Divergent ecological effects of oceanographic anomalies on terrestrial ecosystems of the Mexican Pacific coast
- *Instituto Nacional de Ecología, Periférico Sur 5000, Coyoacán, 04530 Mexico Distrito Federal, Mexico; and
- †San Diego Natural History Museum, 1788 El Prado, San Diego, CA 92101
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Edited by James H. Brown, University of New Mexico, Albuquerque, NM, and approved May 17, 2007 (received for review March 1, 2007)
Abstract
Precipitation pulses are essential for the regeneration of drylands and have been shown to be related to oceanographic anomalies. However, whereas some studies report increased precipitation in drylands in northern Mexico during El Niño years, others report increased drought in the southern drylands. To elucidate the effect of oceanographic/atmospheric anomalies on moisture pulses along the whole Pacific coast of Mexico, we correlated the average Southern Oscillation Index values with total annual precipitation for 117 weather stations. We also analyzed this relationship for three separate rainfall signals: winter-spring, summer monsoon, and fall precipitation. The results showed a distinct but divergent seasonal pattern: El Niño events tend to bring increased rainfall in the Mexican northwest but tend to increase aridity in the ecosystems of the southern tropical Pacific slope. The analysis for the separated rainfall seasons showed that El Niño conditions produce a marked increase in winter rainfall above 22° latitude, whereas La Niña conditions tend to produce an increase in the summer monsoon-type rainfall that predominates in the tropical south. Because these dryland ecosystems are dependent on rainfall pulses for their renewal, understanding the complex effect of ocean conditions may be critical for their management in the future. Restoration ecology, grazing regimes, carrying capacities, fire risks, and continental runoff into the oceans could be predicted from oceanographic conditions. Monitoring the coupled atmosphere–ocean system may prove to be important in managing and mitigating the effects of large-scale climatic change on coastal drylands in the future.
Footnotes
- §To whom correspondence should be addressed. E-mail: eezcurra{at}sdnhm.org
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Author contributions: M.C. and E.E. designed research; M.C. performed research; M.C., C.G.-A., and E.E. analyzed data; and M.C. and E.E. wrote the paper.
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↵ ‡Present address: Center for Conservation Biology, University of California, Riverside, CA 92521.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
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This article contains supporting information online at www.pnas.org/cgi/content/full/0701862104/DC1.
- Abbreviations:
- ENSO,
- El Niño Southern Oscillation;
- SOI,
- Southern Oscillation Index.
- © 2007 by The National Academy of Sciences of the USA
