Maps of global fatal landslides

NB there is an alaysis of the data in thiese maps in this post:
http://daveslandslideblog.blogspot.com/2010/02/analysis-of-fatal-landslides-in-asia.html

I have recently worked up two new maps of the distribution of fatal landslides, based upon the fatal landslide database that I maintain. This first map shows the global distribution of non-seismic landslides for the period 2006-2008. Each dot represents a single fatal landslide. The colours indicate the year:

Red = 2008
Blue = 2007
Green = 2006

The background image is the ETOPO digital elevation model, with the darker colours indicating higher ground (click on the image for a better view in a new window):
There are a whole host of interesting aspects of this map. First, note the clustering of the landslides in areas that are tectonically-active (e.g. Western S. America, the Himalayas, Indonesia, etc). Second, note how the patterns change from year to year (e.g. take a look at the south coast of China - this is related to typhoon landfalls). Finally, note that the vast majority of recorded fatal landslides occur in Asia. This is shown better by the second map, for Asia only:

Please feel free to use the information and figures on websites, reports, theses etc, but please reference this 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 landslide map for 2009 to date

I have been a little remiss in posting these maps of late due to other pressures. Below is the distribution of fatal landslides that I have recorded in 2009 to date. Each red dot represents a single landslide that killed at least one person. All types of landslide (including debris flows and rockfalls) are included:


You can click on the map for a better version in a new window. One thing to note is that I have not heard of any fatal landslides from the L'Aquilla earthquake in Italy - but I would be surprised if there were none in reality.

Below I have plotted the same data, but colour coded the dots. In this case, the coding goes dark blue for January moving to lighter blue for February, blue-green for March, and light green for April and dark green for May:

It is reasonably clear that for Asia the blue colours cluster in the Philippines and Indonesia, whilst the greens are in South Asia. This is of course explained by the seasonality of rainfall.

For info, in 2009 to date I have recorded fatal landslides, killing 715 people. This is about par for this time of year, with the main landslide season about to begin.

Landslides and the UN's Global Assessment Report on Disaster Risk Reduction

The UN ISDR is today launching with a great fanfare the first Global Assessment Report on Disaster Risk Reduction. This report "provides hard-hitting evidence to demonstrate how, where and why disaster risk is increasing globally and presents key findings from a global analysis of disaster risk patterns and trends, including where high mortality and economic loss is concentrated. ." The report is online now and can be downloaded here.

I haven't yet had time to read the whole of the 200 page document - I will do so in due course - but have taken some time this morning to look at the landslide hazard / risk section in Chapter 2n. This was generated by the Norwegian Geotechnical Institute and has been peer reviewed by some eminent people. So how does it look?

I think a good starting point is to say that it has to be recognised that this is a very difficult thing to do. There are all sorts of problems in the collation and analysis of this type of data. However, I also have to say that I have some reservations about the outcomes, which don't to me seem to correspond to what we actually observe.

The landslides section starts with a premise that I find bizarre. The opening sentence is as follows: "Observed mortality in landslides triggered by high precipitation is approximately six times higher than in landslides triggered by earthquakes." Huh? No source or justification is provided for this statement. I just cannot see how it can be justified. In recent years we have large numbers of fatalities from landslides in the Kashmir earthquake and the Wenchuan earthquake, bit of which swamp the fatality signal from rainfall events. Perhaps this study was done before the impact of these events could be included, but there is plenty of documentation of mass fatalities from earthquake-induced landslides even before this event. Perhaps the problem here is that earthquake-induced landslides are included in the earthquake hazard section, but we should be under no illusions that the impact of this is ponce again to greatly under-estimate the risk associated with landslides. This is very frustrating!

The upshot is that the risk model considers only precipitation-induced landslides. We need to keep this is mind when evaluating the study. The headline result of the analysis seems to be (this is a direct quote) "The predicted mortality risk, even in very large countries such as India or China, is less than 100 deaths per year". Being blunt, if this is the mortality risk analysis then the model is frankly wrong as the measured losses are much higher than this. Taking 2008 as an example, a year in which precipitation-induced landslide occurrence was not exceptional, I recorded 778 rainfall-induced landslide fatalities in China, 700 in Haiti and 252 in India. This is typical and is supported by official figures. Of course, every few years these countries suffer a very large landslide disaster (e.g. the Leyte landslide in the Philippines), which increases the average annual numbers. Therefore, the study has fundamentally under-estimated the risks of rainfall-induced landslide mortality still further.

