Global hyper-resolution modeling of historical and future groundwater dynamics

Abstract. The sustainable management of global groundwater resources is a key societal challenge and is central to the Sustainable Development Goals. The localized dynamics of groundwater abstraction, topography, and surface-water interactions, as well as the sensitivity of groundwater-dependent ecosystems, call for high-resolution information to support effective groundwater management. At the same time, groundwater observations are very limited and concentrated in a few regions, rendering large parts of groundwater resources ungauged. To address limited observations and coarse global models, we applied the global groundwater model GLOBGM (v1.1) to simulate past and future groundwater heads and water table depth at 30 arc-seconds (~1 km) on a monthly time step. Model calibration improved mean bias in water table depth predictions from -4.8 m to 3.6 m compared to GLOBGM v1.0, with depth-weighted bias reduced from 34.2 m to 32.5 m across 34 800 observation wells. Groundwater dynamics are simulated for a historical reference period (1960–2019) to support model evaluation and attribution of observed impacts to climate variability and change. Baselines (1960–2014) and three combined socioeconomic-climate scenarios (2015–2100; SSP1-RCP2.6, SSP3-RCP7.0, SSP5-RCP8.5) are simulated with five GCMs, supporting detection and impact assessment of future change. Validation against monthly observations yielded skillful predictions (KGE-NP > -0.41) in approximately 75 % of deep wells (>60 m) and 90 % of shallow to intermediate wells (0–20 m). When validated against annual observations, approximately 80 % of sites showed skillful predictions regardless of depth. Historical trend analysis (1960–2019) accurately reproduced known groundwater depletion regions such as the U.S. High Plains, Arabian Peninsula, and Indo-Gangetic Plain, while also identifying rising water table depths in northern latitudes and Arctic regions potentially linked to climate-driven recharge changes. Future scenario-based simulations suggest rising water table depths for most continents in the next century, with Europe being a notable exception. However, known regions of groundwater depletion are expected to persist. Regions of reduced reliability are mapped, and quality assurance flags are provided to guide the appropriate use and interpretation of the results. The resulting data set offers high-resolution information to assess groundwater dynamics for the past and future, supporting improved global water resource management and climate impact assessments.