Overview

El Nino 1997/98, Natural Climate Variability and U.S. Impacts

Natural climate variability occurs on many timescales, but particularly on interannual to decadal timescales. Some variations seem random; others seem well-organized. The most well known of the coherent phenomena is the El Nino-Southern Oscillation (ENSO). ENSO involves ocean-atmosphere interactions centered primarily in the tropical Pacific. When tropical Pacific sea surface temperatures are warmer than normal this is known as El Nino; when they are colder than normal, this is the La Nina phenomenon. Other known modes of natural variability include the North Atlantic Oscillation (NAO) and the Pacific Decadal Oscillation (PDO). Over the past 130 years both ENSO and NAO have exhibited interannual and decadal variability, both in amplitude and frequency of occurrence. Both contribute to the long-term global land-sea temperature record that is used to calculate long-term changes in climate. Each of these, as well as the PDO, also contribute to the seasonal and decadal variations in U.S. temperature and rainfall.

Fifteen years of research have led to a routine capability to predict El Nino warm events with skill several seasons in advance. The El Nino forecasts are then used to forecast anomalous rainfall and temperature (drought) variations over much of the U.S. and the globe. While warm and cool events have occurred for centuries, the current 1997/98 El Nino is growing faster than previously recorded and is forecast to peak at the end of the year, at that time being comparable in size and intensity to the 1982/83 El Nino, the largest El Nino event in recorded history. For the next six months much of the southwestern U.S., the central U.S., and the Gulf Coast are forecast to have above normal rainfall. During the late fall, winter, and spring of 1982/83, similar conditions caused many regions of the U.S., including California, Utah, Louisiana, Missouri, and Illinois, to experience heavy flooding. Globally, during that same period, Southern Africa, Australia, and Indonesian experienced droughts while coastal areas of Peru and Ecuador experienced flooding. Some of these same impacts are already being experienced worldwide in many of the same regions.

The current U.S. forecasts are based on both statistical techniques and numerical forecasts--both prediction techniques yield the same broad-scale features. Forecasts from numerical models show the large scale features expected to occur during El Nino but lack the detailed regional structure, especially for precipitation. Although there has been considerable decadal variability in the occurrence of El Nino over the past 100 years, the fact that there will now be two "one hundred-year" events during the past 15 years as well as one of the strongest La Nina (cool) events (1988-89) of the century raises obvious questions about whether global warming may be affecting the ENSO cycle. Presently, although there are scientists that find signs of this, more research is needed to clarify this issue.

The El Nino Story: Challenges and Opportunities for Society

The past two decades are replete with evidence of the significant economic and social costs associated with unanticipated disruptions in weather and climate patterns. For example, estimates of global losses associated with the 1982-1983 El Nino event exceeded $8 billion. Of that figure, U.S. losses associated with storms in the Mountain and Pacific states, flooding in the Gulf States, and Hurricane Iwa in Hawaii, were estimated to have cost $2.5 billion. The 1988 U.S. drought resulted in an estimated $2-4 billion in direct losses to agricultural producers, with total losses throughout the economy estimated at greater than $22 billion. The 1993 Midwest floods were associated with about $15-20 billion in damages and costs. The 1995 floods in California and the Gulf States resulted in estimated losses of $7 billion. More recently, significant damage and losses have resulted from the heavy rains associated with tropical storms along the west coast, the Gulf of California, and parts of southern Arizona. Yet these figures alone do not adequately capture the real measure of human suffering, direct losses, and missed opportunities.

During the past decade it has become increasingly clear that the coupled ocean-atmosphere weather phenomenon known as the El Nino-Southern Oscillation (ENSO), plays a dominant role in influencing year-to-year changes in climatic conditions around the world. Based upon enhanced understanding of ENSO, scientists have refined their ability to provide useful predictions on a scale that accommodates local and regional planning decisions. The capability to understand and predict El Nino phenomena also presents government officials, industry, and local communities with an array of opportunities, including: reducing vulnerability to climate-related natural disasters such as floods and droughts; enhancing economic competitiveness; supporting public- and private-sector decision-making for climatically-sensitive regions and sectors; providing scientific information to support U.S. international treaty negotiations; and in assessing and maintaining national and international environmental security.

The forecasts are proving to be very useful. For example, the 1997-98 El Nino forecast for the United States indicates that Southern California and the Gulf States will experience wetter than normal conditions during the fall and winter of 1997-1998. Federal and local emergency preparedness officials are currently reviewing options available to reduce the human and economic costs associated with potential flooding conditions. In California, scientists, forecasters, and emergency management officials expect the increase in rainfall to be accompanied by an increase in the number and severity of coastal storms, so planners are also developing strategies to deal with threats due to coastal erosion as well as flooding. On the other hand, sports fishing for some deep water species which prefer warm-water conditions (e.g. tuna and marlin) could produce record income for this important California industry. Similarly, a shift in the movement of tuna stocks is expected to produce significant benefits to the tuna cannery industry in American Samoa.

Higher forecasted temperatures for most of the northern and central regions of the U.S. provide natural gas and electric utilities with opportunities to adapt their purchasing, shipment, and storage plans accordingly. Commodities trading in crops such as wheat, coffee, cocoa and sugar is already reflecting the predicted impacts of this year's El Nino. While this year's Atlantic hurricane season witnessed little activity, Hawaii, on the other hand, is anticipating a more active season for tropical storms and hurricanes (Hurricanes Iwa and Iniki both struck during years of warmer than normal ocean temperatures--1982 and 1992, respectively). In addition, many Pacific island countries are preparing for El Nino-related drought conditions.

Prior to her work with the U.S. Global Change Research Program, she served for four years (1983-1987) as the Senior Analyst for oceanic and atmospheric research programs in the NOAA Office of Budget and Finance, and five years as a Congressional Affairs Specialist with responsibilities for NOAA programs related to coastal zone management, ocean minerals and energy, Law of the Sea, and the National Weather Service (1979-1983). A native of the Washington, DC area, Ms. Shea earned a Bachelor of Arts and Sciences (BAAS) degree from the University of Delaware in 1975, and pursued graduate work in environmental law and marine resource management at the Virginia Institute of Marine Science (College of William and Mary) from 1975-1979.