Then you can use the nomographs developed by the Weather Bureau to get lake evaporation. Soil evaporation is more complex. Water vapor has to diffuse from the saturated or capillary zone and is thus dependent on depth to water, hydraulic properties of the soil in addition to the other factors such as temp. The combined process of transpiration and evaporation. Transpiration is defined as the loss of water from plants in the form of vapor.
Transpiration is dependant on plant type, density of vegetation, growth stage.
Penmans definition of ET is water transpired in a unit time by a short green crop covering soil with adequate moisture. It often represents the largest term in many water balance equations. May affect the hydrology of the site if major changes occur. Surface Waters Most of the quantitative measures you see as part of a water budget are for surface water. It is relatively easy to measure compared to the other variables.