El Nino

You may have noticed that this year has been wetter than last. It’s rained almost every day this summer, where as last year it was devastatingly dry. It’s not that the South’s long drought is over– it’s actually El Niño. El Niño means “the child” in Spanish, but more specifically refers to the Christ child. It is so named because in South America the phenomenon is most noticeable around Christmas. Also called the Southern Oscillation, El Niño occurs every three to eight years, though it has no well-defined period.

Scientists have known about El Niño for a long time. The phenomenon was observed as far back as the Holocene epoch, 10,000 years ago. The first time this recurring weather pattern was referred to as the Christ child was in the late 1800s. Around that time scientists began to notice that droughts in India and Australia occurred simultaneously. In 1924 Gilbert Walker observed the interactions between warm sea air and cooler land air in the Pacific ocean. He called the predictable pattern the Southern Oscillation. The Southern Oscillation is the atmospheric counterpart to El Niño, and is what drives the system. We now know that the Walker circulation (named for Gilbert), a group of trade winds in the Pacific, begins to falter as one of the first signs that an El Niño event is beginning. When these trade winds die, water in the Pacific produce warm waves that travel along the equator to the South American coast, which is usually cold due to upwellings of cooler, deeper waters. But the added warmth of these waves begins a trend that builds over time until an El Niño event occurs.

Other than the near-daily rain, El Niño also effects the South in other beneficial ways. The summer temperature is lower during El Niño, and the added rainfall reduces the risk of wild fires. We’ll also experience a wetter, milder winter this year. And because it diverts heat from the Atlantic to the Pacific, expect this hurricane season to produce few large storms, thanks to El Niño.

But not all the effects are good. Warmer water off the coast of South America reduce the nutrient content of the water, harming the fishing industry. And a wetter growing season means later and smaller crop harvests, in most cases. Midwestern states are more likely to flood as well. There is also some evidence of a correlation between the increase in algae blooms (or red tide) off the California coast.

Though it can last for up to two years, this El Niño is expected to only last through winter. If it persists Spring 2010 will be colder and dryer. La Niña, the sister system to El Niño, always follows. Expect a hotter, dryer summer next year. So enjoy this respite while you can, because next year promises to be nearly unbearable.