By Paul F. Hudak*
Though less recognized than pavement, hot earthen surfaces can also harm dogs during prolonged walks outdoors. Dire outcomes of heat waves illustrate a need for health precautions when exercising outdoors, including hiking in parks and natural areas. Precautions should accommodate animals as well as people. The panting mechanism that dogs use to keep cool works poorly in warm air (Forgues, 2012). When encountered, high humidity levels compound overheating tendencies by restricting evaporative cooling (Bruchim et al., 2006).
Often neglected, potential for paw burn should also be considered when walking dogs in warm weather (Foley, 2015). Warm ground that is marginally tolerable to humans can harm dogs, because they lack a rich superficial vascular plexus and disseminate accumulated heat much less efficiently (Wohlsein et al., 2016). Heat-related paw hazards of paved streets and sidewalks are well known (FPI, 2019). However, potential dangers from prolonged contact with natural earthen surfaces are less well understood. Recently, a field experiment was conducted to evaluate warming tendencies of natural surfaces encountered by people and dogs.
On a warm summer day, temperatures of ten different earthen surfaces including shallow lake water and various types of mud, sand, cobbles, rock fragments, and grass along a nature trail used for walking dogs were measured with an infrared thermometer in Cross Roads, north-central Texas, USA. The study area is approximately 35 miles north of Dallas, in north-central Texas. Rock and soil encountered in this study derive mainly from the Cretaceous Woodbine (predominantly sandstone) and Grayson (predominantly marl) Formations, as well as Quaternary alluvium. Measurements were taken in seven surveys, starting at two-hour intervals from 8:00 a.m. to 8:00 p.m., on August 30, 2020. The area was partly cloudy in the morning and sunny in the afternoon. The first measurement was taken shortly after sunrise, and the last measurement was made at dusk. Rain fell in the early morning hours preceding the first set of measurements, but not later in the day.
Temperatures varied considerably with ground material and time of day. Materials with lower specific heat capacity warm more quickly with incoming solar energy, thereby reaching higher temperatures later in the day. Several physical properties, including atomic structure, colour, and moisture content, affect specific heat capacity. Rocks and minerals tend to have lower specific heat capacity, and warm more quickly, than organic matter in soil (Kodesova et al., 2013). Darker-coloured material, such as fragments of the iron oxide-bearing Woodbine Formation, tends to absorb more heat and reach higher temperatures than lighter-coloured material. Water has relatively high specific heat capacity; more energy is required to raise the temperature of moist ground than dry ground (Abu-Hamdeh et al., 2003). Thus, moist sand and open water in this study attained relatively low temperatures throughout the day. Additionally, evaporation from moist ground and transpiration from grass takes up heat and has a local cooling effect (Alexander, 2011).
The earliest temperature measurements were lowest for all materials. Ground surfaces accumulated heat during the day and reached their highest temperatures in mid to late afternoon. Temperature variations between different ground surfaces were most pronounced in mid-afternoon. All ground surfaces showed much greater range in temperature than air.
Results outlined above have important implications for dog safety. Earthen surfaces, though typically cooler than pavement, are not necessarily cool enough for prolonged contact with paws on warm days. Burn risks can be reduced by walking dogs early in the day, walking over moist earth or through shallow water, and by finding shade where possible. Dog walkers should pay close attention to potential paw damage from prolonged contact with earthen surfaces, in addition to the better known hazards of paved surfaces, on warm summer days. Trail managers can help by posting signs that alert people to potential walking hazards to dogs. In some settings, it might be possible to reduce these risks by orienting trails to minimize usage of earth materials with low specific heat capacity.
Abu-Hamdeh, N.H. 2003. Thermal properties of soils as affected by density and water content. Biosystems Engineering, 86(1), 97-102.
Alexander, L. 2011. Extreme heat rooted in dry soils. Nature Geoscience, 4, 12-13.
Bruchim, Y., Klement, E., Saragusty, J., Finkeilstein, E., Kass, P. and Aroch, I. 2006. Heat stroke in dogs: A retrospective study of 54 cases (1999-2004) and analysis of risk factors for death. Journal of Veterinary Internal Medicine, 20(1), 38-46.
Foley, C. 2015. Cool that hot dog. The Whole Dog Journal, July, 14-18.
Forgues, S. 2012. Canine Health in the Heat. Available from:https://www.officer.com/tactical/ems-hazmat/environment-hazard-protection/article/10744875/canine-health-in-the-heat
FPI (Four Paws International) 2019. Hot Asphalt: A Danger to Your Dog’s Paws. Available from:https://www.four-paws.org/our-stories/publications-guides/hot-asphalt-a-danger-to-your-dogs-paws
Kodesova, R., Vlasakova, M., Fer, M., Tepla, D., Jaksik, O., Neuberger, P. and Adamovsky, R. 2013.Thermal properties of representative soils of the Czech Republic.Soil & Water Research, 8(4), 141-150.
Wohlsein, P., Peters, M., Schulze, C. and Baumgartner, W. 2016. Thermal injuries in veterinary forensic pathology. Veterinary Pathology, 53(5), 1001-1017.
*Department of Geography and the Environment, University of North Texas, 1155Union Circle #305279, Denton, Texas 76203-5017. He can be reached at email@example.com