- `DOY` day of year in given year

- `Ta` average temperature of given day (Celsius).

- `precip` precipitation in millimeter per day.

- `PAR` photosynthetically active radiation in MJ/m^2^. Can be calculated 
  from average sunlight irradiance `SRad` in J/s/m^2^ as: 
  `PAR = SRad * 0.47 * 24 * 60 * 60 / 1e6`

- `ET0` evapotranspiration in mm.
