gdd: Growing Degree Days
In rsnotivoli/agroclim: Climatic Indices for Agriculture

Description Usage Arguments Details Value References Examples

Growing Degree Day (GDD) or Winkler index. Useful as a zoning tool to differentiate between grape varieties and climate (Winkler et al. 1974).

1	gdd(mx, mn, dates, lati = NULL, iniday, endday)

`mx`	vector of daily maximum temperature series.
`mn`	vector of daily minimum temperature series.
`dates`	vector of dates corresponding with daily temprature series
`lati`	(optional) numeric value indicating the latitude of location.
`iniday`	initial date in text format ("YYYY-mm-dd"). If "lati" is defined, "iniday" and "endday" are automatically set.
`endday`	last date in text format ("YYYY-mm-dd"). If "lati" is defined, "iniday" and "endday" are automatically set.

Depending on the latitude, the function detects the hemisphere and considers growing season from 1st April to 31st October (northern hemisphere) or from 1st October to 30rd April (southern hemisphere).

The sum of growing-degree-days is returned as a numeric value.

Winkler AJ, Cook JA, Kliwer WM, Lider LA (1974) General viticulture. University of California Press, Berkeley, CA

  gdd(mx = daily_tmax,
    mn = daily_tmin,
    dates = seq.Date(as.Date('1981-01-01'),
            as.Date('2010-12-31'), by ='day'),
            lati = 42)