### Land use

#### Indicators:

Management factor Cropping intensity Fertilizer use Harvested yields per growth cycle Biofuel yields per growth cycle Harvested areas Biofuel area Crop Area | Forest area Land cover area Builtup area Land cover Natural vegetation Land cover/natural vegetation lost (relative to 1970) Land cover/natural vegetation gained (relative to 1970) Fractions of Crop types

This land-use view summarizes the characteristics of agricultural plant production and the associated land requirements, and transformations, as described in the Land-Cover Model (LCM), including food crops, biofuel crops and grass and fodder species. The results of the Terrestrial Vegetation Model (TVM) simulations, i.e. potential natural vegetation, are also presented.

Production characteristics in the LCM determining the yields include:

- the management factor, which bridges the gap between theoretically feasible and harvested yields
- cropping intensity, which defines the average number of crop cycles each year on the same land
- fertilizer use with respect to synthetic fertilizers and animal manure
- harvested yields, which defines actual yields per crop-growth cycle
- biofuel yields, which defines actual yields of crops for biofuel production per year.

On the basis of demand for food, feed, biofuels and wood products, the land requirements can be calculated from the production characteristics. Land requirements are presented for:

- harvested areas, representing the total area harvested each year
- crop areas, representing the actual area in use for crop production including fallow. Crop areas are calculated as harvested area divided by the cropping intensity
- biofuel areas, representing actual area where biofuel crops are grown (notice that no cropping intensity is defined for biofuel areas)
- forest areas.

Land cover is also presented in the form of maps for:

- actual land cover with respect to all land-cover types
- potential natural vegetation for the natural land-cover types
- changes in actual land cover relative to 1970
- changes in potential natural vegetation relative to 1970.

| #### Management factor
| unit: none (no dimension) dimension: region, crop

The management factor is an input variable representing the difference between the theoretically feasible yield of crops, based on climate and soil conditions (as simulated by the terrestrial vegetation model), and the actual yield, which is limited by less than ideal management practices, technology and know-how. Management factors are defined for the seven aggregated food crops, four biofuel crops, and grass and fodder species. Usually, its value is less than 1.

The management factor is used to calibrate the model to regional estimates of crop yields (excl. biofuel crops) and resulting land cover and land-cover transformations for the period 1970 to 1995. For biofuel crops, no management factor is defined for the past because biofuel crop production was rather small in most regions. In the regions where biofuel production was significant (such as sugar cane in South America), it was not possible to distinguish between food and biofuel crops. For 1995, the management factor for biofuel crops was derived from the management factor for sugar cane.

For model outcomes after 1995, the management factor is the main scenario input variable for calculating food and biofuel crop yields, and the production of grass and fodder species. Management factors are usually assumed to increase in time as an indication of technological development in agriculture. Maximum values are defined for each crop and region on the basis of historical data and regional conditions. These maximum values, as well as the growth rate of the management factor, are assumed to vary on the basis of the storylines (or narratives) and economic growth for each scenario (see scenario context).

Note that in some cases the management factor drops to zero, which happens when the production of the related crop comes to an end in the region considered. This occurs predominantly in regions where a relatively small area (i.e., 1 or 2 grid cells) was assigned to this crop and where, for example, a small change in climate creates unfavourable conditions to grow the crop any longer.

| #### Cropping intensity
| unit: none (no dimension) dimension: region

The cropping intensity represents the average number of food crop cycles that can be obtained in a region on its agricultural land. In many regions dominated by rainfed agriculture such as OECD Europe, the cropping intensity is less than 1.0, indicating that part of the arable area is left fallow each year. In some other regions such as East Asia, which is dominated by irrigated crop production, the cropping intensity exceeds 1.0, indicating that on the average more than one crop is grown on the same land each year.

