Increasing number of catastrophes and human factor

Peter asked me (here) to discuss the occurrence of natural catastrophes. I have looked at the EM-DAT dataset (here), and more specifically three kinds of risks: earthquakes, floods and storms (in any country over the past century). For earthquakes, we have the following figures,

the blue points are raw data (I mean, public ones, those that can be downloaded on the website), and I added two smoothed patterns, in red (based on splines regressions). This is no reason to assume that there could be an increase of the number of earthquakes. The trend is due to the fact that we look at earthquakes considered as catastrophic, i.e. that caused deaths and severe damages. And as pointed out in Peter’s comment, it means that “the increase in ‘disasters’ might have a lot to do with the development of the population”.
If we look now at storms, we have

i.e. also an increasing trend. But here, we can consider that the trend can be explained by two factors: an inflation due to the value at risk (e.g. increase of concentration of population in some areas as for earthquakes) but maybe also a change that can be related to climate change.  If we remove the pattern du to the increase of value at risk on the raw data (i.e. we divide raw data by the trend observed on earthquakes, the red line), we have

Here it looks like the number of catastrophic storms is increasing (removing the human factor). And it might be possible to relate that trend to climate change. If we look finally at major flood events, we also observe an increase of the pattern,

and we can divide by the trend observed on earthquakes, to obtain

Looking at that graph, it is possible to propose another interpretation about the increase: people might have a shorter memory about rivers than the one they have on earthquakes; and that they think they might influence climate risk, and flood risk, (but not physical ones). I mean that people know where earthquake risk is, and did not really concentrate in those areas during the past century. On the other hand, it is possible to assume that people imagine they can change river design, e.g. building dykes, and though they can control the risk. But obviously they couldn’t.

4 thoughts on “Increasing number of catastrophes and human factor”

  1. I was looking for a post that explains the relation between climate change and catastrophes and I stumbled upon on your blog. I know this blog was written a long time ago, but it is still very helpful. Thank you so much for such a great post. Would love to read your blog from nowonwards.

  2. On ne sait pas toujours très bien (même si on peut deviner dans certains cas) ce qu’il y a en ordonnée …

    Question bête : est-ce que ces courbes sont corrigées de l’évolution de la population mondiale ?

    RÉPONSE: en ordonnée c’est un nombre (pour les données brutes) de catastrophes, au sens retenu par l’ONU. Quant à la “question bête“la réponse est non, et justement, hier, on m’a demandé si je pouvais tenter de corriger par la population… donc j’y travaille…

  3. Thank you for this post. Everything that goes in the direction of capturing real impact of climate change in frequencies numbers is welcome. although -as you already said few weeks ago- it is raising rather small interest when looking for credit research!
    Maybe few constructive -I hope!- hints:
    Here we use E/Q frequency increase as a yard stick to measure the distortion of the curve (this scaring bump on the right) that is assumed to be replicated for Storm and Flood.

    Now this bump is supposed to be consecutive to increase of exposure i.e. more population.
    We might also have to consider a reporting inflation effect. Example: on E/Q occurring in the early 1900 might have been unreported because there was no insured damage or casualties. Same event today has much more chance to be reported.

    We might also want to go more into detail about what is behind increase of exposure due to population expansion. In the case of E/Q, frequency increase can be explained if you start to populate exposed regions where nobody lived before. More concentration in large cities would be less prone to impact frequency as these new constructions are “supposed” to be seismic resistant.
    For Storm or Flood concentration of population would have more effect : you see larger number of new constructions on top of hills or below sea water level etc….
    This topic is quite a challlenge, isn’t it?

    ANSWER: indeed… but I like that kind of challenge…

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