Oceanic-Atmospheric Variability Influences on Baseflows in the Continental United States

摘要

Baseflows are one of the important components of streamflows and the influences of climate change and variability on changes in baseflows in space and time can aid in the management of low flows in watersheds. This study focuses on influences of climate variability on baseflows manifested through individual and coupled oceanic-atmospheric oscillations (viz., Atlantic multidecadal oscillation (AMO), El Nino-southern oscillation (ENSO), Pacific decadal oscillation (PDO), and North Atlantic oscillation (NAO)). Statistically significant differences in monthly baseflows in temporal windows that coincide with two phases (i.e., cool or warm; El Nino or La Nina) of oscillations at 574 gauging across least anthropogenically influenced across the continental the U.S. are evaluated in this study. Nonparametric statistical hypothesis tests are used to analyze these changes. Results from the analyses indicate that the influences of PDO and AMO on baseflows are the largest than other oscillations, and baseflows at only 12.2% of all sites were impacted by ENSO. The New England (01), Mid Atlantic (02), and Souris-Red-Rainy (09) regions displayed statistically significant differences in baseflow in two phases and with dominant influence attributed to the PDO cool phase. A total of 143 stations with higher baseflow median values during NAO warm/cool phase and El Nino. It is noted that the NAO cool phase/El Nino influences regional baseflows in the central U.S. and the NAO warm phase/ La Nina impacts baseflows in the southeastern U.S. The number of sites at which the baseflows were impacted by coupled oscillations was larger than those influenced by one oscillation.