doesn’t seem to affect precipitation much one way or the other.
Anyway, how could you tell the difference in Phoenix AZ where you don’t get squat for rain? “We had 30% less than none?”

commieBob

Here’s a shocker. Urbanization, done properly, might actually decrease temperatures!

In a real-world 2008 case study [10] of large-scale cooling from increased reflectivity, it was found that the Province of Almeria, Southern Spain, has cooled 1.6ºC over a period of 20 years compared to surrounding regions, as a result of polythene-covered greenhouses being installed over a vast area that was previously open desert. In the summer the farmers whitewash these roofs to cool their plants down. http://en.wikipedia.org/wiki/Cool_roof

Perhaps urbanization, done properly, would be good for the environment.

The link in the article has been truncated. Here it is in full:
http://iopscience.iop.org/1748-9326/7/3/034026
John M Reynolds

David Ross

A similar notion was expressed by a team at Stanford

One “geoengineering” proposal for reducing the impact of urban heat islands is to paint roofs worldwide a reflective white. Jacobson’s computer modeling concluded that white roofs did indeed cool urban surfaces. However, they caused a net global warming, largely because they reduced cloudiness slightly by increasing the stability of the air, thereby reducing the vertical transport of moisture and energy to clouds.
http://www.eurekalert.org/pub_releases/2011-10/su-ui101811.php

Which leads to the somewhat paradoxical conclusion that the growth of cities (without white roofs) causes a net global cooling -which doesn’t seem right.
I haven’t read a good description of how urban heat islands affect the “stability of the air” and how exactly this affects “cloudiness” in any scientific paper. But hang gliding enthusiasts are aware of the phenomenon and explain it better.

In a nut shut, thermals are rising columns or pockets of air that are caused by uneven heating of the ground surface. As you know, different color object absorb more heat from the sun than others. One a hot sunny day you’ll notice the surface temperature off asphalt is much higher than the grassy area next to it.
Naturally occurring thermals will most likely form over sandy or rocky surfaces, freshly plowed fields, or any place where the surface is likely to be hotter than its surroundings.
[…]
You will find the strongest thermals when the sun is at its highest on nice sunny day. The strength of thermals is directly proportional to the variation of surface temperature. This means the strongest thermals are most likely to occur on a warm sunny day after a relatively cool night.
The presents of nice pretty cumulus clouds is a sure sign that conditions are right for thermals. As a matter of fact, thermals are what cause the formation of cumulus clouds.
http://www.hooked-on-rc-airplanes.com/thermal-gliding.html

Also, Munich Re, the re-insurance company, that is a big backer of global warming alarm (the alarmists’ Exxon, you might say) also pushes the idea that “megacities” create thunderstorms (and hence floods requiring insurance protection).

The “heat islands” that are clearly recognisable in satellite pictures impact convection and so have an effect on the wind system in the surrounding area. … However, conurbations have a special role not only where causes are concerned but also when it comes to the impact of the weather factors of wind, precipitation and temperature. Here, torrential rainfall can soon lead to local flooding, and even to devastating flash floods and landslides, which then affect mostly the poorer social strata.
http://web.archive.org/web/20080131223004/http://www.munichre.com/publications/302-04271_en.pdf

It appears that neither the Stanford or Arizona team draw much attention to the fact that, according to their own assertions, the clouds and rainfall resulting from urban heat islands are anthropogenic. And that white roofs would mitigate this anthropogenic effect. I thought that was supposed to be a good thing in the worldview of the new eco-religion. I suspect their computer models (and/or press releases) need a bit more tweaking.

