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Friday, August 28, 1998 Published at 18:56 GMT 19:56 UK


Where's the water coming from?

Chinese soldiers try to halt the rising waters

The record-breaking floods in South and East Asia are causing widespread misery and devastation. But as Toby Murcott of BBC Science reports, some of the causes of the floods are still unknown:

[ image: Hundreds of thousands have been made homeless in Bangladesh]
Hundreds of thousands have been made homeless in Bangladesh
In China, the authorities predict that as many as one million people will be left destitute by this year's flooding - the worst since records began.

In Bangladesh, hundreds of thousands of people have been washed from their homes.

And in Japan, record rainfall has brought deadly mudslides and forced mass evacuations from a number of towns.

Seasonal pattern

A natural reaction to any disaster is to search for a cause, yet identifying the reason for this year's extreme floods is going to be difficult.

[ image: Japan has not escaped torrential flooding]
Japan has not escaped torrential flooding
To start with, it's the rainy season in much of the region and floods can be a feature of this time of year.

Much has been made of global climate change, caused by a combination of human activity and natural weather cycles such as El Nino, and this may well be a factor.

As weather patterns change then dry regions can receive more rain than normal and wet areas become even wetter.

There may not be a greater volume of rain in total, but if it falls on land unused to such downpours, more of the water can reach the rivers, causing them to swell and flood.

Agricultural practices

[ image: Millions have been affected in China]
Millions have been affected in China
Clearing land for agriculture or logging can also play a part. Trees and forests absorb rain and when they are cleared much more water can reach the rivers.

Additionally, changing agricultural practices mean water is taken from rivers in different places, something that can upset the natural river flow with unpredictable results.

It is probable that all of these and other, as yet unknown, factors play some part in the flooding.

But it is still too early to say which ones had what effect - there are just so many possibilities to consider.

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