Updates for Pakistan, China and India flood and landslide crises, 10th August

As yesterday, this is a brief review of the state of play with the three substantial landslide and flood crises in Asia.

1. Pakistan
The flood wave continues to work its way down the Indus, and is now in the Province of Sindh.   As forecast, heavy rainfall exacerbated the situation yesterday, with totals of over 100 mm in some areas of the province. Kyber-Pakhtunkhwa also saw falls of 30 mm or more in some areas.  Whilst not enough to cause the sort of devastation that we have seen of late, this is sufficient to keep river levels topped up.

 Working our way down the Indus, the second flood at Besham has now peaked and the hydrograph is showing a rapid decline. 

The peak flow in this econd flood was lower than in the first , but was still substantial.  This water will of course have to work its way down the Indus over the next ten days.  It will be interesting to see how this flood looks when it reaches Taunsa.

Moving down to Guddu, the peak discharge appears finally to have passed, meaning that water levels will be slowly falling.  Note however that if the flow behaviour at Taunsa is a guide, the rate at which the water levels fall will be quite slow, meaning that the people have several more days before they will be able to start rebuilding their lives.  Note also that the flood level is still above the exceptionally high level.  The flat peak component of the flood record causes me to reiterate my suggestion yesterday that the hydrograph shown below has not accurately captured the peak flow:

Going south again, and the main concern is now at Sukkur, where the hydrograph appears to be suffering the same problems of saturation at the peak:

Some media reports have suggested that the peak flow here is actually 1.2 million cubic feet per second.  The media are also reporting concerns about the safety of the Sukkur barrage, with several reports suggesting that deliberate breaches of levees are being considered to try to reduce the peak flow.  It seems that a similar exercise was undertaken upstream at Ghouspur, with the inevitable destruction that followed.  However, it is important to understand that these barrages provide irrigation for vast areas of productive agricultural land that is vital for the sustenance of the population of Pakistan.  Deciding on how to protect them is not an easy task.

However, as at Attabad the apparently poor communications strategy of the authorities is unfortunate.  Whilst putting the hydrographs online is a good step, it would be sensible to accompany this with a decent explanation of what is happening, where the threats lie, and the action that might be needed to mitigate them.  Whilst this would not prevent the destruction, at least people might understand why particular courses of action are being followed.

Finally, for northern Pakistan the Pamir Times has provided two updates in the last 24 hours on the Attabad situation.  Most importantly, the water level is now falling, having apparently risen by 6 feet (about 1.8 metres) at the peak of the floods, which caused further widespread destruction. Meanwhile, they continue to note that other landslides have caused severe hardship, and that the Hunza was blocked at Rahimabad to the north of Gilgit.  As far as I can tell Rahimabad is in the valley shown in the Google Earth image below:

Meanwhile, the Pamir Times has also provided some new images of the state of the Attabad barrier itself:

These appear to indicate little change in the state of the dam over the last couple of weeks.  Operations to lower the spillway level have yet to start, but it is heartening to see in some of the images that a monitoring team appears to still be on the site.

2. China
Rescue operations continue at the Zhouqu landslide site, where the number of known fatalities is now 337.  The reported number of missing people is 1,148.  There can be little chance of recovering many further survivors, although one victim was recovered alive today.  The state media are reporting some tales of real anguish in the aftermath of the disaster, exacerbated of course by the "one child" policy in China.  The government is attributing the disaster to the normal villains - poor geological conditions, the recent drought, the heavy rainfall, and the aftermath of the 2008 earthquake.  This is all likely to be true to at least some degree, but there may be other factors as well, most notably deforestation and the legacy of mining activities.  The internet age has spawned a wave of amateur investigative journalism in China.  This All Voices page reviews recent postings of Chinese documents about the landslide hazard in Zhouqu.  Whilst I am naturally sceptical of some of this material, it does appear that the risks to communities posed by landslides in these mountains is well-documented.  In particular, this newspaper article, from 2008, identifies that the slope problems at Zhouqu are sufficiently serious that they have been the location of various studies by Japanese landslide scientists.  However, to be fair to the government, the range of landslide problems in the aftermath of the 2008 earthquake is so serious that prioritising and finding resource to mitigate appropriately is impossible.  Expect more landslide disasters in central China in the coming years.

