14 May 2008

Sichuan landslide problems – the seasonal issue

Posted by Dave Petley

To illustrate the problems with landslides that the Chinese authorities now face, I have plotted the occurrence of rainfall induced landslides in Sichuan for 2005, 2006 and 2007 by month, using data from the Durham University landslide database. We know that the occurrence of landslides increases dramatically after large earthquakes, especially in the rainy season. Figure 1 shows that landslides in Sichuan occur in the period May to September .

Figure 1: Monthly occurrence of fatalities from landslides in Sichuan, as recorded in the Durham University Landslide Database. (Click on the graph for a better view)

The picture is clear – the occurrence of rainfall induced landslides begins in May and lasts through to October, with the peak occurring in July. In fact, with the exception of a single event in March, the earliest fatal landslide in this period occurred on 20th May.

The implications for the earthquake affected areas are very clear – assuming that the rains do occur as per usual (and there is no reason to believe that they won’t), landslides are going to be a very serious problem in the coming months.