What Are Some Of The Events And Their Consequences Associated With Predicting Significant Changes In Seasonal To Interannual Variability?


Midwest Floods In 1993 And 1995 And West Coast Storms In 1995 Related To El Niño

Analyses of the drought and heat wave in the eastern and central U.S. during the summer of 1988 and of the 1993 and 1995 floods over North America reveal that mature El Niño conditions in the tropical Pacific contributed to the broad-scale circulation and related jet stream pattern over the North Pacific and across North America in the months leading up to these events. In the well studied 1993 case, a broader jet stream and storm track were displaced significantly south of normal. The flow pattern during June was characterized by strong west-to-east flow from the western Pacific to the eastern United States and provided a duct for intense cyclone activity to propagate directly into the Midwest. An analysis of the moisture budgets has revealed a strong river of moisture flowing across the Gulf of Mexico into the eastern U.S. The lower-than-normal latitude of the storm track allowed cyclonic disturbances to tap into the Gulf moisture source and transport moisture into the upper Mississippi River basin where it precipitated. Increases in local soil moisture and evaporation appeared to enhance the precipitation and helped perpetuate and prolong the conditions. Consequently, these effects should be viewed as feedbacks which amplify and prolong the response while, from the standpoint of the atmosphere, the anomalous tropical Pacific sea surface temperatures are a notable (but not sole) external forcing of the patterns. Preliminary analyses of the California and Midwest flooding in 1995 also indicate on influence of El Niño on the forcing of atmospheric circulation patterns that set-up the cyclone tracks which bring the heavy rains.
References: (1) Atmospheric Circulation Associated with the Midwest Floods of 1993, Bell, G. D., and J. E. Janowiak, Bull. Amer. Meteor. Soc. 76, pp. 681-695, 1995; (2) Trenberth, K. E., and C. J. Guillemot, 1995, Physical Processes Involved in the 1988 Drought and 1993 Floods in North America, 1995, Journal of Climate, submitted; (3) ENSO Winter Impacts, California Flooding, Mild to the East, Climate Analysis Center, NOAA Special Climate Summary-95/1, 1995; (4) Flooding in the Central United States, Climate Analysis Center, NOAA Special Climate Summary-95/2, 1995; (5) Issues in Establishing the Causes of the 1988 Drought over North America, Trenberth, K. E., and G. W. Branstator, Journal of Climate, Vol. 5, pp. 159-172, 1992; (6) The Global Climate of June-August 1988: A Swing to the Positive Phase of the Southern Oscillation, Drought in the United States, Ropelewski, C. F., Journal of Climate, Vol. 1, pp. 1153-1174, 1988.

Monitoring El Niño Has Important Implications For Surveillance Of Emerging Diseases

There has recently been a global reemergence of infectious diseases associated with changing temperatures and precipitation patterns. In 1993, a virulent rodent-borne hantavirus appeared in the arid U.S. Southwest. Following 6 years of drought, the heavy rains appear to have dramatically increased population of natural hosts for the virus, which increased the chances that the virus would be passed on to humans. A novel cholera variant also appeared in Asia that year, during which there was an unusual abundance of coastal algal blooms that harbor and amplify the cholera virus. Evidence suggests that the emergence of these diseases, and others such as malaria are associated with heavy rains, result from anomalous weather patterns, such as those which occur during El Niño events.
Reference: (1) Emerging Diseases and Ecosystem Instability: New Threats to Public Health, P. R. Epstein, MD, American Journal of Public Health Vol. 85, No.2, pp. 168-172, 1995. (2) Marine Ecosystems, Epstein, P. R., Ford, T. E., and R. R. Colwell, The Lancet, Vol. 342, pp. 1216-1219, 1993.

Increased Coral Bleaching Appears To Be A Response To Ocean Warming

Coral reef ecosystems are among the most susceptible to rising temperatures, sea levels, soil erosion, and to excess nutrients from sewage and fertilizers. Monitoring their condition thus provides a very sensitive measure of environmental change. Major bleaching events were reported for all major reef provinces between 1983 and 1991. Coral-reef bleaching results from the expulsion of symbiotic zooxanthellae algae from coral reefs. These algae provide reef corals with most of their carbon, their limestone-depositing ability, and their color. When zooxanthellae vacate coral reefs, the reefs die. Investigations indicate that these events occurred following periods when positive temperature anomalies (hot spots) of more than 1o C took place during the months of the year with the warmest ocean temperatures. These hot spots have been identified and can be tracked in real time using satellite data. While the algae can return as the temperature anomaly subsides, many reefs died when the anomalous warming persisted. El Niño warming events can partially explain the recent global pattern of bleachings; further, the susceptibility of reefs to sea-surface warming raises concerns about the effects of continued greenhouse gas-induced warming.
Reference: Coral Bleaching and Ocean Hot Spots, Goreau, T. J., and R. L. Hayes. Ambio, Vol. 23, pp. 176-180, 1994.

