I too live in the desert, and I flower in a large outdoor shed. Temps here are already in the triple-digits. I've got a 12,000 or 13,000 btu window A/C unit. Between that and the techniques below, I can usually keep the temps down to around 90ish.
Walked-in earlier this week, and my A/C had kicked the breaker. Luckily, I keep one of my lights on the same breaker, in case something like this happens. Temp was 108 at canopy top.
My ladies are fine.

...In my situation, reverse lighting schedule is out of the question, and I can't afford to cooltube it.
...During more temperate months, I run two lights. But during the summer, I stagger their cycles, (1 on for 6 hours, then the other comes on for 6 hours) I will also raise the lights a few inches.
...High humidity and high heat don't mix. Mold will form quickly. I virtually never foliar spray, except to correct defeciencies and only with lights off or raised. (each drop is like a little magnifying glass) Altho outside humidity is around 8% on average, the moisture from daily 'surface' watering, and plant transpiration provide plenty of humidity. (25%-35%) I also flush well, once a month or so.
...I cut-back on nutes. (3-part Fox Farms) Instead of a once-weekly nute schedule, I go with twice weekly, at half strength. (less stress but same quantity of nutes going in)
...I am a bit aggressive with the fan, too. Nothing shoo's-away heat like wind. I keep the oscillating fan a foot or so below the height of the canopy, pointed at the space just below the lamps, and let the fan push the hot air up and away.
...Sometimes, when extremely hot I'll (horizontally) hang a sheet of 5/8 plexiglass between lights and canopy to provide a heat barrier, aiming the fans between the plexiglass and the canopy.

I got some Silica Blast (Botanicare) which is supposed to toughen-up the plants, and help 'em survive harsher conditions, like drought and heat.
No Silica Blast results from my garden yet, but stinky says she uses it, too...so it's gotta work, lol.