Conservationists and scientists say deforestation reduces the capacity of the ecosystem to regulate the water and also leads to soil erosion and landslides.

The Sumatra floods are the latest in a series of disasters blamed on deforestation and environmental degradation.

"This is not the first time disasters like these have happened and the lesson still hasn't been learnt," Togu Manurung from the Bogor Institute of Agriculture said.

"Disasters are happening back to back. In the rainy season we have floods and during the dry season we have extreme drought that causes fires and haze," the professor said.

Meteorologists said environmental factors were to blame for the flash floods in Sumatra as rainfall has not been unusually high during the rainy season.

"In the case of the recent floods, the environmental support capacity is the most determining factor since there are no unusual phenomena in the rain pattern," analyst Indro Santoso from the meteorological office told AFP.

Ministry of Forestry secretary general Boen Purnama pointed out that floods occurred even in areas with good vegetation coverage when rainfall was excessive.

"This is why we need technical structures such as dams and other infrastructure in place," he said.

Manurung said the main blame lay in the extensive deforestation of Sumatra and the Indonesian provinces of Central and South Kalimantan on Borneo.

"The fact is forests in Aceh, North Sumatra and Riau are badly destroyed. It's the same story in Central and South Kalimantan where floods also recently submerged thousands of hectares of land," said Manurung.

"Demand for Indonesian wood and also for land for expansion -- including for palm oil plantations -- is still high. I flew over Riau recently and saw massive destruction in the area designated for the expansion of the Tesso Nilo National Park," he said.

Indonesia loses about 2.8 million hectares (6.0 million acres) of forests each year -- among the highest rates in the world.

Environmental activists said the government should stop issuing permits to convert land for plantation use and revoke forest concessions.

"Forest destruction is getting out of hand. Let alone the illegal ones, the legal ones are also destroying the environment," said Greenpeace Southeast Asia's forest campaigner Hapsoro.

Leading environmental group Walhi called on President Susilo Bambang Yudhoyono to warn people of the dangers they faced and to restore the damaged environments.

"We demand the government inform the people, especially those living in high-risk areas, that disaster may hit them at any time," said Walhi director Chalid Mohammad.

"We also demand the government swiftly restore the environment, put an early warning system in place, stop logging and correct the land use policy," he said.

Forestry scientist Manurung agreed people should be alerted to the dangers.

"People living in vulnerable areas should know that they are living in 'danger zones' and should be given alternatives," he said.

Forestry ministry official Purnama said they had drawn up a comprehensive disaster map for Java and hoped to finish the one for Sumatra in the coming year.

"But even if we have these maps, it is always difficult to communicate this to the residents. They cannot easily move from their homes," he said.

Indonesia, home to more than 220 million people, has already endured numerous tragedies blamed by environmentalists on deforestation.

In June this year, floods and landslides triggered by heavy rains killed more than 200 people in South Sulawesi province. Separate floods killed more than 20 people and forced 40,000 people from their homes in Borneo in the same month.

In 2003 more than 200 people were killed when flash floods tore through Bahorok, a popular riverside resort in North Sumatra. Some officials denied deforestation was the cause of that tragedy.

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