sirad (version 2.3-1)

hacal: Calibrate Hargreaves model

Description

Function estimates Hargreaves model coefficients 'A' and 'B' based on reference data

Usage

hacal(lat, days, rad_mea, extraT=NULL,tmax, tmin)

Arguments

lat

Latitude in decimal degrees.

days

Vector of class 'Date' of length n.

rad_mea

Vector of length n containing reference (e.g. measured) solar radiation [MJm-2].

extraT

Optional. Vector of length n of extraterrestrial solar radiation [MJm-2]. If 'NULL' then it is calculated by the function. Providing extraterrestrial solar radiation speeds up the computation

tmax

Vector of length n containing daily maximum temperature [C].

tmin

Vector of length n containing daily minumum temperature [C].

Value

Vector of length 3 containing:

Ha

Hargreaves 'A' coefficient

Hb

Hargreaves 'B' coefficient

Hr2

Coefficient of determination of performed linear regression

Details

Function estimates Hargreaves model coefficients 'A' and 'B' based on reference (e.g. measured) solar radiation data. It performs a linear regression.

References

Hargreaves, G.H., Samini, Z.A. 1892. Estimating potential evapotranspiration. J. Irrig. Darin. Eng., ASCE 108 (3), 225-230.

See Also

'ha'

Examples

data(Metdata)
tmax <- Metdata$meteo$TEMP_MAX
tmin <- Metdata$meteo$TEMP_MIN
days <- Metdata$meteo$DAY
lat <- Metdata$LATITUDE
rad_mea <- Metdata$meteo$RAD_MEA
hacal(lat=lat,days=days,rad_mea,extraT=NULL,tmax=tmax, tmin=tmin)