So sorry about your crab apple tree, Ms. Paben.
You say it just happened. What do you observe has changed since it leafed out in the Spring?
In the photo you sent, I see sprouts at the base of the tree; that tells that your tree is under stress. The leaves look brown and crispy. (Severe leaf scorch? Here’s information about that topic for you: https://extension.colostate.edu/topic-areas/yard-garden/leaf-scorch-2-911/)

I do not see a mulch ring around the base of the tree that would help the soil to retain moisture. The rock mulch is reflecting and retaining heat during this month’s heat waves and dry weather.

If only plants could talk...we’d know exactly what they need. But plants cannot talk in a way I can understand them, Ms. Paben, so this bulletin I am sending you will give you lots of research-based information from Colorado State University Extension about how, when and why to water:
https://extension.colostate.edu/topic-areas/yard-garden/watering-a-home-landscape-during-drought-7-240-2/

Don’t forget about winter-watering: https://extension.colostate.edu/topic-areas/yard-garden/fall-and-winter-watering-7-211/

If you have additional questions, please do not hesitate to contact CSU Extension again.

Stay cool!