Air humidity refers to the amount of water vapor present in the atmosphere - which characterizes whether the air is dry or humid - and varies from day to day. The high amount of water vapor in the atmosphere favors the occurrence of rainfall. With low air humidity, it is difficult to rain.
When we talk about relative humidity, we compare the actual humidity, which is verified by devices like hygrometer, and the estimated theoretical value for those conditions. Relative humidity may vary from 0% (no water vapor in air) The 100% (maximum amount of water vapor that air can dissolve, indicating that air is saturated).
In regions where the relative humidity remains very low for long periods, rainfall is scarce. This characterizes a region of dry climate.
The atmosphere with very high air humidity is a factor that favors the occurrence of rain. Who lives, for example in Manaus knows this well. With humid weather in the Amazonian capital the weather is often rainy.
As we have seen, very low air humidity causes dry weather and a shortage of rainfall.
According to the WHO (World Health Organization), humidity values below 20% pose a health risk, and it is advisable to suspend physical activities, especially from 10 am to 3 pm. THE low air humidity, among other effects on our body can cause nasal bleeding, due to dryness of the mucous membranes.
However, it is also common for people not to feel well on hot days and in places with high air humidity. This is because, with air saturated with water vapor, evaporation of body sweat becomes difficult, inhibiting heat loss. And our body refreshes when the sweat we remove evaporates, removing heat from the skin.