On the Fragile Relationship Between El Niño and California Rainfall

Abstract

The failed influence of the 2015–2016 El Niño on California rainfall has renewed interest in the relationship between El Niño and U.S. rainfall variability. Here we perform statistical data analyses and simple model experiments to show that sufficiently warm and persistent sea surface temperature anomalies (SSTAs) in the far eastern equatorial Pacific are required to excite an anomalous cyclone in the North Pacific that extends to the east across the U.S. West Coast and thus increases rainfall over California. Among the four most frequently recurring El Niño patterns considered in this study, only the persistent El Niño, which is often characterized by the warm SSTAs in the far eastern equatorial Pacific persisting throughout the winter and spring, is linked to such extratropical teleconnection patterns and significantly increased rainfall over the entire state of California. During the last 69 years, only three of the 25 El Niño events (i.e., 1957–1958, 1982–1983, and 1997–1998) are clearly identified as the persistent El Niño. In addition, the monthly rainfall variance explained by El Niño is less than half that caused by internal variability during the 25 El Niño. Therefore, the rarity of persistent El Niño events combined with the large influence of internal variability effectively explains the fragile relationship between El Niño and California rainfall.

Ongoing Increase in Eastern Tropical North Pacific Denitrification as Interpreted Through the Santa Barbara Basin Sedimentary δ15N Record

“…No evidence was found for coherent and significant variations in bulk sedimentary δ 15 N due to ENSO variability, with differences in δ 15 N records between the 1997 and 2015 El Niño event potentially attributable to variations in rainfall and terrestrial δ 15 N inputs (Figure ; Jong et al, ; Lee et al, ; Sweeney & Kaplan, ). A decrease in sediment trap δ 13 C org is associated with both El Niño events.…”

A regime shift in sediment export from a coastal watershed during a record wet winter, California: Implications for landscape response to hydroclimatic extremes

“…Lee et al, 2018). Although large fluvial sediment fluxes in central California tend to correspond to an El Niño phase combined with a warm PDO phase, and to a La Niña phase combined with a cool PDO phase (Andrews and Antweiler, 2012), these general tendencies did not hold in 2015-2017 (cf.…”

“…The El Niño of 2015-2016, one of the strongest in the last 145 years, involved major sea-surface-temperature anomalies, record-setting winter wave energy, and severe beach erosion in California (Jacox et al, 2016;Barnard et al, 2017), but produced average rainfall, only minor landsliding, and unremarkable river discharge in California (Figure 2), whereas the record-wet 2016-2017 winter corresponded to neutral ENSO conditions and the nearly neutral end of a warm PDO phase (University of Washington, 2017; NOAA, 2017b). Although the interactions among the ENSO and PDO cycles, atmospheric-river storm activity, flooding, and landslides remain incompletely understood and are active areas of study (Konrad and Dettinger, 2017;Young et al, 2017;Lee et al, 2018), some researchers have proposed that atmospheric rivers could reach the US west coast most easily during ENSO-neutral conditions (Bao et al, 2006), perhaps creating the greatest risk of atmospheric-river-driven flooding and slope failure in such years. Large landslides and widespread debris flows associated with that storm probably pre-conditioned watersheds to release higher sediment yield during intense rainfall the following winter (the strong El Niño of 1982Niño of -1983, which produced a 10-year flood in the San Lorenzo River).…”

“…These atmospheric-river storms often cause intense rainfall upon reaching coastal and interior mountains, providing an important source of water supply throughout California (Dettinger, 2011;Guan et al, 2016). However, effects of the ENSO cycle on California rainfall show considerable variation spatially and from one El Niño event to another (Hoell et al, 2016;Barnard et al, 2017;Lee et al, 2018) and substantial uncertainty remains as to how these effects can best be conceptualized. El Niño winters generally have been associated with above-normal precipitation, landsliding, greater fluvial sediment flux, and extreme beach erosion along the California coast (Cayan et al, 1999;Godt, 1999;Hapke and Green, 2006;Mertes and Warrick, 2001;Barnard et al, 2011Barnard et al, , 2015Barnard et al, , 2017Gray et al, 2015).…”

Propagating Modes of Variability and Their Impact on the Western Boundary Current in the South Atlantic

“…Despite similarities, ENSO events differ in terms of their magnitude, evolution, and location of SST anomalies in the equatorial Pacific (Fedorov et al, ; S.‐K. Lee et al, ; T. Lee & McPhaden, ; Taschetto et al, ; Xie et al, ) as well as teleconnection patterns. In the South Atlantic, teleconnections from the central Niño modes are found to weaken and shift the Subtropical high equatorward which triggers the negative phase of the SASD.…”