La Niña Impacts in Cuba:
The Opposite Face of the Coin?
Lino Naranjo Diaz National Climate Center
Havana, Cuba
bouzas@ceeti.edu.cu
Introduction
La Niña,or more properly the cold phase of the ENSO process, has to be considered as part ot a seesawing pattern, where El Niño represents the most dramatic extreme which has monopolized almost the entire interest of the worldwide scientific community which deals with the forcing elements of interannual climatic variability.
Glantz (1996) has attempted to put forward an explanation of this fact. He argued that, because cold events produce weather and climate anomalies that often seem to be opposite to those produced by El Niño, they are perceived by many as periods when weather and climate conditions return to normal. However, there still remains a lot of uncertainty about La Niña. Is La Niña really the "good part" of the ENSO cycle to some countries? How "normal" could the climate be in regions under La Niña's influence? In addition, the list of El Niño and La Niña events after 1950 (Trenberth, 1987) shows a smaller number of the later (15 vs. 10). After 1972, the number of El Niño events nearly doubled La Niña's occurrence, suggesting a "warming" tendency in the ENSO cycle over the last 3 decades. All these facts reinforce the main question: What is the role of La Niña in the framework of a "usable science" approach? Should it be considered an important part of climate impacts on society of should it be considered as being only of marginal importance?
Maybe the answer to these questions would be very different, depending on the region of the world under consideration.
Cold Events in Cuba
In Cuba, like many places around the world, studies about La Niña have been closely related to those about the more dramatic El Niño. Cardenas & Naranjo (1995) studied the influence of ENSO events on the climate of Cuba including both warm and cold events. Their study was based on a chronology of the "ENSO Index" undertaken in the Cuban Climate Center. Like El Niño, the influence of La Niña over climate elements in Cuba seems to be most significant in winter. It is far from behaving like the "opposite face of the coin". In rainfall, for instance, El Niño is associated with a significant increase of the winter rainfall, while under La Niña conditions, anomalies are less significant toward a slight deficit of rain, although usually La Niña winters are associated with normal to nearly above-normal rainfall. Regarding temperatures, significant negative anomalies are associated with cold events, whereas during El Niño there is not a clear significant impact.
On this basis, we might conclude that, during cold events, Cuban winter tends to be slightly cooler with near normal to slightly below-normal rainfall and that there is not a significant influence in the summer. However, are these reliable statements? I would guess not. The former conclusions were based on the analysis of monthly mean values and many important statistical features were not considered. Regarding the influence of La Niña over the weather and climate in summer, some factors support the idea of a more significant influence. For instance, during the strong La Niña of 1988, anomalous heavy rainfall was registered over the Central Region of Cuba, producing catastrophic effects, mainly in Cienfuegos Province.
Gray (1984 ) established that, under cold event conditions, tropical storm activity in the Atlantic Basin increases. Consequently, we might expect that the risk of a tropical storm hitting the Cuban territory should be increased under La Niña. However, the frequency of tropical storms that affected Cuba during cold events (in the 1950-1998 period) was the same as the long-term climatic frequency. However, the frequency of El Niño years falls significantly. Naranjo (1997) pointed out the influence of ENSO on some key winter crops in Cuba. For potato crops, production in the 1995-96 winter (a La Niña year) nearly doubled the 1997-98 winter (El Niño) production and was the highest in this decade, suggesting an impact on this crop. However, for sugar cane there are not clear signs of impacts over the same period.
Ortiz & Guevara (1997) found a significant ENSO signal in the interannual variability of Meningitis Meningococica in Cuba. However, this signal is mostly related to a significant increase in this disease during El Niño years, while under La Niña conditions it is nearly normal.
One important reason why methods used to isolate an El Niño signal do not work for La Niña is that many of our time series began after 1970 and these are conditioned by more frequent warm events during this period. Thus, we should not be at all conclusive about La Niña impacts. We need to improve our research on La Niña, but before we can do that effectively we have to improve our understanding of what La Niña is. Indices and thresholds need to be refined and physical mechanisms of the ENSO cycle clarified. We should not forget that El Niño was "rediscovered" by the scientific community only after the devastating impacts of the 1972-73 event. However, the existence of warm events were felt as early as the 1600s through their impacts on fishing and agriculture along the Peruvian coast. Thus, to give La Niña a real sense, we need to be more aggressive in finding its "fingerprint" in the economic and social life of our country. If not, it will remain as a marginal product of statistical analysis and of physical hypotheses.
References:
Cardenas P. and L. Naranjo, 1996: Impacto y modulacion de los efectos ENOS sobre los elementos climaticos en Cuba. Technical Report. Instituto de Meteorologia de Cuba. 15 pp.
Glantz, M. H., 1996: Current of Change: El Niño Impact on Climate and Society. Cambridge University Press. 194 pp.
Gray, W., 1984: Atlantic Seasonal hurricane frequency: Part I. El Niño and 30 mb quasibiennal oscillation influence. Mon. Wea. Rev. 112. 1649-1668.
Naranjo L., 1997: Impacts of ENSO in Cuba. A System approach to ENSO, an NCAR Colloquium, Boulder. Pp 73-75.
Ortiz P.L., A.V. Guevara, 1997: El efecto de un indice de ENOS en la variabilidad de la serie de Meningitis Meningococica. Technical Report. Instituto de Meteorologia de Cuba. 25 pp.
Trenberth, K.E., 1997: The definition of El Niño. Bull. Amer. Met Soc.. 72. 2771-2777.