GLOBAL GROUNDWATER LEVEL CHANGES

Seawater intrusion, groundwater accessibility, streamflow depletion and land subsidence are often influenced by changes in groundwater levels. Here, groundwater level datasets are reviewed with a particular focus on how groundwater levels have changed over time. In recent decades, groundwater level declines have accelerated in a disproportionate share of aquifer systems, especially those underlying cultivated drylands. However, there are dozens of areas where groundwater level declines have been reversed following interventions, emphasizing that groundwater declines are not an inevitable. Together, these analyses provide new constraints on the present-day potential for seawater intrusion, streamflow depletion and wells running dry, while also highlighting ways to avoid these consequences of groundwater declines.