Output of the Global Crop Water Model GCWM

Crop water requirements of irrigated crops and crop water use of rainfed crops is calculated by the Global Crop Water Model (GCWM) for the period 1998-2002 based on a soil water balance performed in daily time steps.Crop yields of rainfed and irrigated crops are distinguished by downscaling yields reported in national and subnational agricultural statistics (Monfreda et al., 2008) by considering drought stress simulated for rainfed agriculture. Virtual water contents are calculated as ratio between crop water use and crop yield. Domestic virtual water flows are determined by calculating a balance between crop production and crop consumption at grid cell level and establishing flows from surplus cells (major production areas) to deficit cells (highly populated regions). Crop growing areas, sowing and harvest dates were derived from the global data set of monthly irrigated and rainfed crop areas around the year 2000 (MIRCA2000). Consequently, crop water use (blue and green) is computed for the crops wheat, rice, maize, barley, rye, millet, sorghum, soybeans, sunflower, potatoes, cassava, sugar cane, sugar beet, oil palm, rapeseed/canola, groundnuts/peanuts, pulses, citrus, date palm, grapes/vine, cocoa, coffee, cotton and unspecified other crops (other perennial crops, other annual crops, fodder grasses). For the calculation of crop yields, virtual water contents and virtual water flows we distinguish in addition the usage of maize, rye and sorghum for grain or forage. Virtual water flows are computed for crops traded mainly as primary commodities (all specific crops except of sugar cane, sugar beet and cotton). The data set has a spatial resolution of 5 arc-minutes by 5 arc-minutes. Format: ASCII-grids (global, 5 arc-minute) or text files (country data).Purpose: Assessments of the impact ofproduction and consumption of crops on water resources or, vice versa, the impact of water management on agricultural production. We advise to use the data set for global assessments or at the scale of world regions