EMBARGOED—NOT FOR PUBLIC RELEASE BEFORE:
Monday, March 30, 2015
 3:00 PM US Eastern Daylight Time
 7:00 PM Greenwich Mean Time
Tuesday, March 31, 2015
 4:00 AM Japanese Standard Time
 6:00 AM Australian Eastern Time
Rainfall, La Niña, and El Niño
Long-term shifts in the nature of the El Niño-Southern Oscillation (ENSO) may explain
changes in the annual number of Australian tropical cyclones over the last 2,000 years, a
study suggests. Historical records of extreme rainfall extend back into the 19th century in
Australia, but geological evidence of these events from prehistory is scant. To investigate
extreme rainfall variability further back in time, Rhawn Denniston and colleagues analyzed
flood-deposited sediment layers trapped within stalagmites and constructed a nearly annual,
2,200-year record of cave flooding in the northwest Australian tropics. Combined with
regional meteorological data, which showed that extreme rainfall is derived principally from
tropical cyclones and secondarily from the Australian monsoon, the stalagmite time series
revealed shifts through time in the average number of storms similar to reconstructed
numbers of tropical cyclones in the North Atlantic. The authors report that the patterns mirror
relationships between ENSO and storm formation in modern times and agree with ENSO
modes reconstructed for the last 2,000 years. The findings suggest that changes between La
Niña and El Niño may have driven multicentennial shifts in north Australian extreme rainfall
activity, largely through controls on tropical cyclone activity, according to the authors.
Article #14-22270: “Extreme rainfall activity in the Australian tropics reflects changes in the
El Niño/Southern Oscillation over the last two millennia,” by Rhawn F. Denniston et al.
MEDIA CONTACT: Rhawn F. Denniston, Department of Geology, Cornell College, Mount
Vernon, IA; tel: 319-350-7074; e-mail: <rdenniston@cornellcollege.edu>
http://www.eurekalert.org/jrnls/pnas/14-22270.htm
AFTER THIS ARTICLE PUBLISHES, it will be available at
http://www.pnas.org/cgi/doi/10.1073/pnas.1422270112