Two images have appeared in the last 24 hours that demonstrate the magnitude of this slide.  This AP image shows the landslide from the opposite bank:

I would really like to see the source of this huge debris flow - has anyone seen an aerial image of the upper reaches of the track as yet?

And this AP image illustrates the likely velocity of the movement, given away by the mud deposit on, and indeed in, the upper part of the building:

Finally, unfortunately tropical storm Dianmu is moving northwards off the east coast of China.  Although it is unlikely to landfall in China itself, expect heavy rainfall across eastern and central China.  Given the intensity and magnitude of the recent rainfall, this is potentially deeply problematic.

3. The Ladakh debris flows in India
The forgotten disaster amongst everything else that is going on is the Ladakh debris flows that occurred on Friday.  To date the number of known victims is reported to be 165 people, with a further 500 thought to be missing (with very little chance of survival now).  However, Save the Children is reported to believe that the true toll is likely to be in excess of 1,000 because several affected villages have yet to be accessed.  Localised heavy rainfall continues in the area, disrupting relief operations and causing further damage.

One of the most seriously affected towns was Choglamsar.  This is the settlement in the foreground of the perspective Google Earth image below - the presence of the huge debris fan in the background is a clear sign of the processes that have allows the formation of the comparatively flat areas upon which the town is built:

Protecting the town against repeats of this event is not going to be an easy task, but debris flows must be expected on a fan such as this.

I will try to provide further updates tomorrow morning, or sooner if events require.

Update on the flood wave in Pakistan, plus an update on the monsoon in India and on typhoon activity in the NW Pacific

The true magnitude of the disaster in Pakistan is now becoming clear - this appears to be the country's equivalent of Hurricane Katrina.  It has to be hoped that lessons are learnt both within the country and by the international community in terms of disaster risk reduction there.

In 2007 the World Health Organisation produced a flood potential map for Pakistan, which I reproduce below:

The flood wave is travelling down the Indus River at present, concentrated initially on the most westerly of the three main tributaries shown above.  The latest PakMet hydrographs show that the flood has now peaked at Taunsa and is rising downstream at Guddu.  Unfortunately the graphs are incomplete on the PakMet site (it appears they have a software issue) - I'll try to put this right later once they have corrected the error.  For locations see the Google Earth map I produced yesterday.

The flood routing model suggests that the peak should reach Guddu in about three days from the peak at Taunsa, and then take a further day to get to Sukkur and finally three days or so to reach the sea.  Hopefully there is sufficient warning to relocate people away from the water, but the potential for damage is high. The government (i.e. the NDMA) in Pakistan is once again coming under severe criticism for its response - this letter, written about Taunsa, gives a flavour of the concerns.  Whilst it is easy to criticise NDMA, the core issue probably remains a lack of investment and capacity building in this agency.  This needs to be corrected.  Unfortunately, the assassination of an MP in Karachi yesterday has also led to severe civil unrest in that city, which is only serving to magnify the range of problems facing Pakistan.

Meanwhile the emergency in Northwest Pakistan continues, but the operation is being hampered by further rain.  Reports now suggest that the loss of life is in the order of 1,400, but note that it is not unusual for estimates a few days into an emergency to be too high, with a further 3 million people reported to have been directly affected.  Stories about the event are truly heartbreaking - it is hard to imagine what it must be like to lose your children, house, belongings and livelihood to a single event.  The impact of the flood in mountain communities is well illustrated by this image, showing the loss of roads and bridges, and extensive riverbank erosion that has triggered house collapses:

 Meanwhile, across a large swathe of northern and western India rainfall activity in this monsoon remains low:

And typhoon activity in the Pacific is also unusually quiet - indeed global tropical cyclone activity is at its lowest level for the 30 year period for which reliable measurements are available (see image below from Ryan Maue's excellent site).  ACE is a measure of the energy expended by tropical cyclones.  Given that tropical cyclones are a major trigger of landslides, this is keeping the overall occurrence lower than might have been expected. 
 

