Blaney-Criddle equation
Encyclopedia
The Blaney–Criddle equation (named after H. F. Blaney and W. D. Criddle) is a method for estimating reference crop evapotranspiration
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...

.

Usage

The Blaney–Criddle equation is a relatively simplistic method for calculating evapotranspiration
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...

. When sufficient meteorological data is available the Penman–Monteith equation is usually preferred. The Blaney–Criddle equation is however ideal when only air temperature data is available for a site.

Given the coarse accuracy of the Blaney–Criddle equation it is recommended that it is used to calculate evapotranspiration
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...

 for periods of one month or greaterhttp://www.fao.org/docrep/X0490E/x0490e06.htm.

The equation calculates evapotranspiration
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...

 for a 'reference crop', which is taken as actively growing green grass of 8–15 cm heighthttp://www.fao.org/docrep/S2022E/s2022e07.htm.

Equation

ETo = p ·(0.46·Tmean + 8)

Where:

ETo is the reference evapotranspiration [mm day−1] (monthly)

Tmean is the mean daily temperature [°C] given as Tmean = (Tmax + Tmin )/ 2

p is the mean daily percentage of annual daytime hours.

Accuracy and bias

Given the limited data input to the equation, the calculated evapotranspiration
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...

 should be regarded as only broadly accurate. Rather than a precise measure of evapotranspiration
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...

, the output of the equation is better though of as providing an order of magnitude http://www.fao.org/docrep/S2022E/s2022e07.htm

The inaccuracy of the equation is exacerbated by extreme variants of weather. In particular evapotranspiration
Evapotranspiration
Evapotranspiration is a term used to describe the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere. Evaporation accounts for the movement of water to the air from sources such as the soil, canopy interception, and waterbodies...

 is known to be exaggerated by up to 40% in calm, humid, clouded areas and depreciated by 60% in windy, dry, sunny areashttp://www.fao.org/docrep/S2022E/s2022e07.htm.

See also

  • Jensen–Haise equation (M. E. Jensen and H. R. Haise, 1963)
  • Penman–Monteith equation

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK