Question

why desert a cooler cool better than on a hot dry day ?????

Answer 1

bcoz in hot day, temp. is high and temp. is directly proportional to rate of evaporation. so due to high temp. rate of evaporation increases. As a result desert cooler has a better effect on a hot dry day.
HOPE... U GOT IT

Answer 2

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.