Science textbooks taught us that only 3% of the Earth’s water is freshwater. However, the majority of this freshwater is not usable as it is frozen in glaciers. Now, will you believe it when someone says that we actually have an unlimited source of freshwater? It is virtually limitless but would take days, weeks, or even months before mother nature process it.
The most abundant source of freshwater is in the atmosphere. It contains about 37.5 trillion of gallons of invisible water, called water vapor. When atmospheric humidity reaches 100%, the air becomes water and then falls into the Earth as rain. This process is known as condensation.
Condensation is the process wherein water vapor in the air becomes liquid. There are two ways for condensation to happen. First is when the air is cooled to its dew point or second, the air becomes saturated with water vapor.
Dew point condensation is what we usually observe early morning. At cold nights, air temperature falls below the dew point. That is why we can see droplets of water on leaves, grass, cars, and windows in the morning despite having no rain the night before.
When will it rain?
Meanwhile, the condensation involving 100% humidity is called water vapor saturation. This is important in the water cycle as evaporated water is sent back to the Earth. Water vapors are formed in the clouds. As more water vapor accumulates, the clouds become saturated and cannot hold anymore. As more water vapor rises, the thinner the surrounding air becomes.
Less air means that there is less pressure between the water vapor and gravity. This pressure is called air pressure. Air pressure is the result of the weight of air molecules above. When there is less air pressure, that means more water vapor in clouds is being formed. You might hear your local weather station talking about “low-pressure areas.” Those areas have cloudy skies that might cause heavy rain.
In normal conditions, water is continuously evaporated and condenses in the atmosphere. When water evaporates, it becomes water vapor. The amount of water vapor in the atmosphere is called humidity. The more water evaporates in a particular area; the more water vapor is formed into the air. The more water vapor there is, the higher is the area’s humidity. Warm places, such as countries near the equator, tend to be more humid because the water in those places evaporates faster.
There are three types of humidity: absolute, relative, and specific.
Absolute Humidity – Absolute humidity is the actual amount of water vapor suspended in the air. They are expressed in “grams of moisture per cubic meter of air.” Sound too sciency, right? Most people will have no idea how humid it feels outside with this measurement. This is why weather reports explain humidity relatively.
Relative Humidity – In layman terms, humidity is often explained in terms of relative humidity. Note that it is not the accurate measurement of atmospheric moisture. This is only invented to express the maximum amount of water vapor the atmosphere can hold regarding the temperature. A reading of 100% relative humidity means that the air is entirely stuffed with water vapor, creating the possibility of rain. Do you observe how and sticky the weather is before it pours?
Specific Humidity – Specific humidity is the ratio of water vapor to the dry air in the area. Specific humidity helps determine the atmospheric pressure.
The most comfortable relative humidity ranges from about 30% to 50%. In humid places, people use de-humidifiers in their houses to suck out excess water vapor in the atmosphere.
Does the air turn into the water at 100% humidity?
Yes and no. For it to rain, meteorologists, or weather forecasters, consider the relative humidity and the surrounding temperature. A 100% humidity reading only means that the air is holding as much moisture at the current temperature. It could be 100% humidity, but at a high temperature, so it will not necessarily rain. It could also be 100% humidity but at a low temperature, and clouds start to condense.
At 100% humidity, you are sure to get dark cloudy skies and a foggy atmosphere. In some parts of the world, humidity does not have to be 100% for it to rain. This phenomenon is called virga.
Did you know? There is a waterfall in Ekom, Cameroon, where the humidity is so high that staying near it would cause you to have difficulty breathing.