The Desert Heat

It's hard to explain the affects of full-on desert heat to the people who have not experienced it.  I think it's because everyone has experienced "heat" to some degree or another and they somehow assess those experiences and conclude that it can be uncomfortable, but really how bad could it be.  Bone-dry desert heat under the direct sun is like no other.  Add a backpack, take a typical day in July or August, begin climbing 500 feet in elevation per mile over the course of nine or so miles, and you have a Grand Canyon desert heat experience.  Even with ample water and food it can challenge the most positive of mental attitudes and seem to suck the life right out of you.  If you plan poorly and end up a bit short on water, it can very quickly become a no-kidding life or death situation.  The content presented here is a mix of some information already presented in the Planning and Preparation page, and a little more detailed explanation of the physiological affects of heat on the human body.

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Timing is Everything · Physiological Effects of Heat · Heat-Related Problems · Heat Exhaustion · Heat Stroke ·
Hyponatremia (Water Intoxication) · Desert Cold · Hypothermia

Timing is Everything

Avoidance Behaviors:Courtesy NPS

Avoid the Summer:  The summer is considered to be the months of May through September

  • Inner Canyon temperatures during the summer commonly exceed 105°F. (41°C.), and can get to 115°F. (46°C.) in the shade.  Temperatures under the direct sun are typically 15-20°F. (9-11°C.) hotter.
  • Expect temperatures in the Inner Canyon to be 20-30°F. (12-17°C.) higher than at the Rim.

Got it Made in the Shade:

  • Avoid hiking during the hottest part of the day -- Between 10 a.m. and 4 p.m.
  • Consider predawn starts and early evening finishes, hunkering down in a patch of shade during the hottest part of the day.  Given this approach to travel, a headlamp becomes a vital piece of gear.
  • High heat affects hiking efficiency.  The result can be a halving of the distance you might normally travel in a day.
  • The further down into the Inner Canyon you go, the hotter it gets.


  • It is possible to acclimate the body to desert heat, but it takes a week or two and some effort, which means it probably won't work too well for an impromptu vacation.  But, here's how to go about it if you have the time and it's actually hot enough wherever you are to do it.
  • Target initial hikes to last 2-3 hours in hot conditions, but avoiding the hottest part of the day.
  • Build up endurance to a point where you can handle 10-15 miles in the heat, carrying a load equivalent to your trip backpack and breaking every couple of hours.
  • Augment this by foregoing air-conditioning while at home as it gets the body more accustomed to cooling through evaporation.
  • Acclimatization makes your body better able to handle the heat through more efficient cooling.  This doesn't mean however that it will reduce the amount of water that you'll need to consume.  In fact, just the opposite is true.  More efficient cooling actually increases the amount of water that you will require.
    • Non-acclimatized you'll sweat between 0.5 and 2 quarts (liters) per hour while hiking in the heat.
    • Acclimatized you can expect to sweat between 1.5 and 3 quarts (liters) per hour.

Enjoy it When You've Got It:  Water, that is...

  • When hiking in the heat, and anytime for that matter in the Canyon, take advantage of an available water source.
  • Tank-Up - Hydrate while at the water source and pre-hydrate before heading out.
  • Cool-Down:
    • Drench your clothing with water for its cooling effect -- Do so from a bucket however when using non-flowing water sources.  It avoids polluting the source for wildlife and other hikers.
    • Wet a bandana or a "cool rag" and wear it around your neck as it tends to last longer than a soaked hat or shirt.
    • Make sure you continue to hydrate while in this "cool-down" mode.  Despite feeling cooler, you are still losing moisture through evaporation.

Protect Your Skin

  • With Clothing:
    • Hat (wide-brimmed or ball cap with a back-flap to cover the neck)
    • Long sleeve shirt
    • Long, lightweight pants
  • With Chemicals:
    • Sunscreen – Liberal and periodic application to ALL exposed skin.  Pay specific attention to the nose, ears, cheeks and back of the neck and the backs of your hands.
    • Lip Balm - Liberal and very frequent application.  It tends to disappear quickly in the desert environment.

Protect Your Eyes: From the intense direct and reflected sunlight, and its UV rays.

