Researchers also blame long periods of dry weather and heavy rain.

VOA: special.2009.05.05

It is even larger in years of heavy rain.

VOA: special.2009.08.12

Dozens of houses on the outskirts of the Sicilian city were swept away or flattened by heavy rain and mud.

VOA: standard.2009.10.10

The Bell 430 helicopter disappeared while flying through a heavy rain storm, en route to an unannounced inspection of a local district.

VOA: standard.2009.09.03

Meanwhile,heavy rain and melting snow have cause flooding in parts of Croatia and Bosnia.

VOA: standard.2010.01.10

In Senegal,the new U.N.assessment says more than 260,000 people are affected by weeks of heavy rain, most living in poor neighborhoods built on lowlands outside the capital,Dakar.

VOA: standard.2009.09.08

Clinton arrived late Friday in a heavy rain at the Taj Palace Hotel on Mumbai's ocean front, which was one of the targets of Pakistan-based terrorists who killed 166 people in a coordinated series of attacks in the Indian business capital last November.

VOA: standard.2009.07.17