Do you think this is the case for the billions of people closer to the equator or in poorer countries?
I could imagine that a place where the nighttime temperatures are in the mid 30s (°C) would not have any cooler water available.
The specific heat capacity of water is about 4kJ/kg/°C so a liter of that cold water can absorb 100kJ of energy in the process of warming up. Once it’s warmed up it can’t do any more cooling.
Your body, when not working hard, produces about 200W of heat. That’s 200J per second.
So that liter of water can absorb your body’s heat output from about 500 seconds of being alive. That’s a little over eight minutes.
So that means the cooling needs for one human for one day can be met by about 170 liters of cold, 50°F water. That’s about 44 US Gallons.
If, however, that water can evaporate - well, the latent heat capacity of vaporization of water is over 2 thousand kJ per kg.
That’s why the wet bulb temperature matters. If water can’t evaporate, that cold water can’t absorb body heat except by just warming up.
Minor quibble, 2000 (kilo)calories / 1 day = ~100 Watts.
At least in my area in central Europe, 10°C would be wildly optimistic in summer. I also presume when submerged in cold water, your body will start heating up, at first. So there is probably only a narrow temperature window for effective cooling. Not to mention, you may have to work and be awake to exchange the water, and being constantly wet for a prolonged time may come with it's own set of health problems.
I imagine there could be a situation with a deadly wet-bulb temperature, but below body temperature, where a large body of water may work to cool the body by convection, no?
The big question though is how long will that lake remain cooler than the air in the face of wet bulb temperatures around body temperature. Thermal equilibrium will win in the end.
So, my thinking would be, if the heat transfer from the body to the water and from water to air (through large surface) is sufficient. In a shaded pool, so all heat transfer from the outside is by convection and conduction.
I guess, if it would be sufficient cooling, you could also "just" drink the water and remove hot sweat from the skin, or dispose urine, instead. In theory, never mind electrolytes.
What if I cover myself in alcohol or gasoline some other easily-vaporized substance? Would that still evaporate at a satisfactory rate when the wet bulb temperature is high?
The tap water in Phoenix can exceed 100 degrees, people will fill a bathtub in the morning so their home A/C and evaporation will cool it off by the evening.
Even river water in India or Southeast Asia can exceed 100 degrees. There is no cold water to wet the rag with unless you have a deep well or refrigeration.
Eww! They probably have chlorine in their water, huh? I imagine, otherwise the microbial game would be out of control.
If you live in a place that gets a bit below freezing every winter -20 is not a problem. I recently survived -33C and have rarely experienced less than -20C, life went on as usual, like going to the store and working.
But if the areas in the article suddenly had -20C that would be a better comparison on how bad it would be.
Was it -33C at the store and at the office?
Try living outside at -33C without the opportunity to go inside.
I'll take heat, every time. Cold is a killer.
-20 with no heating (not carbon friendly in such zones), i will be dead in a few days.