Joe Shaw

@Nylo,
The predictions were purely based on modeling. From the abstract: “Based on a suite of ensemble-based, multi-year simulations using the Weather Research and Forecasting (WRF) model, we quantify seasonally varying hydroclimatic impacts…”.
On the positive side the paper implicitly acknowledges that the climate impact of changing land use are predicted to be as large or larger than claimed GHG impacts. Also, the paper is based on a weather forecasting model (WRF [ARW] version 3.2.1) rather the CGMs used for most other studies. This model has demonstrated skill in forecasting near term (e.g., hurricane tracks) and seasonal weather parameters. I don’t have much confidence in the three year predictions used in the study. However, it is plausible that the model’s parametric response (e.g., temperature, precipitation) to land use changes (e.g., permeability, albedo) can tell us something.
Good summary of WRF is available at http://cires.colorado.edu/science/groups/pielke/classes/at7500/Bianco_PresentationWRF.pdf
In addition, the principle that we should assess likely second (and third) order effects of potential/proposed solutions (to any problem, not just climate related issues) is IMO very sound.
On the negative side, the methodology is very weak and basically boils down to “we ran the model a few times and reported the results without much explanation or thought. The number of replications used in each case is not clearly stated (as few as 12?) and no variance is stated for temperature or precipitation values. Figure 5 does provide error bars for evapotranspiration. By visual comparison, the difference between the adaptive (white roof case) and high case is less than the 1 standard deviation bound for each case indicating that the effect is not statistically significant. No error bars are provided for precipitation which is the parameter we presumably care about. From Figure 7, the three year precipitation difference between the adaptive and high cases appears to be about 70mm or 5% of the toal for the control case. Again, likely not statistically significant.
No data is provided for the assumed roof albedo for the non-adaptive case, the fraction of urban surface area that is assumed to be roof, or the net change in regional albedo between the four cases.
There is no attempt to reconcile the statement in section 3.1 that “For all seasons (except winter, when cooling is simulated) urban-induced warming remains an entirely local phenomenon, and non-urbanizing locales undergo little or no warming.” with the statement in section 3.2 of “… potentially significant consequences via modification of the regional hydrologic cycle associated with this adaptation approach”.
The paper also fails to offer a physical explanation of why use of white roofs would decrease evapotranspiration and precipitation for a given surface permeability.
It is also disappointing that the authors felt the need to include a reference usual GHG induced AGW canard with the statement that “In addition, these impacts are layered on top of large-scale climate change owing to increased emissions of greenhouse gases, adding further stress to an already sensitive system.” in a paper that has nothing to do with this topic. I suppose that this obeisance is a prerequisite for publication in a climate .

Joe Shaw

Oops … “science” publication.

hell_is_like_newark

The energy saving potential of white roofs has been over stated. Installing a coating on a poorly insulated roof will make a difference (over 5% in one project I worked on). However, if the roof is very well insulated, the reflective coating may only give you an additional 1% improvement, which won’t give you a good return on investment for the material cost and labor.
Now if you had HVAC equipment on the roof it would reduce the load on it. How much? No idea.. I have never come across a measurement and verification study looking at just that.
The biggest advantage of a white roof.. it makes the roof good for a deck and plants as it reduces the surface temperature, even in blinding sun, to tolerable levels. My own roof garden did very, very well this year (though it got too hot for some plants). The CO2 levels typically hover around the 500 to 650 ppm range, which does give you a definite boost in growth.

CodeTech

I see others beat me to the obvious observation of “unintended consequences”… because it’s a special kind of fun to point out where someone who thinks they’re “saving the planet” end up messing things up for real (that are not really messed up to begin with).
Now, if this is the result of something as relatively innocuous as white roofs, just image the possible unintended consequences of the more esoteric or ridiculous mega projects like:
* SO2 scattered into the upper atmosphere
* pumping gigatons of Co2 into underground caverns
* dumping iron filings into the ocean
* giant orbital mirrors
* giant wind farms, giant solar installations,
* etc….
Honestly, this is the best part of being old enough to remember the Energy Crisis and Global Cooling scares of the 70s… watching people make the same stupid decisions, wasting money on the same schemes, trying the whole thing all over, and expecting different results.
Of course, the major downside is the poorly informed governments that are handing out OUR money to these wasteful attempts to change something that is not in our power to change…

