Siao Sun & Qiuhong Tang et al. from the Chinese Academy of Sciences used multi-regional input-output (MRIO) method to track the depletion of groundwater from locations of production to end consumers. This is an advancement since previous studies have not investigated the virtual transfer of groundwater.

The paper defines consumption-based groundwater withdrawal as "the groundwater that is virtually embedded in products throughout the supply chain and consumed by end consumers."

Past studies of virtual water transfer or trade often uses the terms blue water and green water. Groundwater falls in the scope of blue water, which is surface water and groundwater sources, and not green water, which is soil moisture sources (Hoekstra et al. 2011; Dalin et al. 2014). Also, the study considers water withdrawal as opposed to consumption, because withdrawn groundwater is unlikely to be recharged back underground and is likely to have degraded quality.

Consumers who receive groundwater depletion intensive products should be aware of the risk from groundwater depletion upstream in their supply chain.

The authors gave a detailed description of a noteworthy methodology that merges MRIO and groundwater simulation techniques. Yearbook statistics only provide provincial water withdrawals at the level of agricultural, industrial, and tertiary sectors. The authors disaggregated the provincial water withdrawals to grid level, and then used the grid-level water withdrawal to drive model simulations that further divided the water withdrawal into from surface water, groundwater, and other sources. The authors then calculated grid-level groundwater depletion as "groundwater withdrawal - natural discharge". The grid-level groundwater withdrawals and depletions are re-aggregated to sectoral and provincial levels that are compatible with the MRIO table.

Calculation of the consumption-based water withdrawal, groundwater withdrawal, and groundwater depletion follows conventional MRIO techinques with environmental extension coefficients.

Assignment of the provincial consumption-based numbers to grid-level was proportional to population.

In the results, the authors had three parallel perspectives: (1) production vs consumption-based accounting of groundwater depletion, (2) inter-provincial transfers of groundwater depletion, (3) exported groundwater depletion.

In broad picture, the total amount of virtually transferred groundwater in China was 38 billion m3 yr-1, with 21 billion m3 yr-1 being groundwater depletion. Embedded groundwater depletion accounts for about 70% of total groundwater depletion. The toal amount of virtually exported groundwater was ~8.6 billion m3 yr-1, with 4.8 billion m3 yr-1 being depletion.

Regarding spatial distribution, groundwater withdrawal is the heaviest in northern China (North China Plain, Northeast provinces, scattered grids in the Norhtwest; these reach 50-100 mm yr-1). A few provinces in the south also have withdrawals, but these are at lower rates. Groundwater depletion driven by local water uses is concentrated in the Hebei province. Smaller clusters of hotspots exist throughout North China. In contrast, ground depletion embedded in consumption is spread out spatially, and major cities are hotspots.

Regarding virtual transfer pathways, the major inter-provincial transfer routes of groundwater withdrawal are from north to south. In some provinces, the virtual groundwater depletion are driven mainly by local production, whereas in others, the virtual groundwater depletion are driven mainly by imported products. Net groundwater-delivering and -receiving provinces are not the same as net water-delivering & -receiving provinces.

Regarding sectoral patterns, the major products in which the virtual water is embdeeded are industrial (84%) and tertiary (11%) products, not agricultural. But agricultural products are often upstream of these products and are the source of the groundwater depletion (53%).

The proportion of groundwater in China's exported virtual water is lower than the global average, but the proportion is higher in the regions where groundwater is most severely depleted (e.g. Hebei, Shanxi, Henan, Beijing).

A noteworthy figure is Fig. 5. It displays the pathway of export of the embedded groundwater by showing the major province-sectors from which the depletion stems, and the major province-sectors where the export actually happened.

#input_output
#groundwater_depletion
#virtual_water
#China
#groundwater_modeling

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021WR030695