Saturday, February 6, 2010
El Nino and Haiti
Haiti has, of course, been in the news of late for the 7.0-magnitude earthquake it experienced on January 12. Nevertheless, some scientists had been making predictions that Haiti was primed for just such an event for years. Those likely went unheeded because many people don't often associate the region with seismic activity.
The natural hazards more commonly connected with Haiti are tropical storms and, with much of the western end of the island of Hispaniola denuded by decades of clear-cut forestry, landslides caused by heavy rain. Fortunately, tropical storms lend themselves to somewhat better prediction than earthquakes—but only just. And with a moderate-to-strong El Niño dominating weather patterns around the globe, perhaps those predictions stand a better chance of playing out this year and of helping the rescue response community prepare for a potential double (or triple) whammy of major storm followed by widespread landslides in a country already reeling from natural disaster.
El Niño is half of a back-and-forth sloshing of warm surface water across the equatorial Pacific Ocean between Indonesia and South America (the other phase of the phenomenon being a La Niña). Collectively, these two are known as the El Niño Southern Oscillation, or ENSO. During an El Niño year, the easterly trade winds of the southern Pacific die down, allowing warm water near Indonesia to spread across the surface of the ocean toward the coast of Peru, pumping moisture into the atmosphere and causing relatively predictable patterns of extreme weather around much of the globe. When La Niña predominates, cold water covers much of the same area of the Pacific and a different pattern appears.
The current El Niño, which began developing last fall, has been behind some of the severe winter storms in North America over recent months. It's also behind some of the nervousness that Olympic planners in Vancouver are undoubtedly feeling right now.
Haiti generally experiences a long rainy season from April to November with two distinct peaks—one around May and the other in September or October. In between, and extending into the tail end of rainy season, is when hurricanes typically make their way across the Atlantic and into the Caribbean basin. With the current El Nino phase expected to continue until March and possibly May, the Haitian people just might be able to breathe a little easier during hurricane season. That's because strong high-altitude winds caused by the Pacific warm water tend to cause something called wind shear, which prevent tropical storms from organizing into the large, deadly systems that have decimated the Caribbean in the past.
The effects of El Niño on the Caribbean rainy season, however, are a little less certain. NOAA is keeping up a weekly forecast for the region that looks two weeks into the future, but the most important period is May, when the potential for heavy rain is already high and even heavier downpours might threaten Haiti's denuded hillsides. Unfortunately, that is also the period when the state of ENSO becomes uncertain.
Forecasters are also keeping their eye on the equatorial Pacific for the signs that a La Niña might form because that would wipe out any protection that atmospheric conditions associated with El Niño might offer. "The worst scenario for Haiti would be for the development of a La Niña during the summer, for it would not only imply a wet 2nd half of their rainy season but also the chances for a tropical cyclone in their vicinity, or even a cyclone hit," Tony Barnston of the International Research Institute for Climate and Society wrote in an email.
So while things remain uncertain in a very vulnerable region, scientists and people on the ground will continue to look to the other side of the world for answers.