Monday, 26 October 2009

Tuesday is the wettest day of the week...?

It was a bit disappointing to get back from a week in the field in Sinai, to find my employers at the University of Manchester advertising the Manchester Science Festival with this story. Apparently, Tuesday is the wettest day of the week in Manchester.

Well, every day is rainy in Manchester. Perhaps predictably, if you look at the data this conclusion is based on, you can see that there isn't exactly an astounding difference in rainfall between different days of the week. Certainly, statistically significant differences have not been demonstrated. The research has some interesting things to say about how rainfall patterns seem to have changed over the last 30 years or so: Manchester is somehow managing to get wetter. This is consistent with warmer temperatures, as more water vapour can be moved around when temperatures are higher. This is interesting stuff, and excellent for illustrating local changes in climate for a science festival. So why emphasise that Tuesday is supposedly the wettest day of the week, when the data surely don't convincingly support that? I suppose the university press office thinks that wet Tuesdays are a more interesting story than local climate changes, but I don't think I would agree.

A quick google shows that the story has been picked up by the Express (Why Tuesday is the day you'll most likely need your umbrella) and the Telegraph (Tuesday is the rainiest day), which are clearly based around the press release. I think a better press release might have been headlined "Manchester getting rainier", which is interesting and also has the benefit of being supported by the data.


Krypto said...

Yeah, I heard this on the radio news and was, um, effusive in my skepticism. I've never heard of any atmospheric cycles that work on a 7-day week - seems pretty unlikely that anything would...

Nash said...

Didn't Saturdays and Sundays used to have less rain as factories were not pumping out smoke/soot at the weekends.

Rain drops are formed by water vapor condensing around a particle such as dust and pollen.