Analysis: Detroit among most impacted cities in the country for the urban heat island effect

Meanwhile, ‘heat domes’ raise Michigan temps and drive powerful storms. Here’s how.
Detroit River at Mariner Park. Photo by Nick Hagen.

By the end of the week, Michigan could see temperatures in the 90s for several days, with warming driven by a heat dome centered over Kansas and Missouri. And Detroit’s strong urban heat island effect will likely amplify the misery.

The term “heat dome” has gained wider currency over the last few years as increasingly brutal heatwaves have hit various parts of the globe, creating conditions that scientists say would be virtually impossible without climate change. This summer, a prolonged heat dome has baked much of the Southwest and South, including Phoenix, which has experienced 26 straight days of over-110-degree temperatures.

Heat domes occur when a high-pressure system moves into an area, pressing warm air toward the ground. This high-pressure bubble can divert storm systems, creating a static weather pattern with mostly clear skies that amplify the heat.

The head of the National Weather Service’s Forecast Operations Branch, Gregg Carbin, said that high pressure adds to the warming, part of a “compressional warming.”

“It’s like adding air pressure to a car tire; as air is compressed by higher pressure, it heats up,” he said.

While experts say Michigan isn’t yet a prime target for an extended heat dome, the odds are increasing with global heating. In the meantime, the area could see stronger storms that tend to occur to the north of these super-heated areas. 

And long term, metro Detroit could be highly vulnerable to an extended heatwave because of factors like health disparities in low-income areas and communities of color, the region’s ongoing problems with unreliable power, and an urban and suburban heat island effect, which can amplify a heatwave’s impact. Children, the elderly, and those with heart, respiratory or kidney disease are especially at risk.

Heat islands amplify heatwaves

This week’s heat coincides with a new analysis from Climate Central showing 86% of neighborhoods in Detroit and many inner-ring suburbs experience an increase in temperatures of 8 degrees Fahrenheit or more because of the heat island effect.

The effect refers to the tendency of areas heavily covered by hard surfaces like roads, buildings, and other infrastructure to trap heat and warm the surrounding area, an impact that can be especially powerful at night.

The analysis of 44 cities places Detroit ninth regarding the number of people impacted by an 8-degree or higher urban heat island effect – just behind Phoenix. However, according to the analysis, Detroit is number one in terms of the percentage – 86% – of the metro population affected.

“Detroit had a bit more spread than many other cities,” said Jen Brady, senior data analyst at Climate Central, referring to the heat island’s geographic extent across the city. The data analyzed by census tract shows additional heating across much of metro Detroit, with a few pockets of relatively warmer and cooler temperatures.

Brady speculated that a lack of green space could account for Detroit’s strong heat island effect.

Trees and other vegetation can help cool cities by directly shading buildings and structures that would otherwise absorb heat. Plants can also cool the surrounding area through evapotranspiration, where water taken up by vegetation is emitted into the air and provides evaporative cooling.

Detroit’s tree canopy coverage stands at around 24%, while the tree-planting nonprofit American Forests suggested 40% should be the goal. According to the Trust for Public Land’s 2023 Park Score rankings, around 6% of Detroit was covered by parks, compared to an average of 18% for the major cities included in the analysis.

However, Climate Central’s analysis looked at census tracts across various cities by “land-use type,” broad categories including high-rise and open low-rise areas. Brady said that large portions of Detroit, where many houses have been torn down and vegetation has been left to grow, “may not be as accounted for” in this analysis. These areas have been referred to as “passive green infrastructure” with the potential to catch rainfall and provide evaporative cooling.

But Climate Central’s analysis isn’t the only study that has found Detroit is at greater risk because of the heat island effect. Fortunately, mitigating the effects of heat islands can often be addressed locally.

“We have solutions at hand,” Brady said, suggesting that painting roofs white is a relatively low-cost intervention that Detroit could pursue to limit heat. 

Jonathon Overpeck, dean of the University of Michigan School for Environment and Sustainability, said that unlike cities in the Southwest that struggle with water access, Detroit has a relative abundance of water for planting trees and other vegetation to help cool neighborhoods.

The outlook for Michigan

Michigan’s current heatwave will be relatively short compared to the heat domes that settled over the South and Southwest this year. Dave Kook, a meteorologist at the NWS Detroit office, said the region will experience cooler air by the weekend, with northwesterly winds from Canada. 

However, this Canadian air could once again bring smoke from the massive wildfires raging in western Canada, meaning more poor air quality.

Kook said today’s weather results from heat being pulled off the heat dome in the center of the country, but this could be moderated by thunderstorms predicted for Wednesday.

He said this type of storm is exactly the kind of thunderstorm that tends to “hug the edge” of a heat dome.

“These storms, while occasionally occurring in areas well removed from the high pressure and hottest temperatures, can still tap into the potential energy (heat and moisture) associated with the ‘heat dome,'” Carbin said.

In July 2019, fast-moving thunderstorms known as derechos formed above a heat dome in the center of the country, leaving a trail of destruction from South Dakota to Michigan, where 600,000 DTE customers lost power.

For now, Overpeck says Michigan is somewhat protected from heat domes by its northern latitude and the moisture provided by the Great Lakes. But he added that the high-pressure ridges formed by heat domes will gradually extend north as more greenhouse gas pollution is pumped into the atmosphere.

Kook cautioned that it’s still important to pay attention to periods of high temperatures, like what Michigan is currently experiencing, especially if nighttime temperatures remain elevated and high humidity is added to the mix.

That’s because high night temperatures don’t allow the body to cool down, increasing the chances of heat illnesses or aggravating existing health conditions. And humidity can combine with heat to raise the “wet bulb temperature,” a measure of heat stress in direct sunlight, which can reach fatal levels when the air temperature passes 90 degrees Fahrenheit. 

Deadly instances of heat stroke among high school football players have led many schools to cancel or limit athletic practice when temperatures climb into the low 90s.


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