cyclones are the most worst natural disaster
As of October 2009, Australia's most recent natural disaster is the massive bushfires in the Rockhampton region.
The famine or the heat
Hurricane Katrina was the costliest U.S. natural disaster, and one of the deadliest. So it ranks as one of the worst U.S. disasters, but probably not the worst.
the black plaque
'dolkvad'e;
Hurricane Hanna hit Haiti September of 2008. It has been the worst reported natural disaster
Granville Train Disaster - 18 January 1977, Granville, New South Wales
The flood of 2008 was the worst natural disaster in the USA
Drought remains an ongoing natural disaster, but early in 2009, Australia was hit badly by both bushfires in Victoria, in the south and massive floods in Queensland's north.
Floods in Brazil Floods in Australia
No such figure will ever be known. Certainly more than half the world will be aware of the disaster.