Hiking in the Heat at National Parks: NPS Safety Advice

Why heat matters

Grand Canyon's Hike Smart page warns that every year many unprepared hikers, drawn in by easy downhill walking, suffer severe illness, injury or death. Its advice applies anywhere hot: desert parks such as Death Valley and Joshua Tree, canyon country in Utah, and any exposed trail on a summer afternoon.

The page notes inner canyon summer temperatures can exceed 110°F (43°C), and that temperatures in direct sun are 15 to 20°F hotter than posted shade temperatures. The farther down you go, the hotter it gets.

1. Time your hike

The single most important factor, according to the rangers, is timing. Their advice:

• Plan so you're not hiking between 10 a.m. and 4 p.m.
• Start before dawn and finish in the late afternoon or evening.
• Rest near shade and water through the hottest hours.

To plan around daylight, check park sunrise and sunset times, and use the turnaround calculator so a late start doesn't leave you on the trail after dark.

2. Water and electrolytes

The NPS's heading says it plainly: don't force fluids, drink when thirsty, and rest and eat often. The page also advises sipping water regularly, because sweat evaporates fast in dry air and you may not notice how much you're losing. Salt stains on clothing are a sign of dehydration.

• Carry plain water and some form of electrolyte replacement.
• Don't count on water sources: at Grand Canyon, only the Bright Angel and North Kaibab trails have potable spigots, and they may be out of service.

3. Salty food, and plenty of it

Rangers recommend salty snacks such as pretzels, crackers and chips to balance water intake, and suggest eating about twice as much as you normally would. Eat regularly even if you're not hungry.

4. Stay wet

One of the most effective tricks, the NPS says, is keeping yourself soaking wet. Soak your shirt, hat or bandana whenever you reach water. The page points out cotton holds water well, which is an advantage in the desert. Spray bottles and a cooling towel help between water sources.

5. Carry the essentials

The Grand Canyon summer list includes water and electrolytes, salty snacks, a first aid kit, a map, sturdy broken-in footwear, sun protection, a whistle or signal mirror, rain gear in monsoon season, and a flashlight with spare batteries. Rangers specifically say not to rely on your phone as a light. A headlamp keeps your hands free if you finish after dark.

Know the warning signs

Heat exhaustion comes from dehydration and heavy sweating. Symptoms: fatigue, nausea, vomiting, cool and moist skin, headache, cramps. NPS treatment advice: stop hiking, rest in the shade for 30 to 45 minutes, drink water with electrolytes, eat, and cool down by getting wet.

Heat stroke is a life-threatening emergency in which the body can no longer cool itself. Symptoms include a flushed face, dry skin, a weak and rapid pulse, high body temperature, confusion and poor judgment, unconsciousness or seizures. The NPS says it's distinguished from heat exhaustion by altered mental status. Cool the person immediately and call for help.

Hyponatremia mimics early heat exhaustion: fatigue, nausea, vomiting, confusion, frequent urination. It's caused by drinking too much water while losing salt. The NPS advises stopping water, eating salty foods and resting in shade, and seeking help if alertness drops.

Pre-existing conditions

The NPS strongly recommends talking with your doctor before strenuous hikes in hot weather if you have any health conditions.

Self-rescue

Grand Canyon's page warns that help can be delayed by staffing, call volume and limits on helicopter flights in extreme heat. Plan to handle problems yourself: carry enough water, food and first aid supplies, know your limits, and have a plan to get back.

When heat is lower

If heat is a concern, consider timing: our least crowded by month guide shows desert parks are busiest in their cooler months for a reason.

Common questions

What time should I hike in summer?

Grand Canyon rangers say to plan your day so you're not hiking between 10 a.m. and 4 p.m., with a predawn start and a late-afternoon finish. They note most people who need emergency help for heat illness in the canyon are hiking during those hours.

How much water should I carry?

It depends on the hike and conditions. Grand Canyon's page notes hikers can lose one or two quarts (liters) of water per hour in the heat, advises carrying plain water plus electrolyte replacement, and warns that water spigots may be out of service.

What's the difference between heat exhaustion and heat stroke?

Heat exhaustion brings fatigue, nausea, cool moist skin, headache and cramps. Heat stroke adds altered mental status, such as confusion, and is a life-threatening emergency.

Can you drink too much water?

Yes. The NPS describes hyponatremia, low blood sodium from drinking too much water while losing salt through sweat. Eat salty foods along with water.