When the heat hits So Cal, I double up on my daily minerals and its helped me, haven't cramped on a ride in years. I used to poo poo the electrolyte 'craze' as a waste of money but now I always take a bottle of GU drink on my hot rides (chews on cooler days) and hit the minerals when I get home. Water alone is not enough.

Also, as was said here already, drink water regularly whether you are riding or not- by the time you are thirsty, you are already dehydrated.

Yes there is some acclimation, but I think it is as much a ratcheting up of the water and minerals that needs to take place, and making sure things like clothing choice and sunscreen fit the weather.

Remember, humidity makes it harder for the body to cool itself by sweating, as the sweat does not evaporate as quickly (if at all, yuck). So I don't go on my 'grunt' rides when the humidity and temperature is high. Thankfully that doesn't happen often in So Cal. It's usually on the dryer side here when it is really hot.

I keep hearing good things about Hammer's Endurolytes, gotta try it after my GU powder runs out...