We call them "acts of God" - but if the Almighty had recourse to the libel laws he would make a killing, for it is usually human actions that turn natural phenomena into disasters. Eighty per cent of earthquake deaths are caused by collapsing buildings, yet even in the fiercest ones properly built structures save lives.

More than half of all buildings in Turkey, according to the local Architects' Chamber, are built in violation of construction rules. Often they are put up without planning permission, with inspectors turning a blind eye; and politicians frequently grant amnesties for illegal buildings as elections approach.

This is just one example of a global problem. Most of the 100,000 people who died in an earthquake in Armenia in 1988 were in cheap concrete buildings. It was much the same in the Peru earthquake of 1970, which killed 60,000. And even in Japan, most of the buildings that collapsed in the 1995 Kobe earthquake, in which 5,000 died, were poor constructions rushed up after the Second World War.

"During this century more than 1.5 million people have lost their lives as a result of earthquakes and the vast majority of this toll is because of building design," said Ed Booth of the engineers Ove Arup and Partners, after the Kobe disaster.

Poverty is also to blame. The Red Cross points out that the poor can often afford only badly built housing. An earthquake in Guatemala City, which killed 23,000 in 1976, became known as the "class quake" because of the accuracy with which it hit the poor.

"Floods," the Red Cross adds, "also target the poor." They are hit disproportionately, whether crowded on to low-lying sandbars off the Bangladesh coast or the steep slopes of Rio de Janeiro. Floods are also turned into tragedies by human actions such as straightening out rivers so that they break their banks more easily, building on flood plains or, above all, cutting down trees.

By the time Hurricane Mitch hit central America last autumn it had been downgraded to a tropical storm. But it caused the worst disaster ever to hit the western hemisphere because its rains hit denuded hillsides, causing mudslides in which 10,000 died. Last year's flooding of the Yangtze in China was made much worse because four-fifths of the trees in the river basin had been chopped down.

The world's growing cities also increase the scale of disasters, because they concentrate people in vulnerable areas and because their compacted and concreted ground cannot absorb flood water.

But the right policies can reduce the impact of disasters. Planting trees, putting bends back into rivers and restoring old flood plains can help to prevent inundation. Improving building design can cut the toll of disasters. Sophisticated techniques, such as those now used in Japan or San Francisco, may be out of range of the poor, but traditional designs, which resisted earthquakes in the past, can be adapted. The Red Cross has found that improvements to traditional huts in Bangladesh stopped them being swept away by typhoons.

Above all, reducing disasters means tackling poverty. In the words of Anders Wijkman, an expert on development and disasters who is now Sweden's ambassador to the United Nations: "Most disasters in the Third World are unsolved development problems."