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Evaporation And Transpiration

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The Meyer equation, developed from Dalton’s law, is one of many evaporation formulas and is popular for making evaporation-rate calculations:

E=C (ew-ea) K

K=1+0.1w

where

E= evaporation rate, in 30-day month

C= empirical coefficient, equal to 15 for small, shallow pools and 11 for large, deep reservoirs

ew=saturation vapor pressure, in (mm), of mercury, corresponding to monthly mean air temperature observed at nearby stations for small bodies of shallow water or corresponding to water temperature instead of air temperature for large bodies of deep water.

ea=actual vapor pressure, in (mm), of mercury, in air based on monthly mean air temperature and relative humidity at nearby stations for small bodies of shallow water or based on information obtained about 30 ft (9.14 m) above the water surface for large bodies of deep water.

w=monthly mean wind velocity, mi/h (km/h), at about 30 ft (9.14 m) aboveground

K =wind factor

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