For centuries the great Yangtze and Yellow rivers have broken their banks, causing huge loss of life and changing the face of the landscape.

Dr Peter Walker of the IFRC: "We have to act to protect the region"

Floods are once again hitting China, a year after more than 4,000 people were killed in the worst flooding for 50 years.

Much of the flooding is the consequence of the natural cycle of seasonal change.

But international aid and donor organisations say that the floods have been made far worse by two decades of deforestation.

Logging explosion

The United Nations estimates that logging has led to the deforestation of an area of land four times larger than Hong Kong.

This has had a massive impact on the environment and the lower reaches of the Yangtze river.

Dr Lei Guangchun, head of the China programme for the World Wide Fund for Nature (WWF), told BBC News Online that his team had been researching the effects of the logging.

"We are now dealing with a serious situation started in the 1980s," said Dr Lei.

"The areas affected have lost around 30% of their forest cover in the last 15 years as logging was carried out without a policy of sustainable forest management.

"This has caused a dramatic contribution to the floods," he said.

"Once deforestation takes place, land suffers soil erosion and sediment is washed down stream from mountainous areas.

"It arrives in the central and lower regions of the river where it builds up on the river bed, raising the level of the water far higher than normal."

Click here to see a map of deforestation.

At the same time, the reclamation of entire lakes has meant a dramatic change in the ratio of agricultural land to wetlands and a significant loss of important flood plain waterways.

Dr Lei said: "Around 60% of the wetlands have been reclaimed for farmland in the lower and central regions of the Yangtze.

"The WWF is campaigning to reverse this change. Local farmers can get income from the wetlands, it doesn't have to be reclaimed."

Policy changes

China says that it has now put in place a 6.6bn Renmimbi ($800m) programme of "ecological engineering".

Beijing has ordered the "relocation" of more than one million logging employees into non-forestry industries - a massive change in the Yangtze's economic profile.

The government has also put more than 60 million hectares of upstream forest under protection and is beginning a major replanting programme on deforested hillsides.

Further north on the banks of the Yellow River, Beijing has ordered the construction of the giant Xiaolangdi dam to be speeded up so that the area can be prepared for feared major floods. The project is second only in size to the Yangtze's Three Gorges dam works.

While environmentalists say that this programme is a step in the right direction, they also fear that the demand for imported timber will put major pressures on other endangered forests in Asia.

Preparing for future

Dr Peter Walker, director of disaster policy at the International Federation of Red Cross and Red Crescent Societies, said that China and the international community must look at other ways of reversing the damage.

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"You cannot grow a forest overnight," said Dr Walker. "It will take years.

"The first thing is to invest in local preparedness. When an event like [these floods] happens, it is people on the ground who react first and that means investment in organisations such as the local Red Cross and local municipalities.

"The second thing is a message that is beginning to be taken on board by the development banks that disaster mitigation has to be part of our development planning.

"Whether we are talking about dam construction, land use or loans, they have got to look at the likely effect on the environment.

"Then there is the long-term issue of global warming and rising sea levels.

"Within 80 years, 30 million people in China are going to be under sea.

"We know it is going to happen so we must look at ways of how to protect the area."