New images of the level of destruction in the Cusco area of Peru

The Spanish language blog El Caminerito has been covering the magnitude of the rainfall, flood and landslide disaster in Cusco, Peru. They have put together a very helpful map showing the locations of serious damage:


Ver Cusco en Emergencia en un mapa más grande

The scale of the disaster, which is still being ignored by the western media in favour of coverage of the tourists at Machu Picchu, is well-illustrated by these images of the Huacarpay region:


Meanwhile, via the Typeboard site, the Spanish language site Peru.com reports that the village of Zurite was severely damaged by a landslide, which sounds to be a debris flow (Google translation):

" the landslide of mud and stones covered the Plaza de Armas, the town’s Church, the main streets of the city and damaged 500 houses. The incident occurred about 3 pm on Thursday after they noticed a crack on a hill and began to take appropriate action, emergency services were able to evacuate the entire population."

This is the Google Earth imagery of Zurite:


There is no shortage of landslide scars on the hillside above the town, plus the quarries, one of which appears to have excavated out the toe of one of the scars.

Here is an image of the central square via the Panoramio site:

The link between rainfall intensity and global temperature

The aftermath of a landslide in Taiwan caused by very heavy rainfall

One of the most interesting aspects of the global landslide database that we maintain at Durham is the way in which it has highlighted the importance of rainfall intensity in the triggering of fatal landslides. Generally speaking, to kill people a landslide needs to move quickly rapid, and rapid landslides appear to be primarily (but note not always) triggered by intense rainfall events (indeed in the reports the term "cloudburst" often crops up). So, a key component of trying to understand the impacts of human-induced global climate change on landslides is the likely nature of changes in rainfall intensity, rather than that of rainfall total. Put another way, it is possible that the average annual rainfall for an area might decrease but the occurrence of landslides increase if the rainfall arrives in more intense bursts.

There is of course a certain intuitive logic in the idea that rainfall intensity might increase with temperature. Warmer air is able to hold more moisture (as anyone who has been in the subtropics in the summer will know only too well!) and of course increased temperatures also drive greater convection, responsible for thunderstorm rainfall. Of course this is a very simplistic way to look at a highly complex system, so it is not enough to rely upon this chain of logical thought. However, until now there have been surprisingly few studies to actually quantify whether there is a relationship between global temperature and precipitation intensity, which has meant that for landslides understanding the likely impact of climate change has been quite difficult.

However, an important and rather useful paper examining exactly this issue has sneaked under the radar in the last few months. The paper, by Liu et al (2009) (see reference below), was published in Geophysical Research Letters a couple of months ago. The paper uses data from the Global Precipitation Climatology Project (GPCP). These data can be accessed online here (so no claims that climate scientists don't publish their data, please!) The dataset provides daily rainfall totals for 2.5 x 2.5 degree grid squares across the globe, extending back almost 50 years. Liu et al. (2009) looked at the data from 1979 to 2007, comparing precipitation density with global temperature in this time period.

Their results are both unsurprising and surprising. The unsurprising part is that they found that the occurrence of the most intense precipitation events does increase with temperature. The surprising part is the magnitude of the change - they found that a 1 degree Kelvin (Centigrade) increase in global temperature causes a 94% increase in the most intense rainfall events, with a decrease in the moderate to light rainfall events. Indeed the median rainfall increased from 4.3 mm day⁻¹ to 18 mm day⁻¹, which is a surprisingly high shift as well.

So why is this important in the context of landslides? Well, I think that there are probably two key implications:

1. It has long been speculated that anthropogenic warming will lead to an increase in landslides, but with little real quantitative evidence to confirm or deny this. The demonstration that higher global temperatures does lead to increased precipitation intensity starts to put some meat on the bones of this idea. Furthermore, if it is possible to directly link rainfall intensity to landslide occurrence (and there is some evidence both from my own work and from that of others that this may be possible), then it should be possible to start to examine the likely increase in landslides as warming proceeds.
2. The current global climate models assume a much lower increase overall in precipitation intensity with increasing temperature than Liu et al. (2009) suggest. Indeed most of the models assume about a 7% increase per degree Kelvin (Centigrade) warming. For the most intense precipitation events this means that the models predict about a 9% increase, which is an order of magnitude lower Liu et al. (2009) found. This suggests that the rainfall projections that are derived from the models are probably overly-conservative, and possibly very much so, which is a concern. If so, then forecasts of landslide occurrence that are derived from these models are likely to under-estimate the true impact.

