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Stuff you're not allowed to know #4: floods

13 Sep 2023 | Science Notes

Our enlightening tour through the officially forbidden paper this week touches on floods. We’ve had lots to say about floods here at CDN, including in our video Pavlov’s Floods. Which if you haven’t yet watched you should because its assessment of reflexive association of floods with climate change probably describes many people you know. Whereas in our continuing review of Professor Alimonti’s assessment of global indicators of extreme weather we find the following statement regarding scientific evidence of flooding: “About floods it can be said that although evidence of an increase in total annual precipitation is observed on a global level, corresponding evidence for increases in flooding remains elusive and a long list of studies shows little or no evidence of increased flood magnitudes, with some studies finding more evidence of decreases than increases.” Could warming even be associated with less flooding? Yes, it turns out it’s happened before… and naturally, of all things.

The authors discuss evidence that shows the Medieval Warm Period, RIP, and the Roman Warm Period were both marked by less flooding than the adjacent cold periods. They review numerous specific studies mainly from European locations that all show flooding was worse in the past than it is observed to be today, and was worst in cold eras. As for possible reasons, Professor Trevor Dickenson discussed some of them in our video on urban flooding, pointing to increased winter melt events in warmer periods that then leave less snow to run off in the spring. The authors of the new assessment make a similar comment: “Some reasons of the decrease in flood magnitudes are listed by Sharma et al. which identify decreases in antecedent soil moisture, decreasing storm extent and decreases in snowmelt among the possible responsible mechanisms.” So if you’re looking to decrease flood risk, it’s warming you want.

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