Thursday, January 15, 2015

Trends in Hydrological Disasters Worldwide

While reviewing the WHO Collaborating Centre for Research on the Epidemiology of Disasters, I decided to focus on the trends in hydrological disasters around the world.

The graph denoting the number of disasters recorded from 1900 to 2012 showed noticeable increases in the number of hydrological disasters beginning in 1965.  The number of events has continued to grow quite steadily, reaching the highest levels recorded in the last 12 years displayed on the graph (roughly between year 2000 to 2012).

(EM-DAT 2012b)
Within the classification of hydrological disasters, floods (flash floods and storm and coastal surges) and storms (tropical and local) have all noticeably increased while the number of unspecified hydrological events have decreased.

Other graphs also showed that while the number of people affected by hydrological has increased in tandem with the rise in the frequency of disasters, the number of people killed by that group of disasters has remained quite low.  In fact, the number of people killed saw a sharp increase around 1960 but dropped back down to a low level afterwards and has stayed around that number ever since.  The graphs displaying the cost of the damage of all disasters has also shown steep increase of late, with the two most expensive being the Honshu Tsunami and Hurricane Katrina, both of which were hydrological disasters.

These trends could be interpreted in a variety of ways.  I believe that the number of all hydrological disasters (floods and storms) has been increasing in large part due to climate change and will continue to either remain high or increase even higher.  I also believe that climate change is causing the scale and intensity of hydrological disasters to become more severe as well.  I believe that the increase in frequency and intensity of hydrological disasters has contributed to increase in the number of people affected.  I also think that urbanisation has resulted in more densely populated areas (more people in one spot that will be impacted if a disaster hits) which has added to the increase in the number of people affected.  On the other hand, I believe that fewer people are now dying as a result of hydrological disasters due to our superior notification systems, evacuation protocols, storm preparation and emergency response capabilities (first response, paramedical and medical training, knowledge and experience).

The increase in the cost of damage due to hydrological disasters has likely been the result of a combination of factors, including urbanisation (an increase in the number, size and cost of buildings in one concentrated area) and the increase in the severity of events (which is causing more damage).  The graphs relating to costs are slightly confusing to read however, as they do not state whether the cost is nominal or adjusted for inflation.  If the figures have not been adjusted for inflation, the increase in the cost of damages could be due in part to the rise in the cost of living over time.

In my opinion, the decrease in the number of unspecified hydrological events has nothing to do with a decrease in frequency of disasters and everything to do with improvements in our ability to monitor, identify and classify exactly what kind of disaster is occurring.

I believe that these trends will continue and even worsen if the world continues on its current crash course trajectory with climate change.


EM-DAT 2012a, Disaster Trends, viewed 11 January 2015, <>.

EM-DAT 2012b, Number of natural disasters reported 1900-2012, viewed 11 January 2015, <>.


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