LAUSR

The Chinese government set up a redline for water resources in 2011, mandating water withdrawals and management criteria to the year 2030. ‘How much water is required to produce sufficient crop to feed a 1.6 billion population in 2030?’ becomes a crucial question to be addressed. The objectives of this study are to: (1) document crop water use and productivity from 1998 to 2017 and (2) define the redline water withdrawal for crop use (REWCU) to 2030. The study inversely inferred REWCU from broadly-defined available water for crop use (BAWCU) and associated parameters. Of all BAWCU, 66.3% had been consumed by crops, in which rainfall-derived water consumption accounted for 71.7% of it, while the irrigation-derived water consumption represented the remaining 28.2%. Of all the rainfall that was available for crop use, 72.1%, or the rainfall depletion rate, had been actually consumed by crop evapotranspiration (ET). Likewise, 55.2%, or the irrigation depletion rate, had been consumed by crops. Crop water productivity (CWP) measured by crop yield per unit ET was computed for six major crop categories. Five broad scenarios have been formulated—business as usual, optimistic, deliberative optimistic, pessimistic, and deliberative pessimistic—under lower, higher, and average population and crop projections, respectively. The projected REWCU was 4166.30 × 108 m3, and the projected agricultural water withdrawal was 4629.22 × 108 m3 to 2030, representing 66.1% of the projected nationwide redline total water withdrawal (RETWW) of 7000 × 108 m3. The study used CWP and BAWCU to inversely infer REWCU since they reflect diverse biophysical and management factors and can be used as reliable proxies. Both methodology and research results may offer references and support when making nation- and region-wide water-for-food decisions by crop and water administrations.