The amount of water vapor present in the atmosphere is called humidity. Water vapor, as we know is the gaseous form of water. Humidity comprises only of the vapor particles and not water in any liquid form like fog, or rain. Approximately 50 percent of the total atmospheric vapor is concentrated in the lower atmosphere up to the height of 2000 meters.
Deserts are the areas that have low humidity and tropical regions have high humidity. If we say, the area is humid, that means the humidity of that region is very high. A humid place gives the feeling of wet air. The temperature is very high in a humid place.
There are three primary measurements of humidity. They are Absolute Humidity, Relative Humidity, and Specific Humidity. Absolute Humidity determines the water content of the air and is represented either in grams per cubic meter or grams per kilograms. Relative Humidity is expressed in the form of a percentage. It indicates the amount of absolute humidity relative to the maximum humidity provided the temperature remains the same. Specific Humidity refers to the ratio of water vapor mass to the total moist air parcel mass.
The instrument used to measure humidity is called hygrometers. Humidity also affects the rate of evaporation. Humidity and the rate of evaporation are inversely proportional. As humidity increases, the rate of evaporation decreases. When the humidity is high, the rate of evaporation of sweat from the skin decreases. In this high humidity, the blood brought to the body surface cannot dissipate heat by the process of conduction. When so much blood is dissipated to the outside world, the amount of blood left for the active muscles of the body, brain, and internal organs decrease. The physical strength of the body decreases and fatigue occurs sooner.