It seems once again that folks underestimate their environment leading to another tragedy.
Trekking in 110F or 43C heat in the desert isn't a good idea in the first place no matter how much water you carry. Typically for 3-4 hrs in these temperatures a minimum would be 8-10lbs of water to carry and a conscious effort is required to down at least 2-3lbs of water per hour.
The difference between this poor lad suffering from terminal hyperthermia, whilst the rest of his group survived could have easily just been the difference in the colour of clothing worn or even not wearing a wide brimmed hat.
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Just as the correct clothing is important in cold climates, it is just as important in very hot climates. i.e. wearing thick wollen socks and using thick felt undersoles in the boots together with wearing string vests in the desert is just as important as wearing them in the arctic.
It sounds as if the group failed to notice the early onset of the victims hyperthermia as well.