Three deadly storms have killed over 640 people in Haiti in the space of a few weeks and more storms could be on their way.

Aid workers say at least 650,000 people have been affected in the country, the poorest in the Americas. Thousands of homes have been destroyed or damaged, and crops and livestock have been wiped out.

At least 520 people have been killed in floods and mudslides triggered by Tropical Storm Hanna which unexpectedly smashed into the country in early September. Hanna battered Haiti just days after Tropical Storm Gustav killed 75 people. Another storm, Fay, killed 50 people in mid August.

Hanna's torrential rains submerged the port city of Gonaives under 2 metres (6.5 feet) of water. The floodwaters are receding, leaving behind deep piles of mud and human bodies as well as the carcasses of goats, pigs and dogs.

President Rene Preval has called the situation "catastrophic", comparing it to the floods from Tropical Storm Jeanne in September 2004 that killed more than 3,000 people around Gonaives.

Many people survived the latest flooding by scrambling on to rooftops.

Bridges and roads have been washed out, making it difficult for aid to reach the city. Food warehouses and hospitals have also been flooded.

Prospery Raymond, country representative for Christian Aid, says the whole of the Artibonite valley has been flooded, which is where 80 per cent of Haitian rice is grown. He says this is likely to put the price of rice even further out of the reach of many families.

The International Federation of Red Cross and Red Crescent Societies has appealed for $3.4 million to help survivors get back on their feet.

Haiti is extremely vulnerable to flash floods and mudslides because most of its hillsides have been stripped bare. Cutting down trees to make charcoal to sell for fuel is the last resort for many rural Haitians who have no other income between harvests.

Forecasters have predicted an unusually busy hurricane season for 2008. An average season has 10 tropical storms, of which six strengthen into hurricanes.

FLOODING IN WIDER REGION

The Atlantic hurricane season runs from June to November in the Caribbean, posing a threat to coastal communities when tropical storms and hurricanes generate storm surges and trigger landslides and flash floods.

Elsewhere in Latin America, torrential rains between December and May can swamp agricultural land, destroy livelihoods, damage homes and services and force mass evacuations.

In early 2008, devastating floods hit Bolivia, Ecuador and Peru as a weather abnormality known as La Nina brought some of the heaviest rains in a quarter-century, swelling rivers and bursting banks. Ecuador and Peru both declared states of emergency.

Meaning "little girl" in Spanish, La Nina is an unusual cooling of Pacific Ocean surface temperatures that can trigger more hurricanes and worse rains in many places.

Death tolls from floods have generally fallen in recent years as countries become more adept at disaster prevention, although experts warn that more people are likely to be affected in future as global warming generates more and bigger floods.

British researchers say they have shown that a half-degree Celsius temperature rise in the Atlantic Ocean can fuel a 40 percent increase in hurricanes. Other factors increasing flood risks include environmental factors such as deforestation and rapid urban growth.