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Stuff you're not allowed to know #3: extreme rainfall

06 Sep 2023 | Science Notes

A reminder that you are not supposed to read this paper on extreme weather trends now that your intellectual superiors have decreed that the implications of you knowing what’s in it are unthinkable, even though they can’t point to any errors. Including when, regarding extreme rainfall, the authors present evidence that there has been a gradual increase in total precipitation worldwide since 1900. But when they ask if this has translated into an increase in extreme rainfall events the answer is... it depends where you look. In most regions around the world, some monitoring stations show an increase, some a decrease, and most no change. Which will never do since everybody knows, or is told to know, that climate change is increasing rainfall and flooding. Or droughts. Or whatever.

Actually thisever, according to the authors. One global study examined data covering extreme rainfall events from 1964 to 2013 at 8,730 locations. Thirteen percent showed an increase, 10% showed a decrease and the rest (77%) showed no change. A more recent study covering 1950 to 2018 found 9% showed an increase, 2% showed a decrease and 89% showed no change. But within their data they found considerable regional variation.

The findings were summarized in the following chart:

For each location green indicates the percentage of stations showing no change, red denotes the percentage reporting an increase and blue the percentage reporting a decrease. Most places exhibit no trend, and in the specific locations with trends there are typically more exhibiting an increase than a decrease. The authors conclude:

“Our review shows that while an increase in total annual precipitation is observed on a global level, an increase in extreme precipitation is observed for a limited number of stations and with strong regional differences. The absence of generalized growth trends in extreme precipitation can be explained by the fact that the genesis of extreme precipitation requires (1) the presence of a relevant source of moisture in the boundary layer, (2) morphology of the relief, circulatory structures at different scales and vertical thermal profile favourable to the rising of air mass with development of clouds of sufficient thickness (e.g. cumulonimbus and nimbostratus clouds) and (3) microphysical characteristics of cloud environment favourable to magnify droplets or ice crystals to give precipitation.”

2 comments on “Stuff you're not allowed to know #3: extreme rainfall”

  1. My state in South Australia declared "Climate Emergency" as one of their first actions after winning the election. My state barely has any weather. It is the most benign "weather" state in Australia. Yes, like everywhere in the world our people go crazy when a windstorm bushes over a plastic chair, or a storm drain has actual water in it. Or a summer that has suffered from dry heat 300 years reaches expected temperature, we go into meltdown

  2. At my early 1950's Sydney suburban Grade 3, a heat wave was when it was "over the century (100F) for a week and we amused ourselves stamping on the bubbles in the playground tar. Mind you, the school milk which sat out there until 10am(?) almost put me off it for good. Moving to the sleepout on the back porch was merely the sensible thing to do. Little did we know we were practicing "climate resilience". Too bad the back porch is no more in the "sustainable" high density highrises that the privileged are to be herded into.

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