Question

why are the days hot and nights cool in deserts​

Answer 1

Deserts are hot primarily because of a lack of water. When the sun shines on the ground, all of the absorbed sunlight goes into raising the ground's temperature. ... DESERTS ARE COLD AT NIGHT:Because of the lack of water in the ground, and little water vapor in the air, most deserts can get quite cool at night.

Answer 2

The particles of liquid in desert cooler absorb energy from the surrounding to regain the energy lost during evaporation. In summer this is fast. Hence desert cooler cool better in a hot dry day.