Urban Sprawl Leads to Burning Summers… and Falls
Here’s a news story from yesterday that has some impact on the Bay Area – maybe even the Real Bay Area (RBA). After all, anyone who lives here knows the hottest time of year in the Bay Area isn’t July and August. It’s September and October.
Sprawling Cities Getting Hotter Faster
livescience.com – Sat Jun 26, 12:20 pm ET
The number of extreme hot summer days is increasing around the world with global warming, but sprawling cities are racking up these sweltering days faster than more compact cities are, a new study finds.
This finding could be important to city planners, particularly because heat waves are a killer worldwide (heat waves kill more U.S. residents than any other natural disaster) and the number of hot days is expected to increase as climate change ramps up.
Researchers at Georgia Tech examined the number of very hot days in 53 U.S. metropolitan regions between 1956 and 2005 to see if there were any differences in the number of hot days between both kinds of cities. (By the U.S. Census Bureau definition, a metropolitan region includes some counties surrounding a city proper.)
The article was clearly written by someone in flyoverland, because unimportant cities such as Atlanta, Tampa, and Grand Rapids (Michigan) were presented as examples of sprawling cities, as contrasted with “compact” ones. Named as the cooler cousins were Boston, Chicago, and Baltimore, where two out of three of them are near a real ocean, and the third near a convincing analogue.
Brian Stone of Georgia Tech (told ya!), an urban planner who authored the study, noted that severe heat waves are responsible for more deaths than any other type of dangerous weather. “Residents of sprawling cities may be more vulnerable to this significant health threat posed by climate change," said Stone.
One could even wonder if the “compact” cities cited are keeping cooler due to ocean breezes rather than tree removal on a large scale. Deforestation in sprawling cities occurred at twice the rate of that in more densely populated areas from 1992 to 2001. This leads to the “urban heat island effect,” where asphalt, roofs, and other artificial surfaces absorb more heat than in rural areas with greater amounts of vegetation. The urban heat island effect shows a temperature increase of 2 to 5 degrees Fahrenheit higher than a nearby rural region.
The actual data showed the sprawlers had 14.8 more “very hot days” on average while the chunkers only had 5.6 of them. These outlying days were identified from the National Climactic Data Center’s “heat stress index” from 187 cities. Heat data were used from 1956 to 2005, but based on city definition in 2000.
Cities were defined as compact or sprawling using the sprawl index, where only the top and bottom 25%were included in the study. This metric uses population density, building proximity (both commercial and residential), also known as neighborhood mix, strength of downtowns and other activity centers, and street network patterns, based on 2000 UC Census data. Stone notes that sprawl is also a factor of the historic development of a city. For example, Boston grew around streetcars, while Atlanta developed during the age of the automobile.
The only Bay Area metropolitan area included in the study was San Francisco. Classified as very compact (big surprise), San Francisco also reported a large increase in very hot days, as did more spread-out Fresno. Los Angeles showed a much smaller increase in hot days, as did San Diego. But take a look at Stone’s map of cities included in the study. Notice something a little odd?
Just in case it doesn’t jump right out at you, here’s another view:
See it now?
How is Atlanta considered more sprawling than Los Angeles? Sure San Francisco is compact (the city is only 49 square miles!), but see how Fresno, LA, and San Diego are all in the same classification of the second most compact group? Los Angeles wrote the book on sprawl, as LA county is tremendous (4061 square miles). It may have millions of people, but most of it is suburban. And yet, Stone relies on Reid Ewing’s measure of the sprawl index, which cites a measure showing Los Angeles, San Diego and San Francisco as being some of the most compact cities in how they handled population growth (see page 9). And then on page 27 is this fascinating note:
The highest ratings on the density factor go mostly to the central PMSAs of large CMSAs. The
New York PMSA is in a class by itself, having a factor score more than five standard deviations
above the mean. While the smaller Jersey City PMSA ranks second, this is followed by other
large PMSAs: San Francisco, Los Angeles, Chicago, and Miami PMSAs. Also high on the
density factor are secondary PMSAs of these same CMSAs: Anaheim, San Jose, Newark,
Oakland, and Ft. Lauderdale. Their large housing and labor markets drive up the bid rent curves
of these CMSAs, making accessible central locations particularly valuable. Valuable land is
naturally developed at higher densities, as housing producers and consumers both seek to
minimize expensive land inputs. The simple correlation of the density factor for 2000 with the
population of the MSA or PMSA is high (r = .614).28 The simple correlation with the population
of the MSA or CMSA is even higher (r = .653).
Wow, looks like we’re back to higher rents, higher density, and higher smarts. Location, location, location! Low on the density scale are the Southeastern cities, and they have the lower rents to match. While we in the Bay Area think of Los Angeles as sprawling, that’s only compared to San Francisco. When it’s stacked up against Atlanta, Los Angeles is downright concentrated.
At the bottom of density rankings are medium-size metros in the Southeast, in ascending order:
Knoxville, TN; Greenville–Spartanburg, SC; Greensboro–Winston-Salem–High Point, NC;
Columbia, SC; Raleigh–Durham, NC; and Birmingham, AL. These are places whose growth
has mostly occurred during the automobile era, and has been without topographic or water-related
constraints that restrict development elsewhere in the Sunbelt. Still, the clustering of low
densities in this particular region is striking and requires further investigation.
And what does Los Angeles have to do with the Bay Area? Simple. Los Angeles is San Jose writ large. And that’s where the Bay Area take on this study comes in. Compared to San Francisco, San Jose also sprawls, despite its attempts to have an urban core with the fake city of Santana Row, and the out of place luxury high-rise of 360 Residences. So if we in the RBA need to take anything from Stone’s study, it’s this. Sprawl means more extreme heat waves. Heat waves mean more deaths. And old people dying of heatstroke in their RBA homes is the only way those places this Special will ever come up for sale.
