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Read observed topsoil organic carbon from HWSD onto WHEP's grid.

Source: R/soil_ph.R
read_hwsd_topsoil_soc.Rd

Read the observed 0-30 cm soil organic carbon stock per 0.5-degree cell from the HWSD (Harmonized World Soil Database) map-unit attribute table and raster. Each map unit's stock is the share-weighted mean over its soil components of t_oc * bulk_density * 30 * (1 - t_gravel / 100), and the map units are then averaged over the native HWSD cells inside each 0.5-degree block by the same aggregation read_soil_ph() uses.

This exists to be a benchmark, not a model input: nothing in the carbon pipeline consumes it. HWSD version 1.2's topsoil is 0-30 cm, exactly the layer build_carbon_balance() reports (see its Soil depth section), so it is the only observational anchor available at WHEP's own modelled depth – and it comes out of the archive the carbon balance already reads for clay, so it needs no new download. Note that HWSD2, which inst/scripts/download/download_hwsd.R fetches, layers its topsoil as D1 = 0-20 cm instead; the two are not interchangeable (whep#851).

Usage

read_hwsd_topsoil_soc(
  hwsd_dir = NULL,
  bulk_density = c("measured", "reference"),
  data = list(),
  example = FALSE
)

Source

FAO/IIASA/ISRIC/ISSCAS/JRC (2012). Harmonized World Soil Database version 1.2. FAO, Rome and IIASA, Laxenburg – topsoil defined as 0-30 cm. Stock equation and the bulk-density caveat: Hiederer, R. & Koechy, M. (2011). Global Soil Organic Carbon Estimates and the Harmonized World Soil Database. EUR 25225 EN, Publications Office of the European Union, 79 pp.

Arguments

hwsd_dir

Path to the directory holding hwsd_data.csv and hwsd.bil. Defaults to Sys.getenv("WHEP_HWSD_DIR").

bulk_density

Which HWSD bulk density to use. "measured" (default) takes t_bulk_density, falling back to t_ref_bulk_density where it is absent; "reference" takes t_ref_bulk_density alone. The default is not cosmetic: t_ref_bulk_density is derived from texture and so knows nothing about organic matter, and over the 1,375 map units with t_oc above 6% it averages 1.33 against a measured 0.37, which would inflate a peat soil's carbon stock roughly 3.6-fold. Recorded in method_soc_obs.

data

Optional named list of pre-loaded inputs: cell_polity (lon, lat, at minimum), used both to crop the HWSD raster to the region of interest before reclassification and as the target grid for gap-filling. When absent, cropping and gap-filling are both skipped (documented fallback above).

example

If TRUE, return a small fixture instead of reading data. Defaults to FALSE.

Value

A tibble with lon, lat, soc_obs_mgc_ha (0-30 cm soil organic carbon, Mg C per ha) and method_soc_obs.

Examples

read_hwsd_topsoil_soc(example = TRUE)
#> # A tibble: 1 × 4
#>     lon   lat soc_obs_mgc_ha method_soc_obs
#>   <dbl> <dbl>          <dbl> <chr>         
#> 1 -0.25 -0.25           41.6 measured