Southern California Coastal Response to the 2015–2016 El Niño

Abstract

Widespread erosion associated with energetic waves of the strong 2015–2016 El Niño on the U.S. West Coast has been reported widely. However, Southern California was often sheltered from the northerly approach direction of the offshore waves. The few large swells that reached Southern California were not synchronous with the highest tides. Although west coast‐wide tidal anomalies were relatively large in 2015–2016, in Southern California, total water levels (sum of tides, anomalies, and wave superelevation) were lower than during the 1997–1998 Niño, and comparable to the 2009–2010 Niño. Airborne lidar surveys spanning 300 km of Southern California coast show the beach response varied from considerable erosion to accretion. On average, the shoreline moved landward 10 m, similar to the 2009–2010 El Niño. Some San Diego county beaches were narrower in the 1997–1998 El Niño than in 2015–2016, consistent with the higher erosion potential in 1997–1998. Beach retreat exceeded 80 m at a few locations. However, 27% of the shoreline accreted, often in pocket beaches, or near jetties. While adjacent beaches eroded, estuary mouths accreted slightly, and several estuaries remained or became closed during the study period. Only 12% of cliffs eroded (mostly at the base), and the average cliff face retreat was markedly less than historical values. Only two cliff‐top areas retreated significantly. Although some areas experienced significant change, the potential for coastal erosion and damage in Southern California was reduced compared to the 1997–1998 El Niño, because of low rainfall, a northerly swell approach, and relatively limited total high‐water levels.

Effects of Elevated Sea Levels and Waves on Southern California Estuaries During the 2015–2016 El Niño

“…2012;Griggs et al 2017), although other estimates suggest that these sea-level rise conditions may occur sooner (e.g., Sweet et al 2017). Anomalously large waves recorded during the 2015-2016 winter along the Southern California coast (Flick 2016;Ludka et al 2016;Barnard et al 2017;Young et al 2018) is consistent with prior El Niño events (Bromirski et al 2003). Young et al (2018) described that, although modeling suggests that storm tracks are projected to shift pole-ward resulting in decreased waves in sheltered regions of the Southern California Bight (e.g., Graham et al 2013;Erikson et al 2016), there is nonetheless likely to be an increase in extreme water level events due to rising seas alone in Southern California (Tebaldi et al 2012;Sweet and Park 2014).…”

“…The 2015-2016 El Niño provided an opportunity to assess how low-inflow estuaries might respond to climate change, as El Niño conditions mimic climate-change effects including sealevel rise and intensified wave events (e.g., Bromirski et al 2003;Ludka et al 2016;Barnard et al 2017;Cayan et al 2008;Cai et al 2014). During the 2015-2016 winter, ocean water levels were persistently above average (Young et al 2018) due to a combination of large-scale atmospheric forcing, thermal expansion effects, storm surge, and large wave events (e.g., Enfield and Allen 1980;Chelton and Davis 1982). The sea-level anomaly at the La Jolla tide gauge during the 2015-2016 El Niño was comparable to the amount of sea-level rise likely to occur by 2030 (National Research Council.…”

“…Anomalously large waves recorded during the 2015-2016 winter along the Southern California coast (Flick 2016;Ludka et al 2016;Barnard et al 2017;Young et al 2018) is consistent with prior El Niño events (Bromirski et al 2003). Young et al (2018) described that, although modeling suggests that storm tracks are projected to shift pole-ward resulting in decreased waves in sheltered regions of the Southern California Bight (e.g., Graham et al 2013;Erikson et al 2016), there is nonetheless likely to be an increase in extreme water level events due to rising seas alone in Southern California (Tebaldi et al 2012;Sweet and Park 2014). At the same time as sea levels were high and wave events were more intense than normal, 2015-2016 winter precipitation was near or below average in Southern California (e.g., Lee et al 2018;Siler et al 2017).…”

Sixteen years of bathymetry and waves at San Diego beaches

“…These datasets have been used to investigate equilibrium behavior of the shoreline 12 and beach profile 13 , beach response to two energetic El Niño winters 14–19 and the evolution of four beach nourishments 17,20–23 . The performance of 1-D (imensional) storm erosion models (XBeach) 22 , and 2-D morphological evolution models (Delft3D) 24 have been assessed.…”

Long Term Ground Based Precipitation Data Analysis: Spatial and Temporal Variability

“…However, the same cannot be said for the modeled time-series. This could be due to the effects of the ocean and land dynamics as climate divisions four and six are coastal lands[80,198].…”