MARCH 12, 2021
By Paul Homewood
Yet another attempt to “prove” that rainfall is becoming more extreme in the UK:
This is the key graph:
United Kingdom’s wettest day of the year. (a) Timeseries of UK mean Rx01 anomalies relative to 1961–1990 from observational data. The observed anomalies in 2020 and 1986 are marked by a cross
The first thing to note is that they are looking at the UK as a whole. We know that Scotland has become considerably wetter in recent years, but what about the rest of the country?
If we analyse the England & Wales Precipitation Series, we actually get a totally different picture:
Note that 3rd October 2020 was a long way from being the record claimed for the UK. (There are concerns with the HADUK dataset, as it now includes many high altitude sites not previously available, which will inevitably bias the results to wetter. The England & Wales dataset, though based on fewer stations, has greater consistency).
Although there is a tiny trend of 0.03C pa, ie 3mm per century, this is well within standard margins of error. The R2 is only 0.024, which is regarded as a very low correlation statistically.
Clearly the trend line is heavily skewed by two outliers in 1986 and 2000, neither of which can be construed as “current climate”.
It is also apparent from the data that there was step change around 1960. Consequently when we begin the series in 1960, there is actually a declining trend. Interestingly, the UK chart also shows this decline, once the 2020 outlier is excluded.
Whatever the reason for that step change, it clearly has no bearing whatsoever on what is happening now, or might in future.
What we can safely say is that there has been nothing unusual at all in the last two decades, which is surely the time when global warming should be impacting heavier rainfall, if the theory is correct. Indeed, it is the 1960s which stand out as being most affected, with four years, 1960, 1967, 1968 and 1969 each seeing daily rainfall totals more then anything seen since 2000.
It may be that Scotland is seeing more extreme rainfall, which the KNMI data seems to suggest:
However, the fact that England & Wales are not seeing the same increases totally discredits the theory that a warmer atmosphere is driving heavier rain. Instead we need to look elsewhere for the factors behind Scotland’s weather.
So often in climate science, we come across shoddy studies like this one, where it is evident that the authors have decided on the conclusions at the outset, and then manipulate the data until it agrees.