HargreavesSamaniModified Subroutine
private subroutine HargreavesSamaniModified(time, Tavg, Tmax, Tmin, etRad, elevation, pet)
Compute potential evapotranspiration at daily time scale with Hargreaves Samani model modified by Ravazzani et al. (2012) to include an elevation correction factor
References: Hargreaves, G.H., and Z.A. Samani (1982). Estimating potential evapotranspiration. J. Irrig. Drain. Eng., ASCE, 108(3), 223-230
Ravazzani, G., Corbari, C., Morella, S., Gianoli, P., & Mancini, M.. (2012). Modified Hargreaves-Samani equation for the assessment of reference evapotranspiration in Alpine river basins. Journal of irrigation and drainage engineering, 138(7), 592–599.
Arguments
| Type | Intent | Optional | Attributes | Name | ||
|---|---|---|---|---|---|---|
| type(DateTime), | intent(in) | :: | time |
simulation time |
||
| real(kind=float), | intent(in) | :: | Tavg |
average daily temperature [°C] |
||
| real(kind=float), | intent(in) | :: | Tmax |
maximum daily temperature [°C] |
||
| real(kind=float), | intent(in) | :: | Tmin |
minimum daily temperature [°C] |
||
| real(kind=float), | intent(in) | :: | etRad |
extra terrestrial solar radiation [mm/day] |
||
| real(kind=float), | intent(in) | :: | elevation |
elevation above sea level [m] |
||
| real(kind=float), | intent(out) | :: | pet |
potential evapotranspiration [m/s] |
Variables
| Type | Visibility | Attributes | Name | Initial | |||
|---|---|---|---|---|---|---|---|
| real(kind=float), | public, | parameter | :: | HC | = | 0.0023 |
empirical coefficient |
| real(kind=float), | public, | parameter | :: | HE | = | 0.5 |
empirical exponent |
| real(kind=float), | public, | parameter | :: | HT | = | 17.8 |
empirical temperature coefficient |
| real(kind=float), | public, | parameter | :: | c0 | = | 0.817 |
empirical coefficient for elevation correlation |
| real(kind=float), | public, | parameter | :: | c1 | = | 0.00022 |
empirical coefficient for elevation correlation |
Source Code
SUBROUTINE HargreavesSamaniModified & ! (time, Tavg, Tmax, Tmin, etrad, elevation, pet) IMPLICIT NONE !Arguments with intent(in): TYPE(DateTime) , INTENT(in) :: time !!simulation time REAL (KIND = float), INTENT(in) :: Tavg !!average daily temperature [°C] REAL (KIND = float), INTENT(in) :: Tmax !!maximum daily temperature [°C] REAL (KIND = float), INTENT(in) :: Tmin !!minimum daily temperature [°C] REAL (KIND = float), INTENT(in) :: etRad !!extra terrestrial solar radiation [mm/day] REAL (KIND = float), INTENT(in) :: elevation !!elevation above sea level [m] !Arguments with intent(out): REAL (KIND = float), INTENT(out) :: pet !! potential evapotranspiration [m/s] !local declarations. REAL (KIND = float), PARAMETER :: HC = 0.0023 !!empirical coefficient REAL (KIND = float), PARAMETER :: HE = 0.5 !!empirical exponent REAL (KIND = float), PARAMETER :: HT = 17.8 !!empirical temperature coefficient REAL (KIND = float), PARAMETER :: c0 = 0.817 !!empirical coefficient for elevation correlation REAL (KIND = float), PARAMETER :: c1 = 0.00022 !!empirical coefficient for elevation correlation !-----------------------------------------end of declarations------------------ !calculate evapotranspiration IF ( ( Tmax - Tmin) < 0.) THEN CALL Catch ('warning', 'Evapotranspiration', '(Tmax - Tmin) < 0.' ) pet = 0. RETURN ELSE pet = (c0 + c1 * elevation) * HC * etRad * (Tmax - Tmin) ** HE * (Tavg + HT) END IF !conversion from mm/day to m/s pet = pet * millimeter / day RETURN END SUBROUTINE HargreavesSamaniModified