It is a nice number to know and it is important in that it provides
us an order of magnitude size measure when we consider other locales.
What is missing in everyone's calculations however is just now much
this can be ameliorated by the semi dense planting of shade trees in
every available corner to produce a local micro climate that is much
cooler and much moister. Water is always an issue, but we are going
there anyway and putting it all back into the atmosphere through
transpiration is a great way to recycle it.
This particular corridor cries out for brilliant water oriented
ideas. Solve it all here and the whole world will follow.
Fill the atmosphere with maximum humidity and we will have down pours
at night on most days.
In the meantime, one of the hottest spaces in the USA is just hotter
because of all that energy dumped to operate air conditioners. We
can and will do better and I expect to see us do better.
ScienceDaily (Aug. 12,
2012) — According to the United Nations' 2011 Revision of
World Urbanization Prospects, global urban population is expected to
gain more than 2.5 billion new inhabitants through 2050. Such sharp
increases in the number of urban dwellers will require considerable
conversion of natural to urban landscapes, resulting in newly
developing and expanding megapolitan areas. Could climate impacts
arising from built environment growth pose additional concerns for
urban residents also expected to deal with impacts resulting from
global climate change?
In the first study to
attempt to quantify the impact of rapidly expanding megapolitan areas
on regional climate, a team of researchers from Arizona State
University (ASU) and the National Center for Atmospheric Research has
established that local maximum summertime warming resulting from
projected expansion of the urban Sun Corridor could approach 4
degrees Celsius. This finding establishes that this factor can be
as important as warming due to increased levels of greenhouse gases.
Their results are reported in the early online edition (Aug. 12) of
the journal Nature Climate Change.
Arizona's Sun Corridor
is the most rapidly growing megapolitan area in the United States.
Nestled in a semi-arid environment, it is composed of four
metropolitan areas: Phoenix, Tucson, Prescott and Nogales. With a
population projection expected to exceed 9 million people by 2040,
the developing Sun Corridor megapolitan provides a unique opportunity
to diagnose the influence of large-scale urbanization on climate, and
its relation to global climate change.
"We posed a
fundamental set of questions in our study, examining the different
scenarios of Sun Corridor expansion through mid-century. We asked
what are the summertime regional climate implications, and how do
these impacts compare to climate change resulting from increased
emissions of greenhouse gases," says Matei Georgescu, lead
author and assistant professor in the School of Geographical Sciences
and Urban Planning in ASU's College of Liberal Arts and Sciences.
The authors utilized
projections of Sun Corridor growth by 2050 developed by the Maricopa
Association of Governments (MAG), the regional agency for
metropolitan Phoenix provides long-range and sustainably oriented
planning. Incorporating maximum and minimum growth scenarios into a
state-of-the-art regional climate model, the researchers compared
these impacts with experiments using an urban representation of
modern-day central Arizona. Their conclusions indicate substantial
summertime warming.
"The worst case
expansion scenario we utilized led to local maximum summer warming of
nearly 4 degrees Celsius. In the best case scenario, where Sun
Corridor expansion is both more constrained and urban land use
density is lower, our results still indicate considerable local
warming, up to about 2 degrees Celsius," Georgescu said.
An additional
experiment was conducted to examine an adaptation where all of the
buildings were topped by highly reflective white or "cool"
roofs.
"Incorporating
cool roofs alleviated summertime warming substantially, reducing the
maximum local warming by about half," Georgescu said. "But,
another consequence of such large-scale urbanization and this
adaptation approach include effects on the region's hydroclimate."
The cool roofs, like
the maximum-growth scenario without this adaptation approach, further
reduce evapotranspiration -- water that evaporates from the soil and
transpires from plants. Ultimately, comparison of summertime warming
resulting from Sun Corridor expansion to greenhouse-gas-induced
summertime climate change shows that through mid-century the maximum
urbanization scenario leads to greater warming than climate change.
However, pinning
precise figures on the relative contribution of each effector is
difficult, the authors state.
"The actual
contribution of urban warming relative to summertime climate change
warming depends critically on the path of urbanization, the
conversion of natural to urban landscapes, and the degree to which we
continue to emit greenhouse gases," said Alex Mahalov, a
co-author and principal investigator of the National Science
Foundation grant, "Multiscale Modeling of Urban Atmospheres in a
Changing Climate," which supported the research.
"As well as
providing insights for sustainable growth of the Sun Corridor and
other rapidly expanding megapolitan areas, this research offers one
way to quantify and understand the relative impacts of urbanization
and global warming,"said Mahalov, the Wilhoit Foundation Dean's
Distinguished Professor in ASU's School of Mathematical and
Statistical Sciences.
The group conducted
their numerical simulations using an "ensemble-based"
approach. By modifying their model's initial conditions and repeating
their simulations a number of times, they were able to test the
robustness of their results. In all, nearly half of a century of
simulations were conducted.
"By incorporating
differing Sun Corridor growth scenarios into a high performance
computing modeling framework with MAG projections, we quantified
direct hydroclimatic impacts due to anticipated expansion of the
built environment," added Mahalov. Simulations were conducted at
ASU's Advanced Computing Center (A2C2).
Georgescu said that
one take-home message from this study is that the incorporation of
sustainable policies need to extend beyond just greenhouse gas
emissions. He also stressed the importance of extending adaptation
strategies beyond the focus on mere average temperature.
"Truly
sustainable adaptation, from an environmental standpoint, must extend
to the entire climate system, including impacts on temperature and
hydrology," he said.
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