London, June 16 : Scientists have built a climate model which has suggested that ocean changes may bring about a megadrought in the US that would span a period of 500 years.
According to a report in New Scientist, Song Feng and colleagues at the University of Nebraska at Lincoln built the climate model to simulate the way changes in sea surface temperature of a few degrees in the Atlantic or Pacific can disrupt atmospheric circulation over North America.
Such shifts caused droughts such as the 1930s Dust Bowl, which followed a cooling of the tropical Pacific.
It also brought about the megadrought that affected North America from AD 800 to 1250.
The team found that the impact of these sea surface temperature changes differs by season.
The effects of a change in the Pacific would hit mainly in winter: ocean cooling of 3 °C would reduce the occurrence of winter storms.
Meanwhile, effects of changes in the Atlantic would strike mainly in summer: warming of 1 °C would reduce the transport of moisture to the Great Plains of the central US and western parts of the continent.
"When both these effects occur together, North America suffers a megadrought," according to Feng.
Though the occurrence of such droughts is normal, Feng has warned that global warming may hasten their arrival.
Similar ocean temperatures and warm climes coincided with the megadrought of AD 800 to 1250.