Dry heat vs humid heat

[lomiller]

Almost gets to what I'm saying, but I think the idea that sweat works really really well in a dry heat so long as you stay hydrated is the main point. I've seen people suffering from heat stroke/exhaustion many times (in AZ). The reason has never been that its too hot, the reason has always been that they aren't drinking enough water, everyone else doing the same activity in the same area is fine.

So I guess that a dry heat can be more dangerous in that its easy for people who aren't prepared or keeping hydrated to get into trouble. If the question is which one is more miserable, no matter how much you hydrate or prepare, I'll give the point to the mugginess.

Again though, there is no credible reason why it would be harder to keep hydrated in a dry heat.

I also want to point out that evaporation doesn’t just make you feel cooler, you feel cooler because you are having an easier time keeping your body temperature regulated. This is the whole point; you don’t overheat because it’s too warm out you overheat because you can’t get rid of the heat. (déjà vu! AKA, no it’s not the Sun...)

 

[RussDill]

Again though, there is no credible reason why it would be harder to keep hydrated in a dry heat.

I'm not saying its harder to keep hydrated, I'm just saying the consequences of not keeping hydrated are more dire.

 

[pipelineaudio]

I'm a hawaiian that spends a LOT of time in Arizona. Temp for temp, I'd take dry heat any day, but that's not usually how it happens

More often people compare 90 degrees of humidity with 115 of dry heat

nevermind that much of Arizona that easterners call "dry heat" is actually extremely humid, were usually told that somehow 90 degrees is far worse than 115

90 degrees in hawaii can be unpleasant, but with the cool breezes and the giant swimming pool surrounding the islands, you aren't going to die

115 with moderate exertion? Not so healthy, and you feel REAL, and immediate effects.

 

[Woolgatherer]

More often people compare 90 degrees of humidity with 115 of dry heatnevermind that much of Arizona that easterners call "dry heat" is actually extremely humid, were usually told that somehow 90 degrees is far worse than 115

Looking at a relative humidity map I can see what you mean (east of Phoenix) but it's not Florida. Much of Florida is what I'd call extremely humid.

 

[Dymanic]

I'm not saying its harder to keep hydrated, I'm just saying the consequences of not keeping hydrated are more dire.

More dire than hyperthermia?

 

[elipse]

OK, but the OP was talking about California. That's why I thought it important to define where we were talking about when saying most people don't have AC.

I'm pretty sure most people participating in this discussion have AC...even in their cars!

I guess it depends where you are in CA... I'm in the SF Bay Area and I can't think of anyone I know who has AC...EXCEPT in their cars. (If they have cars.)

I've lived in CA (central coast and bay area) all my life, and from the time I'm old enough to remember, I've only lived one place (out of 13) that had AC (and that was only in one room that faced west and baked in the afternoon in summer.)

If you go over the hills, east, then people tend to have AC. I suppose maybe farther south they also have AC as a more general rule.

I was just in Maryland visiting friends, and it was different enough to peak my interest that they had window AC units in every major room of the house.

 

[Travis]

[ETA: According to the chart ApolloGnomon posted, the heat index for 115 F temp at 20% relative humidity is about 120 F--about the same as 90 F at 90% humidity.]

Well, the heat index certainly won't be lower than 115F. And 115F heat index is dangerously hot.

Thank you. I'd just like people east of the Rockies to acknowledge this.

I don’t really buy this. If anything I’d give more credibility to the opposite, because there at least you could argue that evaporation in a dry heat would cause your nose, throat and mouth to feel dry triggering an urge to drink more. I’d need more convincing that either environment inherently triggered more hydration.

What I will concede about a dry heat is that it’s almost away going to be clear and therefore sunny, which can create localized temperatures much greater than the reported air temperature which could be a serious problem.

As I said my new roommate is from New Hampshire and he was totally unprepared for our summer. He notes that the difference between sunny and shade is remarkable and that walking along a paved road with dark asphalt is damned near impossible.

Oh and the other thing he talks about is having to remind himself to drink fluids. According to him you feel thirsty all the time so you sort of eventually stop paying attention to thirst and because he was used to gauging how much fluid he lost by apparent perspiration he ended up in trouble from dehydration.

Or maybe there's a confounding factor. Older people tend to dehydrate more easily (for the same reason--they're not aware of it). I'll speculate that maybe more older people live in dry, hot climates!



But seriously, do you have any evidence that people dehydrate more readily in dry heat?

I've never heard any such a thing, and it doesn't really make much sense. I understand they might not realize they're sweating as much because the sweat is evaporating, but when that happens, it cools the body temp, and they in fact sweat less (than someone sweating unproductively in the same temp at higher humidity).

