State and federal scientists confirm that a significant rise in sea levels is inevitable within the next three decades. The year 2050 represents a planning deadline for coastal communities, where the cumulative effects of a rising ocean will fundamentally alter the state’s shoreline and low-lying areas. Projections indicate a statewide average sea-level increase of approximately 0.8 feet, or nearly 10 inches, by mid-century under the most likely scenario. This rise will not result in permanent, chronic inundation across the entire coast, but it will dramatically increase the frequency and severity of flooding, transforming today’s rare events into routine occurrences.
Understanding the Drivers of Coastal Inundation
The acceleration of sea-level rise along the California coast is driven by a combination of global and localized geological processes. The primary global factors are the thermal expansion of ocean water as it warms and the massive inflow of meltwater from land-based ice sheets and glaciers. These two factors account for the bulk of the worldwide sea-level increase.
Local conditions, however, determine the actual, relative rate of rise experienced at any specific point along the coast. Vertical land motion is the largest variable affecting local projections across California. This involves the sinking or rising of the land itself, a process known as subsidence or uplift, which is primarily caused by tectonic plate movement.
Other localized factors that influence the land’s elevation include sediment compaction in river deltas and the withdrawal of groundwater or hydrocarbons. In areas where the land is sinking (subsiding) due to these local effects, the impact of a globally rising sea level is significantly amplified. Incorporating these vertical land movements into models is why sea-level rise projections vary from one tide gauge location to the next.
Vulnerable Regions in Northern and Central California
The San Francisco Bay Area and the Sacramento-San Joaquin River Delta represent the most vulnerable low-lying regions in Northern and Central California. The Bay Area’s extensive, flat perimeter means that a modest sea-level rise can push water far inland, threatening major economic hubs and infrastructure. For instance, the runways and access roads around San Francisco International Airport (SFO) are highly susceptible to increased flooding.
Beyond the airport, infrastructure in Silicon Valley, particularly around communities like Alviso and Sunnyvale, is built on reclaimed wetlands and is at risk. This includes low-lying highways and numerous wastewater treatment plants situated along the Bay’s edge. Scientists estimate that the Bay Area has dozens of miles of highways and railways, alongside thousands of acres of airport land, that face increased flood exposure by 2050.
Further inland, the Sacramento-San Joaquin River Delta faces a dual threat to its vast levee system. The Delta is largely below sea level, protected by earthen barriers that guard significant agricultural areas and communities. Saltwater intrusion, a direct consequence of rising sea levels, threatens the Delta’s freshwater supply, which is pumped to two-thirds of the state’s population. Inundation in this region would compromise the state’s water infrastructure and agricultural output.
Projections for Southern California Coasts
While much of the Southern California coastline features steep cliffs, the region contains low-lying harbors, bays, and beach communities that are extremely vulnerable. In the Los Angeles area, the Port of Los Angeles and two major wastewater treatment facilities are situated close to the water’s edge, within ten feet of sea level. Disruptions to these facilities from increased flooding would have major economic and public health consequences for the urban core.
Orange County’s coastal areas, including parts of Huntington Beach and the infrastructure surrounding Newport Bay, are already experiencing periodic flooding during extreme high tides. Further south, San Diego faces increased exposure in its low-lying coastal lagoons and popular beach communities like Mission Beach. Many of the region’s beaches are projected to experience significant erosion as rising water levels erode the sand.
The rise in sea level exacerbates the risk to critical infrastructure built in these areas. This includes underground utilities and coastal rail lines that run parallel to the shore, which are frequently affected by storm-driven waves.
Translating Projections into Real-World Impacts
The term “underwater” in the context of 2050 projections does not primarily mean permanent, chronic submersion of land. Instead, the most immediate and frequent impact will be increased episodic flooding, which is the temporary inundation of land during specific events. State guidance from the California Ocean Protection Council and federal data from the National Oceanic and Atmospheric Administration (NOAA) emphasize this distinction.
The high-probability scenario of roughly 10 inches of sea-level rise by 2050 means that today’s rare flood events will become commonplace. Currently, mild coastal flooding that occurs once or twice a year is projected to happen nearly 50 times annually by mid-century. This means that infrastructure will be repeatedly compromised by “sunny day” flooding during normal high tides, particularly during seasonal King Tides.
This episodic flooding poses an immediate threat to the functionality of key infrastructure assets, including coastal roads, segments of the state’s rail lines, and utility systems. A small rise in sea level can be enough to push storm surges and high tides over existing seawalls and flood barriers, leading to repeated, disruptive closures of transportation corridors. The repeated exposure to saltwater will also accelerate the corrosion and failure of underground utilities and pipes.