Deadly landslides have been in the news on several occasions in recent weeks. A landslide in Yunnan, China, buried a school, killing 18 children. A series of landslides in Uttarakhand, India, claimed the lives of at least 40 people. In Dorset, U.K., three people died in two landslides triggered by heavy rain.
Given these deadly impacts, it is surprising that until recently we had almost no data on the global cost of landslides nor about where they cause the highest losses. To fill this gap, I have spent the past 10 years collecting data about deadly landslides from around the world.
The results are surprising. In a paper in the journal Geology, I analyzed the data from 2004 to 2010. In this seven-year period I recorded 2,620 rainfall-induced landslides worldwide that killed more than 32,000 people, a much higher toll than previously thought.
The total number of fatalities is even higher than that, as my analysis only considered landslides triggered by rainfall. If other landslides are taken into account, especially those triggered by earthquakes, the death toll rises to a remarkable 80,000.
This is in stark contrast to official figures in the United Nations International Disaster Database, which indicate only about 7,400 deaths from landslides and avalanches during the same period.
Why such a large discrepancy? The explanations lie both in what gets included and the nature of landslides themselves.
Let's address the first issue. A key factor is that the U.N. database includes many other hazard types, such as earthquakes, floods, and volcanic eruptions. Compiling such data is a huge task, so the researchers set a minimum impact threshold for inclusion. This is either 10 fatalities or a large economic loss, meaning that many small events are excluded. This is not a problem for earthquake-related data, as unfortunately almost all events that cause significant damage also kill more than 10 people, but it leads to substantial underreporting for landslides, most of which are small and localized.
A related issue is that the U.N. database records only a single cause for each death. All of the approximately 68,000 fatalities in the 2008 Sichuan earthquake in China, for example, are recorded as resulting from the quake. In a sense this is true, but more than 20,000 people were killed by landslides triggered by the event. This is a general problem: Landslides are typically triggered by another event, often intense rain or an earthquake, so their impacts are consistently underestimated.