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. 
 

Why the Haiti earthquake takes us into new territory for disaster response

The Haiti earthquake rightly continues to dominate the news around the world, with the situation on the ground looking increasingly desperate. The news media are already reporting on the growing frustration amongst the population about the lack of aid, not uncommon in large disasters actually, but probably magnified in this case. Although every rapid onset disaster is different, in a number of ways this event takes us into new territory. This will make the short, medium and long term mitigation of this event very difficult. These are the key issues as I see them:

1. Haiti has no army - and therefore effectively no national capacity to deal with the immediate aftermath
In recent years we have seen large earthquakes in other less developed countries - Kashmir in 2005 and Sichuan in 2008 spring to mind. In both cases, as is generally the case, the immediate response is framed by the national army, who undertake the initial rescue and logistics operations, followed quickly by the international organisations and agencies. Once the immediate rescue phase is over the army usually plays a key role in co-ordinating the response, in particular with the logistics of getting medical aid, food, water and sanitation to the people who need it. Haiti has no army - the military was demobilised in 1995. This is a key factor in the lack of coordination that you can see in the television pictures.

2. The earthquake struck the capital city
Point 1 is hugely exacerbated by what was in effect a direct hit on the capital city. It is clear that many government buildings collapsed and many civil servants were killed. In addition many of the key staff from international agencies were also killed. In a moment a huge component of the in-country organisational capacity was destroyed. This was not the case in other comparable disasters, where the national capability remained intact.

3. Population concentration is a key issue
The earthquake has struck a very densely populated urban area. Port-au-Prince is a natural amphitheatre in which almost all usable level ground has been quickly developed. Finding space to locate large refugee camps and medical facilities will be a great challenge.

4. Haiti is on a key hurricane track
I have used the NOAA Historic Hurricane Track viewer to produce the map below, which shows the hurricanes that have passed within 200 km of Port-au-Prince in the period since 1980:

You will probably have noticed that there are a worryingly high number. Hurricanes bring strong winds, storm surges and, more importantly in this context, very intense rainfall. A direct hit from a strong hurricane would be exceptionally hazardous for those in temporary camps, would test damaged drainage systems, and could trigger extensive landslides (especially mudflows) on slopes weakened by the shaking.

The hurricane season starts on 1st June (less than five months away). This is going to place an extraordinary level of urgency on operations over the next few months. Unfortunately, the December forecasts (which do have a comparatively low level of skill) for the 2010 hurricane season suggest that we should expect an above average season:

"We foresee an above-average Atlantic basin tropical cyclone season in 2010 and anticipate an above-average probability of U.S. and Caribbean major hurricane landfall." For Haiti, the Caribbean and C. America Landfalling Hurricane Probability Project estimates that there is a 49% probability of a named storm tracking within 50 miles.

Synthesis
Given the above, I suspect that there will be a need for the international community to direct considerable resources into Haiti over a prolonged period. I wonder whether this will be possible as the story fades from the news screens, and given the pressure on western government budgets at present.

Landslide potential in the aftermath of the earthquake
Finally, a word on the future landslide potential. In a nutshell we just don't know what will happen and, whiteout proper field investigations, including mapping and modelling, there is no way to estimate the likely future effects. It may be that there will be a large number of slides in the first very heavy (probably hurricane-induced) rainfall event, or it could be that there will be no more than usual. Note here in recent years these have killed hundreds and even thousands of people, but mostly in the area around Gonaives, not Port-au-Prince. The image below, from here, shows a before and after IKONOS satellite image of Gonaives in the aftermath of Tropical Storm Jeanne in 2004. The mud was released by landslides on the hills above the town. Over 3000 people died.

I must stress here that at present we have no way of knowing whether this could happen in the earthquake affected area or not. This requires attention with some urgency.

Google Earth imagery of the Haiti Earthquake

With admirable speed Google have released two high quality images of the earthquake affected areas:

http://www.gearthblog.com/blog/archives/2010/01/imagery_layer_for_haiti_earthquake.html

At the moment the imagery is just for the Carrefour and Port-au-Prince areas (i.e. not the rural upland areas), but it contains the first good news to emerge from the area. This is that on this imagery at least the number of landslides appears to be small and, perhaps most interestingly, there are few signs of slope failures under the shanty towns on the edge of the urban areas, which we feared could be the cause of substantial loss of life.

There are some interesting other aspects of the damage, not least a large oil spill leak into the sea:

The main roads appear to be mostly open.

If landslides have occurred (and this would be the norm for an earthquake of this size) then they are most likely to be in the hills outside the imagery area. However, it could be that the slopes are so denuded and stripped, and prone to hurricane rainfall so frequently, that the material that would normally be available for sliding has already been stripped off.

