Long Term Rainfall Trends In England & Wales

By Paul Homewood

As promised, an update on precipitation trends from the England & Wales Precipitation Series , dating back to 1766.

First the annual trends, with a 10-Year Running Average.

It’s a bit like reading tea leaves, and I have no doubt we’ll all read different things into this. But for me, the following things stand out:

2012 was the wettest year in recent times, but only ranks third since 1766. The wettest year was 1872, followed by 1768.

Last year, at 917mm, was only 2mm above the mean for the period.

The current 10-Year average is not high by historical standards.

The 10-Year average hit a recent peak of 994 mm in 2002, but the wettest 10 years ran from 1874 – 1883, averaging 1017 mm a year.

Any sign that rainfall is on the increase? Not for me.

Seasonal Trends

I thought it worth looking at seasonal trends as well.

In the past, they often looked at “six month” winters and summers, i.e Oct-March, etc. This seems much more relevant than using traditional seasons, as in the UK at least, Oct/Nov/Dec/Jan tend to be the wettest months.

It is also common practice to use “hydrological years”, which begin in October. Clearly the concept of a traditional autumn season is meaningless for this.

Again taking the England & Wales series, for “winter” we get:

There seems to be a shift change to wetter winters from around the mid 19thC.

Since the start of the 20thC, the trend is pretty much flat, albeit with a dip around the mid 20thC.

The last winter of 2012/13 finished with 656mm, ranking 11th wettest.

The wettest was 2000/01 with 809mm.

Next wettest was 1929/30, with 715mm.

The wettest 10-Year spell was 1994-2003.

And “summer”.

The trend in the first half of the record is reversed, i.e summers tended to be wetter till about 1890.

The dry spell during the 1970’s is again evident, since when summer rainfall has recovered to levels common in the first half of the 20thC.

Last summer totalled 328.1mm, ranking 26th driest.