Tree-ring reconstruction of groundwater levels in Alberta, Canada: Long term hydroclimatic variability

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 behavior of groundwater under climatic variability. Groundwater levels at two wells in southern and central Alberta are analyzed in order to document long-term variability of groundwater levels and their sensitivity to climatic events. The instrumental well records span more than 40 years. Strong correlations (r > 0.7, p < 0.01) between mean annual groundwater levels and tree-ring chronologies suggested the use of regression models to reconstruct historical water levels for more than 300 years. From the estimated groundwater levels several periods with five or more consecutive years of low levels were identified (i.e. periods centered on 1698, 1720, 1855, and 1863 at well 117; 1887 and 1923 at well 159). The application of a regime shift method revealed periods with more than 30 years with below-average water levels. Spectral analyses, wavelet and multitaper methods, suggest dominant oscillation modes in groundwater levels in the 2–8 and 8–16 year bands.