Abstract. Under variable and changing climates groundwater storage sustains vital
ecosystems and enables freshwater withdrawals globally for agriculture,
drinking water, and industry. Here, we assess recent changes in groundwater
storage (ΔGWS) from 2002 to 2016 in 37 of the world's large aquifer
systems using an ensemble of datasets from the Gravity Recovery and Climate
Experiment (GRACE) and land surface models (LSMs). Ensemble GRACE-derived
ΔGWS is well reconciled to in situ observations (r=0.62–0.86,
p value <0.001) for two tropical basins with regional piezometric
networks and contrasting climate regimes. Trends in GRACE-derived ΔGWS are overwhelmingly non-linear; indeed, linear declining trends
adequately (R2>0.5, p value <0.001) explain
variability in only two aquifer systems. Non-linearity in ΔGWS
derives, in part, from the episodic nature of groundwater replenishment
associated with extreme annual (>90th percentile,
1901–2016) precipitation and is inconsistent with prevailing narratives of
global-scale groundwater depletion at the scale of the GRACE footprint
(∼200 000 km2). Substantial uncertainty remains in
estimates of GRACE-derived ΔGWS, evident from 20 realisations
presented here, but these data provide a regional context to changes in
groundwater storage observed more locally through piezometry.
Supplementary material to "Groundwater storage dynamics in the world's large aquifer systems
from GRACE: uncertainty and role of extreme precipitation"