Singapore - Research showing an El Nino event in 1918 was far stronger than previously thought is challenging the notion climate change is making El Nino episodes more intense, a U.S. scientist said on Tuesday.

El Nino causes global climate chaos such as droughts and floods. The events of 1982/83 and 1997/98 were the strongest of the 20th Century, causing loss of life and economic havoc through lost crops and damage to infrastructure.

But Ben Giese of Texas A&M University said complex computer modelling showed the 1918 El Nino event was almost as strong and occurred before there was much global warming caused by the burning of fossil fuels or widespread deforestation.

The outcome of the research was valuable for several reasons, Giese told Reuters from Perth in Western Australia.

"It questions the notion that El Ninos have been getting stronger because of global warming," he said ahead of a presentation of his team's research at a major climate change conference in Perth.

The 1918 event also coincided with one of India's worst droughts of the 20th century.

"We know that El Ninos and drought in India are often related to each other," he said.

El Nino is an abnormal warming of the surface waters in the eastern Pacific off South America that causes the normally rainy weather in the western Pacific to shift further to the east.

This causes drought in parts of Australia, Southeast Asia and India as well as flooding in Chile and Peru, colder and wetter winters in the southern United States and fewer Atlantic hurricanes.

The droughts in Australia of 1982-83 and 1997-98 rank among the worst in the nation's modern history. Drought also occurred in eastern Australia from 1918-20.

Giese said his team ran a complex ocean computer model that, for the first time, used the results of a separate atmospheric model produced by the National Oceanic and Atmospheric Administration.

The result was a simulation of ocean temperatures, currents and other measures from 1908 to 1958.

For 1918, the simulation produced a strong abnormal surface warming in the central Pacific and weaker warming nearer the South American coast.

There were very few measurements of the tropical Pacific during 1918, the last year of World War One, and ship-based measurements along the South American coast suggested only a weak El Nino.

This, Giese said, reinforced the point that there is limited data about El Ninos prior to the 1950s and that computer models were one way to get a clearer picture of the past.

"We cannot rely on what El Nino looks like today to try to understand what El Nino patterns looked like in the past."

"It makes it a challenge to talk about El Nino and global warming because we simply don't have a detailed record," he added.