El Niño years bring stronger storms and heavier rainfall, putting added pressure on California’s coastal environment. These conditions intensify the stormwater and coastal issues CERF tracks year‑round, especially as warmer ocean temperatures make rainfall more unpredictable. They also strain water quality, public health, and the coastal habitats that rely on stable environmental conditions.
What is El Niño?
El Niño is a climate phenomenon triggered when ocean temperatures in the central and eastern tropical Pacific rise above normal levels. This added heat transfers to the atmosphere, temporarily rising global temperatures and shifting rainfall and weather patterns worldwide. These changes directly and indirectly affect the United States, particularly coastal regions like Southern California.
How Heavy Rainfall Impacts Coastal Water Quality
Heavy rainfall creates stormwater runoff that carries pollutants, bacteria, and debris from streets, industrial sites, and other developed surfaces into storm drains. This runoff often contains animal waste, fertilizers, and sewage leaks, which raise pathogen levels and fecal indicator bacteria in coastal waters. When this water reaches the ocean shortly after a storm, the risk of illness for swimmers and surfers increases because these contaminants are still highly concentrated.
Runoff also affects wildlife and coastal ecosystems. Floodwaters move trash, chemicals, and other pollutants into lagoons, beaches, and nearshore waters. Sensitive habitats such as wetlands and estuaries are especially vulnerable because they rely on stable water quality and balanced nutrient levels. When stormwater introduces pollutants or vast amounts of debris, these ecosystems can experience declines in species’ health, reduced oxygen levels, and disruptions to the plants and animals that depend on them.
Why El Niño’s Impacts are Stronger This Year
The 2026 El Niño is anticipated to be one of the strongest events on record. Pacific Ocean temperatures are rising quickly and reaching higher extremes than in previous cycles, and this is happening on top of an already warm global climate. Early in the year, sea surface temperatures are well above average, with some scientists predicting increases of 3°C to 4°C.
According to NASA, global temperatures have risen by approximately 1.4°C since the 19th century. Because this El Niño is forming in a much warmer world, its effects are amplified. Storms can become more intense, rainfall can arrive in more concentrated bursts, and coastal impacts tend to be more severe than in the past.
El Niño’s Impact on CERF’s Monitoring Efforts
CERF monitors stormwater and coastal conditions year‑round, but El Niño magnifies the issues we track. Heavy rainfall leads to more polluted runoff entering storm drains and coastal waters, which raises the likelihood of water quality impacts and beach closures. El Niño also heightens risks related to bluff erosion, flooding, and emergency coastal development requests. These conditions intensify the challenges CERF already addresses, making close monitoring during El Niño seasons essential for protecting water quality, public access, and coastal ecosystems.
How Communities Can Prepare
The City of San Diego offers practical guidance for residents and businesses to prepare for El Niño conditions. This includes recommendations for flood readiness, effective stormwater management, and safety considerations. For more information, visit: San Diego El Niño Resources.
Rachel Stewart – Programs Manager













