- Water vapour pressure
Water vapour pressure
is the atmospheric pressure which is exerted by water vapour (water in
its gaseous state). It is one way of measuring the humidity of the air.
At a given temperature, an increase of water vapour in the air corresponds
to an increase in the humidity of the air. Water vapour is supplied to the
atmosphere by evaporation of water from oceans, lakes, wet land surfaces
or from vegetation (transpiration). Water vapour absorbs the sun's radiation.
As a result, the sunlight received at the earth's surface will be more
intense in a drier atmosphere.