Coping With Extreme Heat: Trees Are the Answer

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By Nancy Brannon, Ph.D.

Summer heat has been brutal in the mid-south, with temperatures reaching 100° F in late July and heat indexes even higher. For most people, it’s possible to be in an air conditioned building or vehicle or a swimming pool to get relief. But these options are not available to our horses! Only fans, shade trees, and maybe farm ponds offer relief, as well as a good hosing off with cool water daily or twice daily.

As I covered the Palomino World Show in Tunica, MS, I noted on Thursday, July 21, that the temperature at the parking lot at the Expo Center was 109° F.

On July 22, 2016 NPR posted a report on the cause(s) of extreme heat across the mid-south, as “The National Weather Service predicted temperatures in the triple digits through the weekend in much of the South, Midwest, and along the East Coast.” The National Oceanic and Atmospheric Administration (NOAA) reported: “A heat dome occurs when high pressure in the upper atmosphere acts as a lid, preventing hot air from escaping. The air is forced to sink back to the surface, warming even further on the way. This phenomenon will result in dangerously hot temperatures that will envelop the nation throughout the week.”

The summer of 2015 was the hottest year – ever – globally, and NASA announced in July that the first six months of 2016 have been the hottest since 1880. “Scientists took temperatures from around the world and got a June average. What they found was a world that was 1.62 degrees Fahrenheit hotter than the average June in the 20th century. Every month in 2016 has been warmer than ever, at least since people started keeping reliable records — that was 1880,” NPR’s Christopher Joyce reported.

This year, “2016 is on track to be the hottest recorded year ever for the planet. The last hottest year on record was 2015. In addition to the temperature records, every climate observatory in the world is now recording CO2 greenhouse gas levels higher than any time in the last 4 million years,” wrote Adam Frank, Astrophysics Professor at the University of Rochester, on the 13.7 blog - commentary on science and society.

So what can horse owners and people, in general, do to lessen the stress of extreme summer heat? A bumper sticker from the Society of American Foresters offers sound advice: “Trees are the Answer!” Trees reduce the greenhouse effect by shading houses and buildings. This reduces the need for air conditioning by up to 30 percent which, in turn, reduces the amount of fossil fuels burned to produce electricity.

North Carolina State University Extension Cooperative Extension also provides information about the benefit of trees:

“Trees can reduce air temperature by blocking sunlight. Further cooling occurs when water evaporates from the leaf surface. The conversion of water to air vapor --- a chemical process --- removes heat energy from the air.

“A tree can be a natural air conditioner. The evaporation from a single tree can produce the cooling effect of 10 room size air conditioners operating 20 hours a day.

“Deciduous trees block sunlight in the summer, but allow sunlight to reach and warm your home in the winter – place deciduous trees on the south and west sides of your home.

“Trees can shade hard surface areas such as driveways, patios, building and sidewalks thus minimizing landscape heat load -- a buildup of heat during the day that is radiated at night resulting in warmer temperatures. Ideally, 50 percent of the total paved surface should be shaded.”

The EPA has information on Using Trees to Reduce Heat Islands: “Trees and vegetation lower surface and air temperatures by providing shade and through evapotranspiration. Shaded surfaces, for example, may be 20–45°F (11–25°C) cooler than the peak temperatures of unshaded materials. Evapotranspiration, alone or in combination with shading, can help reduce peak summer temperatures by 2–9°F (1–5°C).”

In an article by Melanie Lenart, “Trees and Local Temperature,” posted on, this author reports that “the temperature difference between shaded and non-shaded ground can be as much as 36°F, based on some studies...” that she cited.
There are plenty more research articles available that document the cooling effect of trees, but I decided to collect my own data for comparison. My car has a feature that displays the outside temperature, so I used that feature to compare the outside temperature at our office in Arlington, TN and the outside temperature at my home, about 15 minutes-drive north of Arlington. The parking lot at our office is concrete, not asphalt, and has no shade cover, except from existing buildings for small portions of the day. My house is complete surrounded by trees and stays shaded for most of the day. I do get west afternoon sun on the front porch.

I collected some data in late June and some in mid to late July, 2016. The times of day varied and were recorded as well as the temperatures.

6/20: 3:45 pm, Arlington, 100°F. 4 pm, home, 88°F [12° difference]
6/21: 6:30 pm, Arlington, 98°F. 6:50 pm, home 87°F [11° difference]
6/22: 6:30 pm, Arlington, 94°F. 6:50 pm, home 88°F [6° difference]
6/23: 3:35 pm, Arlington, 102°F. 3:50 pm, home 90°F [12° difference]
6/24: 6:15 pm, Arlington, 96°F. 6:30 pm, home, 84°F [12° difference]
7/18: 5:40 pm, Arlington, 101°F. 6:26 pm, home, 86°F. [15° difference]

This day I stopped at the grocery store in Arlington and parked in the shade of a crepe myrtle in the lot. The temp in the shade of the parking lot was 98°F. Even just that small amount of shade gave a 3 degrees temperature reduction.

7/19: 6:08 pm, Arlington, 92°F. 6:23pm, home 86°F [6° difference]
7/22: 6:12 pm, Arlington, 102°F. 6: 20 pm, home 88°F [14° difference]
7/23: 4:30 pm, Tunica Expo Center, 100°F. 6:10 pm, home 82°F [18° difference]
7/25: 7:40 pm, Arlington, 91°F. 7:54 pm, home 80°F [11° difference]
7/26: 6:58 pm, Arlington, 95°F. 7:14, home 84°F [11° difference]

My results were similar to those of other research projects. The temperatures at my house were consistently 11 to 12 degrees cooler than at our office, with two exceptions on days when there was cloud cover over the office parking lot. Twice the temperatures were 14° and 15° cooler at home than at the office, and 18° cooler at home than at the Tunica Expo Center.

These results are reflected in my utility bill, too. We first turned on our air conditioner in mid-June. Our electric usage 3/24/16 to 4/26/16: 826 kwh (kilowatt hours); cost $76.77
Electric usage 4/26/16 to 5/24/16: 497 kwh; cost $50.19
Electric usage 5/25/16 to 6/24/16: 769 kwh; cost $77.53
Electric usage 6/25/16 to 7/26/16: 1388 kwh; cost $137

The big jump in electric usage coincides with the onset of the use of the air conditioner – as well as barn fans and a fan in the garage for the dog. The lowest usage was the month when we used neither heating nor air conditioning.

So anything we can do to reduce energy consumption – especially electricity – will have fiscal benefits (reduced costs) as well as positive environmental results (reducing emission of greenhouse gases).

Start planting trees around your house and barn! Or – just don’t mow. In the mid-south, trees will germinate and grow in un-mowed areas, and within 15 to 20 years, what was once a lawn will be a small forest generating cooling effects! There are also some shrubs that grow fast and supply a sun/wind buffer: Red Tip Photinia is one. According to the Clemson University Cooperative Extension, it “grows 10 to 15 feet tall and 5 to 8 feet wide, although it can get larger with age. It is a moderate to fast growing plant.” Consult your local extension agent or gardening expert to find out what trees and shrubs best suit your area. When you and your horses are suffering from the heat, remember that “re-leaf” (relief) is just a tree away.

Heat Dome:
Adam Frank, 13.7 blog:
NCSU Benefits of Trees:
EPA Using Trees to Reduce Heat Islands:
Trees and Local Temperature:

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