UC San Diego

Extreme events, like drought, large storms, and coastal floods are expected to increase under climate change. Along the coast, where an estimated 1 billion people are expected to reside by the end of the century, these hazards threaten infrastructure and livelihoods. Here, we investigate two coastal hazards that are expected to worsen under climate change: coastal storms and their impacts on beaches, and saltwater intrusion (SWI) impacts on coastal freshwater use, which are linked through total water level at the shoreline. To investigate the first coastal hazard, we use stationary lidar data with high spatial and temporal resolution to compare observations of runup with predicted runup using various runup parameterizations in the Outer Banks, NC, USA. We also investigate the performance of the parameterizations using a pre-storm versus a time varying beach slope. The results suggest that a pre-storm beach slope may be sufficient in predicting runup throughout a storm for a number of parameterizations, but that the presence of two-dimensional morphologic features (beach cusps) greatly degrade the performance of the parameterizations. To address the second coastal hazard, we use inland hydrologic and oceanographic datasets to investigate the drivers of SWI in the surface freshwater sloughs of the Pajaro Valley, CA, USA. The results of this study suggest that the co-occurrence of high total water levels (oceanic water level plus wave runup) and low inland flow conditions create the conditions necessary for SWI. Additionally, the closure of the lagoon mouth, which is driven by identical processes, is likely a key component in SWI occurrence. Finally, we expand the SWI study to incorporate future climate scenarios using modelled sea level and precipitation and simulations of wave time series. Under the CMIP5 RCP 8.5, 99th percentile, SWI risk frequency is expected to increase by nearly 20% by the end of the century. This increase is dominated by sea level rise, with some variability contributed by the timing of large wave and low precipitation events. The investigation of these hazards advances the science-informed development of coastal and freshwater mitigation strategies under a changing climate.