California is bracing for a potentially historic El Niño, with federal forecasters indicating the climate phenomenon is already underway and expected to strengthen through the northern hemisphere's autumn and winter.
Experts have warned that the El Niño could unleash extreme weather, including landslides, flash floods, and encroaching sea levels, which could all happen at once. Michael Anderson, a state climatologist, stated that the effects of El Niño will add an additional foot of sea level rise in California.
Governor Gavin Newsom issued a state of emergency on 21 September to mobilise efforts and resources. Preparations are underway at all levels of government to secure infrastructure, preset response resources, and inform the public of incoming hazards.
Marin county experienced high tides last week, causing flooding in a busy intersection north of San Francisco. This event is seen as an early signal of California's vulnerabilities.
While Southern California typically experiences wetter winters during El Niño years, the impact may vary across the state's 770 miles. Dr Ariel Cohen, a meteorologist for the National Weather Service, noted that a strong El Niño shifts probabilities but does not determine exact outcomes.
In areas with recent wildfire burn scars, such as the slopes of Big Sur and neighbourhoods affected by the 2025 firestorm in Los Angeles, there is a higher chance of debris flows. Mark Pestrella, director of the Los Angeles county public works department, stated that flood control systems are ready and optimised, designed to withstand a "100-year event," though El Niño could increase those chances.