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Summer-time climate impacts of projected megapolitan expansion in Arizona


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 change1,2. 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 development3,4.

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Figure 1: Observed time series of the mean summer-time temperature and diurnal temperature range at an urbanizing and non-urbanizing station.
Figure 2: Simulated summer-time two-metre air temperature and evapotranspiration differences.
Figure 3: Simulated summer-time two-metre air temperature variance differences.
Figure 4: Contribution of JJA urban-induced warming relative to projected JJA World Climate Research Programme Coupled Model Intercomparison Project phase 3 warming (relative to 1990–2010) resulting from increased emissions of LLGHGs.


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We are grateful to N. Selover (Arizona state climatologist) for providing observational data and to A. Bagley (MAG) for providing Arizona 2050 growth-scenario data. This work was financially supported by National Science Foundation grant ATM-0934592.

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M.G. carried out the numerical simulations. M.G. and M.M. carried out the analysis. M.G., M.M., A.M. and J.D. designed the study and wrote the manuscript.

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Correspondence to M. Georgescu.

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The authors declare no competing financial interests.

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Georgescu, M., Moustaoui, M., Mahalov, A. et al. Summer-time climate impacts of projected megapolitan expansion in Arizona. Nature Clim Change 3, 37–41 (2013).

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