Vapour-pressure deficit temperature, the relative humidity and, if possible, the canopy air temperature. We must then compute the saturation pressure. Saturation pressure can be looked up in a psychrometric chart or derived from the Arrhenius equation, a way to compute it directly from temperature is where: To convert between Rankine and degrees Fahrenheit: formula_10 We compute this pressure for both the ambient and canopy temperatures. We then can compute the actual partial pressure of the water vapour in the air by multiplying by the relative humidity [%]: and finally VPD using formula_12 or formula_13 when the canopy temperature is known. Vapour-pressure deficit
Water vapor Water vapor Water vapor, water vapour or aqueous vapor is the gaseous phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Unlike other forms of water, water vapor is invisible. Under typical atmospheric conditions, water vapor is continuously generated by evaporation and removed by condensation. It is less dense than air and triggers convection currents that can lead to clouds. Being a component of Earth's hydrosphere and hydrologic cycle, it is particularly abundant in Earth's atmosphere where it