Estimate ET0 by Hargreaves equation.

Estimate reference evapotranspiration (ET0) from a hypothetical short grass reference surface using the the Hargreaves equation.

PET_hg(Tmax, Tmin, Tavg = NULL, Rsi_toa = NULL, lat = NULL, dates = NULL)

Arguments

Tmax

Daily maximum air temperature at 2m height [deg Celsius].

Tmin

Daily minimum air temperature at 2m height [deg Celsius].

Tavg

Daily mean air temperature at 2m height [deg Celsius]. If not provided it would estimated by averaging the Tmax and tmin.

Rsi_toa

Clear sky incoming shortwave radiation, i. e. extraterrestrial radiation multiply by clear sky transmissivity (i. e. a + b, a and b are coefficients of Angstrom formula. Normally 0.75) [MJ m-2 day-1]. If not provided, must provide lat and dates.

lat

Latitude [degree].

dates

A R Date type of a vector of Date type. If not provided, it will Regard the ssd series is begin on the first day of a year.

Value

Reference evapotranspiration ET0 from a hypothetical grass reference surface [mm day-1].