Groundwater could be an increasingly important water supply in the Canadian interior with global warming and declining summer runoff; however, not enough is known about the behaviour of groundwater under climatic variability. A network of over 33 wells is analyzed in order to document variability of groundwater levels and their sensitivity to climatic events. Groundwater wells are spread through the three Prairie Provinces with median monthly groundwater level records spanning up to 40 years. The aquifers are mostly in sand and sandstone which make them highly sensitive to climatic variations. In addition, these wells have not been affected by human activities such as pumping. Multiple analyses, such as the Mann-Kendall non parametric test to detect trends in groundwater levels, are carried out in order to determine and understand the dynamics of groundwater in the Prairie Provinces. Strong correlations (r > 0.7, p < 0.01) between treering chronologies and seasonal and annual groundwater levels enable the reconstruction of 11 annual groundwater level records for more than 90 years in Saskatchewan and more than 300 year in Alberta. Results of the application of the Mann-Kendall trend test suggest that groundwater levels in north central areas show either no or decreasing trend, in contrast, groundwater levels in southern areas are dominated by increasing trend. The spatial distribution of trends coincides with increasing and decreasing trends in evaporation during the warm season. The reconstructions of historical groundwater levels suggest that the range of variability in water levels is greater than the variability recorded in the instrumental period. Also, the magnitude and duration of impacts of historical droughts on groundwater vary between different aquifers. Results of spectral analysis suggest that oscillation modes at ~10, ~15, ~20, and ~25 years explain most of the variability in groundwater in Alberta and Saskatchewan.