Low Flow Variability and Coupled Oceanic-Atmospheric Oscillations

Abstract:

Understanding the influences of four major coupled oceanic-atmospheric oscillations affecting streamflow extremes and characteristics at a regional scale is the focus of this study. The oscillations considered are: Atlantic multidecadal oscillation (AMO), El Nino southern oscillation (ENSO), Pacific decadal oscillation (PDO), and North Atlantic oscillation (NAO) and the main emphasis is on low flows in the South-Atlantic Gulf region of the U.S. Several standard drought indices and a few new ones, streamflow deficit durations, temporal occurrences of these deficits and other characteristics of low flow extremes during two different phases of these oscillations are evaluated. Long-term streamflow data at 43 USGS sites in the region from Hydro-Climatic Data Network (HCDN) basins that are least distributed by anthropogenic influences are used for evaluation. Parametric and nonparametric hypothesis tests are used to evaluate statistically significant changes in the characteristics of low flows. Individual and combined influences of the oscillations are also evaluated at different sites depending on the availability of lengthy records. Inferences about influences of oscillations on droughts from the results of statistical analysis and possible physical basis explanations are expected outcomes of this study. Evaluation and understanding of changes in frequency and intensity (severity) of droughts and their links to climate variability are critical for basin scale water resources and low flow management in region.