Fig. 3: Comparison of aquifer-scale trends in depth to groundwater during the late twentieth and early twenty-first centuries.
From: Rapid groundwater decline and some cases of recovery in aquifers globally
a, Scatter plot of aquifer-scale trends (median Theil–Sen slopes) during 2000–2022 (x-axis values) and during 1980–2000 (y-axis values). The colour of each point indicates one of the following categories of trends: (1) groundwater levels became shallower during 1980–2000 and continued to become shallower (purple points); (2) groundwater levels became shallower during 1980–2000 but have since become deeper (yellow points); (3) groundwater levels became deeper during 1980–2000 but have since become shallower (blue points); (4) groundwater levels became deeper during 1980–2000 and continued to become deeper but at a slower rate (that is, decelerated deepening; orange points); and (5) groundwater levels became deeper during 1980–2000 and continued to become deeper at a faster rate (that is, accelerated deepening; red points). The intensity of each colour scales with the absolute value (that is, magnitude) of the difference between the late twentieth and early twenty-first century trends in groundwater level (see legend). b, Examples of groundwater-level time series illustrating each of our five categories (see legend). c–i, Maps of aquifer systems categorized by their late twentieth and early twenty-first century trends in groundwater levels (colours correspond to categories in the legend). For an expanded version of this figure, see Supplementary Note 9.
