El Niño is a phenomenon that occurs when unusually warm ocean water piles up along the equatorial west coast of South America. When this phenomenon develops, it affects weather patterns around the globe, including the winter weather along the west coast of North America. This unusual pattern of sea surface temperatures occurs in irregular cycles about three to seven years apart.
During an El Niño year, California and parts of the southern U.S. can be subject to a cold, wet winter. Winter is normally the rainy season in California, and during past El Niño winters (especially in really strong El Niño years, like this one), greater-than-usual numbers of storms arrive, one after another, resulting in wetter-than-usual winters with large amounts of rain on the coast and snow in the mountains. Some El Niño years (especially weak to moderate El Niños) result in dryer than average years in California and the West Coast, providing few storms to wet the landscape.
El Niño conditions have frequently brought drier, warmer winters to the northern parts of the continental U.S. Specifically in the Pacific Northwest, an El Niño tends to favor a warmer winter and lower-than-average precipitation. In turn, these conditions tend to favor a thinner winter snowpack and subsequently less meltwater in the spring. An El Niño can potentially create conditions for more severe flooding in the wetter winter months and possibly drier spring and summer months in the Pacific NW. In California, historically some of the heaviest precipitation, and all of the largest flood years have been non-El Niño years.
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| During an El Niño winter, the temperatures in the northern U.S. are usually warmer and drier than average, and the southern parts of the continental U.S. are usually cooler and wetter. Image credit: NOAA. | |
El Niño weather is not just a single severe storm, but it can increase the number and intensity of storms during a season, triggering floods, landslides, coastal erosion, and damage to fragile ecosystems. These changes may occur as early as October in an El Niño year, but typically are strongest in winter and early spring. Now mid-January, California is starting to feel the full force of these sequential El Niño winter storms.
Although the U.S. Geological Survey doesn’t directly study or forecast the weather (our sister agency, NOAA, and its National Weather Service do), the USGS studies and documents the effects and impacts of long-term climate changes and weather phenomena across the U.S. and globally. In particular, the USGS monitors streamflow, floods, landslides, erosion, sea-level rise, and many other earth processes that affect communities and that are often affected by El Niño weather patterns. USGS closely monitors these effects to assist the NWS in its responsibilities for hazard warnings and to assist communities across the country in their preparation, response, and recovery activities.
In addition to the obvious effects El Niño can have on storms, floods and coastal hazards, it can also affect long-distance migratory birds, the snowpack in the mountains of the western U.S., fire seasons in Alaska and across the continental U.S., the health and distribution of oceanic and freshwater fish, and even very local environments such as the sediment and algae in the waters of San Francisco Bay. The USGS studies and monitors these effects and provides much of the scientific basis for planning and responding to them.
The USGS is on the scientific front line in studying the impacts of El Niño. Read further to learn about some of the many ways USGS science helps communities remain resilient in the face of natural hazards.
Hydrologic monitoring and streamgages
USGS monitors the nations waterways with more than 8000 active continuous streamgages across the country. These streamgages tell emergency managers and the public how much water is coming down a river or stream; they are the front line in keeping track of floods and inundation that can be caused by El Niño storms. USGS works to ensure that streamgages in the West and across the country are fully operational during extreme conditions of an El Niño weather pattern.
Most USGS streamgage stations are equipped to transmit information in real time to local, state, and national emergency management and warning agencies such as the National Weather Service and the U.S. Army Corps of Engineers. Real-time streamgage data are also available to the public online. USGS provides streamflow data so that the public has the earliest possible warning of an impending flood.