Focus: The year of the flood

Iit has been a frightful year for floods, but, if we are to believe the weathermen, we have not seen anything yet. For as global warming takes hold, forests are felled and rivers are "tamed", they say that the waters will rise faster, further, and more frequently. This alarming prospect - in the week that has seen Honduras counting the cost of Hurricane Mitch, officially described as the western hemisphere's worst-ever disaster - threatens to redefine the concept of a natural catastrophe. It means that Acts of God are, at the very least, aided and abetted by humanity.

Certainly there have been plenty of them so far this year: the Central America and Honduras tragedy, which looks like claiming the lives of over 20,000 people, and which has made a million homeless, is just one of a deluge of floods. In July, China's Yangtze River produced its worst inundation for nearly half a century, killing 2,000 and displacing 14 million people. The same month, floodwaters submerged two-thirds of Bangladesh and - unlike earlier, briefer disasters - continued to cover the country for months. Also in July three tidal waves engulfed Papua Guinea's north- west coast, killing another 2,000.

In August, 100,000 people were made homeless in Nigeria when a dam burst. And in September severe flooding hit Chaipas in Mexico. Earlier this year, mudslides buried two towns near Vesuvius in Italy's Campania, killing 160, while New Zealand suffered its worst inundation in a century and five central European countries were hit too. Britain has also suffered, if on a less disastrous scale, as rivers reached their highest levels in over a century both at Easter and last month, inundating thousands of homes and claiming lives.

In all, according to the Brussels-based Centre For Research On The Epidemiology of Disasters, there have been 96 so far this year in 55 countries from Uzbekistan to Chad, the Yemen to Nepal, and Peru to French Polynesia. Patrick McCully, campaign director of the International Rivers Network in San Francisco says: "I can't ever remember a year with more extreme floods in more places."

Earlier this autumn, a report from the US's National Centre for Atmospheric Research in Boulder, Colorado, concluded that floods have indeed increased over the last quarter of a century. A report from Amsterdam's University's Institute For Environmental Studies shows that rivers have been fuller, and flooding has increased, in Europe, the United States and Asia since the 1960s. The frequency of floods in Italy has almost doubled in the last quarter of a century; the Rhine at Karlsruhe in Germany has risen 23ft above flood level 10 times since 1977, compared with only three in the whole of the rest of the century and Bangladesh has been experiencing catastrophic inundations every three or four years since the early 1980s.

HIGHER rainfall is partly to blame, says the Amsterdam report: all three countries have got wetter over the 20th century. And global warming will make things worse. "As greenhouse gases continue to accumulate in the atmosphere," it warns, "we should expect an increase in rainfall and river flooding events." It adds it will be "difficult, if not impossible" to prevent them.

Scientists expect more rain in many parts of the globe as the world heats up, partly because warmer air can hold more water. Rainfall is predicted to increase for example over north-western Europe, including Britain in winter, and around the equator and in monsoon countries.

And the rain is expected to be more intense. "Even if the number of wet days do not increase, it will rain more heavily on them," says James Walsh of the Meteorological Office. This is important because the harder the rain falls, the more runs off the ground to cause floods. Global warming is also predicted to increase the number and force of storms and hurricanes and to raise sea levels, inundating coastal areas. One-third of Bangladesh is expected to disappear beneath the waves, and some low-lying island nations, like the Maldives or Tuvalu, may vanish altogether.

Last week Deputy Prime Minister John Prescott told an international conference in Buenos Aires - held to draw up ways of implementing cuts in emissions of the gases that cause global warning - that Hurricane Mitch and the floodings in China were "warnings that the world ignores at its peril". But global warming is only part of this developing story, for it takes more than rainfall to make a flood. Hurricane Mitch may have been the fourth-most powerful hurricane ever to have spawned in the Caribbean, but it had lost much of its force by the time it hit Honduras and had been officially downgraded to a "tropical storm".

Yet the United States government has described the destruction it caused as "the worst disaster we have seen in this hemisphere". The rains caused disaster because the mountains it fell on have been cleared of forests and built on. Trees are vital safety valves, trapping the rain by breaking its fall to the ground and allowing it slowly to percolate into the earth (each tree of one mountain species can hold 400 gallons of water in its roots). When they are cleared, the water runs straight off bare hillsides, causing floods. Eroded soil is carried down the rivers, raising their beds and making it more likely that they will burst their banks.

It is much the same story in many of the sites of this year's floods. Forests have been felled over 80 per cent of the Yangtze basin. Floods in Bangladesh have increased enormously because of deforestation in the Himalayas, where at least 40 per cent of the trees have been cut down in the past 40 years. Before the felling, Bangladesh suffered catastrophic floods about only once a century. The mud slides in Italy were also brought about by deforestation and illegal building.

BUILDING on slopes increases the rate at which the water runs off, and building on flood plains increases the toll of tragedy. The inquiry into Britain's Easter floods was told that half of all the houses built in the country since the Second World War have been "imprudently" sited on areas prone to flood. Poverty and population growth also magnify the effects of disasters - one reason why the toll from floods in poor countries is so much greater than in industrialised ones. People have to live in flimsy housing on fragile hillsides and vulnerable shores and riverbanks.

Efforts to prevent inundations by "taming" rivers, straightening them out and building high embankments, have made things worse: such canalisation makes the water flow faster. In 1926, the US Army Corps of Engineers claimed that such work had made the Mississippi "safe from serious flood damage". The very next year floods made 700,000 people homeless. Another Mississippi flood, in 1993, broke two-thirds of the river's artificial embankments.

In Europe, 90 per cent of the upper Rhine has now been cut off from its flood plains, and now flows twice as fast as before. It flooded disastrously in 1993 and 1995. There are now attempts to restore some of its original wetlands. Every one per cent increase in these natural sponges is thought to reduce flooding by up to four per cent.

It's a small step away from the rush towards increasing disaster, but as we continue to pollute the air, fell trees and canalise rivers we are entitled to predict: "Apres nous, les deluges."

'98 IN FULL SPATE

April: Storms leave more than 3,000 square miles of England and Wales flooded. Many rivers in Midlands, Thames area, East Anglia and Wales reach highest levels in 150 years.

May: 118 killed in mudslides in the Campania region east of Naples. Fast-moving streams of lava-like sludge, exacerbated by rampant deforestation and illegal building, are blamed.

July: 2,000 killed in Papua New Guinea after three 30ft-high tidal waves - caused by offshore earthquake - hit the coast.

August: In China some 3,000 die, 14 million are relocated, and 5.6 million homes are destroyed after Yangtze basin floods. Deforestation and man- made dykes cited as factors. In Bangladesh 700 dead and two-thirds of capital Dhaka under water. Ruined crops, homes and roads affect 20 million.

September: Hurricane Georges hits Dominican Republic at 110mph, leaving 100,000 homeless and almost entire population of 8 million without power. Mexico hit, and across the Caribbean and at Florida Keys, 468 die.

October: Up to 100,000 flee floods in the western part of Nigeria after gates of a hydro-electric dam open. Resulting floods wash away up to 70 villages downstream. In Britain 12 die as Severn and Wye rivers flood.

November: 8,000 killed in Honduras and 2,000 in Nicaragua as Hurricane Mitch strikes at 180mph. Research by Mark Rowe