Details

This Demonstration uses a leaf energy balance equation [1]:

,

where is the leaf temperature (°C), is air temperature (°C), is the apparent psychrometer constant (), is the slope of the saturation mole fraction function (, with being the slope of the saturation vapor pressure function and () being air pressure), is absorbed total radiation (), is emissivity of the surface (leaf), is the Stefan–Boltzmann constant (), is convective-radiative conductance (), is specific heat of air (), and is vapor pressure deficit ).

Transpiration () is calculated using an analogy to Fick's law:

,

where , on the axis, is leaf conductance to water vapor (), is saturated vapor partial pressure in the leaf based on , and is the actual partial pressure of water vapor in air based on relative humidity, on the axis.

Reference

[1] G. S. Campbell and J. M. Norman, An Introduction to Environmental Biophysics, 2nd ed., New York: Springer, 1998.