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Estimate
Confidence (1-10; 1=intuition, 10=an easy-to-estimate number from a reliable source eg demographic statistics from UN, 8=good systematic review, 5 = single well-run study, 3=single less well-run study)
Justification
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Health
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global annual flood deaths52358
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GiveWell moral weight on a death1002
unknown age distribution of flood deaths but likely skews towards kids, so I will use the value closer to GiveWell's 116 for undedr 5s than 73 for over 5s https://docs.google.com/spreadsheets/d/1tytvmV_32H8XGGRJlUzRDTKTHrdevPIYmb_uc6aLeas/edit#gid=1364064522
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proportion of flooding DALY losses from premature deaths0.11
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total flooding health harms in GiveWell units of moral value5.24E+06
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Economics
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increased income (log units) if all floods averted5.28E+067
this number was difficult to calculate, but I am quite confident in it. I cannot provide the full data supporting it as that goes against the terms of use, but the data is from EM-DAT. I downloaded their database of 3296 flood events between 2001 and 2020 (these years aren't special, I just wanted a long, recent range to smooth out the noisy data), which gives the economic damage from each flood. Some rows are blank, I assume these were generally small floods though. I cross-referenced that database with a World Bank databse of population and GDP per capita for each country, and assumed that each flood affected everyone in the country equally, to estimate the lost income in log units. I then summed the log units over all flood events.
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proportion of flooding economic damage captured in reported property damage
0.5
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GiveWell value assigned to increasing ln(GDP/person) by one unit for one person for one year
1.442
https://docs.google.com/spreadsheets/d/1tytvmV_32H8XGGRJlUzRDTKTHrdevPIYmb_uc6aLeas/edit#gid=1680005064
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total flooding economic harms in GiveWell units of moral value
1.52E+07
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Economics sanity check
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total global annual flood damge3.51E+108
https://public.emdat.be/data
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gross world product (2021)9.61E+1310
https://data.worldbank.org/indicator/NY.GDP.MKTP.CD
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world population (2021)7.84E+0910
https://data.worldbank.org/indicator/SP.POP.TOTL?
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increased income per person (log units) if all floods averted3.65E-04
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total flooding economic harms in GiveWell units of moral value
4.12E+06
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sanity check?3.69
the sophisticated estimate is within a factor of two of the simple estimate, which is pretty close
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Cost
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GiveWell units of value lost from flooding2.04E+07
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GiveWell units of value generated per philanthropic dollar spent
0.052
https://docs.google.com/spreadsheets/d/1tytvmV_32H8XGGRJlUzRDTKTHrdevPIYmb_uc6aLeas/edit#gid=1364064522
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Budget to cost-effectively end all flooding4.09E+08
If we solved all flooding by spending this amount of money per year, it would break even on the current cost-effectiveness fronteir
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proportion of harm from health26%
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