Flying_steph
People have already lost their engine in hot & sunny Arizona during an idle descent... most probable cause of the failure: icing !
It might look a bit "overkill" to use the carb. heat when the OAT is 42°C, but it's better to be safe than sorry.
I've only come across unexpected carb ice (or what I thought was carb ice) in AZ when flying low through the moisture laden air of the Colorado over by Blythe. 42°C is a bit on the high side for carb ice, I'd suspect something else first like over lean mixture or fouled plugs. I guess its more theoretically possible if you use Mogas, but not totally impossible.
I agree with you that you should always have carb heat in your mind because you certainly can get complacent in AZ. I remember coming home to the UK and being checked out at Shoreham after having spent several months flying in AZ. I nonchalently did the AZ standard 'carb heat on, yes 150 drop, carb heat off' pre takeoff check, and promptly and correctly had my wrist slapped by the instructor. I was made to put carb heat on again and watch the tach for the next minute. Yep, all of us have something to learn in every session of dual.
Alas they still teach not to use carb heat in AZ. I suspect they don't want the students to forget to turn if off and so get dusty unfiltered air into those expensive engines. Hopefully these students get their wrists slapped by the instructors when they head to damper climates.