  • Sunglasses (Polarized with 100% UV blocking protection).
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Physiological Effects of Heat

  • Heat Causes Problems Through the Loss of Fluids
    • For every 1% loss of body weight in fluids there is an approximate 10% loss in a person's mental faculties.
    • At about a 2% loss of body weight in fluids -- For a 200 lb. person that would be 2 lbs or the equivalent of 2 quarts of water -- The sensation of thirst begins.
    • At a 5% loss of body weight in fluids -- 10 lbs. or 5 quarts of water for that same 200 lb. person -- There is a feeling of illness and the potential to become victim to a more serious heat-related condition (e.g., heat exhaustion or heat stroke).
    • At a 10% loss -- That's 20 lbs. or 10 quarts of water -- The victim enters the realm of extreme heat-related danger.
    • With an average-sized person being capable of losing 1.5 to 2 quarts of fluids (3-4 lbs.) per hour when hiking in high heat conditions it is easy to see how quickly one can get into trouble if they fail to keep properly hydrated.  If you are larger, it can be much worse.  The loss of 2 to 8 quarts per hour is not unlikely.
    • A complicating factor in remaining properly hydrated, or recovering from being dehydrated is the fact that a person can only absorb fluids consumed at a rate of 0.5 to 1 quart (liter) per hour.  This means that while hiking in the heat of the Grand Canyon, you will always be dehydrating.
    • A More Graphic Example:
      • It's August 1st and you plan to hike down the Bright Angel trail to Phantom Ranch for a day-hike.  It's about 80° F on the South Rim as all 150 lbs. of you hit the trail.
      • You're in pretty good physical condition and are sweating about one quart an hour as you're hiking down to the Ranch.
      • It takes you about 3.5 hours to hike the 9 or so miles.  The temperature at the Ranch is forecast to be 105° F, so you are experiencing that warming as you walk and probably sweating more than 1 quart an hour, but let's keep the math simple.  So, you will have sweated 3.5 quarts of fluid (or lost about 7 lbs) if you did not consume any fluids during the hike down.
      • But, let's say you did drink a quart of water, even though going down hill was pretty easy and your weren't very thirsty.
      • That 3.5 quarts is equivalent to about 5% of your body weight, and you only added back 1 quart (about 2 lbs) given what you drank while hiking.  That nets out to be about a 3.3% loss in body weight.
      • At that volume of loss you do not have all of your mental capacity, you should definitely be experiencing thirst and you feel slightly ill... It's odd sensation in your stomach, somewhat like nausea, and, you don't really have much of an appetite.  So now you need to think about hiking back out and up to the Rim.  That thought is not particularly appealing but you know you need to get back to the Rim, so you depart.
      • Despite not feeling well you manage a good pace.  You're working hard given the elevation gain and are now sweating 2 quarts of water per hour in the 90-100° F heat.
      • During the 6 hours it takes you to hike out that's a loss of 12 quarts, or 24 lbs.  You were able to drink 6 quarts of water during the hike out, which restored about 12 lbs.  Your total loss during the day-hike is about 17 lbs. or 11% of your body weight.
      • With this volume of fluid loss, it would be unlikely that you could sustain that 6 hour pace.  Your mental faculties and judgment would be significantly impaired.  Your earlier nausea is still with you and perhaps now there's some dizziness and a headache.  Unfortunately, the affect of the loss of fluid is not just limited to a loss of mental acuity and a headache.  There are other serious problems developing.
      • That loss of fluid has made it more difficult for your body to cool itself since there has been progressively less fluid to sweat out.  This causes your body temperature to rise.  Your blood has also become thicker which is making the heart work harder to maintain circulation.
      • Your body's thermo-regulation system is entering very dangerous territory.  For every 1° F rise in body temperature, your heart rate increases by 10 beats per minute (bpm).
        • Normal body temperature is 98.6°F.  Temperatures of 102°F would be considered entering the danger zone for a Canyon hiker.
        • Temperatures in the range of 104 to 105 manifest the condition known as heat stroke... Not good.
        • There is a direct correlation between resting pulse and normal body temperature.  For example: If your normal resting heart rate is 75 bpm, assume a body temperature of around 98.6°F.  While hiking in heat if you measure your resting pulse and find it to be 85 bpm, then your body temperature will be around 99°F.  95 bpm equates to 100°F.  105 bpm to 101°F.   At 115 bpm you would enter the danger zone with a body temperature of 102° F.
      • This is all very nice, but if you are having these problems, you will not be doing this math in your head and it's unlikely that your hiking partners will know your resting heart rate either.  No matter how well conditioned you are a good rule of thumb is that your resting heart rate should never exceed 124 bpm.
      • Normal body temperature is 98.6°F.  Temperatures of 102°F would be considered entering the danger zone for a Canyon hiker.  Temperatures in the range of 104 to 105 manifest the condition known as heat stroke... Not good.
      • Normal respiration is in the range of 12-20 breaths per minute.  Higher rates drive and increase in heart rate.  If you are hiking and cannot speak in full word sentences, you need to SLOW DOWN!  "Polepole"... Remember?
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Heat-Related Problems

The Hazardous 4 H's... (or 3 of them anyway):

A Watchful Eye:  It's important to keep an eye on each other when hiking... No matter where you might be.  It is even more important when hiking in the heat of the Grand Canyon.  Spotting early warning signs of a problem before it gains traction can make or break a trip.

