Conventional El Ninos, which tend to bring dry conditions to eastern Australia, are associated with warmer than usual tropical water in the eastern Pacific Ocean.

Since the late 1970s, these conventional events have become less frequent, while a second "flavour" of El Nino - called Modoki from the Japanese meaning similar but different - has been on the increase.

In El Nino Modoki events the warm body of tropical water is in the central Pacific, near the international date line, and is flanked on the east and west by cooler water.

In the past 20 years, the Modoki events have increased from about one out of every five to half of all El Nino events, researchers led by Sang-Wook yeh, of the South Korean Ocean Research and Development Institute in Ansan, found.

Their computer modelling predicts Modoki events may occur five times more often by the end of the century. "Global impacts of El Nino may significantly change as the climate warms," said Dr Yeh, whose study is published in Nature.

Andrea Taschetto, of the University of NSW Climate Change Research Centre, said El Nino Modoki events tended to bring drier conditions to larger parts of the continent, including the north west. "If the occurrence of El Nino Modoki becomes more frequent in future, it could cause more droughts over significant parts of Australia," Dr Taschetto said.

The researchers cautioned, however, that more research was needed to confirm the changes were linked to global warming.

Australia is currently experiencing an eastern Pacific El Nino event which is unusual because of warmer than usual conditions in the Coral Sea off the north coast.