Southern California Deep-Water Wave Climate: Characterization and Application to Coastal Processes

Abstract

We consider the effect of decadal climate change on the historic wave climate of the Southern California Bight (SCB) using a 50 year hindcast record (1948–98) for waves generated in the North Pacific winter. Deep-water wave height, period, and direction are examined with respect to the Southern Oscillation Index (SOI) and the Pacific Decadal Oscillation (PDO). Storms occurring during strong La Niña intervals, when the SOI is greater than 1.0, concurrent with either a cool or warm phase of the PDO, are indistinguishable in wave character. In marked contrast, wave conditions arising from storms during strong El Niño intervals, when the SOI is less than −1.0, concurrent with the PDO cool phase (1948–77), differ greatly from wave conditions of storms during strong El Niño intervals concurrent with the PDO warm phase (1978–98). Our statistical analyses characterize the deep-water winter wave climate as consistent during La Niña intervals (mean values Hs =3.3 m, Ts =13.0 s, α =293°, for the highest 5% of waves), but variable during El Niño intervals depending on PDO phase (Hs =3.64 m, Ts =13.8 s, α =292°during the PDO cool phase, and Hs =4.82 m, Ts =15.1 s, α =284°during the PDO warm phase, for the highest 5% of waves). The dominant characteristics for the different operational modes of wave climate determined in this study provide realistic inputs for numerical models aimed at understanding past and future coastal change within the SCB. Simulating WAves Nearshore (SWAN)-modeled wave transformations for the southern portion of the Oceanside littoral cell show that nearshore wave heights during westerly wave conditions are roughly twice those of northwesterly wave conditions for the same deep-water wave heights and periods, indicating increasing wave energy flux at the beach during the westerly storm-source conditions by an average of 320% (74 kW/m vs. 23 kW/m).