Friday, 8 January 2016

Final Word on the 'Unprecedented' Rainfall of December 2015

So, it's official, December 2015 was the 'wettest ever' [smallprint: 'in the UK record going back to 1910']. Much fanfare at the Met Office, Guardian, Indie etc., blah, blah, blah. It beat 1929 to the top spot and 'though El Nino undoubtedly played a part, such events are predicted to become more common as climate change (TM) progresses because of simple physics' - the well worn statement of implicit attribution combined with appropriate caveat and unassailable 'scientific' logic is now very boringly familiar to most.
uk
So, yes indeed it was the wettest December in the UK since 1910, but is there a trend? Hardly, looking at the graph above. Decembers were wetter in the early 20th century, then they got drier and from the 1970's they've got progressively wetter again - but not significantly wetter than they were in 1910 (one record does not a significant rising trend make). If we look at each country of the UK, we see in fact that England has in fact become drier in Dec since 1910:
england
Whereas Scotland shows the only really significant increase in precipitation in December:
scotland
The EWP record which goes back to 1766 and which has not been referenced by the Met Office and alarmist press as far as I know, shows that December 2015 wasn't even a contender for a top spot, exceeded in the record by numerous other years and coming nowhere near the record set in 1876.
ts_ewp_decemberThus we must conclude that, for whatever reason, the ravages of climate change have not been visited upon the Sassenachs!
But I hear them say in climate alarmist land: "Ah yes, but the rainfall intensity in the north and Scotland was unprecedented!" followed by, "We expect this due to climate change and simple physics" . . . blah, blah, blah, etc. etc. etc. Well, OK, yes, it seems that records were set at individual weather stations and the biggie was at Honister Pass - 341.4mm of rain in a 24 hour period (a new UK record). But all may not be as it seems. You see, a 'day' of rainfall has traditionally been measured from 0900 GMT to 0900 GMT. I quote:
"The 09-09 GMT record is important because from a historical context much of the data is daily data recorded over the standard 09-09GMT period."
[http://www.itv.com/news/border/2015-12-07/storm-desmond-breaks-uk-rainfall-record/]
So even though Dec 2015 set a record for most intense rainfall in any 24 hour period (a relatively recent method of measuring rainfall), it failed to set any records for a traditional rainfall day. The records still stand as follows:

Highest 24-hour rainfall totals for a rainfall day (0900-0900 GMT)

CountryRainfall (mm)DateLocation
England27918 July 1955Martinstown (Dorset)
Scotland23817 January 1974Sloy Main Adit (Argyll & Bute)
Wales21111 November 1929Lluest Wen Reservoir (Mid Glamorgan)
Northern Ireland15931 October 1968Tollymore Forest (County Down)
All of them, you will note, set 1974 or earlier, gong back to 1929. 2015 did manage to set the record for rainfall in a traditional 2 day period though, which now stands at 405.0 mm measured at Thirlmere, Cumbria. This was the only recognised traditional short period rainfall record set in December 2015. If we look at periods shorter than 24 hours, Dec 2015 doesn't even get a look in.

UK rainfall records for short durations

MinutesRainfall (mm)DateLocation
Highest 5-minute total32*10 August 1893Preston (Lancashire)
Highest 30-minute total8026 June 1953Eskdalemuir (Dumfries & Galloway)
Highest 60-minute total9212 July 1901Maidenhead (Berkshire)
Highest 90-minute total1178 August 1967Dunsop Valley (Lancashire)
Highest 120-minute total193#19 May 1989Walshaw Dean Lodge (West Yorkshire)
Highest 120-minute total155#11 June 1956Hewenden Reservoir (West Yorkshire)
Highest 155-minute total16914 August 1975Hampstead (Greater London)
Highest 180-minute total1787 October 1960Horncastle (Lincolnshire)
* Approximate value.
# Reservations about Walshaw value, Hewenden value is next highest accepted value.
So much for the expected increase in intense rainfall. You will note that most of the shorter period records are set in summer, as one would expect with strong convective heating. But even so, the most recent year in which an intense short period rainfall record was set is 1989. The rest go way back as early as 1893. 
So overall, we're not seeing evidence of December being particularly exceptional in terms of monthly totals or shorter period more intense downpours. Not exactly what the alarmists want the world to hear.