  • Look for the development of an Altered Level of Consciousness (ALOC) in your traveling companion.
    • ALOC is defined as an altered state of awareness and/or disorientation to time, place or person.
    • Signs of its onset can include:
      • Confusion
      • Lethargy
      • Disorientation
      • Impaired Cognition
      • Inappropriate Aggressiveness
      • Hostility
    • It's important to be aware of the person's baseline level of consciousness to be able to assess the significance of a change.  This is a key challenge if your hiking cohorts are like mine.  Everything's relative... Right?
    • If you suspect a change in ALOC, it's time to take a break.
      • Find some shade and let your buddy cool down.
      • Check the resting heart rate.  If elevated treat for the heat-related conditions noted below
      • If you the situation is one that a break will cure, take some time to hydrate and eat some food to provide energy and restore nutrients. 
      • Ensure that your buddy is sufficiently recovered and able to travel before setting out again.
      • More actively monitor them for ALOC and respond promptly should their condition deteriorate.
  • A tool to help assess the seriousness of a situation with a buddy is the AVPU scale.  In escalating seriousness of underlying issues:
  • A - Alertness:  They should be able to answer simple questions (e.g., Time [what day it is?], Person [what's their name?], Place (where are they?]).
  • V - Verbal:  Is the person able to speak?  If they cannot, they're having a problem.
  • P - Painful:  Does the person respond to a stimuli (e.g., a pinch or prick).  If not, they have a serious problem.
  • U - Unresponsive:  Easy to detect.  They hiker will likely be horizontal.  They have a very serious problem.  The kind in which you send someone out of the Canyon to get help.

Note:  This scale is not intended to be used as a guide for determining when it's appropriate to send someone out to get help.  It's merely a tool to create some perspective around the relative and escalating seriousness of issues that might be encountered by your hiking buddies while in the backcountry.  Each case is unique and the expectation is that members of your team have some of the basic skills necessary to assess and respond to health-related issues that might arise.  This doesn't necessarily mean treatment, but it does mean knowing when to get help.

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  • Heat Exhaustion:  Brought on by dehydration and strenuous activity under high heat conditions, it is a condition of mild to moderate shock.  Blood vessel dilation to accelerate cooling can reduce blood pressure and create shock related to low blood volume.
    • Symptoms:
      • Look for ALOC
      • Moist clammy skin
      • Headache
      • Weakness
      • Dizziness
      • Dilated pupils
      • Possible vomiting
    • Physiological Cause:
      • Under high heat conditions, blood vessel dilation can account for a + 0.5 to 1 liter of blood volume.
      • Dilation creates the perception of blood volume loss so the heart rate increases to maintain adequacy of blood pressure.
      • The body will begin to shut-down different systems to maintain it blood pressure.  The shut-down cascade takes place in the following order: stomach, digestive system, skin, kidneys, brain, liver, heart, and lungs. 
    • Treatment: Do things that will increase blood pressure
      • Get the victim into the shade
      • Cool them off -- Wet their clothing
      • Lie them down, elevate the legs to a position slightly higher than the head
      • Slowly drink water with an electrolyte mix.  Administering fluids too quickly can result in vomiting which will make the dehydration condition worse.
      • Eat high energy foods
      • Note:  Symptoms of heat exhaustion will subside once the victim lies down and starts to cool off.  This is NOT the case if the victim has hyponatremia.
    • Avoidance:
      • A simple pinch test on the back of the hand will help assess hydration adequacy.  Pinch the skin, if it doesn't bounce back quickly, you are likely becoming dehydrated.
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  • Heat Stroke: A much more serious condition that occurs as a likely escalation of heat exhaustion.  It is brought on when your body's heat production is greater that its heat loss.  It is life-threatening.
    • Symptoms:
      • ALOC
      • Dry, hot skin
      • Redness in the face
      • Dry armpits
      • High resting heart rate
      • High body temperature
      • Unconsciousness
    • Physiological Cause:
      • The same basic physiological issues as described above for Heat Exhaustion
      • The body's further decline as a result of low fluid content, low blood pressure and an increasing body core temperature as a result of its inability to cool itself.
      • Bottom-line... Your brain is starting to get cooked...  REALLY not good.
    • Treatment:
      • It is imperative to lower the victim’s body temperature.
      • Get them into the shade.
      • If the ground is cool lay them directly on the ground.  If the ground is hot, lay them down on top of a sleeping pad.
      • Remove clothing and begin cooling their body immediately by wetting the skin with water and fanning to enhance evaporative cooling.
      • If low on water, leave clothing on, wet it down and begin fanning.
      • Get help.  This is a serious condition and evacuation is the best solution.
    • Avoidance:
      • STAY HYDRATED... Where have I heard that before?
      • Monitor yourself with the "Pinch Test."
      • If you can avoid Heat Exhaustion, you avoid this.
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  • Hyponatremia (a.k.a, Water Intoxication):  Over-consumption of water and loss of bodily salts as a result of insufficient intake of food.
    • Symptoms:
      • Similar to heat exhaustion
      • Nausea
      • Vomiting
      • Confusion/Disoriented
      • Irritable/Combative in more severe cases
      • Frequent urination
    • Physiological Cause:
      • The result of low blood sodium
      • Brought on by losing more sodium and other electrolytes than you are taking in.
      • The over-consumption of water without an adequate corresponding replacement of body salts and nutrients results in a dilution of key blood components, and affects the functioning of various systems within the body.
      • This is typically what happens if you eat very little over a 2-3 day period, perhaps because dehydration has affected your appetite, but you consume an appropriate amount of water.
      • An interesting consequence of dehydration is that the ill feeling you get at its onset seems to linger for a couple of days even if you have been able to rehydrate yourself.
    • Treatment:
      • Stop hiking find a suitable area for dining and EAT
      • Salty foods are best initially
      • Eat steadily
      • Monitor ALOC and send for help if alertness decreases
    • Avoidance:
      • EAT, EAT, EAT & EAT
      • Eat even if you are not feeling hungry
      • Plan on consuming about twice the amount you normally would while hiking in the Canyon
        • On average you'll consume about 500 calories per hour when hiking downhill.  So, that 3.5 hour hike down to Phantom Ranch, in our example above, will burn up about 1,750 calories.
        • Double that calorie consumption on the uphill leg to 1,000 calories per hour.  That 6 hour jaunt will burn up an additional 6,000.
        • That's 7,750 in total.  It's easy to see how quickly you can get behind if you are not eating enough.  So, be sure to bring adequate amounts of food and EAT it.  No sense carrying it back out.
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The Desert Cold

