evapD (Granger, 1989; Granger and Pomeroy, 1997)
This module defined in ClassevapD, calculates the evapotranspiration using daily values from after snowmelt to fall snow cover.
Other evaporation algorithm available is Priestley-Taylor.
Observations
- none
Variables
- hru_evapD (mm/d) - average depth of evaporation from an HRU.
- hru_cum_evap (mm) - cumulative evaporation – calculated as the sum of the daily estimates of hru_evap.
- evap_G () - relative evaporation from Granger.
- evap_D () - relative drying power from Granger.
- hru_actet (mm/int) - actual evapotranspiration over the HRU. Evaporation and evapotranspiration are limited by the amount of soil moisture available.
- hru_cum_actet (mm) - cumulative actual evapotranspiration over the HRU.
Parameters
- evap_type (flag) - Evaporation method for HRU, 0 - Granger, 1 - Priestley Taylor.
- Ht (m) - crop height.
- hru_elev (m) - altitude.
- basin_area (km^2) - basin area.
- hru area (km^2) - HRU area.
- F_Qg () - fraction to ground flux. Qg = F_Qg*Rn.
- inhibit_evap (flag) - 0/1 enable/inhibit.
Variable Inputs
- hru_tmean (obs) (°C)
- hru_umean (*) (°C)
- hru_eamean (obs) (°C)
- RnD (*) (mm/m^2*d)
Granger Daily calculation
- Ea = fdaily(u, Ht)*(e*-ea)
- D = Ea/(Ea+(Rn-Qg-Qs))
- G = 1/(0.793 + 0.2*exp(4.902*D) + 0.006*D
- E = (delta(t)*G*(Rn-Qg-Qs) + gamma(Pa, t)*G*Ea)/( delta(t)*G + gamma(Pa, t))
where t, u and ea are the mean of interval values and e* is calculated using the mean daily temperature t.
Priestley Taylor
- 1.26*delta(t)*(Rn-Qg-Qs)/(( delta(t) + gamma(Pa, t))f or positive incoming net radiation,
where values are interval. Evaporation is zero when incoming net radiation is <= 0.0.
Atmospheric Pressure
- P = P0*exp((293.0-0.0065*elevation)/293.0, 5.26),
where P0 = 101.3.