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Sea-Level Rise, El Niño, And The Future Of The California Coastline

Creative Commons 'BY' version 4.0 license

Global mean sea level increased by ~20 cm during the 20th century and the rate is expected to accelerate during this century. Many major cities are already exposed to damaging coastal storms and sea-level rise (SLR) will magnify storm impacts. SLR adaptation can reduce harm, but this new concept is complicated because adaptation plans must be tailored to each community's specifications, due to differences in geologic setting, development, etc. This study designed a process for local SLR adaptation planning, in part through the assessment of the city of Santa Barbara's vulnerability to SLR, including evaluations of shoreline topography and development, historical storm damage, and exposure to SLR. The risk of wave damage to Santa Barbara's shoreline development and infrastructure will be high by 2050 but very high by 2100. The risk of flooding and inundation of low-lying areas will be moderate by 2050 but very high by 2100. The risk of increased cliff erosion rates will be moderate by 2050 but very high by 2100. The threat of beach inundation will be low by 2050 but high by 2100.

Most of the flooding and erosion along the U.S. West Coast are caused by storm surges and wind-driven waves, particularly during strong El Niño events. There is a need to predict El Niño occurrences for planning purposes, but forecasts from most of the best El Niño Southern Oscillation (ENSO) prediction models have plateaued at a moderate level, leaving room for improvement in ENSO observing systems, models, and data assimilation methods. While the effects of ENSO on wave heights along the U.S. West Coast are well known, no prior studies have examined whether wave heights are also predictive of the phenomenon. This study finds that significant wave heights (Hsig) along the U.S. West Coast are slightly suppressed during the summers preceding El Niño winters, but the trend is weak and the data are noisy, so contributions to ENSO forecasts are negligible. The summer Hsig trend is strongly associated with the summer North Pacific (NP) Index, which measures the area-weighted sea-level pressure over the Gulf of Alaska.

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