Weather Gone Wild does a great disservice to statisticians by promoting some 'new' math related to extreme weather. Its like Romper Room math.
The Ocean Breeze resident Frank who has lived there 43 years was interviewed. He was told by a "geologist" that Hurricane Sandy was a 1 in 700 year storm. And Hurricane Irene before was a 1 in 300 year storm. Spring flood the year before 'roughly' 1 in 100 year storm. His conclusion is that in three and a half years they had 1100 "years of storms"!
There you have it folks! The new normal is here. More like the new weather math is here! Does anyone remember what geologists do for a living? I didn't think it was meteorology or extreme weather statistics. I bet kids in Romper Room even know the difference.
Here's how the math really works on extreme weather return periods (new weather math that Weather Gone Wild promotes):
1) never add the years of storm return periods ... those numbers are denominators of fractions that represent the yearly probability of an event occurring. Just to show how bad that "weather math" is, imagine in Romper Room they teach some "pie math" to the kids. Teacher says little Billy has 1/2 a pie, Sally has 1/4 of a pie and Joey has 1/8 of a pie ... together the teacher says they have 2+4+8 = 14 pies ... IT IS SOOOO WRONG! Wrong. wrong. wrong, wrong, wrong. Never add the denominators of probability fractions! Its like Ghostbusters crossing the streams from proton packs!
2) Hurricane Sandy has a return period of 700 years which is not rare for a long time resident meaning:
- chance of Sandy occurring in any given year is 1/700, or 0.14% ... its about the same probability of OLG's Pick 4 12-Way Box Play (all four digits must match the digits drawn in any order, where two of the digits are the same), which is 1 in 833 odds (OLG odds)
- chance of Sandy not occurring any 1 year is 1 - 0.14 = 99.86%
- chance of Sandy not occurring in the 43 years Frank lived in Ocean Breeze = (99.86)^43 = 94.04%
- chance of Sandy occurring in 43 years = 1 - 94.04 = about 6% .. or 1 in 17 chance = not rare
- "the old extremes are the new normal"... quote me ;)
3) Never conflate the probabilities of different processes like hurricanes and spring floods like Frank does. Even though these are both weather/water events, they are statistically independent processes. You might as well say your well pumped failed, say a 1 in 40 chance event and then add 40 to the 1100 years of storms. You might as well add you just won Pick 4 12-Way Box Play so add another 833 to the total based on those odds. And you bought an orange car which is a 0.4% or 1 in 250 chance (popular car colours) so add another 250 to the odds. Yes it gets silly adding the probability denominators for different events like car colour, but that is what adding spring flood and hurricane denominators is like. I bet spring floods were influenced by snow pack, melt cycle, perhaps ice build-up at bridges, joint probabilities of melt plus rain, etc... many things not related to hurricane processes. And I'd have a better chance of winning that bet than the Pick 4 12-Way Box Play.
Ocean Breeze residents, it was said in the doc, are faced with the choices of "build back better or retreat". Uninformed decisions are made based on bad math that underestimates risks. Did Frank's geologist friend tell him how rare a Hurricane Sandy event would be if he settles there (did the geologist say 1 in 17 chance in 43 years (correct math), or it won't happen for 700 years (bad weather math)? Let's build better math skills and weather documentaries to inform the public about risk... let's retreat from sensationalized weather reporting, and "shockumentaries".
In-depth data and analysis on extreme weather and flood risks on www.cityfloodmap.com share engineering insight on complex topics of infrastructure design and performance, urban hydrology, flood risk assessment, and cost-effective risk management. Our goal is to promote critical, evidence-based "Thinking Slow on Floods and Flow" to improve flood and stormwater management policies and achieve effective environmental outcomes. R.J. Muir, Toronto, ON.
Weather Gone Wild - New Weather Math for Shockumentaries
Posted by Flood Advisor
Labels: 100 year storm, climate change, extreme rainfall, extreme value statistics, extreme weather, flooding, rain, rain intensity, rainfall statistics, rainfall trends, return period, storm frequency, storm intensity
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