Box 1.4 Groundwater depletion from global irrigated crop production and trade
The over‐abstraction of groundwater in major food producing areas of the world such as north‐west India, North China, the central United States and California is rapidly depleting groundwater storage in large aquifer systems. The global scale of groundwater depletion due to irrigation is difficult to assess given the lack of research integrating crop water use, groundwater depletion and the embedding of groundwater in international food trade. In the study by Dalin et al. (2017), groundwater depletion linked to irrigation (GWD) (in which GWD is defined as the volume of groundwater abstracted for irrigation use in excess of the natural recharge rate and irrigation return flow, and allowing for environmental flow requirements) is estimated based on 26 crop classes and bilateral trade flow for 360 commodities. The results shown in Table 1.4 for 2010, show the volume of GWD embedded in food production and trade for the top 10 countries with the most GWD.
Table 1.4 Groundwater depletion (GWD) for irrigation embedded in national food production, imported and exported GWD, and corresponding fractions of GWD in global food production, national food consumption and national food production for the year 2010 (Dalin et al. 2017).
(Source: Adapted from Dalin, C., Wada, Y., Kastner, T. and Puma, M.J. (2017) Groundwater depletion embedded in international food trade. Nature 543: 700–704.)
| Country | GWD in production (km3 a−1) | Fraction of global GWD (%) | GWD in imports (km3 a−1) | Fraction of GWD in national consumption (%) | GWD in exports (km3 a−1) | Fraction of GWD in national production (%) |
|---|---|---|---|---|---|---|
| India | 73.5 | 33.9 | 0.2 | 0.3 | 3.0 | 4.0 |
| Iran | 33.3 | 15.4 | 1.4 | 4.2 | 1.2 | 3.5 |
| Pakistan | 27.5 | 12.7 | 0.2 | 1.2 | 7.3 | 26.4 |
| China | 24.0 | 11.1 | 2.2 | 8.5 | 0.3 | 1.1 |
| USA | 16.2 | 7.5 | 1.7 | 15.3 | 6.9 | 42.4 |
| Saudi Arabia | 12.5 | 5.7 | 0.8 | 6.0 | 0.4 | 3.5 |
| Mexico | 11.1 | 5.1 | 1.0 | 10.6 | 2.5 | 22.6 |
| Libya | 2.5 | 1.1 | 0.1 | 2.4 | 0 | 0.1 |
| Turkey | 2.0 | 0.9 | 0.5 | 22.6 | 0.4 | 18.0 |
| Italy | 2.0 | 0.9 | 0.5 | 27.9 | 0.8 | 39.2 |
| Total top ten | 204.6 | 84.8 | 8.6 | 4.5 | 22.8 | 11.1 |
| Total world | 241.4 | 100 | 25.6 | NA | 25.6 | NA |
Note: Also shown are totals for these ten countries and for the world. NA, not applicable.
Global GWD increased to 292 km3 in 2010, mostly due to increases in India, China and the United States. The crops accounting for most depletion globally, both in terms of their large production and GWD intensity, are wheat (22% of global GWD, or 65 km3), rice (17%), sugar crops (7%), cotton (7%) and maize (5%) (Dalin et al. 2017). The countries irrigating crops from over‐exploited aquifers export these crops in various proportions: India retains most of its large GWD‐based crop production for domestic use (only 4% of GWD exported), while the United States, Pakistan and Mexico export significant portions of their GWD‐based crop production (Table 1.4). Globally, about 11% of GWD is embedded in international food trade, of which exports from Pakistan, the United States and India alone account for more than two‐thirds