A Downhill Battle: Landslides Are among the Deadliest Natural Disasters, with Their Impact Felt Most Severely in the Developing World. Natalie Hoare Reports on the Efforts of Two British Geographers to Alleviate the Threat in the Caribbean Using a Combination of Computer Models and Local Community Action

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The stories may be familiar, but that doesn't lessen the tragedy. In March, a mudslide triggered by heavy rains sweeps through a village in eastern Uganda, killing at least 100 people. In April, an extended period of heavy rainfall over Rio de Janeiro triggers dozens of landslides across the city, primarily in shanty towns built on its periphery. In the worst, some 50 houses in a slum in Niteroi are swept away, killing at least 150 people. Less than a week later, a large irrigation pipe on a hillside near Merano in the Italian Alps bursts, sending a wave of mud and water crashing into a passing commuter train, killing nine passengers.

These disasters are both grimly routine and somewhat unusual--routine in that globally, hundreds of landslides take place every year in built-up areas, killing a total of around 1,000 people; unusual in that they made the news headlines. 'Quite often, landslides are underreported and not as easy to recognise as, say, a flood because they happen in very discrete locations, and you can get multiple landslide events,' says Dr Liz Holcombe, a landslide researcher in the University of Bristol's School of Geographical Sciences. 'They are effectively masked by the triggers with which they are associated,' adds her colleague and former PhD tutor Professor Malcolm Anderson.

Hurricane Mitch illustrates Anderson's point well. In November 1998, this category-five hurricane brought record rainfall to Honduras, Guatemala and Nicaragua, causing catastrophic flooding. It went on to become the second-deadliest Atlantic hurricane in history, with as many as 20,000 people killed. Around 2.7 million were left homeless and the total damage was estimated at more than US$5billion.

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'The damage wasn't just a result of flooding,' says Holcombe. 'It was also caused by hundreds of landslides that affected the whole region, blocking the road networks, preventing trade and [the distribution of] emergency aid, and causing a significant reduction in economic growth. So even though a significant proportion of the damage was actually through landslides triggered by that rain, it's recorded as a hurricane, rather than, say, 100 landslides and a flood.'

This intertwining of landslides with other natural disasters, and the multi-faceted nature of their effects, renders their impact equally complex. 'The global scale of the problem depends on how you cut it,' says Holcombe. 'In absolute terms, Asia has the most landslides, the Americas and Caribbean region has the deadliest, and Europe has the costliest, because they're damaging more expensive infrastructure and property. However, in terms of GDP, the landslides turn out to be relatively more expensive to developing economies.'

In developing countries, losses are greatest in cities, where migration and urbanisation link poverty with vulnerability to landslides. Often, only the steep slopes are available to the poor, who live there in densely populated, informal settlements.

SLOPE STABILITY

About five years ago, Anderson realised that the research that he had been conducting into slope stability for highway construction could be used to mitigate against landslides, particularly in informal, unregulated settlements built on land that was already at high risk of collapse.

'I suppose my motivation to understand more about landslides was really driven by the realisation that we didn't know too much about the movement of water through soils,' says Anderson. 'When I started my PhD, I wrote some software that was able to model the movement of water through soils, and I started working in the Far East on big road and highway construction projects.

'We've now migrated that software from planning for road projects to looking at slopes in poor housing areas to do essentially the same sort of thing,' he continues. 'But the issues there are far more complicated. …