| Summary: | The response of groundwater to interannual to multidecadal climate oscillations has important implications for water-resource sustainability, however, there is a poor understanding of how physical processes in the vadose zone dampen and filter climate variability signals prior to recharging the water table. This thesis addresses this knowledge gap by quantifying the teleconnections between six modes of quasi-periodic climate variations and precipitation and groundwater level fluctuations within seven sand and gravel principal aquifers (PAs) in the United States. The six modes of climate variability are the Atlantic Multidecadal Oscillation (50-80 year cycle), Pacific Decadal Oscillation (15-30 year cycle ), El Nino-Southern Oscillation (2-7 year cycle), North Atlantic Oscillation (3-6 year cycle), Pacific/North American Oscillation (1-4 year cycle), and Arctic Oscillation (6-12 month cycle). Singular Spectrum Analysis was used to quantify climate variability signals in climatic and hydrologic time series, and the influence of soil texture, vadose zone thickness, mean infiltration flux, and infiltration period on the damping of sinusoidal signals in the vadose zone was explored using an analytical model. Results indicate that each PA reflects some influence from each of the six modes of climate variability and that the effects of these climate variations on groundwater fluctuations can be characterized spatially based on the degree of damping. There is a consistent increase (decrease) in average percent variance and lag correlation coefficients with longer (shorter) fluctuation periods. These findings highlight the importance of low frequency climate variations on hydrologic fluctuations and indicate that considering these long-term patterns will help with water resource management.
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