El Niño and the Southern Oscillation: Multiscale Streamflow Variability Associated with El Niño/Southern Oscillation

Streamflow responses to the El Niño/Southern Oscillation (ENSO) phenomenon in the tropical Pacific are detectable in many regions. During warm-tropical El Niño and cool-tropical La Niña episodes, streamflows are affected throughout the Americas and Australia, in northern Europe, and in parts of Africa and Asia. In North and South America, correlations between peak- flow season streamflows and seasonal Southern Oscillation Indices (SOIs) show considerable persistence. In South America, correlations between flows in other seasons with December- February SOIs also are notably persistent, whereas, in North America, correlations are smaller when other, non-peak season time periods are considered. At least two modes of streamflow response to ENSO are present in the Western Hemisphere. When interannual North and South American streamflow variations are analyzed together in a single principal components analysis, two of the leading components are found to be associated with ENSO climate variability. The more powerful of these modes corresponds mostly to ENSO responses by the rivers of tropical South America east of the Andes, along with rivers in southern South America and the southwestern United States, with Brazil experiencing less runoff during El Niños and the other regions experiencing more runoff. This streamflow mode is correlated globally with ENSO-like sea surface temperature (SST) patterns on both interannual and interdecadal time scales; indeed, the tropical South American rivers east of the Andes are coherent with SOI on virtually all historical time scales. The second ENSO-related streamflow mode characterizes other parts of extratropical streamflow variation, emphasizing the north-south differences in streamflows in North America during ENSO extremes and (less robustly) streamflow variations along the central Andes. The relation of this extratropical streamflow mode to ENSO seems to be mostly from scattered interannual time scales and, overall, its decadal variations follow North Atlantic SSTs. On decadal time scales, the most remarkable variation identified in the Western Hemisphere ENSO-streamflow correlations or teleconnections is a decades-long contrast between the teleconnections of recent decades and teleconnections from about the 1920s into the 1950s. Correlations between streamflows and SOI, Niño-3 SSTs, and even global SSTs nearly vanished Citation: Dettinger, M.D., Cayan, D.R., McCabe, G.M., and Marengo, J.A., 2000, Multiscale streamflow variability associated with El Niño/Southern Oscillation, in H.F. Diaz and V. Markgraf, V. (eds.), El Niño and the Southern Oscillation--Multiscale Variability and Global and Regional Impacts: Cambridge University Press, 113-146.