Natural Disaster Trends

Since I have broadly touched on the topic of whether our climate is getting more extreme, I will now turn to look at the trends in natural disasters over the years. However, before we begin to look at the stats, let’s begin this post with the second episode of Disaster Bite on the devastating earthquake that struck Bohol, Philippines just last Tuesday 15^th October 2013.

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Disaster Bite: Bohol Earthquake

Epicenter of Bohol earthquake. Source: Inquirer News

•  7.1 (previously reported as 7.2) magnitude on the Richter Scale
• Epicenter was at Bohol (about 620m south-southeast of Manila), at a depth of 33km
• It struck on 08:12 (local time) on a Tuesday 15^th October 2013, which also happened to coincide with a national holiday
• The earthquake was caused by a vertical movement of the East Bohol Fault
• Earthquake did not result in a tsunami
• The death toll has surpassed 100 on Wednesday, with the greatest fatalities in Bohol and Cebu provinces
• Many damaged buildings and stampedes were reported Bohol and Cebu
• Tremor triggered power cuts in both provinces
• Strongest tremor felt in the area in the last 23 years

More information:

http://manilastandardtoday.com/2013/10/16/deadliest-quake/

http://newsinfo.inquirer.net/507373/bohol-earthquake-strongest-to-hit-visayas-and-mindanao-in-over-20-years

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With reports saying that this was one of the deadliest quakes in Philippine history, which released energy equivalent to 32 Hiroshima bombs, it seems like it has joined the ranks of deadly natural disasters that have brought great tragedy to mankind in recent years (think Hurricane Sandy 2012, Tohoku earthquake 2011, Haiti earthquake 2010 etc.). A question that pops into my head right now is: are natural disasters becoming more frequent, intense and devastating?

Frequency

Fig.1 Frequency of natural disasters from 1900 to 2010. Source: EM-DAT

Based on the graph showing the number of natural disasters reported from 1900 to 2011 (Fig.1) produced by The International Emergency Disaster Database (EM-DAT), it does seem at first glance that the frequency of natural disasters have increased tremendously over the last century. However, this graph might actually be misleading as the increase in number of natural disasters over the years could in fact be due to better media reporting and advances in communications (Guha-Sapir et al. 2004). Moreover, with the launch of agencies like Office of US Foreign Disaster Assistance (OFDA) and Centre for Research on the Epidemiology of Disasters (CRED) in the 1960s and 70s, data collection on natural disasters have markedly improved. Hence, what the graph is showing might in fact be the evolution of the registration of natural disasters over time. Guha-Sapir et al. (2004) thus suggested that it might in fact be more appropriate to review the statistics of natural disasters over a shorter time span to spot trends (say between 1980 and 2000). Even so, the frequency of natural disasters during these 3 decades is still increasing. This might partly be due to the increases in hydro-meteorological disasters as seen in Fig.2. Some reports attribute such increases to climate change, which I will cover in the weeks to come. 

Fig.2 Worldwide polynomial trends for the four major types of natural disasters from 1900 to 2003. Source: Guha-Sapir et al. 2005

Intensity

Some studies have proposed that the intensity of some types of natural disasters has increased over the years. This include work done by hurricane expert Kerry Emanuel, who has shown that the total North Atlantic and western North Pacific hurricane power dissipation have more than doubled over the past 30 years (Fig.3) (Emanuel 2005). We’ll discuss hurricanes in greater depth in future posts. However, for other types of natural disasters such as earthquakes, it is much more difficult to spot any trends in intensity over the years. 

Fig.3 Annually accumulated power dissipation index (PDI) for the western North Pacific and North Atlantic, compared to annually averaged sea surface temperatures (SST). PDI has nearly doubled over the past 3 decades. Source: Emanuel 2005

Vulnerability and devastation

Nonetheless, it does seem that the impacts (e.g. loss of life, economic damages) of natural disasters are increasing over the years. It has been proposed that this is due to the increasing vulnerability due to large populations living in high-risk areas as a result of population growth and urbanisation (Huppert and Sparks 2006). Jackson (2006) cites the example of Tehran, which has grown from being a small village town to a megacity with 12 million inhabitants. This has greatly increased the vulnerability of Tehran to earthquakes given that it is built on an active fault system. In fact, in 2012, more than 300 were killed in twin earthquakes that rocked the region. Moreover, as our assets increase, there is more to be lost when a disaster strikes. The UN Office for Disaster Risk Reduction (UNISDR) reported that for the first time in history, the annual economic losses caused by natural disasters have exceeded $100billion for three consecutive years (2010-2012). This is due to the major increases in exposure of our industrial assets and private property to these disasters. 

Based on the discussion above, it seems that it is hard to conclude whether natural disasters have increased in frequency and intensity over the past few years. However, we are indeed becoming more vulnerable to natural disasters due to growth in population and assets. Nonetheless, with the recent IPCC AR5 report (2013) attributing some natural disasters to climate change as well as a recent NOAA report (Peterson et al. 2013) that attributed single natural disaster events to climate change, it is interesting to see how the changing climate as (discussed in the previous post) would have an impact on the intensity and frequency of future natural disasters. Stay tuned over the next few weeks as I continue on my quest to unravel the links between the changing climate and natural disasters.