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Anticipated El Niño No Guarantee of Relief for Drought-Stricken California

November 2, 2015

Brad J. Arnold, UC Davis Center for Watershed Sciences

Possible rain due to a strong winter El Niño has many Californians optimistic that the multi-year drought may finally be coming to an end. However, increased rainfall from El Niño is no guarantee throughout the state, meaning the potential for only minor drought relief with the state’s current water system.

Californians are hopeful winter El Niño brings rain and snow to the Sierra
Nevada Mountains, currently at record lows due to drought. Photo from Pixabay.

El Niño refers to conditions when the Pacific Ocean temperatures warm along the equator. The warming tends to shift west coast weather patterns, causing storm systems of the Pacific Northwest to move farther south. This typically leads to cooler, wetter conditions in the coastal areas. Starting mid-2015 the National Oceanic and Atmospheric Administration (NOAA) has advised southwestern states to prepare for an increasingly strong winter El Niño. With California’s ongoing drought, the idea that El Niño will generate rainfall relief for the state is certainly a pleasant one, however it does not tell the whole story. While conditions may provide some relief for California, people should exercise caution before declaring El Niño a coming “drought savior.”

There are several misconceptions regarding El Niño’s impact on California’s water resources, many of which are discussed in a Sept 2015 report by Golden Gate Weather Services. One of the biggest and most misleading claims is that “El Niño guarantees lots of rain for California.” Although there is speculation of increased rainfall, recall that the benefits of El Niño come from weather patterns shifting southward, and that California is a remarkably long state (north-south extent). While parts of Southern and Central California illustrate stronger relationships between rainfall and El Niño, Northern California does not follow this same trend. That is, California can get more rain during El Niño, but not always and not everywhere.

El Niño likelihood of rain in California during winter season 2015-2016, from NOAA
Climate Prediction Center (July 2015). Figure adapted from Los Angeles Times.

Although rain anywhere in California is a positive when dealing with drought, it may only provide short-term relief. California’s water system is not set up to take advantage of most rainfall south of Sacramento.  It is built as a vast network of conveyance canals and reservoirs mostly located in the northern regions, designed around capturing and conveying the rain and snowmelt runoff from the Sierra Nevada Mountains and other northern watersheds. During wet conditions water is collected and stored in these reservoirs, and is then later moved hundreds of miles south to Central Valley farms and southern coastal cities to fulfill demands as needed, typically months later. This water storage and conveyance is critical in supplying water to the entire state, and is responsible for supplying a large portion of the state’s annual water requirements.

A recent Sacramento Bee article describes this conundrum; California water managers are tasked with storing water in the right locations and quantities to fulfill enormous demands at varying times in regions that normally get minimal precipitation. Many Central Valley farms rely on conveyed water for irrigation during hot and dry summer months. Urban water demands, while more seasonable stable, require water year round. As such, storage and conveyance is critically important towards mitigating droughts and annual water supply restrictions. Therefore while any precipitation is positive, the major downside to it largely occurring in Southern California is that it will do very little to refill northern reservoirs or alleviate limited supplies once the rain stops.

As UC Davis Center for Watershed Sciences (CWS) researchers wrote in 20145, “We all hope wet weather returns to California soon.” Many Californians were optimistic in the past that the developing El Niño would prevent a 2015 drought year, which did not happen. El Niño is driven by rapidly changing atmospheric patterns, making precipitation and weather conditions unpredictable4. Given the uncertainty and the structure of current water systems in the state, Californians should continue to be mindful of their water usage and strive for further conservation efforts to help prepare for continued drought conditions. Any winter precipitation in Northern California resulting from El Niño should be welcome (unless there is a flood).

For more information on California water issues visit the California WaterBlog; an online blog updated by scientists, faculty, students, and researchers at the CWS, a research center with the John Muir Institute of the Environment. Specific drought-related blog articles include: 1) long-term drought impacts on California resources, and 2) past projections of prolonged drought.

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