I don't know if humidity has a direct effect but it may well have an indirect effect as hot, humid climates are obviously more hospitable to all sorts of plant growth, from microbes to palm trees, than hot, arid climates. Add that to increased and more direct sunlight and it seems that conditions to deplete chlorine would be ideal.

If you look at the famous "Best Guess Table" you'll see that for various levels of CYA, there are recommended maintenance levels for your FC and recommended shock levels.

At higher CYA levels, once you establish that maintenance FC level, it should be easier to sustain. The explanation and chemistry of how much chlorine is "bound up" with the CYA and yet how it maintains its levels and protection is beyond me.

CYA is a two-edged sword, but if you follow the "Best Guess" table it's easy to maintain a sanitary pool at most CYA levels. Denizens of the South and South East, where summers are really hot and muggy with more intense sun than, say NJ (where we are 100+ hot and muggy right now!) may find, like aylad, that higher CYA levels work for them.