[MCN] OPEN ACCESS: To keep a town cool enough for pedestrians, ...

Lance Olsen lance at wildrockies.org
Thu Feb 4 10:12:26 EST 2016

Environmental Research Letters Published 2 
February 2016 * © 2016 IOP Publishing Ltd

Micrometeorological simulations to predict the 
impacts of heat mitigation strategies on 
pedestrian thermal comfort in a Los Angeles 
Mohammad Taleghani1, David Sailor2,3 and George A Ban-Weiss1

Author affiliations
1 Department of Civil and Environmental 
Engineering, University of Southern California, 
Los Angeles, California, USA
2 Department of Mechanical and Materials 
Engineering, Portland State University, Portland 
Oregon, USA
3 Current address: School of Geographical 
Sciences and Urban Planning, Arizona State 
University, Tempe, Arizona, USA.


The urban heat island impacts the thermal comfort 
of pedestrians in cities. In this paper, the 
effects of four heat mitigation strategies on 
micrometeorology and the thermal comfort of 
pedestrians were simulated for a neighborhood in 
eastern Los Angeles County. The strategies 
investigated include solar reflective 'cool 
roofs', vegetative 'green roofs', solar 
reflective 'cool pavements', and increased 
street-level trees. A series of 
micrometeorological simulations for an extreme 
heat day were carried out assuming widespread 
adoption of each mitigation strategy. Comparing 
each simulation to the control simulation 
assuming current land cover for the neighborhood 
showed that additional street-trees and cool 
pavements reduced 1.5 m air temperature, while 
cool and green roofs mostly provided cooling at 
heights above pedestrian level. However, cool 
pavements increased reflected sunlight from the 
ground to pedestrians at a set of unshaded 
receptor locations. This reflected radiation 
intensified the mean radiant temperature and 
consequently increased physiological equivalent 
temperature (PET) by 2.2 °C during the day, 
reducing the thermal comfort of pedestrians. At 
another set of receptor locations that were on 
average 5 m from roadways and underneath 
preexisting tree cover, cool pavements caused 
significant reductions in surface air 
temperatures and small changes in mean radiant 
temperature during the day, leading to decreases 
in PET of 1.1 °C, and consequent improvements in 
thermal comfort. For improving thermal comfort of 
pedestrians during the afternoon in unshaded 
locations, adding street trees was found to be 
the most effective strategy. However, afternoon 
thermal comfort improvements in already shaded 
locations adjacent to streets were most 
significant for cool pavements. Green and cool 
roofs showed the lowest impact on the thermal 
comfort of pedestrians since they modify the 
energy balance at roof level, above the height of 

Original content from this work may be used under 
the terms of the Creative Commons Attribution 3.0 
licence. Any further distribution of this work 
must maintain attribution to the author(s) and 
the title of the work, journal citation and DOI.

"As an endangered species and an endangering one, 
we need, collectively, all the
self-understanding and self-direction that we can muster."

M. Brewster Smith. "Perspectives on Selfhood."
American Psychologist, December 1978

"Š. the earth's atmosphere is so thoroughly mixed 
and so rapidly recycled through the biosphere
that the next breath you inhale will contain 
atoms exhaled by Jesus at Gethsemane and Adolf 
at Munich."

Preston Cloud and Aharon Gibor.   "The Oxygen Cycle." 
Scientific American, September 1970
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