Global Groundwater Pumping Reduction Targets

Groundwater pumping reduction thresholds were estimated using simulations from the global VIC-WUR v3.0-MODFLOW 6 modelling framework. This framework dynamically couples the VIC-WUR land-surface and hydrological model with the physically based MODFLOW 6 groundwater-flow model. VIC-WUR calculates groundwater recharge from the soil column and transfers it to MODFLOW, while MODFLOW simulates transient groundwater flow, groundwater heads, groundwater-river exchange, and groundwater contributions to the land-surface water balance.

Groundwater withdrawals represented irrigation, industrial, and domestic water uses. Irrigation demand was calculated dynamically based on crop water requirements, soil-moisture deficits, irrigated area, crop distribution, and irrigation-efficiency assumptions. Industrial and domestic withdrawals were derived from national water-use statistics and spatially downscaled using proxies such as population density and economic activity. The water-demand inputs, originally available at a spatial resolution of 0.5 degrees, were downscaled to the model resolution of 5 arc-minutes, or approximately 10 × 10 km at the equator.

The model was run globally at a monthly time step from 2015 through 2100 using climate forcing from the GFDL-ESM4 global climate model under the SSP3-7.0 emissions pathway. GFDL-ESM4 was selected because it represents an intermediate response within the CMIP6 ensemble, while SSP3-7.0 was used to evaluate groundwater responses under substantial future climate forcing.

Six groundwater-pumping scenarios were evaluated by retaining 100%, 80%, 60%, 40%, 20%, and 0% of baseline pumping. These scenarios are equivalent to pumping reductions of 0%, 20%, 40%, 60%, 80%, and 100%, respectively. The scenario retaining 100% of pumping represents baseline or business-as-usual conditions, whereas the scenario retaining 0% represents the complete removal of future groundwater pumping. An additional natural-reference simulation, with no historical or future pumping, was used to help distinguish climate-driven groundwater changes from the effects of historical and ongoing human water use. Monthly outputs included groundwater head, depth to groundwater, and baseflow and were provided at the native model-grid resolution.

For the basin-scale assessment, simulated groundwater-head values were aggregated to 4,734 HydroBASINS Level 5 basins. The groundwater-level time series for each basin was calculated as the area-weighted mean of all model grid cells located within that basin. Late-century groundwater conditions were then evaluated by applying a Seasonal Mann-Kendall trend test to the monthly basin-average groundwater-level time series for 2071–2100. Each basin and pumping scenario was classified as having a statistically significant declining trend, no statistically significant trend (stable), or a statistically significant rising trend.

The groundwater pumping stabilization map summarizes the scenario comparison by showing the pumping level at which each basin reaches a stable or rising late-century groundwater-level trajectory. For basins that decline under baseline pumping but become stable or rising when pumping is reduced, the scenarios were compared to identify the highest amount of baseline pumping that could be retained while achieving a non-declining trend. The map therefore reports five pumping-retention ranges: 80–100%, 60–80%, 40–60%, 20–40%, and 0–20% of baseline pumping. Their equivalent pumping-reduction ranges are 0–20%, 20–40%, 40–60%, 60–80%, and 80–100%, respectively.

For example, a basin classified as reaching a stable or rising condition with 20–40% pumping requires an estimated 60–80% reduction relative to baseline pumping. Because the model was evaluated at 20-percentage-point increments, these values should be interpreted as ranges rather than precise thresholds.

The map also identifies basins in which groundwater levels continue to decline even when future pumping is completely removed. These basins do not have an achievable stabilization threshold within the scenarios evaluated and are likely strongly influenced by projected climate conditions, historical depletion, or delayed groundwater-system responses. Basins that are already stable or rising across the tested scenarios, together with basins lacking sufficient data, are shown separately and are not assigned a pumping-reduction threshold.

The resulting stabilization threshold should be interpreted as a basin-scale screening estimate rather than an exact local abstraction limit. It is conditional on the selected climate model and emissions pathway, the model representation of groundwater processes and water demand, the HydroBASINS Level 5 aggregation, and the discrete pumping scenarios evaluated. Consequently, the map is most appropriate for identifying broad spatial patterns and prioritizing basins for more detailed regional analysis and management planning.

1 References

Datadien, K., and de Graaf, I. (2026). Groundwater Pumping Reduction Scenarios: Testing, Accuracy & Validation and Groundwater Pumping Reduction Scenarios: Groundwater Level Stabilization & Recovery Potential. WWF-US and Wageningen University & Research deliverable reports.