The importance of weather and short period climate events in driving projected high sea level extremes along the California Coast

Relative sea level rise along southern and central California over the last century has been observed at nearly 2mm/year, similar to estimated global rates. Sea level rise scenarios over the next several decades vary widely, but recent projections tend to be much larger than the historical rate. However, even if sea level rise is amplified considerably, weather and short period climate effects will play a key role. Historically, the most severe high sea level conditions have arisen when North Pacific storms and ENSO conditions have coincided with high astronomical tides. In many instances, high wind-generated waves exacerbate high sea level events, and in some settings, heavy fresh water runoff also contributes. A model which includes these mechanisms, driven by factors derived from a set of global climate model simulations, provides an ensemble of hourly sea level projections that demonstrate that the occurrence high sea level events along the California coast will continue to be dominated by high tide and large storm occurrences during the next several decades, although their amplitude and duration will increase progressively. In the Sacramento/San Joaquin Delta estuary, fresh water flooding that sometimes accompanies large winter storms will compound high oceanic sea level impacts.