An analysis of fatal landslides in the Asia-Pacific region for 2006 to 2008

In my last post I published two maps of fatal landslide occurrence in the years 2006 to 2008 inclusive, based upon my long term fatal landslide database. In this post I focus on the Asia Pacific region. This analysis does not include seismically-induced landslides, most notably the Wenchuan (Sichuan) earthquake, which triggered a large number of slides, killing over 20,000 people.

The basic statistics of the data are in the table below - as per usual you can get a better version of the table and figures by clicking on the image:

In total, I recorded 796 fatal landslides (note that in this context I use landslides generically to include all non-avalanche mass movements, including rockfalls) in which 9941 people were killed. In terms of fatalities, the Philippines ranks highest (Fig. 1), although India is the country with the most fatal landslides (Fig. 2). Of course if the Wenchuan earthquake were included China would be the top of both lists

Fig. 1: The number of recorded fatalities organised by country

Fig. 2: The number of recorded fatal landslides organised by country

The seasonality of landslide occurrence varies greatly within this area. In South Asia there is a very strong influence from the S. Asian monsoon, which is very apparent in the monthly data (note that for these three graphs I have used the same y-axis scales so that they are directly comparable):

Fig. 3: Monthly recorded fatal landslide occurrence (line graph) and loss of life (bar graph) for South Asia

In East Asia there is also a very strong seasonal signal, but note that here there is a more distinct peak in July and a decline thereafter (Fig. 4):

Fig. 4: Monthly recorded fatal landslide occurrence (line graph) and loss of life (bar graph) for East Asia

In South-East Asia there is no strong seasonal signal - this is unsurprising in an area that is mostly tropical. Two distinct peaks do occur, one in February and one in November.Fig. 5: Monthly recorded fatal landslide occurrence (line graph) and loss of life (bar graph) for South-East Asia

As with yesterday's post, I have no problem with this information being used elsewhere, but please reference the figures and information as follows:

Petley, D.N. 2010. An analysis of fatal landslides in the Asia-Pacific region for 2006 to 2008. Dave's Landslide Blog URL: http://daveslandslideblog.blogspot.com/2010/02/analysis-of-fatal-landslides-in-asia.html

Fatal landslides in S. Asia in 2009

The key driver of landslides in S. Asia is the SW (summer) monsoon, which brings prolonged and sometimes heavy rainfall across much of the Indian subcontinent. This year the monsoon has been comparatively weak so far, with only a month or so to go. Indeed, the Indian Institute of Tropical Meteorology maps of the total monsoon rainfall give a picture of considerable rainfall deficit, although it should be noted that heavy rainfall in the last few days may have started to reduce this:So I wondered to what degree this is being reflected in the landslide pattern for S. Asia. The graph below shows the monthly occurrence of rainfall-induced fatal landslides for S. Asia for the period 2002 to 2008, with the 2009 figures up to the end of August included (click on the graph to view a bigger version in a new window):

The black line is the long term average, and red line is 2009. I have used a lighter line for previous years to make the graph clearer. As I have pointed out previously for similar graphs, this graph shows clearly the impact of the monsoon, with a clear, asymmetric summer peak and low levels the rest of the year. Note that there is some inter-annual variation, with 2007 and 2008 varying somewhat from the patterns seen in other years for reasons that are not at all clear.

So what of 2009? Well, perhaps surprisingly 2009 shows a very unexceptional picture. May was somewhat above average, and June below, whilst July and August are almost exactly as per the long term mean. There is some evidence that in previous El Nino years September has been the month with the most intense rainfall in S. Asia, so it will be interesting to see what is to come.