El Niño Events Found To Significantly Reduce Carbon Dioxide Flux Out Of The Equatorial Pacific Ocean

Measurements of carbon dioxide concentrations in the atmosphere and in the surface waters of the equatorial Pacific Ocean during the spring and autumn of 1992 indicate that the 1992-1993 El Niño event reduced the "normal" (non-El Niño) carbon dioxide release to the atmosphere from this region by more than 50 percent. This may be a contributing factor in explaining the slower rates of increase of atmospheric carbon dioxide during the period of time in question.
References: (1) CO2 Distributions in the Equatorial Pacific during the 1991-92 ENSO Event, Feely, R. F., et al., Deep-Sea Research, in press, 1995; (2) Seasonal and Lateral Variations in Carbon Chemistry of Surface Water in the Eastern Equatorial Pacific During 1992, Wanninkhof, R., et al., Deep-Sea Research, in press, 1995; (3) Surface Water CO2 Values in the Eastern Equatorial Pacific during the 1992-93 El Niño, Wanninkhof, R., et al., Journal of Geophysical Research, submitted, 1995.

Effects Of El Niño Found To Be Very Long-Lived

El Niño events have generally had significant local effects lasting up to two years. However, it has been believed that the long-range effects of El Niño are restricted to changes transmitted through the atmosphere, for example causing precipitation anomalies in distant locations. New evidence from observations and modeling studies suggests that planetary scale ocean waves generated by reflection of equatorial shallow-water waves from the American coasts during the 1982-83 El Niño have crossed the North Pacific, and a decade later caused northward re-routing of the Kuroshio current that normally transports large amounts of heat from the southern coast of Japan eastward into the mid-latitude Pacific. This phenomenon has led to increases in sea surface temperature at high latitudes in the northwestern Pacific of the same amplitude and with the same spatial extent as those observed in the tropics during significant El Niño events. The influence of these changes on the North American climate during the past decade is being evaluated.
Reference: Decade-Scale Trans-Pacific Propagation and Warming Effect of El Niño Anomaly, Jacobs, G. A., et al., Nature, Vol. 370, pp. 360- 363,1994.

Variability In Atmospheric Circulation Patterns Found To Affect Coastal Estuaries

Estuaries, their freshwater source or watershed, and the oceanic processes which affect them are dynamically linked together by the atmosphere. Preliminary research shows that much of the year-to-year variability, and part of the long-term trend in the salinity of the San Francisco Bay, for example, are the result of natural fluctuations in the large-scale patterns of atmospheric circulation over the eastern North Pacific Ocean, rather than from upstream freshwater diversions. Improved understanding of climate variability, including forecast information, will thus have significant implications for estuarine management and freshwater availability.
Reference: The Role of Climate in Estuarine Variability, Peterson, D., et al., American Scientist, Vol. 83, pp. 58-67, 1995.

ENSO Events And Crop Yields Of Various Countries Worldwide Have Been Found To Be Highly Correlated

USGCRP research has investigated the relationship between El Niño and crop yield statistics in countries throughout the world and found that thirty- nine economically important crops in thirty-three countries exhibited significant correlation to eastern equatorial Pacific sea surface temperatures. Because coupled dynamical models can predict the ENSO signal with a lead time of up to twelve months, these strong ENSO-crop yield correlation's illuminate the possibility of using ENSO predictions for agricultural planting and crop selection decisions in many countries around the world.
References: (1) Statistical Survey of Relationships between ENSO and Global Crop Productivity, Kane, A. I., C. Rosenzweig, and M. A. Cane, Nature, submitted, 1995; (2) Forecasting Zimbabwean Maize Yield using Eastern Equatorial Pacific Sea Surface Temperature, Cane, M. A., G. Eshel, and R. W. Buckland, Kane, A. I., C. Rosenzweig, and M. A. Cane, Nature, Vol. 370, pp. 204-205, 1994.

Economic Studies Indicate Significant Value Of El Niño Forecasts

When experimental forecasts of El Niño are fully implemented in an operational context, similar to present day weather predictions, immediate benefit is expected in agriculture, forestry, fishery, hydroelectric, and insurance sectors of the U.S. economy. This has already proven true in practice for countries such as Peru, Brazil, and Australia. Economic research indicates that El Niño has a deleterious impact of up to 15 percent on the agriculture sector of the southeastern tier of the United States. The value to the southeastern U.S. economy of El Niño forecasts is estimated to be more than $100 million per year.
Reference: The Value of Improved Long-Range Weather Information: Southeastern U.S. ENSO Forecasts as They Influence U.S. Agriculture, R. M. Adams et al., Contemporary Economic Policy, in press, 1995.

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Last updated 04/10/96