get_growing_season_climate: Truncate weather data to one growing season

In ebimodeling/biocro: Modular Crop Growth Simulations

Truncate weather data to one growing season

Description

Attempt to restrict a year of weather data to a growing season; not intended to be a general-use function (see below for a detailed discussion of its shortcomings).

Usage

  get_growing_season_climate(climate, threshold_temperature = 0)

Arguments

climate	A data frame representing one year of weather data, typically intended to be passed to run_biocro as its drivers argument. This data frame must have columns for the day of year (doy) and the air temperature in degrees C (temp).
threshold_temperature	The value of air temperature in degrees C to use when locating the beginning and end of the growing season.

Details

DISCLAIMER: This function is included here primarily to reproduce the output of older BioCro calculations, where it used to be hard-coded into every simulation. It has several severe limitations which are discussed below, and is not intended to be a general-use function for subsetting weather data.

To determine the growing season, this function locates its beginning and end based on the air temperature data. The start of the growing season is set by the last day in the first half of the year where the air temperature is below (or equal to) the threshold temperature, or day 90, whichever is later. The end of the growing season is set by the first day of the second half of the year where the air temperature is below (or equal to) the threshold temperature, or day 330, whichever is earlier.

This is not a sophisticated function and no attempt is made to ensure that the output is reasonable. For example, if the air temperature never exceeds the threshold value, a growing season beginning on day 183 (the last day of the first half of the year) and ending on day 184 (the first day of the second half of the year) will be returned. If the air temperature always exceeds the threshold value, the growing season will go from day 90 to day 330.

This function also assumes that the air temperature generally increases early in the year and generally decreases later in the year, and is only applicable for locations where this is the case. It is therefore unlikely to work properly in the Southern Hemisphere or the tropics.

In general, an appropriate threshold temperature would depend on the species that is being modeled. For a perennial grass, the growth season might be said to begin after the last freeze, requiring a threshold temperature of 0 degrees C. Of course, this is an oversimplification of a complicated biological process, and a plant has no way of knowing when it has experienced the last freezing day of the year.

On the other hand, annual crops like maize or soybean are not typically sown until conditions are warmer and might require a higher threshold. Again, this is an oversimplification of a complicated process. Farmers typically take trends in temperature, historical data, soil conditions, and weather predictions into account when deciding to sow, and they may also be constrained by external factors like the availability of machinery, seeds, or labor.

It should also be noted that as the threshold temperature increases, the likelihood of that air temperature occurring at night, even in the middle of summer, also increases. Consequently, if the threshold is set too high, an unrealistically short growing season may be predicted. For example, calling get_growing_season_climate(weather$'2005', 15) returns a two-day growing season (days 183–184) because the temperatures in the late night of day 183 and the early morning of day 184 both dip below 15 degrees C.

Thus, the logic encoded here is an oversimplification in several ways. It is likely not appropriate in many situations, and more tailored approaches would be required.

Value

A copy of the climate data frame truncated to the growing season.

Examples

  # Truncate the 2002 Champaign, Illinois weather data to an estimated growing
  # season
  truncated_weather <- get_growing_season_climate(weather[['2002']])

  # We can see which days were included
  list(
    doy_start = min(truncated_weather$doy),
    doy_end = max(truncated_weather$doy)
  )

ebimodeling/biocro documentation built on April 23, 2024, 7:06 p.m.