Rainfall In South West England & Wales (part 1)

The Somerset Rivers Authority has spoken… so I decided to get the kettle on and check a few of their facts

Let us start out with a screenshot of a FB post that recently caught my eye:

And let us declare the link to the report at the centre of all this, being the Environmental Agency’s Monthly water situation report: Wessex Area.

The Rub

But here’s the rub. Being a mere mortal I don’t have access to the fancy data that the Environmental Agency sit on so I am required to sweat and toil by the bread of my brow to hunt for anything remotely useful. As it so happens data that might be jolly useful are observations gathered by the Met Office Hadley Centre, this being the HadUKP precipitation dataset that can be found here.

If we flip to the download page we discover South West England & Wales (SWEP) is one of the regions for which we can obtain monthly precipitation records dating back to 1873. Now that sounds terribly and terrifically tasty to me, and what is even more tasty is the effort the Hadley crew have put in to ensure the 152-year time series isn’t past its sell by date:

Please note, the last 6 months' values are subject to change as a result of quality control. Also please note that, in 2011, we re-calculated all daily and monthly UKP values from January 2006 to date using a more representative selection of stations, as described in this Climate Memorandum, to counter the effects of various station closures over the past several years and to take advantage of some new stations which are now available. In doing this, we took steps to ensure that this will not have affected the homogeneity of the series. The above Memorandum includes lists of all stations used.

Fair enough, I say! I certainly wouldn’t want to be the head honcho trying to make these ancient observations meaningful to modern audiences, so let us be thankful for what we can pilfer free of charge… and get that biscuit tin open!

Claim Checking

Please do bear in mind that my claim checking concoction is using data for South West England & Wales and not the dragon-laden county of Somerset, so we must take my results with a pinch of salt, and perhaps a pinch of pepper.

Claim #1: September 2024 was the wettest September since records began in 1871

Not according to HadUKP. We shall start with a pretty slide:

Yes indeed, September 2024 was well wet across South West England & Wales, but it wasn’t a special kind of wet, as witnessed by the four blue blobs sitting at higher values than 168.7mm. Gold goes to 1918 (212.5mm), with 1974 taking silver (182.2mm), and 1896 nabbing the bronze with 173.7mm. Also finishing strongly were 1981 (173.0mm) and 1876 (168.7mm).

One of the first questions climate-minded folk may well ask is whether SWEP Septembers are getting wetter. To answer this we may start with a consideration of the grand mean for the series that comes to 83.2mm (dashed blue line). The thin black line is a linear regression that is indistinguishable from the overall mean, so we may conclude right here and now, using eyeball power alone, that there is no long term trend for SWEP September total rainfall either way, with the regression output confirming this and offering up an insignificant wetting rate of +1.80mm per century (p=0.815).

The orange snaky line is a locally estimated scatterplot smoothing (LOESS) function that helps guide the inexperienced eye in detecting any underlying patterns. As we may observe this bobs up and down about the overall mean, and so we learn that September rainfall in the West is sometimes heavy and sometimes not, there being what appears to be a long term cycle of around 100 years. Right now we appear to be at the beginning of an upward swing.

Claim #2: September 2024 was the wettest month since January 2014

Not according to HadUKP. We shall start with another pretty slide:

The old-fashioned way to do this is print this slide out, take a ruler and a decently sharp pencil and mark a thin grey line at 168.7mm, then tick off all those blobs sitting above that line. I have taken pity on those with just a smartphone at their disposal and have got my graphics module to draw a pencil line. We can see January 2014 right over in the left corner and, unless my eyeballs are deceiving me, I count 12 blobs bobbing above the line since then. An A-Z sort of my spreadsheet confirms that January 2014 indeed saw a great deal of rain (235.4mm), but there have been a dozen wetter months than September 2024 since then, these being: December 2020 (201.7mm), February 2024 (200.5mm), February 2020 (196.0mm), February 2014 (193.8mm), December 2023 (193.7mm), November 2022 (186.0mm), January 2016 (179.9mm), October 2019 (177.3mm), October 2020 (174.6mm), October 2023 (172.3mm), October 2021 (170.5mm) and March 2023 (169.4mm).

The keen will want regression results, so here they are:

We are looking at a totally insignificant wetting trend of +0.074mm per month (p=0.534). The ultra keen might want me to run one of those Wald-Wolfowitz tests for randomness (runs test) and they’d be right to do so, for the series is indeed a random walk (p=0.742). The eagle-eyed statsbod might also figure the variance of the series is fairly constant over time.

These results do not favour alarmism but do favour weatherism. As I stated on my personal FB wall recently, if every story being pushed by the MSM is 'climate change' then what we used to call 'weather' no longer exists. A government promising to fix the weather though taxation, digital ID, CBDC, green energy and all the rest is one we should distrust with every optic fibre of our being!

Claim #3: October 2023 - September 2024 was the wettest water year on record

HadUKP agrees! Let us take a look and put this into as much perspective as we can muster given the data record only spans 152 years and not 15,200:

At 1496.0mm the water year of 2023/24 gets the gold medal, with silver going to 1929/30 (1432.1mm) and bronze going to 1987/88 (1376.1mm). Despite the wetness of the record-breaking current water year there is no evidence of a long term upward trend that passes muster, with the linear regression (black line) only barely lifting from the overall series mean of 1047.4mm. The stats output for this confirms the lack of trend (p=0.130). Cyclical behaviour is not evident and so we may assume once again that the series is a random walk, this being confirmed by a Wald-Wolfowitz test for randomness (runs test), which returned p=0.294.

Coffee & Cogitation

What we have, then, is a situation where wet and dry months and/or water years come and go in what appears to be a random fashion, though all will depend on weather systems across the Atlantic. Being cynical I’m viewing the current water year record as one of those outliers that pops up now and then from a pool of randomness… but is this a sensible statement to make as a mature adult? And what's with this water year weirdness; is this a fudge to get the figures favouring alarmism? Let’s get that kettle on and have a rummage…

Kettle On!