For the future, cropping intensities are assumed to increase towards a maximum value, determined on the basis of historical data and the regional production conditions. These maximum values are outlined in the scenario context, together with the growth path towards these values.

| #### Fertilizer use
| unit:1000 Gg/yr (teragram NPK, nitrogen, phosphorous and potassium, or N, nitrogen, per year) dimension: region, fertilizer type

Fertilizer use represents the use of nutrients (NPK or N) applied as synthetic fertilizers and animal manure in the production of crops and grass, and fodder species. It is assumed that animal excretion during grazing and animal manure used as a fuel is not available for application as fertilizer. Both fertilizer types are important sources of nitrous oxide (N2O). Animal manure is also a source of methane (CH4).

In all scenarios, livestock production systems become more intensive and increasingly depend on crops as animal feed. The importance of grazing therefore decreases and the availability of animal manure as fertilizer increases. This allows reduction in the use of synthetic fertilizers. In the simulations animal manure can substitute synthetic fertilizers. Different maximum nutrient input rates are assumed for future scenarios.

| #### Harvested yields per growth cycle
| unit:Mg/km2 (ton fresh weight per square kilometer per growth cycle) dimension: region, aggregated food crop

The harvested yield of food crops (i.e. temperate cereals, rice, maize, tropical cereals, pulses, root and tuber crops, and oil crops) is the production in fresh weight per km2 for one growth cycle. The management factor is the main factor determining future yields. Notice that in some cases, the harvested yields show large discontinuities. This occurs in regions where a relatively small area, i.e. 1 or 2 grid cells, is assigned to a crop. If one of these cells switches to another crop, the harvested yield value will suddenly depend on the grid cells left.

| #### Biofuel yields per growth cycle
| unit:Mg/km2 (ton per square kilometer per growth cycle)* dimension: region, biofuel crop *fresh weight per year for sugar cane and maize, in dry matter for woody and non-woody crops.

The biofuel yield is the harvested yield of biofuel crops (i.e. sugar cane, maize, woody- and non-woody biofuel crops) For woody and non-woody biofuel crops, which often have growth cycles of more than one year, yields are defined as the yearly increase in biomass for the crop considered. No biofuel yields are defined explicitly for the past. They are implicitly accounted for in the food aggregate 'other crops'. The management factor is the main factor determining future yields of biofuel crops.

| #### Harvested areas
| unit:1000 km2 (thousand square kilometer per year) dimension: region, aggregated food crop, food crop area

The variable 'Harvested areas' is related to food crops, distinguishing between rainfed and irrigated agricultural land. If more than one crop is grown each year (i.e. the cropping intensity is greater than one), the total harvested area of all crops is larger than the actual food crop area. This especially holds true for East Asia (i.e., China), where double cropping practices are very common. In regions where part of the land is left fallow each year, the harvested area is smaller than the total arable area for food crops (i.e. the cropping intensity is less than one).

| #### Biofuel area
| unit:1000 km2 (thousand square kilometer per year) dimension: region, biofuel crop

The biofuel area is the area where biofuel crops (i.e. sugar cane, maize, woody- and non-woody biofuel crops) are grown. In the IMAGE model, the surface of biofuel areas in the past was zero. Obviously, biofuel crops were grown in some regions (especially South America), but reliable data is not available to distinguish between food and biofuel crops. Therefore, (the limited) past biofuel crop production is included in the food aggregate 'other crops'.

| #### Crop area
| unit:1000 km2 (thousand square kilometer per year) dimension: region, aggregated crop

The crop area represents the area allocated to three aggregated crop types: i.e. food crops, biofuel crops, and pasture and fodder species. These values can deviate from the graph of harvested areas because in several regions more than one crop can be grown on the same area of land each year, while in other regions on the average less than one crop is grown each year. The quotient of the harvested area of a crop and the cropping intensity yields the crop area, which is the area actually needed for production. The total crop area equals the areas of agricultural land and extensive grasslands, where extensive grasslands are part of the crop 'Pasture and fodder' (see Land cover area).

