Extreme rainfall has been notably infrequent in the last decade.
Further to my earlier post on Phil Jones’ paper on UK precipitation extremes, which showed little trend in extreme rainfall in England & Wales, I have taken a closer look at one of the regions used in the England & Wales Precipitation Series, the Central region, concentrating just on winter rainfall.
Using the England & Wales Precipitation Series, which although it dates back to 1766 only gives regional data since 1873, let’s look at the trends for winter precipitation in total.
Although rainfall last winter severely affected some parts, the Central region was only the 174 wettest on record. More significantly though, the 10-Year average is actually slightly below the mean (152mm v 156mm respectively).
We can also look at rainfall/rainday, the latter defined as having >1mm of rain. The EWP Series only gives daily data going back to 1931.
Again we find daily rainfall in recent years has been pretty normal, with the 10-Year average just below the mean, 4.2mm v 4.3mm. This is certainly strong evidence that extreme rainfall days have neither become more common nor intense in recent years.
We can actually go one step further though, and look at the really extreme days. I have analysed all winter days with precipitation over 15mm. There have been 38 such days since 1931/32, out of a total number of raindays of 3031. This gives effectively a 99th Percentile.
Figure 3 shows the number of days with >15mm each winter, smoothed as a 10-Year running average. The biggest peak occurred from 1976 through 1980. There were other peaks in the 1950’s/60’s and again in the 1990’s.
By contrast, extreme rainfall has been notably infrequent in the last decade.