Influence of Groundwater Extraction Costs and Resource Depletion Limits on Simulated Global Nonrenewable Water Withdrawals Over the Twenty-First Century

Future rates of global groundwater depletion will depend on the economic and environmental viability of extracting water from increasingly stressed aquifers. Here we analyze global groundwater depletion by considering these factors explicitly. Global gridded groundwater availability and extraction cost data are aggregated to produce nonrenewable resource supply curves for 235 major river basins and geopolitical regions. These resources are then exposed to dynamically generated demands for water in a fully coupled, multisectoral, global simulation. As groundwater head levels drop, imposing greater capital and operating costs to bring water to the surface, modeled water use sectors are able to deploy a range of supply- and demand-driven adaptive responses. Results demonstrate large sensitivity in global groundwater depletion rates to adjustments in resource exploitability. Extraction costs moderate demands for nonrenewable water substantially, resulting in the onset of a decline in global groundwater depletion rates within the twenty-first century. New groundwater depletion hot spots may emerge as crop producers abandon overexploited basins and expand croplands in regions with cheaper, more plentiful water resources. Plain Language Summary In many regions of the world, groundwater reserves are being depleted rapidly. This raises concerns for the sustainability of irrigated agriculture and global food supplies. It is therefore important to study groundwater depletion and possible exhaustion of water resources at the global scale. A problem for such analysis is the lack of a detailed understanding of when a depleting resource becomes unviable for further exploitation. The question is not simply how much water is physically available; we need to know when the financial costs and environmental impacts of extracting more groundwater render the resource unviable for human applications. In order to study these effects, we employ a global, gridded data set that specifies the cost of groundwater extraction as a function of depletion. We then simulate water users as rational economic actors to understand how they will adapt as extraction costs increase. Results indicate that future rates of global groundwater depletion will be heavily moderated by increasing extraction costs. Regions that deplete water to costly levels lose competitive advantage for crop production, which shifts to regions where water resources are cheap and plentiful. We conclude that projections of global groundwater depletion will not be credible if extract costs are neglected.