| Summary: | Groundwater responses to climate variability on interannual to multidecadal scales have substantial implications for water-resource sustainability, yet are poorly understood in the United States. This study quantifies the effects of the El Nino Southern Oscillation (ENSO) (2-7 year cycle), the North Atlantic Oscillation (NAO) (3-6 year cycle), the Pacific Decadal Oscillation (PDO) (10-25 year cycle), and the Atlantic Multidecadal Oscillation (AMO) (50-70 year cycle) on precipitation and groundwater levels in the Central Valley aquifer, the Basin and Range aquifer system, and the North Atlantic Coastal Plain aquifer system. Singular spectrum analysis (SSA) and wavelet analysis were used to analyze climate variability effects on hydrologic time series and to estimate recharge rates. In the Central Valley and the Basin and Range, the PDO contributes to the greatest amount of variance (ranging from 13.6-83%) in all hydro logic time series, with moderate lag correlations (ranging from 0.19-0.75). In the North Atlantic Coastal Plain, a 2-7 year cycle contributes to the greatest amount of variance (6.0-51.2%), and could be associated with the ENSO or the NAO. Wavelet analysis also reveals strong coherence with the hydrologic time series at the associated periodicities of the climate cycles. Recharge rates were accurately estimated using a modified lag-based hydrologic time series method. These findings support the conclusion that climate variability contributes to fluctuations in groundwater and is important to integrate into water resource management.
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