Satellites help combat the urban heat island effect by Daniel P. Johnson
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.
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 have 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.
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.
One recent study found that the poorest areas were significantly hotter than the richest in 76% of urban U.S. counties. It also found that neighborhoods with large Black, Hispanic and Asian populations were in significantly hotter areas in 71% 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.
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.
A longer version of this article was published earlier in the Conversation.org.
