Effect of ENSO modulation by decadal and multi-decadal climatic oscillations on contiguous United States streamflows

Study Region: The contiguous United States (CONUS). Study Focus: This study assesses the effects of the large-scale oceanic-atmospheric oscillations such as El Niño southern oscillation (ENSO), Atlantic Multidecadal Oscillation (AMO), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO) on streamflow levels. Two robust and powerful non-parametric procedures, namely, the Joint Rank Fit (JRFit) and the rank-based partial least squares regression are used to identify and quantify the strength and direction of teleconnections (individual analysis). Further, JRFit is used to model the interactive effects (coupled analysis) of ENSO with AMO/PDO/NAO cycles on streamflows. New Hydrological Insights for the Region: Individual analysis results identified new significant ENSO, PDO, AMO and NAO tele-connections with streamflows across CONUS. PLS analysis showed a stronger AMO teleconnection with streamflows compared to other oscillations. The coupled analyses results were categorized into three groups based on the types of interactions of the ENSO phases. Type 1 interactions where a phase of ENSO is modulated by phases of decadal/multidecadal cycles, are seen across all (majority of) regions in CONUS. Interesting results were obtained for type 2 (type 3) interactions as the effects of ENSO phases were opposite (similar but enhanced), compared to individual analysis of ENSO, when associated with the phases of PDO/AMO/NAO. The results provide several new findings and useful information for forecasting of water resources in the CONUS region