| Summary: | El Niño episodes have historically been associated with an increased frequency of extratropical cyclones and cold front passages in Southern California, largely as the result of a southward shift in the Jet Stream. Thus, increases in precipitation, along with hazards, such as flooding and coastal erosion, normally increase during winters when El Niño circulation is strong. However, the strong El Niño episode of 2015-2016 did not confirm this expectation, further contributing to the growing body of evidence that El Niño episodes vary considerably. A common classification system, as outlined by Yu and Kim (2013), differentiates El Niño circulation modes based on the location of the initial appearance of warm water in the Equatorial Pacific. Quantitative and qualitative analyses are used to assess whether this classification of El Niño episodes is useful in the context of winter storm impacts in California. There is some evidence that Central Pacific (CP) episodes may be associated with higher levels of rainfall than Eastern Pacific (EP) episodes, owing to increased storm duration. Eastern Pacific episodes, most notably in 1982-1983, and 1997-1998, generated energetic waves and caused severe beach erosion, although nearly as much coastal impact was observed during the 2009-2010 CP El Niño episode. Overall the influence of circulation mode appeared to be weak, variation between El Niño years appears to be more strongly determined by the tracks and characteristics of individual winter storms than by overall mode of El Niño circulation. However, since winter storms are the only significant source of precipitation and are the primary cause of episodic coastal erosion in Southern California, further study of the differing effects of EP and CP El Niño episodes is crucial for planning for the future in the region.
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