Coupled oceanic‐atmospheric variability and U.S. streamflow

Abstract

A study of the influence of interdecadal, decadal, and interannual oceanic‐atmospheric influences on streamflow in the United States is presented. Unimpaired streamflow was identified for 639 stations in the United States for the period 1951–2002. The phases (cold/negative or warm/positive) of Pacific Ocean (El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO)) and Atlantic Ocean (Atlantic Multidecadal Oscillation (AMO) and North Atlantic Oscillation (NAO)) oceanic‐atmospheric influences were identified for the year prior to the streamflow year (i.e., long lead time). Statistical significance testing of streamflow, based on the interdecadal, decadal, and interannual oceanic‐atmospheric phase (warm/positive or cold/negative), was performed by applying the nonparametric rank‐sum test. The results show that in addition to the well‐established ENSO signal the PDO, AMO, and NAO influence streamflow variability in the United States. The warm phase of the PDO is associated with increased streamflow in the central and southwest United States, while the warm phase of the AMO is associated with reduced streamflow in these regions. The positive phase of the NAO and the cold phase of the AMO are associated with increased streamflow in the central United States. Additionally, the coupled effects of the oceanic‐atmospheric influences were evaluated on the basis of the long‐term phase (cold/negative or warm/positive) of the interdecadal (PDO and AMO) and decadal (NAO) influences and ENSO. Streamflow regions in the United States were identified that respond to these climatic couplings. The results show that the AMO may influence La Niña impacts in the Southeast, while the NAO may influence La Niña impacts in the Midwest. By utilizing the streamflow water year and the long lead time for the oceanic‐atmospheric variables, useful information can be provided to streamflow forecasters and water managers.