(Helmholtz Association of German Research Centres) For 20,000 years, climate variability in East Africa has been following a pattern that is evidently a remote effect of the ENSO phenomenon (El Nino Southern Oscillation) known as El Nino/La Nina. During the cold phase of La Nina, there is marginal rainfall and stronger winds in East Africa, while the El Nino warm phase leads to weak wind conditions with frequent rain.

(Helmholtz Association of German Research Centres) For 20,000 years, climate variability in East Africa has been following a pattern that is evidently a remote effect of the ENSO phenomenon (El Nino Southern Oscillation) known as El Nino/La Nina. During the cold phase of La Nina, there is marginal rainfall and stronger winds in East Africa, while the El Nino warm phase leads to weak wind conditions with frequent rain.

Scientists at the International Research Institute for Climate and Society (IRI), based at the Earth Institute at Columbia University, predict high probability for El Niño-Southern Oscillation (ENSO, commonly referred to as El Niño) conditions from July 2009 through to the end of the year.

The El Niño phenomenon is a fluctuation in ocean surface water temperature that causes shifts in normal global climate patterns such as drier and hotter conditions in Southeast Asia and Northern Australia, a milder hurricane season in the Caribbean and North Atlantic, and wetter, warmer winters in the Midwestern U.S.

El Niño conditions recur irregularly, with successive events typically happening three to seven years apart. Once an El Niño or La Niña event develops, it tends to persist for approximately one year. ENSO forecasts enable those in climate-sensitive industries such as agriculture and fishing to adjust business plans accordingly and government agencies to make projections about disaster relief need.

IRI is one of the leading sources worldwide for global climate forecasting and monitoring and has a long history of successfully predicting El Niño conditions. Mark Cane, G. Unger Vetlesen Professor of Earth and Climate Sciences, and Stephen Zebiak, IRI director-general were co-authors of the first computer model used to successfully forecast the El Niño.

A May forecast from IRI predicted that, “By Jul-Sep season and enduring through the end of 2009, the probability for El Niño conditions rises to 45%.” The probability for ENSO-neutral (near normal) conditions is 45 to 50 percent, and 5 to 10 percent for La Niña conditions. For the current May-July season, the probability for ENSO-neutral conditions is 75 percent.

The El Niño-Southern Oscillation is a system of interactions between the waters of the equatorial Pacific Ocean and the atmosphere above it. Seasonal shifts in ENSO influence climate elements such as temperature, wind and rainfall in many parts of the world. In addition to forecasting ENSO conditions, the IRI maintains an ENSO information page with basic as well as more technical information about these climate phenomena.