Satellites Zoom in on Cities’ Hottest Neighborhoods

Local governments can use data to help combat the urban heat island effect.

Spend time in a city in summer and you can feel the urban heat rising from the pavement and radiating from buildings. Cities are generally hotter than surrounding rural areas, but even within cities, some residential neighborhoods get dangerously warmer than others just a few miles away.

People cool down in New York City’s Washington Square Park fountain. With rising global temperatures increasing the likelihood of dangerous heat waves, cities need to know which neighborhoods are at high risk. Photo by Guillaume David.

Within these “micro-urban heat islands,” communities can experience heat wave conditions well before officials declare a heat emergency.

I use Earth-observing satellites and population data to map these hot spots, often on projects with NASA. Satellites like the Landsat program have become crucial for pinpointing urban risks so cities can prepare for and respond to extreme heat, a top weather-related killer.

Among the many things we’ve been able to track with increasingly detailed satellite data is that the hottest neighborhoods are typically low-income and often have predominantly Black or Hispanic residents.

Two types of urban heat, both dangerous

The urban heat island effect was first described in 1818, over 200 years ago, in “The Climate of London” by Luke Howard, an early pioneer of meteorology.

There are two distinct types of urban heat island: the atmospheric urban heat island and the surface urban heat island. They are measured in different ways.

The atmospheric urban heat island, the phenomenon described by Howard, is simply the warmer air in urban areas relative to cooler air in outlying locations.

The surface urban heat island is the result of surfaces made up of heat-absorbing materials, such as asphalt, concrete and metal. Such materials are highly effective absorbers of heat energy from the Sun, and their surfaces warm rapidly and in turn emit the absorbed energy. You can feel the heat when you touch them.

The surface urban heat island directly contributes to the atmospheric urban heat island and is usually most intense on sunny days. Urbanization also contributes to the heat island effect through deforestation and the removal of other vegetation that would provide some cooling.

Where Communities Face the Highest Heat

With rising global temperatures increasing the likelihood of dangerous heat waves, cities need to know which neighborhoods are at high risk. Excessive heat can lead to dehydration, heat exhaustion, heat stroke, and even death with prolonged exposure, and the most at-risk residents often lack financial resources to adapt.

Satellite instruments can identify communities vulnerable to extreme heat because they can measure and map the surface urban heat island in high detail.

For example, industrial and commercial zones are frequently among the hottest areas in cities. They typically have fewer trees to cool the air and more pavement and buildings to retain and radiate heat.

Certain residential layouts are also more prone to higher surface temperatures than others. These neighborhoods usually have minimal vegetation, and homes are built close together, with more roads and sidewalks and little green space. Often, especially in northern climates, homes in these neighborhoods were built with materials such as brick that retain heat to keep occupants warmer in the winter. Communities with many apartment buildings and stores surrounded by parking lots are also at high risk.

My research has found that on warm summer days, low-income communities of color can experience extreme heat conditions that are often more than 10 degrees Fahrenheit (5.5 C) warmer than surrounding areas. Other research has found similar differences among neighborhoods and stark racial and economic disparities when it comes to heat exposure.

One recent study found that the poorest areas were significantly hotter than the richest in 76 percent of urban US counties. It also found that neighborhoods with large Black, Hispanic, and Asian populations were in significantly hotter areas in 71 percent of counties, and that that difference remained even when adjusting for income. These areas tend to have less vegetation and a higher density of homes.

Another study looked at communities that had once been redlined, a discriminatory practice banks used in the early to mid-20th century to deny loans in racial and ethnic minority communities. Nationally, these formerly redlined neighborhoods were 4.6 F (2.6 C) warmer than nonredlined areas.

50 Years of Landsat

Several satellite systems can now measure the surface urban heat island, but the Landsat program, which celebrates its 50th anniversary in 2022, provides decades of continuous, comparable data in the detail necessary to examine variations within a city. That continuity helps scientists measure the impact of changes and track how development patterns change a neighborhood’s heat profile.

The first Landsat satellite was launched on July 23, 1972, with a sensor that collected data in green, red, and near-infrared wavelengths that made it useful for mapping vegetation. Beginning with Landsat 4, launched in July 1982, scientists could map and measure thermal characteristics of Earth’s surface. Today, Landsat 8 and Landsat 9 are operating, and a 10th is being developed.

How Cities Can Use this Data to Help

There are numerous ways cities can use this data to help residents combat extreme heat.

In Indianapolis, local government and faith-based organizations have used extreme heat vulnerability indices, which use indicators of heat-health risk and past heat waves to highlight high-risk communities. Knowing which communities are likely to be at the highest risk allows them to guide outreach to the most vulnerable people both before and during periods of elevated temperatures.

New York’s “Cool Neighborhoods NYC” program includes strategically planting trees and vegetation to increase shade and evapotranspiration, which cools the surrounding area. It also discusses painting roofs and pavement light colors to reflect solar energy and educating at-risk communities about heat risk and ways they can get help.

As the climate continues to warm and affect urban health, the Landsat satellites’ sensors are among our best tools for monitoring the thermal variations of the urban heat island. Such work also serves as one of the best examples of employing satellite-based measurements to monitor and implement response to public health threats.

The Conversation

You Make Our Work Possible

You Make Our Work Possible

We are standing at a pivotal moment in history, one in which education and advocacy around the climate emergency, public health, racial injustice, and economic inequity is imperative. At Earth Island Journal, we have doubled down on our commitment to uplifting stories that often go unheard, to centering the voices of frontline communities, and to always speak truth to power. We are nonprofit publication. We don’t have a paywall because our mission is to inform, educate and inspire action. Which is why we rely on readers like you for support. If you believe in the work we do, please consider making a tax-deductible year-end donation to our Green Journalism Fund.

Donate
Get the Journal in your inbox.
Sign up for our monthly newsletter.

The Latest

Bill to Ban Wildlife Killing Contests on Public Lands Needs Support

The Prohibit Wildlife Killing Contests Act of 2022 would save thousands of animals from cruel bloodsport.

Camilla Fox and Michelle Lute of Project Coyote

Supreme Court Rules against EPA, Hobbles Government Power to Limit Emissions

Court sides with Republican states as ruling represents landmark moment in rightwing effort to dismantle ‘regulatory state.’

Oliver Milman The Guardian

Feeding Insects to Cattle Could Make Meat and Milk Production More Sustainable

Adding black soldier fly larvae to cattle feed can reduce the amount of methane cows produce, research shows.

Merritt Drewery

Avocado Farms Dry Up Water Resources in Mexico

Rich tradition of cultivating and collecting medicinal plants in Michoacán state is at risk as Indigenous community loses access to water.

Monica Pelliccia

Satellites Zoom in on Cities’ Hottest Neighborhoods

Local governments can use data to help combat the urban heat island effect.

Daniel P. Johnson

Maasai Leaders ​Arrested in Protests over​ ​Tanzanian Game Reserve

Dozens wounded in clashes with police over eviction from ancestral lands to make way for hunting and safaris.

Katie McQue and Mattha Busby The Guardian