Fig. 4: The median groundwater-level change rate (a–c) and the fraction of monitoring wells exhibiting declining groundwater levels (d–e) across US aquifer systems included in our US Aquifer Database (see Methods section entitled: Delineating aquifers across the US).
From: Widespread and increased drilling of wells into fossil aquifers in the USA
The upper row of figures displays the median Theil-Sen slope of the groundwater-level trend (expressed in meters per decade) analyzing all water level measurements within the years (a) 1950–1975, (b) 1975–2000, and (c) 2000–2015 (the median trend was calculated by determining the Theil-Sen slope for every monitoring well within the aquifer boundaries, and then calculating the median among these Theil-Sen slope values; see Supplementary Fig. 5 for schematic of method). The lower row of figures displays the proportion of all monitoring wells that have a Theil-Sen slope exceeding zero (panels d–f), thus presenting the fraction of monitoring wells within the aquifer boundaries that exhibit declining groundwater levels for the years (d) 1950–1975, (e) 1975–2000, and (f) 2000–2015. We only present aquifers for which we analyzed groundwater-level time series for at least five unique monitoring wells (over the specified time interval).
