Monday numbers: A closer look at urban heat mapping in the era of climate change

By: - August 2, 2021 6:00 am
The still waters at Beaver Marsh Nature Preserve harbor fish, turtles and frogs. (Photo: Lisa Sorg)

The white tail of a doe streaked by like the trail of a meteor. A stand of cattails rose from stagnant marsh, their heads as brown as corndogs. Dragonflies — Common Whitetail Skimmers and Banded Pennants — alighted on a sweep of swamp rose-mallows.

As a volunteer for an urban heat mapping project, I had drawn the long straw and been assigned to the Beaver Marsh Nature Preserve in north Durham. An oasis among urban heat islands, the 34-acre tract lies off busy Roxboro Street — a four-lane asphalt hellscape — and behind Harbor Freight, whose parking lot is as blinding as an airport tarmac.

Beaver Marsh, though is quiet, calm and comparatively cool.

Co-sponsored by several organizations, including the Museum of Life and Science and the NC State Climate Office, the project dispatched more than 150 people across Raleigh and Durham, equipped with sensors connected to a smartphone app. 

For an hour on a sultry mid-afternoon in July, walkers, cyclists and drivers collected data on heat, humidity — and the dreaded heat index — in different parts of their cities: tree-less neighborhoods, shaded parks, and places in-between.  

When the data are released later this month, we’ll know some of the places where residents are most vulnerable to extreme heat, induced by climate change. We can then pinpoint where to plant trees and set up cooling centers. Some cities, like New York, are helping low-income households buy air conditioners. We can build parks instead of parking lots.

Redlined communities are particularly at risk. These neighborhoods are where the federal government and its racist housing and lending policies segregated Black people. It’s where racist transportation decisions destroyed neighborhoods, parks and curbside trees for highways.

These areas tend to be barren, flood-prone heat magnets.  A recent study in the journal Nature Communications found that because of the urban heat island effect, Black neighborhoods were hotter by 5.6 degrees Fahrenheit; Latinx areas by 4.8 degrees, and white neighborhoods by just 2.5 degrees. Similarly, low-income communities are hotter by nearly 5 degrees.

In East Durham, there are long stretches of sidewalk — and dozens of bus stops — without shade. In another historically redlined community, Lyon Park, many of the mature trees grow in Maplewood Cemetery. The dead enjoy more shade than the living.

A beaver lodge (Photo: Lisa Sorg)

Marshes provide many ecological benefits, including wildlife habitats and flood control. For the purposes of combating climate change, they hoard carbon dioxide and remove the greenhouse gas from the atmosphere. Plus, they’re good for the human soul.

Near the entrance to Beaver Marsh Nature Preserve, the temperature registered a toasty 93 degrees. But as I delved deeper into the forest, the temperature dropped, to 89, then 86. 

Not surprisingly, with the marsh and the trees and the abundant plant life, the humidity reached 53 percent. The air was still, which meant my sweat did not evaporate. This indeed, was a forest bath.

But I am fortunate. I could go home to a cool house. 

In North Carolina, nighttime temperatures are increasing faster than those in the daytime. It’s at night when our bodies are supposed to recover from the day’s thermal insults. Without air conditioning, that recovery never happens, and sometimes it kills people. 

(We’ve seen the deadly effects of inadequate cooling during the heat wave in the Pacific Northwest.)

The lack of recovery time is particularly dangerous for outdoor workers, like roofers whose bodies are beaten by the sun all day. Ironically, new housing developments are partially responsible for deforestation, which in turn releases carbon dioxide into the atmosphere, which in turn warms the planet, which then hurts the roofers.

Road pavers, whose job is to steamroll asphalt into tarry pancakes: Even under the klieg lights at midnight, how do they do it? Another irony: Lane widening and ramp building along I-40 near Raleigh, as well as the I-540 toll road took out enormous swaths of trees, which in turn releases carbon dioxide … and well you know the rest.

Agricultural workers who pick our food often return to migrant housing, little more than hot boxes in open fields. The food is perishable, transported by refrigerated trucks to the cool spas of produce aisle. 

We should not forget that people are perishable, too.

The trails of the Emerald Ash Borer, a destructive insect that has killed millions of ash trees nationwide. Ash trees, like this one in Beaver Marsh Nature Preserve, are being wiped out by both the borer and climate change. (Photo: Lisa Sorg)


1-7 — daytime degrees warmer recorded in cities than in outlying areas because of the heat island effect

2-5 — nighttime degrees warmer

10,527 — number of heat-related deaths in the U.S., 2004-2018

105 degrees — high temperature at Raleigh-Durham International Airport, Aug. 21, 2007

106 — number of days that a record high maximum has been recorded at RDU, 2000-2021

57 — number of days a record high maximum, RDU, 1980-1999

120 — number of days a record high minimum, RDU, 2000-2021

15 — number of days those record high minimums occurred in 2020

91number of fires in the western U.S., Aug. 1

1.8 million — acres burned by those fires

8.5 billion — tons of surface mass lost by the Greenland ice sheet, July 27

2 inches — equivalent amount of water that could cover the entire state of Florida

8.4 billionadditional tons of surface mass lost by the Greenland ice sheet, July 29

100 billion — tons of ice lost by Greenland since early June

67 degrees — high temperature in Greenland, July 28

Our stories may be republished online or in print under Creative Commons license CC BY-NC-ND 4.0. We ask that you edit only for style or to shorten, provide proper attribution and link to our web site. Please see our republishing guidelines for use of photos and graphics.

Lisa Sorg
Lisa Sorg

Assistant Editor and Environmental Reporter Lisa Sorg helps manage newsroom operations while covering the environment, climate change, agriculture and energy.