MIRCA2000 - frequently asked questions
The following 26 crops or crop classes are considered: (1) Wheat, (2) Maize, (3) Rice, (4) Barley, (5) Rye, (6) Millet, (7) Sorghum, (8) Soybeans, (9) Sunflower, (10) Potatoes, (11) Cassava, (12) Sugar cane, (13) Sugar beets, (14) Oil palm, (15) Rape seed / Canola, (16) Groundnuts / Peanuts, (17) Pulses, (18) Citrus, (19) Date palm, (20) Grapes / Vine, (21) Cotton, (22) Cocoa, (23) Coffee, (24) Others perennial, (25) Fodder grasses and (26) Others annual. => back to top of the list
Sub-crops are used to represent multi-cropping systems, varieties of the same crop growing in different seasons in different areas of the grid cell or different specific crops included in crop groups like "others annual". One example for multi-cropping is rice. In many regions of the world rice is grown more than once a year on the same field. Different sub-crops represent here the different growing seasons. An example for varieties of the same crop growing in different seasons in different areas within a given grid cell is barley. In many regions, both spring barley and winter barley are grown. However, different from rice, winter and spring barley are usually not grown consecutively on the same field. An example for different specific crops included in crop groups are vegetables, here included in the crop group "others annual". For some countries the growing area and the growing periods of different types of vegetables are known from the statistics and the literature. Then sub-crops were used to represent the growing periods of these specific types of vegetables. => back to top of the list
The cropping periods of irrigated crops are defined according to crop calendars collected from different sources and presented in Portmann et al. 2008 (Frankfurt Hydrology Paper 06). The definition of cropping periods for rainfed crops followed other sources as documented in Portmann et al. 2010 (Global Biogeochemical Cycles). In general, the crop calendar is fixed for all grid cells belonging to the same spatial unit (or entity, see the figure below showing the density of spatial units). However, in many cases specific sub-crops may grow in one grid cell but they don't grow in another because the available growing area in the latter cell is already completely occupied by other crops growing during the same period. We tried to maximize the consistency of our product to the four input data sources. In particular this means that:
- The sum of monthly growing areas is in each unit and eachmonthsimilar to growing areas and cropping periods reported in the cropping calendars.
- The sum of growing areas of irrigatedcrops should for each grid celland each monthbe equal or less than the area equipped for irrigation in version 4.0.1 of the Global Map of Irrigation Areas.
- The sum of growing areas of irrigated and rainfedcrops should for each grid cell and each monthbe equal or less than the cropland extent in Ramankutty et al. (2008).
- The sum of the annual harvested areasof irrigated and rainfedcrops should for each grid cell be equal to the harvested area of the crop in the data set of harvested crop areas described in Monfreda et al. (2008).
Because of inconsistencies between the four input data sets it was, however, in many cells not possible to completely fulfil all these requirements. Anyway, the spatial pattern of our crop distribution is mainly determined by these four conditions.
|Units for which crop calendars are available.|
No, it is generally not considered, with the exception of temperate cereals. That means that crops are in general also located in grid cells that are not suitable. However, it should be mentioned that the spatial resolution of the statistics used to generate the input data sets (e.g. Monfreda et al., 2008) was much higher than the density of units used here. As a special case, for temperate cereals wheat, barley, and rye, for cropping periods in winter, preferrably cells were used that comply with vernalization requirements according to Heistermann et al. (2008), i.e. with long-term average monthly air temperature between -10°C and +6°C in the coldest month. Therefore there might be some confidence that the crop distribution in MIRCA2000 is not too far away from reality. => back to top of the list
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