Build per-crop physical cropland extension. — build_crop_land

Convert gridded crop harvested area into per-crop physical land area and aggregate it to commodity-balance items, producing a land extension keyed by (year, area_code, item_cbs_code) for the FABIO footprint model.

The gridded land-use pipeline (build_gridded_landuse()) distributes FAOSTAT harvested area across grid cells; per-crop totals therefore conserve to harvested area, which over-counts multi-cropped land and under-counts fallow. This function turns that harvested area into physical occupied land:

"cropland_apportion" (default): within each cell, the cell's physical cropland (cropland_ha, from LUH2) is split across crops in proportion to their share of the cell's harvested area. Per-crop physical area then conserves to physical cropland rather than to harvested area, capturing both double-cropping (scaled down) and fallow (resting land charged to the crops the rotation supports) at the resolution of the grid.
"intensity_divide": each crop's harvested area is divided by the cell multi-cropping intensity (mc_rainfed, mc_irrigated). Requires multicropping.

Unlike a single country-level cropping-intensity factor applied uniformly to every crop, both methods distribute physical cropland by the actual spatial pattern of each crop.

Coverage note: with "cropland_apportion" the per-country crop total is bounded by the LUH2 cropland layer, which can under-represent perennial or plantation crops (e.g. oil palm, rubber) classified outside cropland; such crops may receive less land than a harvested-area baseline implies.

Usage

build_crop_land_extension(
  gridded_crops,
  gridded_cropland,
  items_prod_full = whep::items_prod_full,
  method = c("cropland_apportion", "intensity_divide"),
  multicropping = NULL
)

Arguments

gridded_crops: Tibble of gridded crop harvested area, the crop-level output of build_gridded_landuse() (built without CFT aggregation). Must have columns lon, lat, year, area_code, item_prod_code, rainfed_ha, irrigated_ha.
gridded_cropland: Tibble of physical cropland per cell. Must have columns lon, lat, year, cropland_ha.
items_prod_full: Crosswalk from production items to commodity-balance items. Defaults to items_prod_full. Must have columns item_prod_code and item_cbs_code.
method: Physical-area conversion method. One of "cropland_apportion" (default) or "intensity_divide".
multicropping: Tibble of per-cell multi-cropping intensity, required for method = "intensity_divide". Must have columns lon, lat, mc_rainfed, mc_irrigated (and optionally year).

Value

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

Examples

gridded_crops <- tibble::tribble(
  ~lon, ~lat, ~year, ~area_code, ~item_prod_code, ~rainfed_ha, ~irrigated_ha,
  0.25, 50.25, 2000L, 1L, 15L, 600, 0,
  0.25, 50.25, 2000L, 1L, 27L, 200, 0,
  0.75, 50.25, 2000L, 1L, 15L, 400, 0
)
gridded_cropland <- tibble::tribble(
  ~lon, ~lat, ~year, ~cropland_ha,
  0.25, 50.25, 2000L, 1000,
  0.75, 50.25, 2000L, 500
)
items <- tibble::tribble(
  ~item_prod_code, ~item_cbs_code,
  15L, 2511L,
  27L, 2805L
)
build_crop_land_extension(gridded_crops, gridded_cropland, items_prod_full = items)
#> # A tibble: 2 × 5
#>    year area_code item_cbs_code impact_u method_land       
#>   <int>     <int>         <int>    <dbl> <chr>             
#> 1  2000         1          2511     1250 cropland_apportion
#> 2  2000         1          2805      250 cropland_apportion