Cities are getting hotter. This guide can be the simple start to cooling them down.


This hot city summer reading guide is for all you hot boy and girl urbanists out there.

Large oak trees along brick path

Photo: Adam Baker.

This hot city summer reading guide is for all you hot boy and girl urbanists out there.

Houston's own Megan Thee Stallion has already provided the soundtrack for this hot girl summer we're all experiencing—with last month as the hottest June ever recorded—so Urban Edge is here to offer up some reading instead.

Here in Houston, the health department issues occasional advisories on extreme heat days, publicizing the location of cooling centers and providing a list of tips for keeping cool, including drinking water, cooling off in those cooling centers or other facilities "open to the public, such as libraries, malls, or community centers if you don't have air conditioning." Considering library hours are shrinking and the wide geographic expanse a handful of cooling centers must offer relief for, tackling extreme heat in Houston presents a challenge.

Surviving extreme heat, though, is about more than individual tips.

Consider the reading guide below an advisory for all cities:

Roofs and roads

Following its Sea-Level Rise Tool Kit in 2011, the Georgetown Climate Center put out an Urban Heat Tool Kit in 2012. Cities, the document points out, already have the urban heat island effect to deal with but, it turns out, cities are also more vulnerable to rising temperatures. "[P]rojected temperature rise is likely to be even greater in urban areas, where over 80 percent of the United States population lives," according to the tool kit. While emergency response plans, and things like cooling centers, are useful for extreme heat days, they don't "help residents when summer is merely hot and not at declared emergency levels" even though many of the same risks and costs associated with heat exist.

So what to do? Start with the buildings. "Cool roofs mean cooler cities," the document notes and since roofs typically represent roughly 20 to 25 percent of a city's land cover, cooling roofs is a great starting point. "Creating a cool roof can be as simple as spraying on a light-colored, paint-like coating." Though not at as effective as green roofs, cool roughs offer a relatively low-maintenance start to cooling a city, particularly in areas with hot, sunny summers and roughly uniform-height buildings.

Many jurisdictions have already taken this step. The Sacramento Municipal Utility District, for example, "operated the first cool roof program for commercial buildings from 2001 to 2005," according to the tool kit.

Green roofs, on the other hand, don't just cool a building, they "improve human health," buffer sound, reduce stormwater runoff and offer a space to gather. Those often disadvantaged neighborhoods near airports and highways could benefit the most from a green roof program. Green roofs can be incentivized or built into land-use zoning or building codes, as was the case in 2009 in Toronto, which "became the first city in North America to change its building code to mandate green roofs on all new development over a certain size."

Streets also offer opportunities for cooling. Asphalt, that ubiquitous canvas of urban life, is pretty much designed to heat up. "Because of its dark color, low reflectance, and high heat retention," the tool kit notes, "asphalt pavements reach temperatures up to 150 °F on summer days and in turn raise surrounding air temperatures." Two ways to combat this: "minimize the amount of paved surfaces," per the report, and "use cool pavements for surfaces that must be paved," which can include permeable pavements (yes please, Houston) and light-colored pavements.

The report details existing efforts as well as the steps necessary to implement them through local government.

Urban greenery

A few years back, Louisville realized it had fewer trees than was typical for cities in its region and so the deputy mayor at the time, Katy Schneider, set about creating a preservation ordinance. But she had a hard time getting people convincing people that "greenery was an urgent matter," according to The New Yorker. So she got help, enlisting a researcher to capture the stakes of urban greenery. With city planning professor Brian Stone, the city "assembled one of the most sophisticated models of local heat ever created for an American city, using satellite and meteorological data to help them estimate the risk of death by heat throughout the city...How many lives could be spared, the researchers then asked, if the city planted more trees and grass, replaced dark asphalt and concrete with light-colored and reflective roofs and pavement, and cut back on the excess heat seeping out of buildings and the tailpipes of cars and buses?"

It's a question other cities and researchers are tackling as well.

In Dallas, a team of nonprofits and advocacy groups found that "when the temperature soars above 100 degrees, it might be as much as 10 degrees hotter in some neighborhoods," according to a Forbes piece on the city's effort to map and supplement the city's tree canopy. There, as in many cities, tree cover tended to be a privilege of affluent neighborhoods. With the help of volunteers, the team planted more than 500 trees in a low-income neighborhood along some of the most commonly used routes. According to a study by Georgia Tech and the Texas Tree Foundation, one of the groups behind the project, planting more trees "could help cool some areas as much as 15 degrees on hot days."

