There are two distinct terms under the term humidity:
– absolute humidity showing the amount of water vapour in the air (g/m3),
– relative or relative humidity showing the ratio of water vapour in the air at a given temperature in relation to the possible saturation.
Air temperature (°C): -10; -5; 0; 5; 10; 15; 20; 25; 30;
Water content (g/m3): 2,4; 3,4; 4,8; 6,8; 9,4; 12,8; 17,3; 23,1; 30,4;
Relative humidity is the humidity that is scaled to 100% liquid water at a given temperature. Higher temperature air can absorb and store more water, lower temperature can store less.
E.g. 90% relative humidity at -2 °C, means much less water vapour in absolute terms than 50 % relative humidity at +20 °C. (That’s why the cold air in the winter is dry, or the warm air in the summer is more humid.)