It's not hard to explain the affects of a cold wind when your clothing is damp or wet.  It can make you shiver just thinking about it.  What's harder to explain is that cold and windy conditions are quite common in the Grand Canyon during the fall, winter and spring.  Yes, even in Arizona.  It is not uncommon to encounter winter driving conditions at the Rims in September and May.  Being prepared for these situations goes back to planning and being sure to have the right gear in your pack.  The potential for hypothermia is just as real in the state of Arizona and in the Grand Canyon as it is just about everywhere else.  The problem is, you just might not think so.   



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The Fourth Hazardous H

  • Hypothermia:  Brought on by being wet or damp and exposed to cold and windy conditions.  Most common when the air temperature are between 30° and 50°F (-1° - 10°C.).  
    • Don't be fooled by the Canyon residing in Arizona.  Or, be led to believe that given all of the precautions about about "Heat" that the hazards of extreme cold aren't particularly important in the Canyon.  The weather there can be highly variable between its 8,000' and 2,500' elevations, and the danger of hypothermia is VERY real.
    • In fact, heat stroke and hypothermia related rescues have been documented as occurring on the same day in the Grand Canyon.  Now that's "variable weather conditions." 
    • Symptoms:
      • Shivering (sustained and potentially progressing toward more violent)
      • ALOC
      • Speech issues (e.g., slow, slurred, incoherent)
      • Stumbling
      • Exhibits poor judgment
    • Physiological Cause: 
      • Evaporative cooling drives the core body temperature down below safe levels.
      • Clinically, hypothermia occurs when the core body temperature falls below 95°F (35°C).  Not that big of a drop from normal, which is 98.6°F (37°C).
    • Treatment:
      • Seek shelter from the wind
      • Get the victim warm:
        • Have them put on dry clothes and extra layers
        • Get them into a sleeping bag
        • Use skin-to-skin contact with another person to transfer warmth in sever cases
      • Have them drink warm/hot fluids
      • Keep them awake if the case is severe
    • Avoidance:
      • Bring the right kind of clothing to ensure you remain dry
      • Have sufficient layers to allow you to adjust to changing temperatures
      • Strip layers to avoid becoming overheated, making your clothes damp with perspiration
      • Select gear for its moisture-wicking properties and that will provide insulation value even when wet.
      • Select wool, polypropylene and other synthetics over cotton.
      • Fuel up -- Eat.  The body burns a lot of calories keeping itself warm, so you need to replace them.  Shivering alone can consume as many as 3,000 calories per hour.  So, EAT.
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We're not doctors, although we enjoy sounding like them in a website.  We recommend that everyone who spends any amount of time in the outdoors take a Wilderness First Aid course and include an appropriate first aid kit in their gear list