Influence of ENSO on Flood Frequency along the California Coast

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Abstract
The influence of the El Niño–Southern Oscillation (ENSO) phenomenon on flooding in California coastal streams is investigated by analyzing the annual peak floods recorded at 38 gauging stations. The state of ENSO prior to and during flooding is characterized by the multivariate ENSO index (MEI), where MEI < −0.5 is defined as the La Niña phase and MEI > 0.5 as the El Niño phase. Flood magnitude in all 20 streams located south of 35°N has a significant positive correlation (r = 0.3 to 0.6), whereas in 3 of the 4 streams located north of 41°N flood magnitude has a significant negative correlation (r = −0.3 to −0.4), with MEI from −2.2 to +3.2. Correlations with MEI are uniformly weak and insignificant, however, when the floods are subdivided into El Niño and non–El Niño phases. A comparison of the geometric mean El Niño flood to the geometric mean non–El Niño flood determined that the means were statistically different at gauging stations south of 35°N and north of 41°N. For 20 streams located sout... Abstract The influence of the El Niño–Southern Oscillation (ENSO) phenomenon on flooding in California coastal streams is investigated by analyzing the annual peak floods recorded at 38 gauging stations. The state of ENSO prior to and during flooding is characterized by the multivariate ENSO index (MEI), where MEI < −0.5 is defined as the La Niña phase and MEI > 0.5 as the El Niño phase. Flood magnitude in all 20 streams located south of 35°N has a significant positive correlation (r = 0.3 to 0.6), whereas in 3 of the 4 streams located north of 41°N flood magnitude has a significant negative correlation (r = −0.3 to −0.4), with MEI from −2.2 to +3.2. Correlations with MEI are uniformly weak and insignificant, however, when the floods are subdivided into El Niño and non–El Niño phases. A comparison of the geometric mean El Niño flood to the geometric mean non–El Niño flood determined that the means were statistically different at gauging stations south of 35°N and north of 41°N. For 20 streams located sout...