Shuttleworth-Wallace evapotranspiration calculator, sample input, Rosa D. Aguilar, Victor Miguel Ponce, San Diego State University

online_shuttleworth_wallace: Calculation of evapotranspiration using the Shuttleworth-Wallace method

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

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

References:

Aguilar, R. D., and V. M. Ponce. 2013. Evapotranspiration using the Shuttleworth-Wallace method.
Shuttleworth, J. W., and J. S. Wallace. 1985. Evaporation from sparse crops-an energy combination theory, Quarterly Journal of the Royal Meteorological Society, III, 839-855.

Formulas
Δ = (0.00815 T_a + 0.8912)⁷
r_a^c = r_b /(2L)
r_s^c = r_ST /(2L)
R_a = (Δ + γ) r_a^a
R_s = (Δ + γ) r_a^s + γr_s^s
R_c = (Δ + γ) r_a^c + γr_s^c

R_n^s = R_n e^-CL
A = R_n - 0.2R_n^s
A_s = 0.8R_n^s
C_c = 1 / {1 + (R_c R_a) / [R_s (R_c + R_a)]}
C_s = 1 / {1 + (R_s R_a) / [R_c (R_s + R_a)]}

PM_c = [ΔA + (ρ_ac_pD - Δr_a^cA_s) / (r_a^a + r_a^c)] / [Δ + γ {1 + r_s^c/(r_a^a + r_a^c)}]
PM_s = [ΔA + (ρ_ac_pD - Δr_a^s(A - A_s) / (r_a^a + r_a^s)] / [Δ + γ {1 + r_s^s/(r_a^a + r_a^s)}]
λE_c = C_c PM_c
λE_s = C_s PM_s
λE = λE_c + λE_s

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

♦ Air temperature T_a (°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 r_b (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 r_ST (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 r_a^a (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 r_a^s (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 r_s^s (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 R_n (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].

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