Groundwater is the world’s largest freshwater resource and is critically important for irrigation, and hence for global food security1,2,3. Already, unsustainable groundwater pumping exceeds recharge from precipitation and rivers4, leading to substantial drops in the levels of groundwater and losses of groundwater from its storage, especially in intensively irrigated regions5,6,7. When groundwater levels drop, discharges from groundwater to streams decline, reverse in direction or even stop completely, thereby decreasing streamflow, with potentially devastating effects on aquatic ecosystems. Here we link declines in the levels of groundwater that result from groundwater pumping to decreases in streamflow globally, and estimate where and when environmentally critical streamflows—which are required to maintain healthy ecosystems—will no longer be sustained. We estimate that, by 2050, environmental flow limits will be reached for approximately 42 to 79 per cent of the watersheds in which there is groundwater pumping worldwide, and that this will generally occur before substantial losses in groundwater storage are experienced. Only a small decline in groundwater level is needed to affect streamflow, making our estimates uncertain for streams near a transition to reversed groundwater discharge. However, for many areas, groundwater pumping rates are high and environmental flow limits are known to be severely exceeded. Compared to surface-water use, the effects of groundwater pumping are markedly delayed. Our results thus reveal the current and future environmental legacy of groundwater use.
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All data needed to evaluate the conclusions in the paper are presented in the paper (Figs. 1, 2) and are available through the University of Victoria, https://doi.org/10.5683/SP2/D7I7CC. Additional model outputs (as part of the sensitivity analysis and model evaluation presented in the Extended Data) are prohibitively large to store in a repository but are available from the corresponding author on reasonable request.
The model code used to run the global-scale surface water—groundwater model is provided through a GitHub repository, https://github.com/UU-Hydro/PCR-GLOBWB_model/tree/develop/modflow.
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We thank S. Rangecroft, Y. Wada, E. Luijendijk, B. Ahner and S. de Kock for generously sharing data that supported the analysis done in this study. This study’s calculations were computed on the Dutch national supercomputer Cartesius with the support of SURFsara. This research was funded by the Netherlands Organization for Scientific Research (NWO) under the programme ‘Planetary boundaries of the global fresh water cycle’.
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Peer review information Nature thanks Laura Foglia, Mary C. Hill and Timothy R. Green for their contribution to the peer review of this work.
Extended data figures and tables
a, Cumulative groundwater depletion trend (in km3) since 1960 for different climate scenarios. After 2010, the estimate assumes a ‘business-as-usual’ scenario for water demands and uses three GCMs—HadGEM2-HS, GFDL-ESM2M and MIROC-ESM-CHEM—using RCP 8.5. b, c, The first time the environmental flow limit is or will be reached (by year) averaged over watersheds using the sub-watershed level of hydroBASINS28 for the climate scenarios GFDL-ESM2M (a) and MIROC-ESM-CHEM (b) using RCP 8.5.
Extended Data Fig. 2 Gridded estimates of cumulative groundwater water depletion (in m3 per m2) for 1960–2099.
Four major heavily pumped aquifers are magnified. Aquifer magnifications are from WHYMAP, BGS/UNESCO.
Extended Data Fig. 3 Model evaluation of simulated groundwater head changes owing to pumping compared to observations.
Three of the largest, intensively pumped, and best monitored alluvial aquifer systems of the world are shown: the High Plains aquifer (left) and Central Valley aquifer, USA, (middle) and the Upper Ganges and Indus basin, India (right). a, Observed data and published maps. b, This study’s estimates. A comparison between a and b shows that the model results matches the observations well. Nonlinear colour scales are used. The Ganges basin map is from a previous work38.
Extended Data Fig. 4 Model evaluation of the estimated first time that the environmental flow limits are reached.
a, Observed versus simulated first time that the environmental flow limits are reached (x and y axes in years) for several groundwater-pumping-impacted catchments. b, Locations of the studied catchments are indicated on the map; the three dots in Kansas represent nine sub-catchments used in the analysis.
Extended Data Fig. 5 Distribution of surface water–groundwater interaction classes for north America as simulated using the physically based global-scale GSGM.
The figure distinguishes four classes: gaining streams, losing streams, intermittently disconnected streams and continuously disconnected streams. Results are shown for the month of July (generally the driest month of the year, on the basis of monthly discharge) and represent five-year moving averages of river drainage and groundwater levels. A stream is classified as a continuously disconnected stream if the stream is disconnected for at least two years in a row over the moving average window of five years. a, Spatial maps of surface water–groundwater interaction for July 1964 and 2004 under natural conditions and including human water withdrawal. b, Temporal variation of the total area covered by each surface water–groundwater interaction class. The thinner continuous lines are yearly values, thicker dashed and dotted lines are the five-year averages.
Extended Data Fig. 6 Evaluation of observed versus simulated water table averaged for sub-watersheds.
a, Scatter plot; the red line shows the 1:1 slope. b, Histogram of relative residuals, calculated as (observed − simulated)/observed. c, Global map of relative residuals. All watersheds with no available data are mapped in grey.
Extended Data Fig. 7 Model evaluation of simulated groundwater table depth to well observations for two well monitored aquifer systems in the USA.
a, b, Location of the wells used for this analysis within the Central Valley aquifer system (a) the High Plains aquifer system (b). c–h, Averaged water table depths (‘wtd’) (c, d); standard deviation (‘std’) of monthly wtd (e, f) and head drops (g, h) were estimated (‘obs avg’) and compared to simulated results (‘sim avg’). In each plot, the values per well in the watershed are given in grey (well data) and the statistics show the wide spread in observations. The value n indicates the number of wells within the watershed. The watersheds are numbered from north to south over both aquifers, indicated by the watershed number (the exact location of the watersheds is not relevant).
a, b, Comparison of groundwater head declines (a) and groundwater discharge (GD; b) at different spatial levels, simulated by a calibrated regional-scale model (‘calb.’); results modified from previous work41 using the Republican River Groundwater Model39 and the global-scale surface water–groundwater model (‘glob.’). c, The full basin covers the entire Republican River basin, which is situated in the central-north of the High Plains aquifer, USA. The larger sub-basins are the level 2 and 3 regional basins that consist of more level 1 basins. In b, the solid lines present the simulated groundwater discharge, the dashed lines present the trends of the groundwater discharge. Groundwater discharge trends simulated by both models are comparable.
a, Table showing the different parameter settings used; varying the sub-surface conductivity, the river depth and the river conductance by decreasing or increasing the settings of the baseline (‘bl’) run. The baseline run uses the average parameter settings. b, Frequency plot of the first time the environmental flow limits are reached under different parameter settings for 1960–2010. The fractional increase or decrease of estimated environmental limits compared to the baseline run is given in the fourth column of the table in a. The runs with the smallest and largest limits are indicated in bold in the table and presented in blue and yellow, respectively, in the graph.
a, Table giving the different criteria of the Q90 windows and consecutive years used to estimate the environmental flow limits. b, c, Histograms of the limits reached, estimated using the Q90 over five years (b) and the Q90 over ten years (c). The fractional increase or decrease of the estimated environmental limits compared to the baseline run (Q90 over five years, for two consecutive years) is given in the third column of the table in a. Difference in the estimated environmental flow limits are only limited when using different criteria.