# Natural disasters

For natural disasters, we work based on orders of magnitude using the EM‐DAT database, and focus on direct economic losses, disregarding human losses and indirect and second‐order losses (Hallegatte 2014; Hallegatte 2012). We start from current economic losses due to natural disasters, which have evolved between $50 and $200 billion in recent years, i.e. between 0.05 and 0.2 percent of the world GDP.

Defining the affected population is very difficult. Here we use the people who are directly and negatively affected by disasters, and suffer from significant loss of income. We estimate that the number of directly affected people is between 0.2 and 3 percent of the world population, i.e. between 15 and 200 million person per year. We use a “best guess” of 100 million affected people per year (1.4% of the world population).

We assume that the disasters in the no climate change scenarios are already included in the baseline socio‐economic scenario, and we add to our simulations the additional disaster losses due to climate change. We make crude assumptions on how climate change will affect disaster losses, reflecting the large uncertainty on the effect of climate change on extreme events and the fact that losses will be highly dependent on how protections and other adaptation measures change over time.

We know that economic losses from natural disasters are expected to increase due to climate change, and that the increase could be rapid if appropriate adaptation measures are not implemented (see a review in IPCC 2014). Hallegatte et al. (2013) show for instance that in coastal cities, floods will increase very rapidly if protections are not upgraded regularly to account for sea level rise.

Here, we assume that the fraction of the population that will be affected annually by a disaster increases from an average today around 1.4 percent of the world population to 2 percent in the low‐impact case and 3 percent in the high‐impact case. It means that between 0.6% and 1.6% of the world population would be affected by natural disasters because of climate change and in addition to the baseline risk without climate change. These numbers will depend on how effective and timely adaptation to new climate conditions is, so that these two assumptions can be considered as two assumption on adaptation performance. Further research will be needed to refine these numbers and link them to explicit assumptions regarding the adaptation process.

We assume that poor and non‐poor people are as exposed to natural disasters, consistently with the global average in (Winsemius et al. 2015), even though a bias with more poor people being exposed to disasters is observed in some countries, and in most local‐scale studies.

In the low‐impact case, we assume that affected people lose 20 percent or 10 percent of their annual income, depending on whether they are poor or non‐poor. In the high‐impact case, we assume that they lose 30 percent or 15 percent of their annual income, depending on whether they are poor or non‐poor. These numbers are in line with post‐disaster household surveys, even though much higher values are sometimes observed (Patankar 2015; Patankar and Patwardhan 2014; Noy and Patel 2014; Carter et al. 2007).

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