UK Daily Rainfall Extremes

By Paul Homewood

 

 

Following last year’s wet weather in the UK, Julia Slingo had this to say:-

The trend towards more extreme rainfall events is one we are seeing around the world, in countries such as India and China, and now potentially here in the UK. The long-term trend towards wetter weather is likely to continue as global air temperatures rise.

But what have been the trends in the UK?

 

The Met Office provide daily rainfall data back to 1931 for England & Wales, from which I have extracted the top 50 rainfall days. (This equates to days of 21.92mm or more). The distribution of these events is shown in Figure 1.

 

Figure 1

The wettest day was 25th August 1986, when 43.23mm fell on average across the country. The wettest day last year recorded 28.50mm, yet there have been seven days in earlier years which recorded higher amounts, all prior to 2001.

It is unusual for there to be three such days in a single year, as we saw last year. But it is not unprecedented, as both 1971 and 2000 also recorded three each.

We can also look at the decadal trends in Figure 2.

Figure 2

Although the last decade has been seen more heavy rain days than the 1990’s, it has been pretty much on a par with the 1961-1990 period, and significantly down on the 1970’s, even when 2012 is taken into account.

The Met figures are, of course, nationally averaged, and there are bound to be regional variations. Nevertheless, there is clearly nothing to back up Slingo’s assertion that extreme rainfall in the UK is on the increase, either in frequency or severity.