First off I will admit I haven’t fully read the study “Changing climate shifts timing of European floods” by Günter Blöschl and numerous other contributors from across Europe. The study has been picked up on by the BBC in this news article (fig 1), because they obviously see that it’s just another byproduct of AGW, rather than just climate change, and yes I do think there is subtle distinction. As far as I can see, none of the many contributors are employed by the UKMO, which I find unusual.
I have highlighted in yellow the areas in the news article that I have misgivings about, the first one is from Matt McGrath
The scientists believe this is due to changes in the North Atlantic Oscillation (NAO), the weather phenomenon that pushes storms across the ocean into Europe.
The North Atlantic Oscillation is simply an index of the pressure difference between the Azores and Iceland, as far as I know this index doesn’t push anything across any ocean, you might say that the Azores high or Icelandic Low are weather phenomena, but surely the difference between the pressure at two points is just a number?
Günter is the quoted as saying:
In southern England, it has been raining more, longer and more intensely than in the past. This has created a rising groundwater table and higher soil moisture than usual and combined with intense rainfall this produces earlier river floods
I refute that, unless the changes that the study is talking about have suddenly started to occur in the last five years. Cue some evocative pictures of rivers in southern England that have dried up in recent years that I’ve found on the Internet (figs 2 & 3). (N.B. to the BBC, two can play at that game!). Yes, I know these images are from 2012, but what about the River Derwent in the Lake District in May 2017 (fig 4). So it’s a well-known fact that river levels and groundwater tables do fluctuate, and can do so very quickly, that’s what they naturally do.
Figure 2 – The River Lavant, West Sussex in February 2012 courtesy of Press Associates and the Daily Mail.
Figure 3 – The River Pang, Berkshire in February 2012 courtesy of Press Associates and the Daily Mail.
Figure 4 – The River Derwent, Cumbia in May 2017 courtesy of Paul Kingston and Twitter
I can’t get any daily rainfall climate data for anywhere in the UK without paying loads of money to the Met Office, so I am stuck with the free 1910 monthly rainfall gridded data that they produce, I wonder if they used this kind of data or if the Met Office felt pity on their research and gave them the ‘real’ rainfall station data that they guard so jealously on our behalf? From that data here are some graphs with a simple linear trend for the southeast and central southern England region for winter, spring and summer (figs 5-7). I can’t see any discernible upward trend in rainfall in any of those three seasons, although I will admit that the 10 year moving average for summer is on the rise, and won’t be any lower after this wet summer.
Günter goes on further to say:
Half the stations recorded floods at least 15 days earlier than previously. A quarter of the stations saw flooding more than 36 days earlier than in 1960.
This one is a hard one to counter, especially without daily rainfall climate data and the dates of all fluvial flooding incidents since 1960, which I simply don’t have. But I don’t see that there is some kind of flood or monsoon season across the UK that starts at any precise date that you can readily identify, and if you can’t identify it, then how can you then go on to say that it’s starting 15 days earlier than it did in 1960? I do know from my interest in CET, that the spring is probably around 15 days earlier and it was in 1960, and that temperature is linked to increased convection and heavier rainfall, but I see little sign of it from the rainfall climate data that I can access.
Finally, here’s the last 12 months rainfall over southeast England (fig 8). It’s been a funny last 12 months as far as rainfall goes, up until mid May there was talk of an impending drought later in the year across southern and eastern areas, but the wet summer has put paid to that. There have definitely been some wet days in the last 12 months across the southeast of England, but they can occur in any month as far as I can see, and the accumulated rainfall is still only 84.7% of the annual average at the end of July 2017. What I really need is now is data from the environment agency, some kind of daily count on the number of alerts that they issue for rivers across the UK, a bit like the NAO, but not a phenomena, just a daily count.
PS I’ve just download the report to read – for a change it’s free to do so – and better still it’s only four pages long.