Well my friend that was in the Marines noted that they had to go out of their way to teach people from the east coast to drink lots of water even when they aren't necessarily thirsty when they did their training at 29 Palms.

So it would appear that the Marine Corps at least thinks it is an issue.

 

[JoeTheJuggler]

[ETA: According to the chart ApolloGnomon posted, the heat index for 115 F temp at 20% relative humidity is about 120 F--about the same as 90 F at 90% humidity.]

Well, the heat index certainly won't be lower than 115F. And 115F heat index is dangerously hot.

Thank you. I'd just like people east of the Rockies to acknowledge this.

In your OP, nothing you said indicated that they think otherwise. In fact, the comment you objected to shows awareness of the role of humidity which sounds like someone who would agree that a 115+ heat index is dangerous.

Again, 115 F heat index is dangerous--even if the temperature is 90 F.

Well my friend that was in the Marines noted that they had to go out of their way to teach people from the east coast to drink lots of water even when they aren't necessarily thirsty when they did their training at 29 Palms.

So it would appear that the Marine Corps at least thinks it is an issue.

Boot camp trainers do the same thing even for natives here. I don't think the issue is nearly as much being unprepared for the climate as is the fact that that sort of training is usually the toughest exertion people have faced in their lives.

I also see distance running trainers stressing hydration to newbies even when neither heat nor humidity is especially bad.

Much of Florida is what I'd call extremely humid.

That blows my confounding factor theory!

 

[CelticRose]

On an unrelated note: they're about to finish a new bridge spanning the Mississippi at St. Louis, and they have to do the final bits at night when the materials are less expanded due to the heat. (I would say when they're contracted, but even at night, it's nothing like the cold they'll face in the winter.)

Reminds me how the sidewalks around here used to buckle before they figured out the correct spacing for the cracks to allow for expansion of the concrete in the heat.

Back on topic, Travis is right about dry heat causing dehydration, although it's really just dry air in general -- hot or cold. I have to apply lotion to my hands every single time I wash them or they will crack and bleed. The dry air just sucks the moisture right out of your skin.

He's also right about people from other areas not having a clue about staying hydrated when in a desert climate. I drink water all day long: I always have a beverage to hand, and I carry a water bottle whenever I go out. People who didn't grow up in a desert usually haven't acquired that habit. Also, when they do get thirsty they tend to reach for beverages with dehydrating ingredients such as caffeine or alcohol.

Also, people from other areas generally don't realize how dangerous heat can be. Not only that, but they're just not acclimated to the heat. A lot of our heat-related illnesses and deaths are caused by stupid tourists thinking they can go hiking up mountains in the 90-100 degree heat without a hat or sufficient food and water. I even recall once they had to do a mountain rescue when it was only in the eighties (cool to us) because some fool from Alaska decided to go on a hike and it was, naturally, way too hot for him.

 

[JoeTheJuggler]

Back on topic, Travis is right about dry heat causing dehydration, although it's really just dry air in general -- hot or cold.

Do you have anything to support this?


To be clear, we're talking about this and not dry, chapped skin.

ETA: FWIW, from the NWS data on heat-related deaths in 2012, the state with the highest number (absolute, not per capita) was Missouri with 34. Second was Illinois with 32. Arizona had 4. The total for the U.S. was 155.

http://www.nws.noaa.gov/om/hazstats/heat12.pdf

I don't know if that year was typical, but it sure seems to blow a hole in the theory that dry heat is more dangerous than humid heat.

ETA again: I've scanned a few more years of that data (it's all in pdf files from 2012 back to 1995--just change the last two digits to the appropriate year), and it sure doesn't look like deaths correlate with states that tend to have dry heat. I'd love to see the same figures given per capita and adjusted for age. Ideally would be data ranked by humidity too (as some have noted, parts of the southwest can be humid sometimes).

 

[CelticRose]

Do you have anything to support this?


To be clear, we're talking about this and not dry, chapped skin.

I mentioned dry skin because it's one of the symptoms of dehydration. See https://www.mayoclinic.com/health/dehydration/DS00561/DSECTION=symptoms

Dehydration occurs when there isn't enough water to replace what's lost throughout the day. Your system literally dries out.

https://www.mayoclinic.com/health/dehydration/DS00561/DSECTION=causes

Because wintertime humidity is so low, what little moisture that is around is quickly sucked up into the air. Moisture also evaporates from your body, leaving your skin, nose, and throat parched.

http://women.webmd.com/home-health-and-safety-9/dry-indoor-air

That last quote is about dry winter air, but the same principle should apply to any low humidity situation.

