Euan asked me to put together a short post on UK precipitation during December 2015 to supplement his forthcoming “unprecedented weather” post, so here is a brief graphical summation:
The data are from three UK Met Office sites:
England & Wales from:
Northern Ireland from:
Figure 1 plots monthly precipitation for England and Wales, where the MO’s records begin in 1766. The 141.5mm recorded in December 2015 was above average but not in the least unusual. The month was in fact only the 129th wettest on record:
Figure 1: Monthly precipitation, England & Wales since 1766
Figure 2 plots monthly precipitation for Scotland, where records don’t begin until 1931. The 278.2 mm of precipitation in December 2015 was the most recorded since 1931 but it only barely exceeded the 273mm that fell in January 1993 and the 269.6mm that fell in December 1986. Another 50mm of precipitation would have been needed to make December 2015 a “three-sigma” occurrence, which is the threshold sometimes used to define extreme weather events.
Figure 2: Monthly precipitation, Scotland since 1931
Figure 3 plots monthly precipitation for Northern Ireland, where records also begin in 1931. With 188.8mm of precipitation December 2015 was indeed unusually wet but it was still only the sixth wettest month on record.
Figure 3: Monthly precipitation, Northern Ireland since 1931
Figure 4 shows monthly UK precipitation since 1931. I constructed the graph by area-weighting the Figure 1, 2 and 3 data with England & Wales contributing 62%, Scotland 32% and Northern Ireland 6% to the final value. The 190.3 mm recorded in December 2015 is well on the wet side of average but again not unusual.
Figure 4: Area-weighted monthly precipitation, UK since 1931
In summary, only Scotland measured record-breaking rainfall in December 2015 and here the record was only barely broken. Over the rest of the UK December 2015 was wet but not unusually so. The wet weather in UK in December 2015 was clearly not “unprecedented”.