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Will the coming El Niño save California’s agriculture?

10 November 2014
With the entire state experiencing moderate to exceptional drought, farmers find themselves hoping for severe weather.

According to a report released in June 2014 by the National Drought Mitigation Center in Lincoln, Nebraska, 100% of California is in a severe drought, 77% is in an extreme drought, and 3% is in an exceptional drought.

Since the National Drought Mitigation Center began keeping detailed data in 1999, California has not seen an exceptional drought. Now, one-third of California—from Santa Barbara in the south to the Bay Area, Sacramento and the agriculture-rich Central Valley in the north—is experiencing these most dire of weather conditions. The prolonged nature of the current drought prompted California governor Jerry Brown to declare a state of emergency in January of 2014. Cities and other municipalities across the state are using all possible means to conserve as much water as possible.

With rain totals in some parts of the state at 100+ year lows, and much of the western US suffering through an equally arid period, we must ask: Is there an end in sight? And what will be the consequences of a such a period of climatic extremes?

One of the areas suffering exceptional drought is the Central Valley, an area that cuts a large rectangular swath of approximately 58 000 km2 (22 500 square miles) through the middle of California and contains some of the richest farmland in the US. According to a recent report from the Department of the Interior, this area is responsible for 5% of the nation’s agricultural output.

The current moisture deficit in the Central Valley has potential implications on our nation’s food supply and could lead to rising prices of fruit, tree nuts, and dairy. More than half of California’s agricultural crop value comes from its production of fruit and tree nuts, which is almost 60% of total US fruit and tree nut farm values. Shortages in groundwater used to irrigate the fruit crops could increase production costs or force farmers to reduce acreage, raising fruit prices for years to come.

Drought-shriveled almond trees in California's Central Valley. CREDIT: House Committee on Natural Resources

Drought-shriveled almond trees in California's Central Valley. CREDIT: House Committee on Natural Resources.

But the weather that has caused California’s current predicament may change in the coming months: We may be due for an El Niño. This is a complex weather phenomenon that occurs every two to seven years and brings warmer temperatures to the east and central tropical Pacific waters for about a year. An El Niño event typically coincides with a change in the mid-latitude trade winds. As the El Niño sets in, the trade winds weaken, and, when paired with warmer Pacific Ocean waters, it causes significant changes in weather.

Although the extent and nature of these changes depend on the strength of the El Niño, the changes can bring heavier rain to South America, drought to Australia and Indonesia, warmer and drier winters to the Midwest and Eastern US, and wetter winters to California and the Southwest US. Because the decrease in trade winds associated with El Niño affects the movement of the jet stream, the US usually feels the changes in weather during the winter months when much of our weather depends on the location of the jet stream.

Although the El Niño’s warmer Pacific Ocean waters and weakened trade winds do influence our weather, El Niño is not the singular deciding factor of the weather in an El Niño season. Many other influences around the world can dampen the strength and the resulting effects of the El Niño. Initial data suggested an increasing likeliness for an El Niño to occur this year. In September 2014 Pacific Ocean waters were rising unusually quickly, and forecasters were calling for the 0.5 °C sea surface rise in temperature above historical average, the traditional indicator of the onset of an El Niño, with 80% confidence. But additional data accumulated in recent months has altered the prediction, and confidence in the occurrence of an El Niño event has dropped to 66% (as of early October 2014).

The most recent occurrence of a significant El Niño happened during the winter of 1997–98. During that event, sea surface temperatures in the equatorial east-central Pacific increased to nearly 29 °C and up to 4 °C departures from normal were observed in the waters off the west coast of South America. The repercussions for US weather were dramatic; The first two months of 1998 were the warmest and wettest on record for the contiguous 48 states dating back to the beginning of temperature and precipitation measurement collection in 1895. California experienced its wettest February in history and broke monthly precipitation records at nineteen stations including Santa Barbara (currently experiencing exceptional drought), which received an astounding 21.74 inches of rain in February 1998.

This year's El Niño

How do the current Pacific Ocean conditions compare to that of the El Niño of 1997–98 and what does it mean for California’s drought-stricken land? Many scientists have been pondering these questions, including CLIMAS climate scientists Zack Guido and Mike Crimmins. In their June 2014 Southwest Climate Podcast they described summer sea surface temperatures in the eastern Pacific Ocean to be at similar levels as the 1997–98 event. Warmer water temperatures do not guarantee an El Niño event will take place. This was the case in 2012, when, despite all indications that an El Niño was likely to occur, the event did not materialize.

Scientists agree that this is the warmest Pacific Ocean waters have been since the 1997–98 event, and this leaves conditions very favorable for an El Niño event to occur—assuming that the atmosphere decides to follow the lead of the warmer surface waters. If atmospheric coupling does not happen, the 2014 El Niño will be much weaker, and may not happen at all, which means that California will remain parched and perhaps experience even more exceptional drought.

Given that El Niño strength corresponds to storm energy, a small El Niño could mean another dry winter for the southwest US and California. The good news for California farmers: Forecasters are still calling for an El Niño event to occur in the coming months with a 66% probability. The bad news: Forecasters are also observing other unusual conditions, like the Pacific Decadal Oscillation trending towards positive for the first time in over 10 years, which could send the potential El Niño in many different directions. With little comparison to previous events, it is difficult to say what will come of some of these rare conditions and the impending El Niño.

In the midst of all this uncertainty, one thing is perfectly clear: Drought-stricken California needs a change in meteorological fortune, possibly in the form of a strong El Niño, to rectify its ongoing water crisis. After a long summer of hot and dry weather and four consecutive winters of below-normal precipitation, a wet winter would be a welcome sight to many California farmers. However, if the precipitation comes all at once, or in a few quick storms, the land may not be able to absorb all of the water, which could cause widespread flooding.

Absent a strong El Niño, California might find itself in the odd position of hoping for a hurricane to bring relief. Summer 2014 had an exceptionally active start to the hurricane season in the Pacific Ocean. The earliest category 4 hurricane on record in the eastern Pacific was observed this summer, together with several other well-defined hurricanes that ultimately turned back to sea. With the warmer Pacific Ocean waters, we will likely see more hurricanes in the eastern Pacific this hurricane season, and can expect that a couple of storms will make landfall.

A hurricane might not be the most ideal solution for California but a smaller (tropical) storm would bring some water relief without the corresponding wind-related damage. In any event, with all of the unusual conditions ongoing in the Pacific Ocean, the end of 2014 is likely to yield a few, hopefully beneficial, surprises.

Kristy Carter is a graduate student in the Department of Geography at the University of South Carolina in Columbia. Korey Carter is a graduate student in the Department of Chemistry at the George Washington University in Washington, DC.

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