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).

本数据集由全球作物水模型（Global Crop Water Model, GCWM）基于以日时间步长执行的土壤水量平衡计算得到，覆盖1998-2002年期间灌溉作物的需水量与雨养作物的耗水量。通过考虑雨养农业模拟得到的干旱胁迫，对国家及次国家农业统计数据（Monfreda等，2008）中记录的产量进行降尺度处理，以此区分雨养与灌溉作物的单产。虚拟水含量以作物耗水量与作物产量的比值计算得出。国内虚拟水流量则通过计算栅格单元层面的作物生产与消费间的平衡，并确定从盈余单元（主要产区）到赤字单元（人口稠密区域）的流量来确定。作物种植面积、播种与收获日期源自2000年前后的全球月度灌溉与雨养作物面积数据集（MIRCA2000）。本数据集针对以下作物计算了作物耗水量（蓝水与绿水）：小麦、水稻、玉米、大麦、黑麦、粟、高粱、大豆、向日葵、马铃薯、木薯、甘蔗、甜菜、油棕、油菜籽/卡诺拉油菜（rapeseed/canola）、花生、食用豆类、柑橘类作物、海枣、葡萄/藤本作物、可可、咖啡、棉花，以及未明确分类的其他作物（其他多年生作物、其他一年生作物、饲用草本）。在计算作物单产、虚拟水含量与虚拟水流量时，还需区分玉米、黑麦和高粱的籽粒用与饲用两种用途。虚拟水流量仅针对主要作为初级商品交易的作物（即除甘蔗、甜菜和棉花外的所有上述特定作物）进行计算。本数据集的空间分辨率为5弧分×5弧分，数据格式可选：ASCII栅格（全球范围，5弧分）或文本文件（国家级数据）。