A recent study tried to quantify just how much cover was needed to produce significant cooling benefits. "The data show that forty percent canopy cover is the threshold required to trigger the large cooling effects that trees have to offer," according to Adam Hinterhuer, writing for the University of Wisconsin-Madison, which produced the study. "The greatest amount of cooling happens once that threshold is crossed over the scale of a city block or larger."

The study's lead author, Carly Ziter, currently an assistant professor at Concordia Univerity, suggested that city planners focus first on areas near that threshold to target planting initiatives. “It’s not really enough to just kind of go out and plant trees, we really need to think about how many we’re planting and where we’re planting them,” she told Hinterhuer. “We’re not saying planting one tree does nothing, but you’re going to have a bigger effect if you plant a tree and your neighbor plants a tree and their neighbor plants a tree.”

Meanwhile, The Trust for Public Land has said that cities should "ensure that every resident lives within 10 minutes’ walk of a park as part of their climate action strategies." According to the Trust's latest annual park rankings, Houston falls near the bottom of the list, ranking 85th out of 100, though with 58 percent of residents living within a 10-minute walk of a park, it was slightly better than the national average of 54 percent. In Houston, residents also have to consider how navigable that 10-minute walk is, between missing or busted up sidewalks, lack of shade and auto-oriented roads that can endanger pedestrians.


So cities can plant trees, create parks, use better materials and building codes but cities can also help shape the very way we use and live in cities.

There are more cars than drivers in America today, writes Nathan Heller for The New Yorker.

"Collectively, cars and trucks account for nearly one-fifth of all US emissions," the Union of Concerned Scientists, a 50-year-old nonprofit, notes, "emitting around 24 pounds of carbon dioxide and other global-warming gases for every gallon of gas. About five pounds comes from the extraction, production, and delivery of the fuel, while the great bulk of heat-trapping emissions—more than 19 pounds per gallon—comes right out of a car’s tailpipe." The site goes on to list cleaner fuels, fuel-efficient vehicles and electric cars and trucks as among the solutions but cities should also be investing in public transportation.

The Federal Transit Administration lists the benefits of public transportation, including improved air quality, reduced greenhouse gas emissions, saved energy and its ability to support "compact development, conserving land and decreasing travel." To that last point, Houston has an ordinance supporting transit-oriented development in certain corridors but few developers have opted into the program. The city seems poised to strengthen that, however, with new proposals from its Walkable Places Committee, the recent expansion of its market-based parking area beyond downtown to lift minimum parking requirements and talk of more to come.

Social infrastructure

What those advisories from the health department about hot weather days indicate is the need for robust social networks. Check on your vulnerable neighbors, the advisories often tell residents, but how many people know who those are? Go to public places to cool off, but how do residents get there, who is welcome and what happens when public resources are cut, leaving a less accountable private sphere to fill in the gaps?

In July 1995, Chicago experienced a heatwave that killed at least 465 people and probably closer to 739 people all told. Sociologist Eric Klinenberg wrote a landmark investigation into exactly what made the heatwave so deadly. "I wrote Heat Wave to make sense of these numbers—to show, for instance, why the Latino Little Village neighborhood had a much lower death rate than African American North Lawndale," Klinenberg said in an interview in 2002. "Many Chicagoans attributed the disparate death patterns to the ethnic differences among blacks, Latinos, and whites—and local experts made much of the purported Latino 'family values.' But there’s a social and spatial context that makes close family ties possible," said Klinenberg, adding "Chicago’s Latinos tend to live in neighborhoods with high population density, busy commercial life in the streets, and vibrant public spaces. Most of the African American neighborhoods with high heatwave death rates had been abandoned—by employers, stores, and residents—in recent decades. The social ecology of abandonment, dispersion, and decay makes systems of social support exceedingly difficult to sustain."

In other words, the strength of social connections, which has much to do with the urban fabric upon which those connections get built and investments from the city, is a critical component of this fuzzy thing called resilience.

"The only way to prevent another heat disaster is to address the isolation, poverty, and fear that are prevalent in so many American cities today," said Klinenberg. "Until we do, natural forces that are out of our control will continue to be uncontrollably dangerous."

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