hacal: Calibrate Hargreaves model In sirad: Functions for Calculating Daily Solar Radiation and Evapotranspiration

Description

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

Usage

 1 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].

Details

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

Value

Vector of length 3 containing:

 Ha Hargreaves 'A' coefficient Hb Hargreaves 'B' coefficient Hr2 Coefficient of determination of performed linear regression

Author(s)

Jedrzej S. Bojanowski

References

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

'ha'

Examples

 1 2 3 4 5 6 7 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)

Example output

Ha         Hb        Hr2
0.1732065 -0.1358756  0.8446852

sirad documentation built on May 1, 2019, 7:42 p.m.