Figure 1 from Georgescu et al 2012: with caption “Observed time series of the mean summer-time temperature and diurnal temperature range at an urbanizing and non-urbanizing station”.
I was alerted to a news report on the excellent Nature Climate Change article by Matei Georgescu and colleagues.
Georgescu, M. et al 2012: Summer-time climate impacts of projected megapolitan expansion in Arizona. Nature Climate Change. doi:10.1038/nclimate1656
with the abstract [highlight added]
Efforts characterizing the changing climate of southwestern North America by focusing exclusively on the impacts of increasing levels of long-lived greenhouse gases omit fundamental elements with similar order-of-magnitude impacts as those owing to large-scale climate change. Using a suite of ensemble-based, multiyear simulations, here we show the intensification of observationally based urban-induced phenomena and demonstrate that the direct summer-time climate effects of the most rapidly expanding megapolitan region in the USA—Arizona’s Sun Corridor—are considerable. Although urban-induced warming approaches 4 °C locally for the maximum expansion scenario, impacts depend on the particular trajectory of development. Cool-roof implementation reduces simulated warming by about 50%, yet decreases in summer-time evapotranspiration remain at least as large as those from urban expansion without this mode of adaptation. The contribution of urban-induced warming relative to mid- and end-of-century climate change illustrates strong dependence on built environment expansion scenarios and emissions pathways. Our results highlight the direct climate impacts that result from newly emerging megapolitan regions and their significance for overcoming present challenges concerning sustainable development.
The news article by Rebecca Thomas on this new research article is reproduced below [with highlighting]
ASU study: Urban sprawl might cause higher summer temps
TEMPE, AZ (CBS5) -We live in a desert and expect our summer heat.
But, how much worse can it get?
According to a new study by Arizona State University’s School of Geographical and Urban Planning and its School of Mathematical and Statistical Sciences, temperatures in a large portion of our state could jump between 2 to 7 degrees in the several decades as a result of urban sprawl.
They say because we live in the fastest growing megapolitan in the United States, we could see an expansion of what we’ve come to know as the “Heat Island Effect.”
Basically, the more concrete you have in terms of buildings and roads, the hotter it gets during the day.
And, because concrete and asphalt absorbs and then releases heat, it cools off less at night.
“Further potential urbanization can make things considerably warmer,” said Matei Georgescu, the study’s lead author and an assistant professor at ASU’s School of Geographical Sciences and Urban Planning.
Using growth projections by the Maricopa Association of Governments for Arizona’s Sun Corridor, which includes Phoenix, Prescott, Tucson and Nogales, researchers identified potential temperature increases by 2050.
“Worst-case scenario locally, we’re looking at an increase during the summertime of 7 degrees,” said Georgescu.
Best-case scenario with less growth, we’re looking at a 2- to 3-degree increase in summer temps.
Georgescu says even if the Sun Corridor grows unchecked, maximum potential temperature increases could be cut in half by simply painting building rooftops white.
“What happens is a lot more of the incoming radiation is reflected back to space,” he said.
Looking ahead, Georgescu points out there are things we can do to offset the consequences of urbanization, such as planting trees for shade.
Using porous asphalt will prevent run-off and allow monsoon rain to be absorbed and then released back into the atmosphere.
“Direct evaporation is an immediate cooling effect, he said. So, it allows for an additional way to cool the local land surface.”
Georgescu stresses this is an important area of study because urbanization-induced warming can have up to three times the impact on our climate than green house gases.
“Really, what this tells you is there is tremendous opportunity for Arizona to grow sustainably and incorporate different strategies for adaptation and mitigation.
If you’d like to read more about this ASU study, it’s published in the journal Nature Climate Change.
This excellent study is yet another example of why the role in human climate forcings must broaden well beyond just the role of added greenhouse gases. We have urged this broader view, for example, in our paper
Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell, W. Rossow, J. Schaake, J. Smith, S. Sorooshian, and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union.
Other news articles on the Georgescu et al 2012 study include
ASU Study: Arizona will only get hotter by Jared Dillingham
and
City Temps May Soar From Urbanization, Global Warming by Michael D. Lemonick
where the end of the article reads
“It’s possible, it’s practical, and it could cut the projected temperature increase in half,” Georgescu said. Unfortunately, he added, it doesn’t help at all with another urbanization-related problem. When you pave or build over undeveloped land, you seal in whatever moisture there is in the soil. It can no longer evaporate, which cuts off an important source of humidity, and ultimately, of rain.
“So one of our take-home messages,” he said, “is that to be truly sustainable, you can’t just focus on temperatures. The climate system isn’t only about warming.”
Climate Science: Roger Pielke Sr. 