My brother-in-law runs multiple half marathons and shorter races throughout each year. Living in the Las Vegas desert, where temperatures exceed 100°F (38°C) through most of the year, long runs are impractical.
You can’t run outside in such extreme heat for more than half an hour, not even in the morning (as temperatures don’t drop below 80°F many days, and that’s already rather hot for running). And running 10+ miles on a treadmill, if the gym will even allow it, isn’t psychologically feasible for most.
So how does he train for half marathons? He runs halfs at around 1:40, so he clearly gets in excellent shape for them. But he attests he certainly doesn’t do long runs.
So what does my brother in law do?
Here’s how he outlined it for me (and I’m describing this some in my words rather than his):