18 May 2020

The current landslide crisis in East Africa

Posted by Dave Petley

The current landslide crisis in East Africa

In recent months I have highlighted the increasing occurrence of fatal landslides in Africa associated with bouts of heavy rainfall.  I have noted on a number of occasions that I seem to record more landslides now in this region than was the case in the past.  However, this was an observation rather than a measurement, so I decided this morning to take a look at the data in more detail.

I have good quality data on fatal landslides for this region from 1 January 2004 to the present.  The graph below shows the cumulative number of fatal landslides in this region from 1 January 2004 to 16 May 2020 (I have yet to update the data for the weekend just gone):-


Landslides in East Africa

The cumulative number of fatal landslides in East Africa since 1st January 2004.


There is a very marked steepening of the curve in the data.  In the early years of this work I recorded few fatal landslides in this region, perhaps anomalously so.  From about 2008 this seems to have changed; perhaps at this point reporting from this part of the world improved, or perhaps there was an genuine increase in the number of landslides. There are a number of steps in the graph, marking periods of particularly heavy rainfall.

But from about 2018 the number of fatal landslides has markedly increased, and at the moment the curve is much steeper than it has been previously in the record.  The key question is of course why?

Seasonal rainfall in East Africa is controlled by the Indian Ocean Dipole, which is the local equivalent of El Nino.  The BBC Website has a good explanation of the Indian Ocean Dipole.  The graph below shows  an indicator of the state of the Indian Ocean Dipole, using a NOAA dataset called the Dipole Mode Index (DMI):-

Rainfall in East Africa - the Indian Ocean Dipole

Graph of the Indian Ocean Dipole indicator, the Dipole Mode Index, which controls seasonal rainfall in East Africa.  Data from NOAA.


In the very early years of my dataset the DMI was largely negative, which might explain the low number of fatal landslides.  But what is marked here is that since 2018 the value has been positive, and indeed reached a level not seen anywhere else in the period snce 2004.

Others have suggested that the current prolonged period of heavy rainfall in East Africa might be associated with this unusual pattern in the Indian Ocean Dipole.  The fatal landslide data would seem to support this view.


On reflection 1: More fatal landslides at Ramban

Recently I highlighted the high incidence of fatal landslides on the Srinagar-Jammu National Highway. Over the weekend two more people were killed in the infamous Ramban area.


On reflection 2: larger earthquakes trigger larger landslides

A new study by researchers from the USGS and NASA shows that larger earthquakes trigger larger landslides.