(Adds U.N. comment paragraphs 7 & 8)

By Alistair Thomson

DAKAR, Aug 15 (Reuters) - A few weeks ago farmers in parts of Africa's arid Sahel region were fretting that late rains had failed their crops.

Now many are struggling to survive after downpours swept away food stocks, destroyed thousands of homes and killed well over 100 people across the Sahel, which stretches from Senegal on the Atlantic seaboard to Port Sudan on the Red Sea.

"This country is a paradox. Floods are just one of the natural disasters which hit it regularly, after bush fires and drought," said Hamani Harouna, head of the humanitarian Early Warning System in impoverished Niger, at the heart of the Sahel.

Last month, farmers in nearby Ivory Coast were complaining seasonal rains had failed to arrive on time, meaning seeds had not germinated and key crops such as cotton were under threat.

Since then there has been a deluge.

Scientists have told the United Nations Intergovernmental Panel on Climate Change that rising temperatures around the world will contribute to changing weather patterns in the Sahel.

"Not only are natural hazards becoming more frequent, but rapid urbanisation and population growth mean more people are now at risk," U.N. Assistant Secretary-General for Humanitarian Affairs Margareta Wahlstrom said in a recent article.

"Disasters triggered by these hazards have affected five times more people than they did only a generation ago," she said, warning of more extreme weather around the world.

In Sudan, Africa's biggest country and the worst affected by recent weather, floods have carried away or drowned more than 70 people since rains began, which in Sudan was earlier than usual.

"The rains started at the very beginning of July. Normally they start a bit later with this intensity," Maurizio Giuliano, spokesman for U.N. humanitarian coordinator OCHA, told Reuters.

At least 365,000 people there have lost food stocks, possessions or part of their home, including 50,000 whose homes were completely destroyed, OCHA said.

DISEASE

The agency expects further rainfall and flooding will affect 265,000 more people in the coming weeks, while flood waters have contaminated water sources and spread cholera, bringing the death toll from the water-borne disease to 53 this rainy season, according to the World Health Organisation.

"We have to be prepared for the worst possible scenario," Giuliano said.

In neighbouring Chad, violent storms last weekend destroyed hundreds of homes and killed thousands of livestock, the main form of wealth for many of the region's farmers and nomads.

"It's a disastrous situation. Lots of people have taken refuge in trees or in schools -- those which were not flattened," Bakary Tchaksam, a journalist working a local radio station in southwestern Chad, told Reuters.

"This is the first time anything like this has happened here. There's a sense of being powerless," he said.

After a late start in western parts of the Sahel, the sheer force of the rain storms took people by surprise.

Mud houses, which are cheap and practical during the dry season and generally survive the rains with a few annual repairs, proved no match for this year's violent weather.

"Houses flooded and some have collapsed," Gueladio Ba told Reuters by phone from Thies in Senegal, where local media reported 127 mm (5 inches) of rain fell on Sunday night alone.

"In some parts of town the water was more than a metre (yard) deep," he said. "The destruction is enormous. We haven't seen rain like this for 30 years." For FACTBOX on floods damage click headline at [ID:nL15811873] (Additional reporting by Abigail Haulohner, Opheera McDoom, Abdoulaye Massalatchi, Betel Miarom, Tiemoko Diallo, Diadie Ba & Katrina Manson)

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