A New Analysis Shows a Huge Death Toll From Landslides

New Scientist
Stories from New Scientist.
Oct. 28 2012 7:30 AM

Landslides Are Even Deadlier Than We Knew

And they may be getting worse.

(Continued from Page 1)

A second key factor is that fatal landslides are concentrated in populous but remote mountain areas prone to heavy rainfall or earthquakes. The global epicenter is along the southern edge of the Himalayas; other hotspots are Indonesia, the Philippines, western China, some Caribbean islands, and Colombia.

In such places, obtaining information about landslides that kill small numbers of people has been hitherto impossible. The availability of digital and social media has made it easier.

The ultimate goal of such data gathering, of course, is to reduce landslide deaths. In the past three decades, several countries have set up successful programs to manage landslide risk. A good example is Hong Kong, which suffered a series of major accidents in the 1970s. Their program has reduced loss of life to a handful of fatalities per decade through a combination of engineering works—such as building retaining walls and installing drainage—public awareness, relocation of people most at risk, and an early warning system. While replicating this in full in less-developed countries is probably not feasible, some of the measures should be possible even with limited budgets.

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An interesting question is whether deaths from landslides are increasing. There are good reasons to think they might be. My research shows that as population density increases, so does the number of fatal landslides. In part, this is probably because rising population forces people to live and work on unstable land and, of course, when there are more people in the landscape, it becomes more likely that any given landslide will hit someone.

Other factors will also be at play. Environmental degradation, especially deforestation, seems to be making landslides more likely. And the widely observed increases in rainfall intensity, which are probably associated with a warming atmosphere, may also be contributing.

My data set is still too small to determine whether there is a long-term upward trend. The impact of landslides varies considerably from year to year. Although 2010 has the highest number of recorded landslides, the number is considerably lower for 2011, and 2012 looks like it will be lower still. This probably reflects the state of global weather systems such as the El Niño/La Niña cycle and continental systems such as the Asian monsoon, which has been much weaker than normal in 2012.

The landslide data set has very similar characteristics to a weather one; in the latter case about 30 years of data are required before a trend can be determined. It is likely that I will need to continue to compile data for 20 more years before this question can be addressed.

Rainfall-induced landslides are for the most part a manageable hazard, and a coordinated effort to reduce landslide deaths in poorer nations could be highly effective. The first step needs to be a research program that seeks to better understand the occurrence of landslides and the mechanisms responsible for them. Unfortunately at present there is little indication that this is a priority.

Dave Petley is a professor of geography and co-director of the Institute of Hazard, Risk, and Resilience at the University of Durham in the United Kingdom.

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