Why is humidity important?
People often mention humidity in relation to weather forecasts, but why do we need to know about it and why is it important?
There are three main areas surrounding meteorology that humidity has an important influence upon:
Water vapour is one of the key greenhouse gases. Indeed, without it we would not be able to live on Earth. A greenhouse gas allows the sun's energy to pass through and warm the Earth. The Earth then radiates energy away but some of this is trapped on the way out by greenhouse gases adding extra warmth. The average temperature of the Earth at the surface is 14.5 °C. Without any greenhouse gases it would be around -18°C. Water vapour is the most prolific greenhouse gas in the atmosphere.
Water vapour is important for moving energy around the Earth. Energy from the sun is used to evaporate water into water vapour. This water vapour can easily be move around the atmosphere. At some point the water vapour condenses back into water, releasing energy as heat. This is a key component in the formation of storms.
The amount of water vapour present plays a role in the amount of rainfall since it is dependent upon the energy balance and the availability of small particles to develop rain drops. In very heavy rainfall events, where all of the water in the atmosphere is often rained out, the water vapour content does govern the amount of rainfall. A heavy rainfall event in high specific humidity conditions is likely to result in more rainfall than in low specific humidity conditions.
Humans and animals
Humidity can affect human health through governing thermal comfort. In warm, high RH situations the body finds it hard to keep cool which can lead to dangerous levels of over heating. Severe illness or even death can result from heat stress or triggering of other problems with breathing, heart attacks or strokes.
It also affects animals. High RH in warm conditions can be a problem for both dairy and beef cattle because the animals' bodies are under stress and they eat less.