Fig. 4: Twenty-first century aquifer-scale trends in depth to groundwater in the context of climate and cultivation.

a, The percentage of aquifer systems with rapidly deepening groundwater (median Theil–Sen slope steeper than 0.5 m year⁻¹) when categorized by climate conditions and cropland prevalence. Aquifer systems with rapidly deepening groundwater are most common in hyper-arid, arid and semi-arid climate zones (see categories on the x axis) and where a larger proportion of land is under cultivation (see categories on the y axis). b, Scatter plot of aquifer-scale average annual precipitation divided by potential evapotranspiration³⁹, and the percentage of land area under cultivation⁴⁰ (estimated for the year 2015). The colour of each point represents the twenty-first century aquifer-scale groundwater-level trend (median Theil–Sen slope). Blue and red points indicate shallowing and deepening, respectively, of groundwater, with darker colours indicating faster rates. Background shades represent climate zones classified by annual precipitation divided by potential evapotranspiration (that is, x-axis values). Several aquifer systems are absent from this plot because either no land is under cultivation (incompatible with the log scale of the y axis) or precipitation divided by evapotranspiration values fall outside the shown range of x-axis values. For alternative versions of this figure showing these aquifer systems, see Supplementary Note 11.

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