Tuesday, 1 January 2013

wet 2012

April was wet. Very wet.  For April.

But what about the whole of 2012?  It certainly felt wet.  How wet was it?

Well, since records began (our records, that is, which began in mid-2005), 2012 was indeed the wettest year ever:

annual rainfall, in mm
It certainly bucked the trend of the previous two "drought" years.  No hosepipe bans for a few months more, I expect.  So, April was wet; 2012 was wet.  Was April a particularly wet month in 2012?

mean, median, and 2012 monthly rainfall, in mm
So, April was only the third wettest month, beaten by December, and washed away by July. Strangely, when the north of England was being flooded out in September, down our way (near Cambridge) it was one of the driest months of the year!

Those mean/median figures don't tell anything like the whole story, though.  Here's more information:

min, lower quartile, median, upper quartile, max, and 2012 monthly rainfall, in mm
The box plots summarise the 2005-2011 data, and the blue bars are the 2012 data.  A blue bar within the lower/upper quartile box is nothing special: half the data falls there.  So May, September (the flooding month!), and November were fairly typical.

A blue box between the min/max lines is a little bit special, as only a quarter of the data falls in the first or last quartile (hence the name!).  So January and March were a bit on the dry side, while June, October and December were a bit wet.  (Well, December was quite a bit wet, being nearly at the maximum.)

I love that difference between the May and June data: very similar medians, minima and maxima, but wildly different lower and upper quartiles.  May is essentially bimodal -- wet or dry (this year was one of the dry ones) -- whilst June is middling damp with a couple of outliers (this year was an outlier, too).

A blue box outside the min/max lines is a driest/wettest seen so far.  Four months in 2012 managed this (but since we have only 8 years of prior data, I'm not going to over-interpret the significance of this).  2012 had the driest February (despite it being a longer leap-year month!) and  August, and the wettest April and July (by far!) since our records began.

So, a bit difficult to make any general statements about the rainfall, then.  This is why in the UK were talk about the weather all the time.  It changes, all the time.  All we can conclude from above is the lovely statement I saw in a newspaper many years ago: "it's usual to have unusual weather this time of year" -- or any time, really!

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