Beat The Heat

This week, the weather has been hot for the upper Midwestern U.S. with temperatures topping out above 100°F.  Combined with high dew points in the mid-70s, the heat index temperature was upwards of 110°F.  Here are some ways that plants and animals keep cool in the extreme heat.

Desert environments, where hot conditions exist daily, are home to numerous animal species that live underground.  Heat from the sun penetrates soils and sand layers for several inches, but at 20″ below the surface of the sand in the Mojave Desert, temperatures are fairly constant around 86°F while the surface may be over 110°F.  Few large mammals are known to use burrows, although kit foxes and humans are two examples.  Basements and lower levels in buildings are often preferred areas on hotter days.

Shade from trees is highly effective in creating cooler areas.  Leaves are lighter in color than most soils and paved areas, and leaves reflect much of the sun’s radiation upwards, away from the shady area underneath.  Denser foliage and rough leaf textures enhance the cooling effect.  Under a shade tree, temperatures may drop up to ten degrees and other surfaces no longer exposed to direct sunlight, including our skin, may be 20 to 40 degrees cooler. 

^{African elephant by Petr Polak, Getty Images: Black-tailed jackrabbit by Rancho_Runner, Getty Images; Fennec fox by Nattanan726, Getty Images}

Vasodilation occurs when blood vessels near the skin’s surface expand so more blood flows next to the skin.  Many animals living in hotter climates, including fennec foxes, black-tailed jackrabbits, and African elephants, have large ears with broad, flat surfaces devoid of hair, fur, or other insulation.  The ear’s large surface area is covered by a thin layer of skin and blood vessels.  During hot weather, heat carried in the blood through the ear is readily lost to the outside environment, providing a cooling effect for the rest of the body.

Evaporative cooling is another method through which heat can be dissipated from a body.  Trees use this method by losing water vapor through their leaves during photosynthesis, cooling the air under the leaves.  Humans employ this method in a process called sweating.  We lose warm water through skin pores directly to the air around us.  Sweating also moistens our skin’s surface, indirectly providing additional cooling as air moves across the skins surface and wicks away additional heat.  An important aspect enhancing the effectiveness of this method is our posture.  Being supported by two legs, rather than four, exposes much less surface area to the direct rays of the sun, and much more surface area to air currents.

While sweating is good for cooling, it is removing water from the body, which must be replaced for the process to continue.  Exposure to today’s temperature extremes may result in a loss of three gallons of water or more from an average-sized human.  As you are out enjoying nature during hot days, remember to keep hydrating to stay cool and keep other bodily systems healthy.