The influences of Type 1 El Nino and La Nina events on streamflows in the Pacific Southwest of the United States

Journal Article · Wed Jun 01 04:00:00 EDT 1994 · Journal of Climate; (United States)

DOI:https://doi.org/10.1175/1520-0442(1994)007<0965:TIOTEN>2.0.CO;2· OSTI ID:6824267

Kahya, E; Dracup, J A ^[1]

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1. Univ. of California, Los Angeles, CA (United States)

Streamflows in the Pacific Southwest of the United States in relation to the tropical Type 1 El Nino-Southern Oscillation (T1ENSO) and La Nina events are examined using composite and harmonic analyses for each event during a 24-month evolution period. The hydroclimatic signals associated with either extreme phase of the Southern Oscillation (SO) are explored based on data from 50 streamflow stations in California, Arizona, New Mexico, Colorado, and Utah. A significant level for the results is assessed by the use of a hypergeometric distribution. Highly significant, coherent signals are demonstrated to exist for both events, with opposite sign and almost identical timing. Pacific Southwest streamflow responses to the T1ENSO thermal forcing are characterized by a wet December-July season in the subsequent year of the event. Similarly, a dry February-July season is detected as a period at which the La Nina-streamflow relationship is strong and spatially coherent. An index time series is plotted to determine the temporal consistency of the signal. It was found that the respective seasonal signal for each event was confirmed by all episodes. Amplification (suppression) of the regional annual streamflow cycle is noticed during the subsequent year of the typical T1ENSO (La Nina) event. A lag cross-correlation analysis is conducted between the time series of the seasonal December-July streamflow index and the SO index. The March-May season in the previous year of the seasonal T1ENSO signal was determined to be the logical period in which the SO index can be averaged to obtain the highest correlation and the maximum time lag. A Mann-Whitney U test reveals statistically significant differences in the means of seasonal streamflows associated with T1ENSO and La Nina events. Plausible explanations for the observed teleconnections are presented. 34 refs., 7 figs., 2 tabs.

• OSTI ID: 6824267
• Journal Information: Journal of Climate; (United States), Journal Name: Journal of Climate; (United States) Vol. 7:6; ISSN JLCLEL; ISSN 0894-8755
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540110
540310* -- Environment
Aquatic-- Basic Studies-- (1990-)
DEVELOPED COUNTRIES
ENVIRONMENTAL EFFECTS
FLOW RATE
NORTH AMERICA
SOUTHERN OSCILLATION
STREAMS
SURFACE WATERS
USA
VARIATIONS