Compute the Century DEFAC annual climate rate modifier.

Annual Century DEFAC rate-modifying factor: the original monthly-Century Poisson temperature factor (which is 1 at the 35 degree optimum) and the precipitation-over-evapotranspiration logistic moisture factor, multiplied and averaged over the supplied series.

Both terms are SoilR's, and so is their pairing. Sierra et al. (2012) Table 1 lists two Century temperature functions: fT.Century1, attributed to Burke et al. (2003), and fT.Century2, attributed to Adair et al. (2008), which is the same expression multiplied by 3.439. This function implements fT.Century1, which carries no such prefactor; the moisture term is fW.Century verbatim; and fT.Century1 * fW.Century is exactly the climate decomposition index Sierra et al. compute in their own Sect. 4.4. The rate constants this modifier scales are SoilR's Century defaults as well (whep::soc_turnover_params: 0.094, 0.35, 0.14, 0.0038 and 0.00013 per week for the structural, metabolic, active, slow and passive pools), so rates and modifier come from one implementation rather than two.

What that does NOT establish is the calibration basis of the weekly rates themselves: whether Parton et al. (1987) publishes them as the maxima reached at DEFAC = 1. If they are not, every Century stock is biased high. That question needs the paper and is open as whep#345.

Usage

soc_rate_modifier_century(temp_c, precip_mm, pet_mm)

Source

Parton, W. J., Schimel, D. S., Cole, C. V. & Ojima, D. S. (1987). doi:10.2136/sssaj1987.03615995005100050015x ; SoilR implementation: Sierra, C. A., Mueller, M. & Trumbore, S. E. (2012). doi:10.5194/gmd-5-1045-2012 . Temperature function (fT.Century1): Burke, I., Kaye, J., Bird, S., Hall, S., McCulley, R. & Sommerville, G. (2003). Evaluating and testing models of terrestrial biogeochemistry: the role of temperature in controlling decomposition. In Models in Ecosystem Science, Princeton University Press. The 3.439-scaled variant fT.Century2, which this function does NOT implement: Adair, E., Parton, W., Del Grosso, S., Silver, W., Harmon, M., Hall, S., Burke, I. & Hart, S. (2008). doi:10.1111/j.1365-2486.2008.01674.x .

Arguments

temp_c

Numeric monthly air (or soil-surface) temperature series (degrees Celsius).

precip_mm

Numeric monthly precipitation series (mm).

pet_mm

Numeric monthly potential evapotranspiration series (mm).

Value

The annual mean of the temperature-by-moisture product (a single numeric).

Examples

soc_rate_modifier_century(
  temp_c = c(15, 25, 35),
  precip_mm = c(40, 60, 80),
  pet_mm = c(50, 70, 90)
)
#> [1] 0.6914709