More El Salvador lahar satellite imagery

In an earlier post today I highlighted the availability of satellite imagery covering the El Salvador lahar disaster, triggered by Hurricane Ida earlier this month. Whilst sitting in a conference session this morning it occurred to me that the Disaster Charter, which provides satellite images for disaster relief and recovery operation, was also triggered by this event. So I had a quick look at the web page for this triggering of the charter, and sure enough there are some good materials there.

Perhaps the best image is this interpretation of the lahar tracks, produce using the Taiwanese Formosat2 satellite (famous for its images of Beichuan and Tangjiashan after the Wenchuan Earthquake) - do click on the image to see this properly, it is worth it!:

There is also a more detailed look at the town of Guadeloupe using the same satellite, showing before and after images of the town:

Viewed in conjunction with the NASA images in my earlier post, this is a very useful resource.

Satellite imagery of the El Salvador lahars

NASA has released before and after satellite images of the lahars (volcanic debris flows) triggered by Hurricane Ida in El Salvador earlier this month. The final toll of the landslides remains unclear, over 60 is the widely reported statistic.

The images are false colour composites collected by the ASTER instrument. These images differentiate between vegetation, which appears as red colours, and bare ground, which appear as a blue-grey colour. Such images are ideal for delineating new landslides, which usually strip away vegetation to leave bare soil.

This is the before image of the area affected by the landslides:

As usual, click on the image for a better view in a new window. Here is the image after the hurricanes passed through:


The lahar tracks are pretty clear. Note that they start high on the volcano, mostly with small, translational landslides. These slides then enter the channel, entraining (eroding and incorporating) material along the channel. The towns are quite clear on the images - the debris flows have hit the settlements in several locations, leaving this type of damage (Image from here):


When the landslides reach the plains below the volcano they spread out and stop, leaving a large area covered in debris. This is also clear on the image.

Reports of a very large landslide tragedy at San Vicente volcano in El Salvador caused by Hurricane Ida?

It is becoming clear that Hurricane Ida has wreaked havoc in El Salvador over the last 48 hours, with many landslides. Over 100 people are known to have been killed, with the toll expected to rise over the next few days as more remote areas resume contacts. Intriguingly, the El Salvador news site ElSalvador.com has a report on the disaster here. It reports:

"Según los últimos reportes, en Verapaz, en las faldas del volcán de San Vicente, un alud ha cubierto un área de ocho kilómetros aproximadamente. El panorama es sombrío: Grandes rocas y árboles se observan por todos lados, por lo que la movilización es difícil. La tierra ha cubierto colonias enteras. Familiares y socorristas buscan desesperadamente a las víctimas. Testigos afirman que la tragedia es similar a la que ocurrió en Las Colinas, Santa Tecla, en 2001 cuando el país fue afectado por un terremoto."

This roughly translates as:

"According to recent reports, in Verapaz, in the foothills of the San Vicente volcano, a landslide has covered an area of eight kilometres. The outlook is grim: Large rocks and trees are found everywhere, so that mobilization is difficult. The earth has covered entire colonies. Relatives and rescuers desperately looking for victims. Witnesses say the tragedy is similar to what occurred in Las Colinas, Santa Tecla, in 2001 when the country was affected by an earthquake."

The Santa Tecla landslide killed about 600 people.

I have no way to validate or refute this report at this time, so let's hope that this report is erroneous. This is a Google Earth perspective view of the volcano in question, San Vicente:

I will post again when information becomes available.

Latest update on Typhoon Lupit (Typhoon Ramil) and Hurricane Rick

Latest update here

Unfortunately the news on typhoon Lupit (Ramil in the Philippines) is not getting any better. The storm has now turned towards the west and is picking up speed. It is now moving on a bearing of about 300 degrees at about 9 knots (c.17 kmh). This means that it is forecast to start to make landfall on the northern side of Luzon on Wednesday / Thursday. The current forecasts are that it will weaken slightly over the next few days, but this will still be a very strong storm if it does come ashore on Luzon:

The best hope at the moment is that it takes a more northerly track and shoots through the gap between Taiwan and Luzon. A more northerly track than this could be bad news for Taiwan - this is of course the area that was hit by Morakot (see images here and a review here) in August.

Meanwhile, in the Eastern Pacific Hurricane Rick is now weakening slightly but is heading northwards to make landfall on Baja California, also on Wednesday:
This storm also has the potential to bring very heavy rainfall, in this case to Mexico, with a very real threat of landslides.

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.

The Casita landslide revisited

One of the most deadly hurricanes of modern times was Hurricane Mitch, which tracked across Central America in late October 1998. Many of the tens of thousands of victims were killed by landslides. Perhaps the most notable event was a lahar (a volcanic landslide) that swept down from near the summit of Casita volcano in Nicaragua, killing about 2500 people over the course of its 6 km path (and some more in the hyper-concentrated flow (debris rich flood) events that travelled a further 10 or so kilometres from the toe of the slide. Unfortunately, despite the magnitude of this event the amount of published literature about it has remained quite limited. It is therefore terrific that a paper has just been published by Graziola Devoli and her colleagues (Devoli et al. 2009) that seeks to summarise the published and unpublished reports about this remarkable landslide.

