According to NOAA, heat is the number one weather-related killer in the U.S., accounting for 162 deaths annually. A person just sitting in the shade on a 90°F day for 24 hours will lose a minimum of six quarts of water (through perspiration, urination, and respiration), reports the Department of Defense. And hikers? Here’s what happens:
>> What you lose Depending on fitness and conditioning, the average person sweats 27.4 to 47.3 ounces per hour while exercising, says Stacy Sims, PhD, an exercise physiologist and nutrition scientist at Stanford University. For a 155-pound hiker, that’s 2 percent of your body water. Lose that, and you’ll also sacrifice 11 percent of your VO2 max—your body’s ability to take in and use oxygen—significantly reducing your cognition and reaction time. >> What to put back Pack 2 to 6 quarts of water per person, per day depending on the length of your trip—more if you can. But water alone won’t work. Drink too much without replacing electrolytes and you can suffer from life-threatening hyponatremia. So, each hour, suck down at least two 16-ounce bottles of water with a drink mix with 150-200mg sodium and at least 50mg potassium. Try products from GU (guenergy.com) or Vitalyte (vitalyte.com). >> Be prepared One reason hikers get into trouble: They don’t realize how temperature and humidity combine, making conditions more severe than the thermometer suggests. Use the heat index—which is geared toward slightly lower-exertion exercise than backpacking—to get a real measure of what you face.
>> Things that sting The golden rule of desert living? Look before you step or touch, and you’ll avoid surprise encounters with rattlesnakes, scorpions, and spiders. Check your shoes, sleeping bag, and anywhere you’re about to sit. If you’re stung by one of the more venomous breeds—like a brown recluse spider or black widow—reduce swelling by keeping the limb cold, then get to a hospital as soon as possible. The most incidents? Africanized bees found in the Southwest. They’ll attack with little provocation when you’re in their territory. Pull your shirt collar tight up around your neck. And run. Carry Children’s Fastmelt Benadryl (or an EpiPen if you have a history of anaphylaxis) in your first-aid kit. >> Flash floods In the Grand Canyon, 80 percent of flash floods happen between noon and 8 p.m. during the monsoon season from July to September. Check the weather and avoid narrow canyons during the rainy season. If water rises and runs faster or muddier, get to high ground. Stuck? Find a wall or boulder to protect your body from debris. If you’re carried off, keep your legs in front of you with bent knees.