Everyone knows that during the day the desert is hot, very hot. Temperatures in excess of 100 degrees fahrenheit are not uncommon. Yet at night, the same deserts can have temperatures fall into the 40s or 50s? Why?

Deserts cool down so rapidly because there is not enough vegetation and trees to retain the heat through the night. Also, due to low humidity, there is no insulation, so they cool down at night very quickly.

Other biomes are insulated by their humidity (water vapor in the air). The temperate deciduous forest may have 80 percent humidity or more during the day. This water reflects and absorbs sunlight and the energy it brings. At night the water acts like a blanket, trapping heat inside the forest. Since deserts usually have between 10 and 20 percent humidity, they heat up quickly during the day, and cool down rapidly at night.

For the very same reason, deserts heat up quickly once the sun rises in the morning.