Evaporation: Conversion of liquid water into water vapour.
Evaporation
1. Humidity of air must be less than that of the surface, so that a vapour pressure deficit exists.
- Vapour pressure deficit: if air is dry, there is a steep vapour pressure gradient between a wet surface and the air, so evaporation is rapid.
2. An energy input to convert liquid into water vapour (2480kJ are needed to convert one litre of water at 10 degrees C).
- Energy inputs: solar radiation, sensible heat (temperature), wind: turbulence disperses saturated air.
Other controls on evaporation: Surface moisture availabilty, vegetation cover (shading, increased RH, leaf litter shields surface, reduction of nearsurface wind).
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