Coupling between annual and ENSO timescales in the malaria-climate association in Colombia

We present evidence that the El Nino phenomenon intensifies the annual cycl e of malaria cases for Plasmodium vivax and Plasmodium falciparum in endemi c areas of Colombia as a consequence of concomitant anomalies in the normal annual cycle of temperature and precipitation. We used simultaneous analys es of both variables at both timescales, as well as correlation and power s pectral analyses of detailed spatial (municipal) and temporal (monthly) rec ords. During "normal years," endemic malaria in rural Colombia exhibits a c lear-cut "normal" annual cycle, which is tightly associated with prevalent climatic conditions, mainly mean temperature, precipitation, dew point, and river discharges. During historical El Nino events (interannual rime scale ), the timing of malaria outbreaks does not change from the annual cycle, b ut the number of cases intensifies. Such anomalies are associated with a co nsistent pattern of hydrological and climatic anomalies: increase in mean t emperature, decrease in precipitation, increase in dew point, and decrease in river discharges, all of:which favor malaria transmission Such coupling explains why the effect appears stronger and more persistent during the sec ond half of El Nino's year (0), and during the first half of the year (+1). We illustrate this finding with data for diverse localities in Buenaventur a (on the Pacific coast) and Caucasia (along the Cauca river floodplain), b ut conclusions have been found valid for multiple localities throughout end emic regions of Colombia. The identified coupling between annual and intera nnual timescales in the climate-malaria system shed new light toward unders tanding the exact linkages between environmental, entomological, and epidem iological factors conductive to malaria outbreaks, and also imposes the cou pling of those timescales in public health intervention programs.