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An urban heat island: How average summer temperatures keep rising in Nashville

Posted at 10:02 PM, Jul 21, 2022
and last updated 2022-07-22 23:19:13-04

NASHVILLE, Tenn. (WTVF)  — We’ve seen more than two dozen days this summer with temps of 90 degrees or higher.

With Nashville being so hot, it was chosen as one of 14 cities to take part in the National Oceanic and Atmospheric Administration’s Urban Heat Island Campaign.

The campaign, which started in 2017, works with cities and volunteers to gather temperature and humidity data from special sensors attached to volunteers' vehicles during three specific times of a day. This will take place on one day in August.

“This is really exciting because a lot of cities apply for this and only a few are chosen. The exciting part is we actually get to get straight model data on heat throughout the urban core,” said Dr. Alisa Hass with MTSU Department of Geosciences.

An urban heat island is explained below.

Nashville looks at what it means to be an urban heat island

Nashville is actually an Urban Heat Island. That’s a metropolitan area where buildings and pavement cause it to be hotter than outlying areas. Areas like downtown Nashville, North Nashville and other places that lack green space are at a greater risk when it comes to extreme heat.

“When we look at heat waves and extreme weather events, they tend to disproportionately impact communities of color,” according to Dr. Kendra Abkowitz, Metro Nashville’s Chief Sustainability and Resilience Officer.

“There's two different parts. We can mitigate heat. So we can actually reduce the amount of heat in an urban area by planting more trees, removing concrete, anything to make it lots of less packed buildings, less concrete. The other part is an adaptation so when the heat is actually here, how do we make sure our bodies cool down, making sure we're not taking on too much heat at once. That can be water misters, that can be cooling centers,” said Dr. Hass.

Why some areas of Nashville are hotter than others explained.

Understanding hot spots, Nashville serves a heat island

The green space we see in our outlying areas is not only beautiful, it’s critically helpful when it comes to reducing periods of extreme heat. These areas don’t trap as much heat as urban city centers do. The structures within our downtown areas, like roads and buildings, absorb and reemit the sun’s heat more efficiently than natural landscapes. The temperature difference between green spaces and cities can be as much as 15-20 degrees.

Green roofs, like the one at the Kenect Apartment building in Midtown, can also help. These roofs can be 30-40 degrees cooler than other roofs. Plants on green roofs absorb less heat than standard building materials and can also help cool the air through evapotranspiration. That’s the process of how soil and plants evaporate water into the air, which has a cooling effect.

From 1970 to 2020, we’ve seen the average summer temperature in Nashville rise by 2.8 degrees.

Green spaces are important to have. Bree Smith explains why.

Green spaces fight against extreme heat in Tennessee

Dr. Abkowitz says this “City on the Rise,” is considering additional strategies to help with the Urban Heat Island.  

“Two strategies that I think are well suited to explore for a growing city are cooling pavements as well as green roofs and vegetative roofs. I think with either of those measures understanding where they are functional and feasible is really important. Those are definitely strategies that could be deployed again, where circumstances would be suitable for that. Heat mapping information could help us understand where those types of installations are most necessary.”

The Cumberland River Compact leads Nashville in an urban tree planting effort called Root Nashville to help mitigate urban heat. 

CRC says some areas are too dangerous for homes and businesses to be built on them so they’re returning it to the ecosystem by partnering with the city of Nashville on a program called De-Pave.

“It's basically peeling up the asphalt and returning grounds like this to green space,” said Mekayle Houghton, Executive Director of Cumberland River Compact.

Projects like this though take time. They started working on one area near Brown’s Creek a year ago. It will take about four more years to complete.

“We're in the process of planting trees, remediating the soil so it can sustain plant material. Once this is done, this will be a little bit of an oasis in a very hot part of town. We'll have trees, green space. We'll have a creek that's on its way to getting cleaner every year in the middle of what we know is a very hot, very impervious part of town,” said Houghton.

A warming climate can also lead to more rain. A warming climate means the atmosphere can hold more moisture, leading to more rain coming down with each storm. Flood Ready Tennessee is a coalition working to better prepare for future floods across the state by investing in statewide coordination efforts, green infrastructure solutions and hazard mitigation.

"We're not going to be able to get rid of flooding, flooding is always going to happen. But does it have to be that bad? What can we do better?" said Metro Council Member Courtney Johnston, whose district is still recovering after floods destroyed homes along Seven Mile Creek in March 2021.

“It was just unbelievable, you have people that were completely wiped out, everything that was in their home was destroyed," said Johnston.

For every one degree of warming, the atmosphere can hold four percent more moisture. That can lead to heavier downpours and more rain in a shorter period of time.

“Climate change is happening and so we are going to continue to see these major rain events, tornadoes, just very, very volatile weather patterns, and we will be affected by it. So we've got to start doing something yesterday," said the Lead Forecaster for the National Weather Service in Nashville, Sam Shamburger.

You can take precautions if flooding is expected. Make sure you have several ways to get alerts, especially if you live near a river or creek. Johnston says another good thing you can do is get flood insurance. If you do suffer from a flood in your area, make sure to clean up any debris. The debris could block the water flow from any additional rainfall or flooding that occurs later, which could lead to more flooding of your property or home.

You can learn more about each of these organizations by clicking the following links:

To take part in the Heat Mapping project, contact Dr. Kendra Abkowitz at Kendra.Abkowitz@nashville.gov.

To learn more about CRC, click here (https://cumberlandrivercompact.org/)

To learn more and volunteer with Root Nashville, click here (https://rootnashville.org)

To learn more about Flood Ready Tennessee, click here (https://floodreadytn.com/)