The grassland areas show a decrease for some major countries in the early 1990s after a period of constant areas, or of constant increase or decrease. This agrees with other FAO reports which discuss a general trend of gradual substitution of grazing-based livestock production by feed-crop-based systems. This is in line with the observation of the IPCC that a slowdown in deforestation may have taken place in the early 1990s. In the land-cover model (LCM) a abandoned grassland is replaced by the natural vegetation type, which causes an increase in the carbon uptake. This aspect is also in line with the possibility that land has taken up more carbon during the 1990s than during the 1980s.

| #### Forest area
| unit:1000 km2 (thousand square kilometer per year) dimension: region, forest type

The forest area represents the extent of different forest types:

- mature forests: these are more-or-less in equilibrium, i.e. CO2 uptake equals CO2 emissions, although net uptake can take place as a result of CO2 fertilization until a new equilibrium has been reached;
- regrowth forests after abandonment of agricultural areas (which sequester atmospheric CO2 until they have reached the 'mature' state);
- regrowth forests after timber extraction;
- carbon plantations, which are excluded from the current implementation. This forest type will be used in future versions of IMAGE to explicitly account for 'Kyoto Forests'.

Forest areas are derived from the actual distribution of natural vegetation based on the (changes in) potential vegetation and the actual land use. For each vegetation class a specific, prescribed fraction is assumed to contain forest, e.g. 10% for tundra, 30% for grassland and steppe, 50% for savanna, 60% for scrubland, 90% for tropical woodland and 100% for tropical forests (and other forest types).

| #### Land cover area
| unit:1000 km2 (thousand square kilometer per year) dimension: region, land-cover type

The land cover area contains the surface of the different land-cover types for each region. Note that the sum of the area of agricultural land and extensive grassland equals the total area of crops (see Crop area). Extensive grasslands are defined as agricultural land by the FAO, but are distinguished within IMAGE 2.2 because of the low productivity (if the productivity is less than 25% of its maximum potential, the land is defined as 'extensive grassland'). Extensive grasslands can be found, for example, in the Western part of the USA, the western part of Australia and in Mongolia.

#### Builtup area |
unit:1000 km2 (thousand square kilometer per year) dimension: region |

The builtup area contains the surface of the .... area for each region.

| #### Land cover
| unit: N.A. dimension: Land-cover types

The land cover map shows the land-cover type for each 0.5 by 0.5 degree latitude/longitude grid. Cells may contain built-up area or water. The initialization of the land-cover map in 1970 is described in the Initial State Indicators.

| #### Natural vegetation
| unit: N.A. dimension: Vegetation types

The natural vegetation map shows the natural vegetation for each 0.5 by 0.5 degree latitude/longitude grid in the absence of anthropogenic influences, i.e. by not taking agriculture and infrastructure into account.

The natural vegetation is derived from the potential vegetation and is the result of the relatively slow response of longer lived biomes (such as forests) to gradual environmental changes and land use. The potential vegetation is calculated under conditions of equilibrium by the Terrestrial Vegetation Model (TVM), and illustrates those areas where a typical ecosystem can occur in a fully developed and undegraded state. The actual distribution of natural vegetation can therefore be different from the potential vegetation distribution.

| #### Land cover/natural vegetation lost (relative to 1970)
| unit: N.A. dimension: Land-cover types / Vegetation types

The "land cover lost" or "natural vegetation lost" map present the land cover or natural vegetation of 1970 in those locations where it has been changed to some other land-cover type.

| #### Land cover/natural vegetation gained (relative to 1970)
| unit: N.A. dimension: Land-cover types / Vegetation types

The "land cover gained" or "natural vegetation gained" map presents the current land cover or natural vegetation for those locations that have changed since 1970.

#### Fractions of crop types |
unit: fraction. dimension: Crop types. The crops are extra divided into fraction of crop not irrigated,and no biofuel, irrigated fraction of crop, fraction used for biofuel ??? |

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