Build a per-crop physical land extension from CROPGRIDS. — build_cropgrids_land

Convert FAOSTAT harvested area into per-crop physical cropland using CROPGRIDS, then return a land extension keyed by (year, area_code, item_cbs_code) for the FABIO footprint model.

CROPGRIDS (Tang et al. 2024) reports, per crop and country, both harvested area and crop (physical) area for 2020. Their ratio is a genuinely per-crop multi-cropping correction — e.g. rice ~0.81 (heavily double-cropped), most other crops ~0.95-1.0 (single-cropped) — which a single country-level cropping-intensity factor, or a cell-level apportionment by harvested share, cannot reproduce. This function applies that per-(area, item) physical / harvested ratio to WHEP harvested area in each year: \(physical = harvested \times (physical_{cg} / harvested_{cg})\).

Note: CROPGRIDS physical area is the land where each crop actually grows; it excludes fallow land (unlike fallow-inclusive cropland-apportionment), so totals are typically a few percent below harvested area.

Coverage: crops absent from CROPGRIDS (notably the FAOSTAT fodder items and a few minor crops) have no physical/harvested ratio and fall back to a ratio of 1 (physical = harvested, no multi-cropping correction). The share of harvested area hitting this fallback is reported via a warning.

Usage

build_cropgrids_land_extension(
  harvested = NULL,
  cropgrids = NULL,
  source = c("cropgrids", "cropgrids_fallow"),
  max_ratio = 1.5,
  min_cropgrids_ha = 100
)

Arguments

harvested: Tibble of harvested area with columns year, area_code, item_cbs_code, harvested_ha. If NULL, built from get_primary_production() (unit == "ha").
cropgrids: Tibble of national crop areas with columns area_code, item_cbs_code, physical_ha, harvested_ha. If NULL, the remote pin selected by source is read via whep_read_file().
source: Which CROPGRIDS pin to read when cropgrids is NULL: "cropgrids" (cropgrids-land: physical crop area, excludes fallow) or "cropgrids_fallow" (cropgrids-fallow-land: physical area with rotational fallow attributed to crops by attribute_fallow_to_crops()). Also recorded in method_land.
max_ratio: Cap on the per-area physical/harvested ratio (default 1.5). CROPGRIDS occasionally pairs a normal physical area with a near-zero harvested area for minor/aggregate crops, yielding a spurious ratio in the hundreds; physical area cannot realistically exceed harvested by more than the fallow share, so the ratio is clamped here.
min_cropgrids_ha: Minimum CROPGRIDS harvested area (ha, default 100) for a per-area physical/harvested ratio to be trusted. CROPGRIDS leaves rounding stubs of a few hectares for marginal crop-country pairs whose ratio is unreliable; below this floor the crop falls through to the global per-item ratio instead.

Value

A tibble with columns year, area_code, item_cbs_code, impact_u (physical land area in hectares), and method_land.

Examples

harvested <- tibble::tribble(
  ~year, ~area_code, ~item_cbs_code, ~harvested_ha,
  2000L, 33L, 2511L, 1000,
  2000L, 33L, 2807L, 500
)
cropgrids <- tibble::tribble(
  ~area_code, ~item_cbs_code, ~physical_ha, ~harvested_ha,
  33L, 2511L, 990, 1000,
  33L, 2807L, 400, 500
)
build_cropgrids_land_extension(harvested, cropgrids)
#> # A tibble: 2 × 5
#>    year area_code item_cbs_code impact_u method_land
#>   <int>     <int>         <int>    <dbl> <chr>      
#> 1  2000        33          2511      990 cropgrids  
#> 2  2000        33          2807      400 cropgrids