Dodgy Geezer

@richardscourtney
“However, the reflectance continued to degrade as a result of dirt, bird droppings, algae, etc. accumulating on the surface. It was clear that similar accumulation would occur on tarred roofs. Hence, within about a year following installation there would be surprisingly little difference between the reflectance of a flat roof covered with a ‘traditional’ tarred roofing felt and and a flat roof with the aluminium-coated roofing material. And the ‘traditional’ roofing felt was cheaper.
So, on the basis of existing experimental data (which I helped to acquire) I think the effect of painting the roofs would be much less than the reported model study suggests.”
NOT if a bylaw is passed requiring all owners to maintain a minimum of 60% reflective efficiency, on penalty of a $5000 fine. And for those who can’t climb up to their roofs for medical reasons, a $200 roof tax will be applied to pay for support staff.
You just aren’t thinking like a green….

Steve from Rockwood

mwhite says:
September 8, 2012 at 3:37 am
—————————————-
On my way into town I drive through a large well-treed marshland. The outdoor temperature (as shown by my car) drops at least a couple of degrees. By the time I get to the city, especially when I park in an asphalt covered parking lot, the temperature can be 4-6 degrees warmer than at my house. When we build cities we cut down all the trees, fill in the marshlands and then pave them over with asphalt. I don’t want to sound like Joni Mitchell but we should stop worrying about global warming and start worrying about city warming. We are cultivating our cities to be 3-5 degrees warmer than they should be.

Jon Moore

Well, paint the roof to prevent it..lol
ASWD Law Divorce Kentucky

barryjo

Sounds like some more taxpayer funded, brilliant research done by those folks at Biosphere2.
Last I heard, they still were claiming CO2 caused global warming.

Hot-arid is not my area of experience, but their reference to “impacts on the hydrologic cycle are aggravated via enhanced evapotranspiration reduction” seems a bit odd. If the area they are talking about is hot-arid, then the dominant flora will be resistant to moisture loss due to transpiration. If this is replaced by buildings, with people in them breathing, perspiring, cooking, etc then the resulting moisture will either be extracted to the air outside or recovered by the building systems.

Jeff L

3 thoughts come to mind immediately :
1) This is a model, not hard data. We all know the limits of climate models & how much faith we should put in them (not much).
2) Heat – If the desert urban area is growing so much, evidently these are heat-loving people. Why are they even concerned about reducing the urban heat island?
3) Adaptation – If that many people can adapt to summer time desert heat, why is anyone worried about a degree or two of AGW – we’ll adapt just fine :))

pk

two things:
can you imagine driving the run from los angeles to phoenix in september/october with a bright white road. the eyestrain and headaches would be houmoungas.
these twits that advocate light colored roofs (anything other than light grey is not practical over even the short term) have never looked out an aircraft on approach to LAX. there is a good 40-50 miles of industrial/commercial buildings with white/light roofs and they have been that way for decades.
go to the local hardware store. look at the “rolled roofing”. as i remember in the hot parts of the country there are only two colors offored. light grey and lighter grey.
these guys are floogging a horse thats been dead and gone for nearly a century.
C

Gibby

As has been pointed out, the authors didn’t bother to establish the statistical significance between “white” roof tops and rainfall. They just assumed that there was a statistically significant correlation and went from there. It is not the mathematicians fault for not noticing this since he is not a scientist, he just got asked to work the math associated with the problem. However, this is a typical representation of the Liberal Arts degrees in Climate Science and why I have a major issue with the University that I am an Instructor for. No science degree should ever be offered as an Arts degree as is all of the new “green” politically motivated science degrees are.

richardscourtney

Dodgy Geezer:
re your comment on my post which you provide at September 8, 2012 at 6:08 am.
I enjoyed that. Yes, of course you are right: I failed to think as a ‘green’.
And I did laugh. Thankyou.
Richard

Rob Dawg

> “They conducted continuous multi-year, multi-member, continental scale numerical experiments for several 2050 Sun Corridor growth and adaptation scenarios …”
Those are not experiments. Those are simulations. It doesn’t matter what they found. Anyone who doesn’t know the difference is not conducting science.