Spatially explicit assessment of global consumptive water uses in cropland: Green and blue water

An accurate estimate of global water uses with high spatial resolution is a key to assessing global water scarcity and to understanding human's interference with the ecosystems. In spite of the progress made previously, there is a lack of spatially explicit assessment of both green and blue water uses in agriculture. In this paper, we estimated consumptive water use (CWU) in cropland on a global scale with a spatial resolution of 30 arc-minutes. A GIS-based version of the EPIC model, GEPIC, is used for the estimation. The results show that in crop growing periods, global CWU was 5938 km^3 a^(-1) in cropland around the year 2000, of which green water contributed to 84%. On an annual basis, global CWU was 7323 km^3 a^(-1) in cropland, of which green water contributed to 87%. We compared the simulated consumptive blue water use (CBWU) with the statistical CBWU at the national level among individual countries, and at the federal state or province level in the USA and China. The comparison indicates a good agreement between the simulated and statistical CBWU, suggesting a satisfactory performance of the GEPIC model and reliability of the estimation in irrigated cropland. The importance of green water in both crop production and food trade calls for a better management of green water, in addition to blue water.
KEYWORDS: Water scarcity; Consumptive water use; Virtual water; EPIC; GEPIC; Green water

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