growing_degree_days {cropgrowdays}

Degree days as the sum of capped average daily temperature above a baseline value

Description

Calculate the sum of of degree days (average temperature - base temperature base_temp for each day) during specified dates for a tibble or data frame of daily weather data. Alternatively, a number of days before or after a specific date may be specified. Note that the maximum temperature is capped at maxt_cap when calculating the average temperature.

Usage

growing_degree_days(
  data,
  varmax = NULL,
  varmin = NULL,
  datevar = NULL,
  maxt_cap = 30,
  base_temp = 5,
  na.rm = FALSE,
  ndays = 5,
  startdate = NULL,
  enddate = NULL,
  monitor = FALSE,
  warn.consecutive = TRUE
)

Arguments

data

Tibble or dataframe of daily weather data

varmax

Name of variable containing max temp (default 'maxt')

varmin

Name of variable containing min temp (default 'mint')

datevar

Date variable specifying day (Default: date_met)

maxt_cap

A numeric value set to the temperature considered to be the maximum necessary for plant growth. Maximum temperature is capped at this value for calculating average daily temp (Default: 30)

base_temp

A numeric value set to the temperature considered to be the minimum necessary for plant growth (Default: 5)

na.rm

Used for calculations (Default: FALSE)

ndays

Number of days after/before the start or end date, respectively. Ignored of both the start and end dates are specified (Default: 5)

startdate

Start date of data to be extracted

enddate

Final date of data to be extracted

monitor

For debugging. Prints data and dates. (Default: FALSE)

warn.consecutive

A logical indicating whether to check that dates are consecutive, that none are missing and provide a warning if not (Default:TRUE)

Details

The value returned is the sum of of degree days GDD = \sum_i (Tmax_i + Tmin_i) / 2 - Tbase during specified dates for a tibble or data frame of daily weather data. The maximum temperature Tmax is capped at maxt_cap degrees when calculating average temp (see https://farmwest.com/climate/calculator-information/gdd/ or McMaster, GS, & Wilhelm, WW (1997)). Baskerville, G & Emin, P (1969) provide variations on this method.

The sum of degree days is returned but if there are any missing values, then the value returned will be NA since the default na.rm is TRUE. Note that if there are any missing dates, then a warning is issued but the sum of non-missing values is returned.

If any values are missing, while the sum of degree days may prove useful, it will not include all the data and so will lead to biased underestimates. Hence, in these cases it is unlikely that the value returned is a good estimate but the appropriateness of the estimate will depend on the exact circumstances of the missing data and so this decision is left to the user.

Value

Numeric variable containing the sum of degree days during the period

References

• Baskerville, G., & Emin, P. (1969). Rapid Estimation of Heat Accumulation from Maximum and Minimum Temperatures. Ecology, 50(3), 514-517. doi:10.2307/1933912

• McMaster, G. S., & Wilhelm, W. W. (1997). Growing degree-days: One equation, two interpretations. Agricultural and Forest Meteorology, 87(4), 291–300. doi:10.1016/S0168-1923(97)00027-0

• Anon. (2021). GDD. Farmwest. Retrieved June 15, 2021, from https://farmwest.com/climate/calculator-information/gdd/

See Also

cumulative, daily_mean, stress_days_over, and weather_extract

Examples

## Selected calculations
## library(tidyverse)  # only purrr used here for crop2 example
library(dplyr)
library(purrr)
growing_degree_days(boonah, enddate = crop$flower_date[4], ndays = 3,
                    varmax = maxt, varmin = mint,
                    monitor = TRUE)
growing_degree_days(boonah, enddate = crop$harvest_date[4], ndays = 3,
                    varmax = maxt, varmin = mint,
                    monitor = TRUE)
growing_degree_days(boonah, startdate = crop$flower_date[4],
                    varmax = maxt, varmin = mint,
                    enddate = crop$harvest_date[4], monitor = TRUE)

## Add selected growing degree days at 'boonah' to 'crop' tibble
## using 'map2_dbl' from the 'purrr' package
## Note: using equivalent 'furrr' functions can speed up calculations 
crop2 <- crop |>
  mutate(gddays8_post_sow_7d =
          purrr::map_dbl(sowing_date, function(x)
            growing_degree_days(boonah, startdate = x, ndays = 7,
                                base_temp = 8)),
          gddays_flower_harvest =
            purrr::map2_dbl(flower_date, harvest_date, function(x, y)
              growing_degree_days(boonah, startdate = x, enddate = y)))
crop2