Of course, this is only one study, and it should also be noted that the most intense rainfall events are usually associated with tropical areas and with those in the path of hurricanes and in particular typhoons. There is a great deal more work to do on this topic, but the initial results provide real cause for concern.

Reference
Liu, S., Fu, C., Shiu, C., Chen, J., & Wu, F. (2009). Temperature dependence of global precipitation extremes Geophysical Research Letters, 36 (17) DOI: 10.1029/2009GL040218

Large landslides in Peru and Kyrgyzstan, the Afghanistan earthquake plus heavy rain expected in the Wenchuan area

Each year in mid-April we move into the global "landslide season", when the development of the Northern Hemisphere summer, and the associated weather patterns elsewhere, means that the number of landslides starts to increase dramatically. This is all too clear from the range of landslide events in the last few days, plus the threat of heavy rainfall in the earthquake affected areas of China:

1. Major landslide in Peru
A range of news agencies (for example AFP and CRI) are reporting that there was another large landslide in Peru, again in La Libertad Province (the second major landslide this week in that province). Although details are sketchy, this time the landslide appears to have been very large (one report suggests 1 km long), hitting two villages (Chamanacucho and Aricapampa). Reports suggest that about 30 people were killed. The coordinates of Aricapampa are (-7.80583, -77.7172), which yields the following Google Earth images:


It appears that the landslide is still active, which is hampering the recovery operation substantially.

2. Major landslide in Kyrgyzstan
According to RIAN there was also a large landslide in Kyrgyzstan yesterday. The landslide appears to have hit Raikomol village Jalalabad province in in south Kyrgyzstan, killing 16 people and a large number of cattle. All of the victims, 11 of whom are apparently children, have been recovered. The ENG24 website has posted this rather grainy, but very helpful, image of the slide:

The reports suggest that it is about 300 m long. It appears to be a massive earthflow. Unfortunately the source zone is not in the image - I would be very interested to see how and where this started.

3. The Afghanistan earthquakes
The two moderately-sized (USGS Mw=5.5 and 5.1) but shallow (USGS depth = 5.7 and 3,.2 km) earthquakes in Afghanistan this morning appear to have caused damage in at least some villages, with about 20 reported fatalities at the moment. A Google Earth image of the area affected suggests that it really is a very remote zone:

Given the remoteness of the area and the rugged terrain the number of reported fatalities might well rise during the day. Earthquakes of this size would not normally cause much damage, but the early indications are that these two events really are exceptionally shallow. I would anticipate that there will have been at least some landslides in the upland areas, but probably over quite a limited area.

4. Heavy rain forecast for the earthquake affected areas of China
Xinhua is forecasting that heavy rain will hit the areas affected by the Wenchuan earthquake over the next few days. Up to 100 mm is expected to fall. This will be the first heavy rainfall of this years rainy season. Given the amount of mobile sediment on the hillsides, and the occurrence of debris flows in heavy rainfall last September, some further problems might be expected if this heavy rainfall does occur:

Karst landslide in China

Xinhua is reporting a landslide in Jinjiling Hill in Guilin, Guangxi yesterday that buried several houses and killed four people. Whilst in global terms the event was not huge, the images that Xinhua have published are quite interesting:


Xinhua describes the event thus: "...several hundred tonnes of rocks and dirt gushed down from the mountain at about 9:20 p.m. Wednesday. Four workers in charge of a cave-digging project in the hill, the project contractor and his wife were in the houses when the accident took place, the city's public security bureau said. Jiang Mingyi, head of the city's geological environment monitoring station, said ongoing rain over the past few days triggered the landslide and the local karst-landform is prone to mountain collapse in the rainy season."

It would be easy to ascribe this collapse to the caving digging work that was going on at the toe of the slope. However, the failure appears to have occurred on an unfavourably orientated joint high up on the slope. The initial collapse was possibly quite small, but the failure has accrued debris on the way down to create quite a large failure. Thus, the interpretation that the failure was rainfall-induced looks spot on.

Of course, what is not clear is the degree to which the work at the toe of the slope disturbed the joints upslope. If blasting was being used this is of course quite possible.