So let's take a look at the maps. They have produced landslide risk maps on a 10 x 10 km grid. Three maps have been generated, which I reproduce below. The maps are for Asia, Central America (plus the NW of S. America) and Central Africa, presumably because these are the three areas with the highest level of landslide risk. Click on the maps for a better view in a new window. Note that the label on the legend of "tropical cyclone risk" is presumably just an error, albeit a rather serious one.

This is my map of fatal landslides for 2006, 7 and 8. Each black dot represents a single fatal landslide:

This map is close to being a direct realisation of the mortality risk analysis, although care must be taken given the short time period that my map covers and to remember that population density may be an important factor. The first thing to note is that the C. American and Asian areas are well-chosen given the high incidence of fatal landslides that I record. I am far less sure of the African area - I really don't record much for that part of the world, although I recognise that this might be because I just don't capture events in this part of the world, perhaps. In Asia the distribution seems to be vaguely right in that it picks up the swathe of events through the Himalayan arc and the high risk in Java, etc. However, it does appear to fail to pick up the landslide risk associated with Central China at all well. This may reflect the high population density here (i.e. although there are lots of fatal landslides, the risk to individuals is low), but I doubt that this is the whole story. My feeling is that the analysis is failing to represent landslides in this area well. A similar problem occurs in SW India, which is a notable hotspot. In Central / S. America the analysis seems to do rather better.

Overall I am left feeling that the representation of landslide risk is really unsatisfactory. It must be possible to do this better. I hope that the analysis of the other hazards is rather better - I am sure that it must be.

Comments welcome.

Losses in catastrophes in 2008 - initial statistics from Swiss Re

Tropical Cyclone Nargis montage from the Brisbane Times

Swiss Re Sigma has just released its initial statistics on losses in catastrophes in 2008. Of course it is important to understand that reinsurance look at catastrophes in a particular way, meaning that the statistics are weighted in particular to low frequency - high magnitude events, rather than iterative processes, and to losses causing a high level of financial loss. There is no problem with this of course, but it is important to keep it in mind.

So what do the statistics show? Unfortunately the picture is pretty grim. Swiss Re estimate that these large loss events cost over 238,000 lives, most notably as a result of tropical cyclone Nargis in Burma (Myanmar), which led to 138,400 fatalities, and the Wenchuan (Sichuan) earthquake, which killed 87,400 people. In terms of economic losses, Swiss Re estimate that catastrophes cost about US$225 billion in 2008, of which about $50 billion was insured. The greatest costs were from the Wenchuan earthquake ($85 billion) and Hurricane Ike (USA) ($40 billion).

All in all 2008 has been the second worse year for insured losses on record (2005 was the worse because of Hurricane Katrina). I guess that this is unwelcome given the global financial malaise.

I have to say though that for me perhaps the interesting aspect is the following graph within the report (download a hard copy of the report here):

So let's take a quick look at the recent trends. First, the palest blue line is the total insured losses. There is a huge amount of scatter from year to year, but the general trend is clearly upwards. However, the other two losses show that this increase arises primarily from the weather related perils (the darker blue line). Over the last decade there is no obvious trend in losses from man-made disasters, with a single obvious peak in 2001 - no prizes for guessing the cause of that. Note also that very large-scale earthquake losses to the insurance industry are comparatively rare - most earthquakes occur in areas that have very low levels of insurance cover. Thus the 2005 Kashmir earthquake and the 2008 Wenchuan earthquake hardly appear on the above graph.

The trends in losses interests me greatly. I wanted to check that there is a net increasing trend in losses from weather-related perils. A quick, back of the envelope graph shows that there is indeed a clear upward trend:


I fitted a fairly simple exponential function above, although it may not necessarily be the best choice. There is a very clear upward trend in insured losses from natural perils. This rise in economic losses from natural perils is generally ascribed to increasing vulnerability - i.e. we have more economic assets in the "firing line". However, note that insured losses from man-made perils are not following the same trend. Presumably, this is also the case for man-made perils, but in this case the improvement in management and control is keeping track.

I will return to these data in the future.