LECT6 (ET) - AOM 4932 Evaporation and Transpiration...

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AOM 4932 Evaporation and Transpiration Evaporation - change of water from its liquid to its vapor phase Potential Evaporation - climatically controlled evaporation from a surface when the supply water to the surface is unlimited Transpiration - evaporation occurring from plant’s leaves through stomatal openings. Function of stomata is to provide a place where CO 2 can dissolve into water and enter plant tissue. Evaporation unavoidable in this process - driven by same process as evaporation. Ratio of water transpired to that used to form plant matter very large 800. Potential transpiration - Transpiration which would occur if water supply to plant roots and through vascular system to stomata was unlimited. Controlled by climate and plant physiology. Two main forces influencing evaporation rate are: 1. Supply of solar energy to provide the latent heat of evaporation. 2. Ability to transport evaporated water away from surface affected by wind velocity and vapor gradient. Transpiration affected by above plus ability of plant to extract and transmit water from soil to stomata. We will discuss four methods of estimating evaporation from free water surfaces (or completely saturated soil) 1) energy balances methods 2) mass transfer or aerodynamic methods 3) combination of energy and mass transfer (Penman) 4) pan evaporation data 1) Energy Balance Method Assumes energy supply the limiting factor. Consider energy balance on a small lake with no water inputs or evaporation pan: heat stored in system sensible heat transfer to air H s R n Q e G net radiation energy used in evaporation heat conducted to ground (typically neglected)
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This note was uploaded on 03/27/2012 for the course AOE 4643 taught by Professor Graham during the Fall '11 term at University of Florida.

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LECT6 (ET) - AOM 4932 Evaporation and Transpiration...

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