The slow-burn rainfall disaster in China, whilst the monsoon in South Asia is weak so far

Although it has received scant attention in the west, China is currently undergoing a classic slow-burn weather disaster associated with exceptional rainfall.  The scale is remarkable - Xinhua reports that since 1st July, 273 people have been killed and 218 people are missing, 3 million people have been displaced from their homes and 58 million people have been affected directly.  Economic losses are estimated to be about US$8.6 billion.  This means that over 1,000 people have been lost to floods and landslides so far this year in China.  As of 15th July (i.e. before these most recent storms), economic losses from rainfall-induced disasters in China this year were estimated to be US$17.6 billion. A week earlier than that, on 8th July, the Ministry of Civil Affairs estimated that natural disasters (now including earthquakes) in China  in the first six months of 2010 have left about 4,000 people dead or missing, and caused about US$31.2 billion in direct economic losses.

Unfortunately the situation could deteriorate considerably in the next 24 hours as Typhoon Chantu is just making landfall in southwest China, as this Tropical Storm Risk map shows:

Meanwhile, the monsoon in S. Asia is off to a slow start.  Although the weather system progressed northwards more quickly than is normal, the rainfall totals to date are some way short of normal:

Whilst this is good news from a hazards perspective, S. Asia is dependent upon monsoon rainfall.  Very anomalously low years cause water supply issues.  However, there are now signs that atmospheric conditions that generate monsoon rainfall are developing, so expect to see this situation change soon.  The result will inevitably be an increase in the number of landslides in S. Asia, in line with the normal seasonal pattern.

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

The annual cycle of fatal rainfall-induced landslides

On the flight to San Francisco yesterday I spent some time preparing for one of my AGU presentations - the one on Friday on the impact of landslides on society. I have been looking at my landslide fatality database, which now stretches back for over seven years. There is still some way to go with this to really understand long term trends in fatal landslides, but the dataset is now big enough to do some quite interesting things.

I have divided each year into five-day blocks (we often call one of these blocks a bin), and then taken the average number of recorded fatal landslides within that bin over the seven year period. So, bin number one is 1st to 5th January, the second is 6th to 10th, etc. I have then looked at the cycle through time by plotting a graph in which I have smoothed the data using a 25 day filter - this is a noisy dataset, so this is needed given the comparatively short window:

The resulting graph is pretty interesting I think. First, the peak in aggregate recorded fatal landslides (the black line) clearly occurs in the northern hemisphere summer, the minimum is around about now. The peak is actually on about 25th July. This is coincident with the peak of the SW Monsoon over the Indian subcontinent. Notice though that the graph is asymmetric - i.e. it rises to a peak more quickly (about 100 days) than it then declines (about 150 days). I assume that this is because in this post-SW monsoon peak the influence of the monsoon in East Asia and of tropical cyclone landfalls becomes significant.

The minimum period coincides I think with the onset of winter in the northern hemisphere (which is a dry period for many of the most landslide prone areas) but is before the rainy season really gets going in SE Asia. By early January the rains in for example Indonesia are really under way, and the occurrence of landslides increases.

The standard deviation is a measure of variability between years. So, if for a specific bin the number of fatal landslides was always three then the standard deviation would be low. If however one year there were none, the next six, the next ten and the next two then the standard deviation would be much higher. It is interesting that as the average number of fatal landslides increases in the N. Hemisphere summer so does the standard deviation - this is to be expected. However, in the post-peak period the standard deviation remains high for a while before declining. I think that this probably reflects the influence of tropical cyclones in this period, which tend to landfall rather sporadically but then to cause many landslides over a small area. Over the seven year period many of the bins in this period have been affected by a tropical cyclone.

I hope to see you at the session!

A late monsoon landslide incident in Nepal

Regular readers will know that Nepal is country in which I have a particular interest. The landslides there are dominated by the very strong monsoonal signal seen in the summer months. Usually by late September the monsoon is fading and normal life resumes. Not this year, which has seen a sudden late burst of rainfall in the west of the country. The map below shows the TRMM data for the last three days, with areas of intense rainfall highlighted in red and yellow colours:


It is possible to extract from the TRMM site the actual rainfall data that sits behind this map. So here is the cumulative rainfall for this region over the last week. This should be taken as being indicative only, but it is clear that there has been a substantial amount of rain:

The consequence has been a large number of landslides, several of which have killed people. To date the list that I have collated is as follows:

Date	Location	Number of fatalities
06/10/2009	Mastamandu VDC 1, Garkhagaon, Dadeldura	12
06/10/2009	Dewrali VDC 3, Tanahu	1
06/10/2009	Silgadhi-14, Pagari in Doti district	1
06/10/2009	Patalkot VDC of Achham	13
06/10/2009	Bindyabasini-1, Accham	1
06/10/2009	Majhigaun-3, Bajhang	2
06/10/2009	Malladehi-7, Baitadi	1
06/10/2009	Siddheswari VDC, Accham	5
07/10/2009	Thapakhana village, Parvat	4
07/10/2009	Marku VDC of Achham	3
08/10/2009	Syadi VDC, Dhangadhi	4
Total		47

This is a pretty grim total. Fortunately, the weather does now seem to be improving.

