Why is the desert so lifeless compared to the tropical places if its more comfortable?
All life on earth needs water, and the lack of water in deserts puts a limit on the amount of life that can exist there as compared to a more humid climate. Organisms can survive in hot, humid climates because they are adapted to those conditions. We humans, however, evolved in a tropical semiarid climate and cool ourselves by the evaporation of sweat. Evaporative cooling is much more efficient in arid climates, meaning that we feel cooler in the desert even though the actual air temperature may be higher than in a tropical rain forest. The “heat index” takes both temperature and humidity into account to calculate how well the human body is able to cool itself. Air can be saturated with water vapor at any temperature, so there is no upper temperature limit to 100% humidity, but the highest heat index ever recorded was 176F/80C (air temperature of 108F/42C and relative humidity of 67%). First link is a discussion of the heat index, second includes heat index charts as well as the mathem
