GEMS-GER: a machine learning benchmark dataset of long-term groundwater levels in Germany with meteorological forcings and site-specific environmental features. - Ohmer, Marc; Liesch, Tanja; Habbel, Bastian; Heudorfer, Benedikt; Gomez, Mariana; Clos, Patrick; Nölscher, Maximilian; Broda, Stefan (Earth System Science Data, 2026)