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.

The low level of NH hurricanes and typhoons in summer 2009

One of the reasons that the northern hemisphere summer is essentially the global landslide season is that landfalling tropical cyclones (typhoons and hurricanes) represent a rather efficient way of triggering slope failures. This is especially the case in the Caribbean, Taiwan, Japan, SE and S China, the Philippines and Vietnam. Typhoon rain is astonishing to experience for the first time - peak intensities of 100 mm per hour are not unusual in the largest events. The hourly rainfall data below is for the passage across Korea of Typhoon Rusa in 2002, taken from Lee and Choi (2007):

Note that at Gangneung the peak hourly precipitation was 100.5 mm (4 inches) and the peak 24 hour rainfall was 870.5 mm (35 inches). It is unsurprising that such events cause landslides on a large-scale.

The northern hemisphere tropical cyclone season is primarily associated with warm sea surface temperatures, and hence runs primarily through the summer and early autumn months. Interestingly, and for reasons that are far from clear, the energy associated with northern hemisphere tropical cyclones has been reducing for a number of years. Ryan Maue at Florida State University runs a superb web page that tracks tropical cyclone occurrence globally. He has the following graph of global and northern hemisphere tropical cyclone energy (note smoothed using 24 month running sums):

Levels of tropical cyclone activity are now approaching a 50 year low. However, even by recent standards the level of Northern Hemisphere tropical cyclone activity to date this season has been exceptionally low. Ryan also provides the following graph of Northern Hemisphere tropical cyclone energy (ACE) for the first three months of each season since 1979:

It is not for me to speculate on why tropical cyclone activity should be at such a low level (Ryan is much better qualified to do so), but it is clear that so far the Northern Hemisphere tropical cyclone occurrence has been a damp squib. The occurrence of landslides reflects this (I will post my monthly update in the next few days). This is of course good news in terms of landslides and floods, but it is bad news for farmers who rely on rainfall for irrigation, the hydro-electric industry in these areas, and many others whose livelihood and.or welfare depends upon water derived from tropical cyclones.

It will be interesting to see whether level of activity dramatically increase later in the season.

Meanwhile, the S. Asian monsoon remains very weak, with the Indian Meteorological Department noting that total precipitation in the monsoon season is 19% below the long term average. Again, the occurrence of fatal landslides that I have recorded is mirroring this pattern. Meanwhile, much of China is suffering from unusually intense monsoon rains. For example, Shanghai has just suffered its heaviest rainfall for 70 years.

Update on the South Asian Monsoon

The seasonal landslide pattern in South Asia remains very substantively below the long term mean this year - to date at least the monsoon is failing. The level of the problem is illustrated rather well by this map of the monsoon season rainfall anomaly for India, from Monsoon Online:

The result is that the number of landslides in South Asia is very much below average, which is of course good news.

It is interesting to compare this year with 1997. This is part of a press release from 26th June 1997, put out by the Indian Institute of Tropical Meteorology:
"Unfavourable conditions trigger worry over south-west monsoon (26 June 1997)
Weather experts at the India Meteorological Department are keeping their fingers crossed over the performance of the south- west monsoon, as the waters of the Pacific Ocean are getting warmer. Warming of the Pacific is of significance since it means that there is no hope, at least for the time being, for the El Nino factor, which has a important influence on the monsoon, to become favourable. On the contrary, it only meant that it could have a more adverse impact than what was envisaged a month ago. To add to the problem, the Southern Oscillation, which is another global climatological phenomena that influences the monsoon, has also become more unfavourable. While El Nino is a reflection of the warming of some regions in the tropical Pacific Ocean, Southern Oscillation is an index of difference of pressure between the Pacific Ocean and the Indian Ocean. El Nino is considered favourable if the temperatures in the Pacific Ocean, particularly off the coast of Peru are low, and Southern Oscillation is considered to be advantageous if the atmosphere pressure in the Pacific Ocean is less than that in the Indian Ocean. The officials have, however, not given up hope on the ground that there was still a long way to go before the monsoon, which is active for four months, comes to an end in September. "

Interestingly the monsoon was 8-10 days late across most of the country that year. In the end the monsoon rainfall total was slightly above average, but characterised by very heavy rainfall, which caused floods and landslides, in late August.

