Desert regions have very low levels of humidity — often less than 10%. The low levels of water vapour in the air and, indeed, the general scarcity of water makes conditions for life very difficult. Agriculture is practically impossible in such areas and is only really successful in places where levels of humidity tend to be moderate.
Deserts cover 20 percent of the earth’s surface yet are the driest regions in the world. Their lack of humidity is particularly striking because hot areas can hold so much moisture. Rainforests, for instance, combine warm air and high precipitation to produce some of the highest areas of humidity in the world. Deserts, on the other hand, are very dry, so they’re antithetical to most life.
Deserts are prone to having long periods of little to no rain before receiving short bursts of precipitation, but the amount of humidity that does enter the air is rare. The desert air is so dry that the rate of evaporation regularly exceeds the rainfall rate, and the rainfall may even evaporate before it hits the ground.
Desert conditions are also exacerbated by the fact that desert organisms respond to the low humidity by preserving as much water as they can without losing it to evaporation. Many desert plants have evolved a waxy structure called a cuticle that can keep water inside. Small leaves and white hairs that reflect heat may also be strategies for dealing with desert conditions.
Humidity also affects human health conditions in general (some more and some less of course). For example, high humidity levels in the hot temperatures will make the feeling of heat much worse, since the sweat which regulates our body temperature cannot evaporate as quickly. The best relative humidity, that feels the most comfortable is somewhere around 45%. But nor extremely high neither extremely low humidity is good for human health, even though both high and low humidity climate conditions have pros and cons.
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