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The short-term future of the Earth is a warming planet, as urban sprawl and greenhouse gas emissions fuel the effects of climate change. Current climate projections indicate that in US cities, temperatures are expected to increase by 2 to 7 degrees Celsius by 2099.
To try to adapt to this warming and maintain the quality of life of the planet, researchers are studying new ways of designing and building cities with technologies to mitigate climate change and find that when their predictive models become more and more sophisticated, they reveal a complex interdependence of effects.
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For example, a new modeling reveals the dynamics of climate change and urban sprawl at a more detailed level, leading to a new understanding of what could be reserved for growing cities and warm regions. This information could be essential in determining what might or might not work if we try to adapt to future heat.
A team of researchers led by Arizona State University has completed the most sophisticated modeling of the effects of climate change and urban centers in the United States, and found that some of the current solutions would provide only a fraction of the projected heat. .
The researchers examined the daily interaction between urban sprawl, climate change and US adaptation in the 21st century. Their badysis revealed a non-linear interaction between urban sprawl and the greenhouse gas emissions that occurred over a vast expanse of land – the continental United States – with special attention to megapolite areas growing. They then examined a range of heat mitigation strategies including street-level trees and technical solutions to combat the urban heat phenomenon.
"Previous studies have shown that conventional warming reduction strategies work primarily by lowering daytime temperatures rather than nighttime temperatures," said Matei Georgescu, badociate professor in the Faculty of Geography and Town Planning. ;KNEW. "However, cities tend to have their greatest impacts on the regional thermal environment in the evening and at night."
"We have simulated the effects of conventional heat attenuation approaches with more widely accepted cooling strategies, but we have also simulated the impacts of near-surface temperatures on technical materials," he said. he adds. "We have seen moderate nighttime attenuation with low heat input materials."
The researchers published their results in "Daytime interaction between urban sprawl, climate change and adaptation in US cities of the 21st century" in the first issue of Nature Climate Change online. The co-authors are E. Scott Krayenhoff of the University of Guelph in Ontario (Canada), postdoctoral fellow with Georgescu of the ASU, and Mohamed Moustaoui, Ashley Broadbent and Vishesh Gupta, all affiliated with the Research Center on the ASU urban climate.
A focus on the United States
The new research takes an badytical look at the American continent and makes it at a higher level of sophistication than previous studies. For example, previous studies badumed that the effects of urbanization and greenhouse gases could be determined by simply summing the effects of both. The new approach allows researchers to determine to what extent these two factors of regional climate change interact in a non-linear fashion.
"The effect of urban development and greenhouse gas emissions is less than the sum of individual components," said Georgescu. "This is obvious only during the night. The magnitude of the non-linearity reduces the total warming of 1 C (1.8 F) locally. But he says: "We have to remember that this is considerably less than the total warming itself (from 4 to 8 C, from 7.2 to 14.4 F) depending on the simulated GHG scenario. "
In addition, Georgescu's team explored the data. Previous work used the 24-hour average temperature of each day as a data point. As part of this research, the team produced much more data (about 100 terabytes) via computer simulations performed on the high-performance compute clusters available at ASU and examined the impacts on a 24-hour scale. diurnal "at intervals of three hours.
"Providing this data to the research community will allow for related research such as biometeorological badessments by health researchers and energy badessments by the community of building scientists," said Scott. Krayenhoff, lead author of the study.
Modeling reveals a warming continent, particularly in US regional urban centers.
"In summer, the urban warming resulting from a dynamic combination of interactions between urban sprawl and climate change is 1 to 6 C (1.8 to 10.8 F) in the afternoon and from 3 to 8 C (5.4 to 14.4 F) at night, at the end of the century, "Moustaoui team member said.
Overall, the simulations predicted that afternoon urban warming would be more pronounced in the eastern United States and that nighttime warming would be more pronounced in the Appalachian, Great Lakes and Central Valley regions. California, mainly because of the urban expansion of these regions.
The researchers then simulated the operation of various heat attenuation technologies given the higher regional temperatures predicted. These technologies include cold roofs, green roofs and street trees, all of which can be used to mitigate outside temperatures near the surface of an area.
S & # 39; adapt to heat
"Using dynamic interactive simulations, we have examined several adaptation strategies to offset the projected urban warmth of the 21st century," said Krayenhoff. "We combined the high-intensity implementation of cold roofs, green roofs and street trees (ie.. a full adaptation scenario) and found that it resulted in an average afternoon cooling in the summer of 1.3 to 2.0 C (2.3 to 3.6 F) depending on the region, but less than 1 C (1.8 F) overnight. In the afternoon, the local cooling in many planned metropolitan areas in the United States was slightly higher, notably in California, Texas and the Northeast. "
Even with these heat mitigation technologies in place, simulations have shown that heat will persist.
"What struck me most was that the combined and high-intensity implementation of all adaptation strategies did not offset the projected global warming in the climate scenario. RCP 8.5 – or status quo – leaving the average urban warming in the continental United States at 1 to 4 C (1.8 to 7.2 F) during the day and between 3 and 6 C (5.4 to 10.8 F) at night and the expected large increases in extreme heat days in the country's cities, "explained Krayenhoff.
"Even with substantial reductions in greenhouse gases, that is to say in the RCP 4.5 emissions scenario, the nocturnal warming was not negligible after full application. adaptation measures, "he added. "This means we can build" cold "buildings and plant trees on our streets, but US cities are likely to become much hotter without reducing greenhouse gas emissions simultaneously and substantially."
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