1997 was of course the start of the largest El Nino in the last 60 years. It is unsurprising that the monsoon is currently showing a similar pattern as a new El Nino develops. The landslide pattern is apparently reflecting this.

Early May is the start of the landslide season

Whilst the transition towards the Northern Hemisphere summer is rather pleasant for many of us, the start of May also marks the start of the landslide season in the Northern Hemisphere. Of course the main problems kick in when the SW monsoon really gets going in Asia and the tropical cyclone season properly begins in the N. Pacific and N. Atlantic basins, but already there are clear signs that the land is starting to move. Overnight, a number of Pakistani news agencies have reported a large landslide in the Neelam Valley:

"At least 28 people were trampled to death due to landslide in Neelam Valley on Tuesday, Geo news reported. According to sources 28 people have been trapped under the landslide in Jora area here in Neelam Valley, part of Azad Jammu and Kashmir (AJK). The rescue activities have been kicked off after the tragic incident and the trapped dead bodies of the unfortunates are being dug out, sources added."

Of course the Neelam Valley was pretty badly affected by the 2005 earthquake (the image below shows a part of the valley in 2006), so ongoing landslide problems here are not a surprise.


Meanwhile, the Philippines has already been battered by one typhoon (named Kajira in the Pacific-wide system, or Dante in the Philippines), which triggered a landslide in Sorsogan that killed 23 people. Unfortunately, there is another one (Chan-Hom) en route for northern Philippines at the moment (Tropical Storm Risk):


The good news is that Tropical Storm Risk (see long term forecast here) are forecasting a below average season for typhoons (activity is anticipated to be 20% below the long term mean). The long term forecast for the monsoon in India is essentially average (forecast rainfall = 96% +/-5% of long term mean.

The influence of the summer monsoon on fatal landslides in Asia

I am currently putting together a keynote paper for the forthcoming International Conference on Slopes, which is being held in Malaysia in November. I have been looking at the occurrence of fatal landslides in Asia, using the Durham Landslide Database as the source of data. I have plotted the number of fatal landslides by month for 2002-2007 for three areas - South Asia (i.e. the Indian subcontinent), East Asia (which includes China, Taiwan, Korea and Japan) and SE. Asia (which should be self evident). The graphs are shown below (note the different magnitudes of the y-axis scales by the way).

First, South Asia shows a very strong monsoon signal. Look in particular at the mean trend for the five years. The level of fatal landsliding in the winter months is very low, with most of the events occurring in June to September. It is also clear that the number of landslides increases rapidly at the start of the monsoon as the rain bands push northwards, but then decline slowly as the monsoon disperses. There is also considerable year-on-year variation; in particular the very strong and prolonged monsoon rainfall across parts of India is very clear for 2007.

East Asia (below) also shows a strong monsoon signal, of course slightly modified by the impact of typhoons too. Here though the pattern is quite different - again look at the graph of the mean of the other data. In this case the monsoon signal is far more symmetrical, again reaching a peak in July but rising and declining at about the same rate. Again there is considerable year-one-year variation both in terms of number of events and the variation through the year. The big spike in July 2006 is particularly clear.

SE. Asia present a completely different picture (below). As much of SE. Asia is tropical there is far less monthly variation. Unsurprisingly no monsoon spike is seen. The occurrence of landslides is slightly higher in the latter part of the year as the rainy season affects Indonesia for example. Of particular note are the variations in the distribution between years - this really does reflect the occurrence of extreme tropical cloud bursts.


So the impact of the really large scale climate systems on Asian landslides is absolutely clear. This is particularly interesting in the context of climate change - exactly how the Asian monsoon in particular will change will partially determine the landslide impact. Unfortunately the models are not resolving this issue too well at the moment, but most do suggest an increase in the occurrence of the most intense rainfall events. The implications for landslides of this are stark.