So, dehydration is caused by not replacing the water you lost throughout the day. You can lose water by simply being in dry air; you don't have to be hot or sweating.

As for the stats on heat-related deaths, access to air conditioning needs to be factored in. States that have high heat tend have more air conditioners per capita. You're not as likely to die if you can get relief from the heat.

ETA: I take a break from the internet on weekends, so I'll get back to this thread on Monday.

 

[Olowkow]

This is a video of some guys throwing cups of water into the air at 40 below zero (C or F, same thing). They are in their shirt sleeves, wearing no special arctic clothing. The air is so dry that the surface capillaries and hair are enough to insulate and keep skin from freezing...for a while.

 

[MetalSeagull]

At equivalent temperatures, humid heat is worse. I remember a trip to the NC zoo many years ago in July. It was in the low 90s. I don't know the humidity, but it's usually around 80%. The polar bear exhibit and the desert pavilion were the only areas that offered any relief. We hung out in the desert room until we cooled off.

 

[Travis]

He's also right about people from other areas not having a clue about staying hydrated when in a desert climate. I drink water all day long: I always have a beverage to hand, and I carry a water bottle whenever I go out. People who didn't grow up in a desert usually haven't acquired that habit. Also, when they do get thirsty they tend to reach for beverages with dehydrating ingredients such as caffeine or alcohol.

This is what I was referring to. In a dry environment you need to constantly be rehydrating and lots of people are not used to that. They are used to drinking fluids a few discrete times a day or just whenever they feel thirsty. What I always stress to new arrivals is that they need to be drinking fluids all the time when it is hot not just when they feel thirsty. It can seem a drag to many but it is a habit we have to get into out here.

 

[Dymanic]

Also, people from other areas generally don't realize how dangerous heat can be. Not only that, but they're just not acclimated to the heat. A lot of our heat-related illnesses and deaths are caused by stupid tourists thinking they can go hiking up mountains in the 90-100 degree heat without a hat or sufficient food and water.

With a particular trend toward stupid young tourists, going by the data here:
http://www.azdhs.gov/plan/report/heat/heat09.pdf

A number of interesting conclusions might be teased out of some of those numbers.

 

[pipelineaudio]

With a particular trend toward stupid young tourists, going by the data here:
http://www.azdhs.gov/plan/report/heat/heat09.pdf

A number of interesting conclusions might be teased out of some of those numbers.

A big factor in that is some sort of weird illusion which seems to makes things look WAY closer than they actually are. It seems like every time you drag out a hiker they say "well, it looked like that mountain was right there...."

I have no idea why this happens but it seems to be a ridiculously common theme

 

[Skeletor]

You sure they're not just paraphrasing Hudson from Aliens?

When I saw this thread...Hudson was exactly who I was thinking of.

As for dry versus humid heat. I lived in Qatar, and during the summer months, it was horrific. During the day the sun was oppressive, and at night it turned into a steamy sweat bath.

 

[GlennB]

As for dry versus humid heat. I lived in Qatar, and during the summer months, it was horrific. During the day the sun was oppressive, and at night it turned into a steamy sweat bath.

Ah, the place that's hosting the World Cup in the summer of 2022? That'll be fun

 

[GlennB]

Meanwhile, is it not possible that the effectiveness of sweating in dry heat reduces water loss relative to the same person in high humidity (who is uselessly sweating buckets)?

Experiment - take many pairs of identical twins and get them equally prepared, hydrated, weighed and blood tested etc. Put one from each pair into a chamber at 35° with 30% humidity and a nice fan. Put the other into an identical chamber but with 80% humidity. Let them sweat it out for a decent time and then weigh and blood test them afterwards.

 

[JoeTheJuggler]

I mentioned dry skin because it's one of the symptoms of dehydration.

But it's certainly not a necessary symptom. Someone drenched in sweat can be dehydrated. Also someone with dry chapped skin (especially from cold dry air) might be perfectly well hydrated.

So, dehydration is caused by not replacing the water you lost throughout the day. You can lose water by simply being in dry air; you don't have to be hot or sweating.

True. You lose water with every exhalation. You can also lose a lot of water from diarrhea.

But the topic of this thread is dry vs. humid heat. [ETA: And this is why I keep using the phrases "ceteris paribus" or "all other things being equal".]

I've yet to see anyone substantiate the claim that all other things being equal, people are more prone to dehydration in dry heat than in humid heat.

As for the stats on heat-related deaths, access to air conditioning needs to be factored in. States that have high heat tend have more air conditioners per capita. You're not as likely to die if you can get relief from the heat.

The states with heat related deaths are by definition all states that have high heat. The assertion I'm contesting is that everything else being equal dry heat is more dangerous than humid heat.