if it's over 90 degrees, will stay away from big climbs (more than 4 miles long and 4%+ grade) and stay away from "boonies" rides unless i know for certain
that there is dependable suppport/provisions at (a) key point(s) along the route.
riding on hot days near civilization, i can stop/regroup at a water fountain, gelato place, convenience store for a slurpee, etc at any two of three points: before, during, after.
if it's a longer ride, i've probably prehydrated pretty well and am carrying at least two large bottles. on a really hot day, i'll carry four and resupply/refill
before i really need to
hottest ride i ever did was at valley of fire state park just northeast of las vegas. 108 degrees. had 4 bottles and had prehydrated well the day before.
still took advantage of completely soaking my baselayer, (head) bandana and jersey both times at the visitor center outdoors water source when i twice passed it
during a 25 mile ride. at that temp, you dry completely in less than 10 mins. it feels fantastic going 20mph on the flats or 30mph downhill on a day
that warm when you're (temporarily) soaked. did end up supplementing/dumping entire water bottles over my head more than a few times.