Water debt for the annual production of nine major crops globally at 5 arcmin resolution for the year 2000

Definition of the Water Debt (WD) Repayment Time:
The WD is calculated, at a 5' × 5' spatial resolution for the production of year 2000, as the ratio of the cell annual water footprint, WFs, cr, l, which is specific for each source s, crop cr, and location l, and the average renewable volume of water annually available in the cell.

The annual renewability rate is calculated as a long-term average along the period 1987–2013. In this way, we obtain an average measure of the water availability in the cell, which smooths out potential extremely dry or extremely wet years. The water footprint (WF) estimates are computed for year 2000 because this is the most referenced year in agricultural datasets available in the literature.

The WFs, cr, l estimate is obtained as the product of the local crop water footprint (CWF) by source, (CWFs, cr, l, expressed in cubic meters per ton of crop), and the annual crop production (Pr), (Pcr, l, expressed in tons of crop).

The total WD of the sources, arising from all the crops cultivated in the grid cell, WDs, l, equals the sum of debts generated by each crop.

Owing to the simultaneous replenishment of soil water, surface water, and groundwater by precipitation, the crop WD across the threes sources, WDcr, l, is given by the maximum WDs, l, cr value across sources s.

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Global greenhouse gas emissions associated with the production of crop and livestock products at 5 arc minutes resolution, 1997-2003