HUMIDITY

One of the other important chemicals in the air is water (H2O). You can feel it around you when it’s hot and sticky. Sometimes you can see it around you as mist or fog. The most common way you can see water in the air is by looking up at the clouds. Clouds are water molecules bunching together and reflecting light.

Humidity is the amount of water vapour in the air.

Water can exist in three forms: solid, liquid, and vapour.

Humidity is affected by winds and by rainfall

Did you know that you release water vapour when you breathe? Plants do this too but it is called transpiration.

Transpiration is the process by which water moves through trees and plants, from their roots to the small openings on the underside of their leaves, where it changes to water vapour and is released to the air.

Transpiration is part of the Water Cycle. The Waitakere Ranges have more rainfall than in Auckland city.

Forests like the Waitakere Ranges, create habitats that are natural ecosystems important to our world.

The Waitakere Ranges influence our local climate, the trees affect the climate by reducing the speed of the wind, lowering temperature highs and lows and increasing atmospheric humidity. Forests are like amazing machines working to create a healthy atmosphere, purifying the air, they absorb nasty gases like CO2 and produce oxygen.

The winds influence:

If it is hot outside (the temperature) and the humidity (water vapour in the air) is low, but the wind is blowing, there will be more evaporation (water turning from liquid to vapour), making everything very dry, which is not good for the trees.

The rains influence:

A high water vapour content in the air helps to produce clouds and rain (precipitation).

You can do this experiment to see how humidity works:

On hot days in Summer it can feel even hotter when it's really humid outside.

Why?

Try this experiment?

Soak a cloth in some warm water.
Twist the clot to wring out the water (make sure that no more water can drip out of the cloth, you might need help to wring it out enough).
Make sure that the cloth is still warm, after you have wrung it out - Feel the warmth of the cloth on your skin.
Wave the cloth around in the air for a little while, like a flag.
When you're finished, feel the cloth against your skin again.
Does it feel cooler?

It should.

As moisture evaporates, it carries heat with it. When you waved the cloth around in the air, water evaporated from it, taking heat with it and making the cloth cooler. A similar thing happens in the air. When water vapour remains in the air as humidity, it makes the temperature feel warmer. As the humidity lowers, the air feels cooler!

This website has good easy to understand information on the water cycle

http://www.kidzone.ws/water/index.html

Relative Humidity in Titirangi (Auckland)

Just like a paper towel, the air can hold water. That’s how clouds form! Relative humidity is a measure of how much water does the air hold, compared to how much water it could possibly hold at that temperature and pressure. High relative humidity means that the air is nearly full of water and it can’t take up much more (that’s when the washing takes longer to dry outside) while low relative humidity means that the air can take more water from the surfaces (making it easier to dry the clothes outside). Because Auckland is surrounded by water, the relative humidity tends to be high (almost always above 60%). In other cities, like Christchurch, relative humidity around 40% is not uncommon. The plot below shows the relative humidity (in percentage) of the air in Titirangi over the past few days. (Copyright: Data from Open Weather Map)

HUMIDITY

Relative Humidity in Titirangi (Auckland)

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