Initialization of agricultural land

The discrepancies between agricultural statistics used from the Food and Agriculture Organization of the United Nations and geographic patterns for the distribution of forests, crops and agricultural production have made it impossible to consistently simulate land-cover shifts under climate change. Therefore a new global land-cover database was constructed to provide a realistic initialization for 1970 for simulations of global land-cover change with IMAGE 2.4. Important criteria used in the land cover initialization are:

Meeting these criteria guarantees a smooth transition between observed and simulated future land-cover patterns in IMAGE 2.4 runs. Computing initial patterns of agricultural land for the land-cover database consists of several steps. Agricultural land is defined here as land where food, grass and fodder or biofuel crops are cultivated.

  1. The Digitized Soil Map of the World is converted to a 5 x 5 minutes grid classified by the dominant soil type.
  2. The resulting 5 x 5 minutes soil map is aggregated to a 0.5 by 0.5 degree grid, each cell having its own frequency for different soil types.
  3. Each 0.5 by 0.5 degree cell containing at least one soil type, which is not water, is included in the land-cover database. Other cells are excluded. Soil types are used in the terrestrial vegetation model (TVM) to compute agricultural (potential) productivity (see also step 8).
  4. Cells for Greenland and Spitsbergen are added from the Zobler soil data.
  5. Cells are prioritized to become classified as agricultural land in the initialization process. This is done by ranking cells within a country according to their likelihood to be related to agriculture. For this ranking we use the following data sources.
  6. One by one, grid cells within a country are allocated to agricultural land until the total agricultural area within a country agrees with the estimate reported in FAOSTAT. Cells that are classified as protected bioreserves are excluded from the allocation algorithm.
  7. The area within particular agricultural cells is assigned to specific crops. Mixed cropping systems in single cells are allowed. The assignment of specific crops is based on:
  8. The cells classified as agricultural cells are divided into two land-cover categories:
  9. Finally, all remaining cells are assigned the potential vegetation, as simulated by the terrestrial vegetation model.

The above procedure has led to IMAGE 2.4 's grid-specific global distribution of agricultural land for 1970, which allows it to be used for initializing global land-cover simulations (as dealt with in the Land Cover model); it is also consistent with Food and Agriculture Organization of the United Nations data for 1970. The resulting initial data set consists of the gridded crop and pasture distribution and crop yield, with explicit entries for each crop.
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