Wikipedia has a very decent image of the upper track of the landslide, which gives a pretty good idea of the scale of this event:

Whilst MDA have a great overview image of the source, track and runout zone:

Complex landslides such as this are poorly understood. In particular, as in the landslides that I highlighted in Sichuan, the mechanisms of initiation and movement are quite intricate. Devoli et al. (2009) have used a range of geological, geotechnical and analytical techniques to get a better idea of what happened.

The landslide was triggered by very heavy rainfall - they suggest that about 750 mm (that's about a years worth for where I live) of rain fell in a little over 80 hours. Interestingly, they conclude that the landslide can be divided into three key phases:

1. Failure started in a fractured and altered volcanic breccia in the northern area of the scarp which released a volume of about 260,000 cubic metres. The flow that developed from this failure swept downslope and entrained colluvium deposits at the toe of the slope in the southern part in less than about 40 seconds.
   
2. The rapid removal of the colluvium on the slope triggered a second failure. This also originated in the scarp shown on the image above. In this phase about 640,000 cubic metres of volcanic breccia slipped over a unit of clay-rich pyroclastic deposits. It is unclear as to whether this flow joined the first one or occurred separately. Either way, blocks in this flow travelled 9 km or more downslope.
   
3. The third and final stage consisted of a as a sudden debris / rock avalanche that originated in the uppermost section of what is how the landslide scar. This failure, with a volume of 690,000 cubic metres, appears to have occurred very soon after the first two events.

In the aftermath there has been considerable concern raised about the likelihood of failure of the entire flank of Casita Volcano (indeed, even I have published on this theme - see van Wyck de Vries et al. 2000). The paper concludes that under conditions of high groundwater instability of these flanks can occur, although as we understand these very large failures so poorly I would be cautious in the interpretation of this particular result. This is a slope that needs an active monitoring programme for sure.

References
Devoli, G., Cepeda, J. and Kerle, N. 2009. The 1998 Casita volcano flank failure revisited — New insights into geological setting and failure mechanisms. Engineering Geology, 105, 65-83.

van Wyk de Vries, B., Kerle, N., Petley, D., 2000. A sector collapse forming at Casita
volcano, Nicaragua. Geology 28, 167–170.

Hurricane landslides in Haiti

A perennial landslide story at this time of year is the triggering by a tropical cyclone of landslides in Haiti. This year the hurricane season has been particularly cruel, with three large events in a month. Hanna, the most recent, appears to have stalled close to Haiti for a day or so, causing torrential rainfall. At the moment reports suggest that 136 people have been killed in flash floods and landslides as a result of Hanna, but that figure may well rise as the picture becomes clearer. Unfortunately, there is another, very intense "Cape Verde" type hurricane (called Ike) lurking to the east. Current forecasts suggest that the track will swing north of Haiti (in fact Florida could get a direct hit), but at this stage such forecasts are at best tentative. A direct hit from a hurricane as large and intense as this, on the back of Hanna, could be disastrous for Haiti.

So why is Haiti so vulnerable to hurricanes? Basically, Haiti is the most extreme illustration of the impact of deforestation on landslides and flash floods. Haiti is the poorest country in the Caribbean - over half the population live on less that $1 per day ($1 is the recognised mark of extreme poverty) and over 75% live on less that $2. More that 60% of the working population do not have formal employment. The consequence of this has been extreme deforestation, primarily for firewood to create charcoal.

This is rather well illustrated by this Google Earth image:

The border between Haiti and the Dominican Republic is the river that runs across the centre of the image. On the west (leftish) side is Haiti, to the east (right) is the Dominican Republic. The contrast between the two is striking - in the Dominican Republic deforestation has been limited, in Haiti the loss of forest is almost total.

The result is that during hurricanes the landscape has little capacity to intercept and store water, and once flows across the surface begin the landscape rapidly erodes. This is perhaps best illustrated by the following Google Earth image of the city of Gonaives in the east of the country. Gonaives has been very seriously affected by erosion and landslides again in the most recent floods. The image shows the hills on the outskirts of the edge, with the suburbs clearly visible. The hills are clearly suffering from extreme deforestation. In September 2004, Hurricane Jeanne triggered mudslides and debris flows from these hills that killed over 3000 people in the city. Bearing in mind the fact that Haiti should be densely vegetated with tropical forest, the disaster that is the landscape in this country is all to clear to see. Unfortunately, posts about landslide disasters in Haiti will be a feature of this blog in the late summer for years to come.