21 June 2011
The summer solstice seems to be a good point to reflect upon landslides in 2011 to date. As of yesterday I had recorded 135 landslides worldwide that have caused loss of life, with 1867 victims. The graph below shows the cumulative total number of fatalities by month for the period 2003 to 2011. The average cumulative number is also shown:
Interestingly, and perhaps surprisingly, to date 2011 is a very average year in terms of fatality-inducing landslide occurrence worldwide, although the number of victims is higher than usual. In terms of overall trend it resembles very closely 2008. It is then interesting to look at a graph of the monthly NOAA El Nino index for all of the years shown above:
A quick note about this data – each month number represents two months – i.e. 1 = Dec-Jan; 2 = Jan-Feb, etc. Negative numbers represent La Nina conditions, positive El Nino. What is clear here is that 2008 and 2011 both had strong La Nina conditions at the start of the year, in stark contrast to, for example, 2010, which had strong El Nino conditions. It is not reasonable to argue that the landslide pattern in the early part of the year is controlled solely by the El Nino – La Nina cycle of course, but a good working hypothesis for further investigation would be that it does play a role.