Question

A desert cooler cools better on hot dry day or a humid DAY??

Answer 1

Because a desert cooler cools better on a hot dry day because on a hot dry day temperature is high and humidity is less which helps in better evaporation. Due to the higher rate of evaporation it gives better cooling effect.

Answer 2

A desert cooler on hot dry day the water vapor is low and temperature is high which causes evaporation.
Evaporation causes cooling.