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Statement from the Pacific South America Climate Outlook Forum

October 28, 1997
Lima, Peru

THE OUTLOOK FORUM

A Climate Outlook Forum was convened in Lima, Peru on October 28, 1997 to formulate a consensus assessment for the summer season in Pacific South America. The Forum was comprised of representatives of Meteorological Services and climate researchers from universities and national and international research agencies. These specialists reviewed the state of the global climate system and its implications for Pacific South America. One of the principal factors taken into account is the strong El Nino event currently underway in the tropical Pacific Ocean. Recent El Niño events resulted in extreme rainfall in some regions of Pacific South America and extreme dry conditions in other regions. The Forum was co-sponsored by the Inter-American Institute for Global Change Research (IAI); the Instituto Peruano de Investigaciones Pesqueras (INPESCA); the Instituto Geofísico del Perú (IGP); SeaLand Advisory Services, Inc.; the Office of Global Programs of the U.S. National Oceanic and Atmospheric Administration (NOAA/OGP); and the World Meteorological Organization (WMO)

Participants at the Forum included representatives of Meteorological Services of several countries of the region (Bolivia, Chile, and Ecuador) and climate scientists and other experts from national, regional and international institutes: Universidad Nacional de Colombia, Universidad de Chile, University of Washington, Instituto del Mar del Perú (IMARPE), Instituto Geofísico del Peru (IGP), Instituto Peruano de Investigaciones Pesqueras (INPESCA), Dirección de Hidrografía y Navegación de la Marina (DHN), National Oceanic and Atmospheric Administration's (NOAA) National Centers for Environmental Prediction (NOAA/NCEP) and Office of Global Programs (NOAA/OGP), International Research Institute (IRI) for climate prediction, and the Inter-American Institute for Global Change Research (IAI).

METHODOLOGY

This regional climate assessment began with consensus that the current strong El Nino event will remain strong over the forecast period (December-March 1997-98). The Sea Surface Temperature (SST) forecast and other factors affecting the climate of Pacific South America were based on coupled ocean/atmosphere models, physically-based statistical models and expert interpretation. The Forum endorsed the use of the NOAA National Centers for Environmental Prediction (NCEP) coupled model as the most reliable indicator for the evolution of this El Nino event in terms of sea surface temperature over the next four months.

OUTLOOK

The Climate Outlook addresses the summer season (December-January-February-March 1997-98) for Pacific South America. The experts provided probability distributions to indicate the likelihood of below-, near-, or above-normal rainfall for each sub-region (see attached Map). Users are strongly advised to contact participating institutions and other climate information sources for interpretation of this Outlook and for additional guidance.

• Above normal rainfall is expected along the coast of Ecuador and northern Peru, with the detailed structure reflecting the topographic relief of the region.
• Proceeding north, the regions of eastern Ecuador, Colombia, and northern Peru are expected to experience drier than normal conditions, especially the northwest region of Colombia.
• The altiplano region of southeast Peru and western Bolivia is expected to experience drier than normal conditions. Most of northeastern Bolivia has a slightly higher than average probability of a wet summer season. Although we note that among our different forecast products, there was not complete consistency among our climate forecasts and other indicators for this region.*
• South-central Chile is expected to see above normal precipitation for the remaining austral Spring season.

*Further contributing to this uncertainty, information received following the Climate Forum suggests that the Chaco region of southern Bolivia may experience drier than normal conditions associated with El Nino.

The NCEP coupled model predictions of sea surface temperature (SST) and SST anomalies for the three month intervals Nov 1997 - Jan 1998, Feb - Apr 1998, and May - Jul 1998, based on Oct 1997 initial conditions. Left hand panels show total SST predictions; right hand panels show corresponding anomalies, or departures from climatological monthly mean SST.

For each sub-region, during the 1997-98 season, the Climate Outlook is represented by the probabilities of that sub-region receiving below-normal, near-normal, or above normal precipitation (see key on map), based on model results and expert interpretation. Over many years, rainfall will fall equally frequently into all three categories. For example, between 1961 and 1990, ten of the years will fall into the above-normal category, ten will be normal and ten will be in the below-normal category.

If all three outcomes were equally likely during this current season, the chance for each category would be about 33%. A qualitative Outlook of climatology indicates that there is no basis for favoring any part of the range of rainfall totals experienced in recent decades. Such regions are indicated with stippling. Otherwise, for example, in the case of the northwest region of Colombia during the December-January-February-March 1997-98 (See Map), there is a 55% probability for precipitation to be in the below-normal category; that is, within the range of the driest third of historically-recorded rainfall, a 30% chance in the near-normal category; and a 15% chance of being in the above-normal category. Boundaries between the sub-regions should be considered transition zones. Lastly, no Climate Outlook was provided for the following countries: Argentina; Brazil; French Guiana; Guyana; Paraguay; Suriname; Uruguay; and Venezuela. These regions will be addressed by meetings later this season.