online_shuttleworth_wallace:   Calculation of evapotranspiration using the Shuttleworth-Wallace method

 Solar evaporator at Red Rock Ranch, Panoche Water District, Fairbaugh, California

 Formulas Δ = (0.00815 Ta + 0.8912)7 rac = rb /(2L) rsc = rST /(2L) Ra = (Δ + γ) raa Rs = (Δ + γ) ras + γrss Rc = (Δ + γ) rac + γrsc Rns = Rn e-CL A = Rn - 0.2Rns As = 0.8Rns Cc = 1 / {1 + (Rc Ra) / [Rs (Rc + Ra)]} Cs = 1 / {1 + (Rs Ra) / [Rc (Rs + Ra)]} PMc = [ΔA + (ρacpD - ΔracAs) / (raa + rac)] / [Δ + γ {1 + rsc/(raa + rac)}] PMs = [ΔA + (ρacpD - Δras(A - As) / (raa + ras)] / [Δ + γ {1 + rss/(raa + ras)}] λEc = Cc PMc λEs = Cs PMs λE = λEc + λEs

 RECOMMENDED PARAMETER RANGES: [Main Page]     [Sample Input]

♦ Air temperature Ta (°C):  15 - 35

Changing the air temperature from 15°C to 35°C changes the evaporation from 1.05 cm d-1 to 1.20 cm d-1 [Sample data input set].

♦ Mean boundary layer resistance per unit area of vegetation rb (s m-1):  5 - 50

Changing the mean boundary layer resistance from 5 s m-1 to 50 s m-1 changes the evaporation from 1.1232 cm d-1 to 1.124 cm d-1 [Sample data input set].

♦ Mean stomatal resistance rST (s m-1):  200 - 800

Changing the mean stomatal resistance from 200 s m-1 to 800 s m-1 changes the evaporation from 0.9656 cm d-1 to 1.2404 cm d-1 [Sample data input set].

♦ Projected area of leaf per unit ground area L (dimensionless):  0 - 5

Changing the projected area of leaf per unit ground area from 0.1 to 5 changes the evaporation from 0.92 cm d-1 to 1.167 cm d-1; the evaporation from the plant canopy changes from 0.067 cm d-1 to 1.0583 cm d-1; and the evaporation from the substrate changes from 0.8536 cm d-1 to 0.1091 cm d-1 [Sample data input set].

♦ Aerodynamic resistance between canopy source height and reference level raa (s m-1):  21 - 84

Changing the aerodynamic resistance between canopy source height and reference level from 21 s m-1 to 84 s m-1 changes the evaporation from 1.1774 cm d-1 to 1.0848 cm d-1 [Sample data input set].

♦ Aerodynamic resistance between the substrate and canopy source height ras (s m-1):  64 - 256

Changing the aerodynamic resistance between the substrate and canopy source height from 64 s m-1 to 256 s m-1 changes the evaporation from 1.147 cm d-1 to 1.11 cm d-1 [Sample data input set].

♦ Surface resistance of the substrate rss (s m-1):  0 - 2000

Changing the surface resistance of the substrate from 0 s m-1 to 2000 s m-1 changes the evaporation from 1.1236 cm d-1 to 1.0902 cm d-1 [Sample data input set].

♦ Net radiation flux into the complete crop Rn (W m-2):  200 - 600

Changing the net radiation flux from 200 W m-2 to 600 W m-2 changes the evaporation from 0.7089 cm d-1 to 1.5382 cm d-1 [Sample data input set].

♦ Vapor pressure deficit at reference height D (Pa):  0 - 2000

Changing the vapor pressure deficit from 0 Pa to 2000 Pa changes the evaporation from 0.8293 cm d-1 to 1.4178 cm d-1 [Sample data input set].

♦ Extinction coefficient C (dimensionless):  0.7

Changing the extinction coefficient from 0.5 to 0.9 changes the evaporation from 1.1241 cm d-1 to 1.1233 cm d-1 [Sample data input set].

♦ Atmospheric pressure P (Pa):  100000 - 101325

Changing the atmospheric pressure from 60000 Pa to 101325 Pa changes the evaporation from 1.3427 cm d-1 to 1.1236 cm d-1 [Sample data input set].