Bookmark added to your notes.
View Notes

What is Humidity?

Humidity is the amount of moisture or water vapour or water molecules present in the atmospheric gas. The more is the water in the vapour, the more will be the humidity. Humidity arises from water evaporating from places like lakes and oceans. Warm water evaporates quickly. That’s why, you may find the most humid regions near to warm water bodies in the places like the Red Sea, the Persian Gulf, and Miami.

Here, we will learn about the humidity and its types viz: specific, relative, and absolute humidity.

Types of Humidity

  • Relative humidity

  • Specific humidity

  • Absolute humidity

Relative Humidity

A meteorologist uses the term ‘relative humidity’. The relative humidity is a comparison of the amount of moisture present in the air to the amount of moisture air can hold. The amount of moisture the atmosphere can hold totally depends on the temperature

The formula for the relative humidity is given by:

Relative Humidity =  Actual amount of water in the air/saturated amount of moisture in the air can hold at that temperature

The relative humidity is the function of both water content (moisture) and the temperature.

Point to Remember

The relative humidity is 100% when the air is saturated to water vapour and 0% when no vapour is present in the atmosphere.

Relative Humidity Explained

Think of the atmosphere as a sponge and it is capable of absorbing a fixed amount of water, i.e., a mug of water. Now, think of a rise in temperature as an increase in the sponge size. 

When the sponge has got no water, it means the relative humidity is zero. Now, pour a half bucket of water on the sponge, the relative humidity reaches 50%. 

We know that a sponge saturated with a half mug of water has 50% humidity, on increasing the size of the sponge (increasing the temperature) without adding water further, the relative humidity decreases because the sponge becomes bigger and is capable to take on water vapour; however, the amount of water remains the same.

Soaking a sponge (atmosphere) with water more than the capacity it can hold can lead to dripping; however, it doesn’t symbolize rainfall.  So, how does rainfall occurs?


Rainfall occurs when the rising air cannot hold enough water molecules that are gathered in the form of clouds in the sky.

Specific Humidity

  • We define specific humidity as the mass of water vapour present in a given unit mass of moist air. 

         (Image to be added soon)

  • Specific humidity is equal to the ratio of water vapour mass and the air parcel’s total (including dry) air mass.

  • Specific humidity is also known as the humidity ratio. It does not change with the expansion or compression of an air parcel.

  • We usually express specific heat as grams of vapour per kg of air, or in air conditioning as grains per pound. 

  • The specific humidity has great usage in meteorology. 

Absolute Humidity

We define the absolute humidity in the two following sentences:

  • Absolute humidity is equal to the mass of water vapour per unit of volume of air, i.e., grams of water/cm3of air. The formula for the absolute humidity is given by:

              Absolute humidity = Mass of water/volume in cm3

  • Absolute humidity does not take temperature into consideration.

Absolute humidity in the atmosphere is between zero and approximately 30 gm/m3 when the air is saturated at 30℃

Effects of Humidity

Humidity can cause various uncomfortable conditions, let’s discuss these one-by-one:

  • Bacteria and viruses spread easily in humid conditions because of which people often fall sick especially from respiratory issues. 

  • When the relative humidity goes above 60%, the viruses spread among people, and they get ill.

  • The rise in the moisture content of air leads to the rise in temperature because of which the evaporating rate of sweat from our bodies slows. This slowdown leads to the following problems:

  1. Overheating in our bodies

  2. Exhausts easily, and

  3. Consequences are lethal to health like Altered blood circulation, increased respiration rate, and sweating.

  4. During humidity, higher levels of dust mites and fungi lead to allergies among people.

  5. The spread of airborne chemical contaminants.

  6. Detrimental to asthma sufferers.

Fun Facts

  • In 1783, a person named Horace Bénédict de Saussure was the person to build the first hygrometer with hair. A hygrometer is a humidity measuring device.

  • Humidity provides us with a tonal language

Our vocal cords consist of a pair of mucus membranes that stretch across the larynx (our voice box). These membranes vibrate, controlling the air from the lungs that flow as we speak or sing. It means the level of moisture present in the air affects the elasticity of our vocal cords. 

Singers can tell us how hard it is to carry a tune in a dry environment.

  • As per the latest research, we are better at detecting smells in a humid environment because, in heat and high humidity, there are more water molecules in the air to bind and carry odorous particles into our nostrils. 

FAQ (Frequently Asked Questions)

1. When dew occurs? What is the dew point temperature?

Dew occurs when the relative humidity reaches 100%. 

We define a dew point temperature as an absolute measure of the amount of water vapour in the air. Dew point temperature is the best indicator of how comfortable or uncomfortable your day might go.

2. List some dew points with their conditions.

The below table lists the kind of a day with their respective dew points:

Dew Point

Kind of a Day

Dew Point

Kind of a Day


Perfectly summer day


An uncomfortable day


Comfortable day


Intolerable day


A little steamy day

3. What is saturation?

When gas holds maximum water vapour at a given temperature, the capacity of the air of holding the moisture increases with the rise in temperature.

4. How humidity affects asthma sufferers?

Microorganisms like mould and fungi are known to cause respiratory issues like asthma. In a humid environment because of the easy spread of fungi in the atmosphere, even normal people experience hypersensitivity. 

These microorganisms grow sharply when the relative humidity goes beyond 75% because of which it becomes detrimental to people suffering from asthma.