UK Rainfall 2012: The Report The Met Office Should Have Produced
It would appear that the Met Office have very little idea as to what will actually happen to future rainfall.
According to the Met Office, UK has just had the second wettest year on record, just behind 2000. These claims, however, are based on records dating back to 1910. The Met Office also keep a rainfall series for England & Wales, which date back to 1766, and these cast a slightly different light on the matter.
(As Scotland and N Ireland have been drier than normal, the England & Wales portion becomes particularly relevant).
Figures 1 and 2 show the annual rainfall for this series, with 10 and 30 year running averages.
The following points stand out:-
1) The wettest year was 1872, when there was 1284mm, compared to 1244mm in 2012. It was also wetter in 1768. Clearly the impression given by the Met Office, that the rainfall last year, and in 2000, is somehow “unprecedented” is not true. One is entitled to wonder why they made it.
2) The 30 year trend would suggest that rainfall was lower for most of the 19thC, but that it has been relatively stable since.
3) Both on 10 and 30 year trends, there have been many years previously at the same level as now. The wettest spell was during the 1870’s and 80’s. The 1920’s were also comparatively wet.
4) Inter-annual variability, of the sort seen in the last two years, is not uncommon, for instance 1871-72.
The winter graph, of course, is for Dec 2011 – Feb 2012, but shows the trend in recent years to drier winters, (not withstanding December 2012, which was much wetter). In contrast, summer rainfall has been on an increasing trend. (Figures for Spring and Autumn seem not to offer much of a trend).
The change in Winter and Summer patterns is significant because they run counter to projections made in the UK government’s Climate Change Risk Assessment, presumably put together with the help of the best brains that the Met and CRU can offer, and which forecast much reduced summer, and much higher winter precipitation.
Either their models are hopelessly wrong, or the global warming, they are predicated on, has stopped.
North v South
As the map at the top indicates, Scotland has been relatively dry, suggesting that rain belts have shifted southwards, bringing some of the rain Scotland normally gets down to England. And, of course, it is no secret to Brits that the jet stream has been shifted south of its normal position for much of the year.
Rainfall in Scotland is much higher normally than in England. Scotland usually receives about 1600mm of rain each year, compared to 855mm for England. Last year, England’s total was 1123mm, so it can be seen that Scotland has still been, by far, the wetter of the two.
Julia Slingo has been quick to blame higher rainfall on warmer temperatures. But does Scotland receive more rain than England because it is warmer? Is it surrounded by warmer seas? Her argument simply does not hold water.
I mentioned the jet stream moving south, but it would be more accurate to describe it as a meridional pattern.
Low pressure systems, that tend to move faster with a zonal flow, often become blocked with a meridional flow. for much of the year, the UK has been stuck in the “bulge” coming down from the north, at the same time, of course, as parts of the US has seen a block of high pressure.
It is pretty much par for the course, that many climatologists have been linking this phenomenon with the melting of Arctic ice. It is, however, worth bearing in mind that Hubert Lamb found exactly the same meridional jet flow in the 1960’s and early 70’s. In his volume, “Climate: Present, Past & Future”, he describes the effects of the changing climate at that time, when Arctic ice was expanding:-
…….much smaller changes over middle latitudes, where the most significant feature has been the very awkward type of variability from year to year, associated with the behaviour of blocking systems and meridional circulation patterns.
Examples of the consequences of these features include a number of serious items besides the extremes of cold and warmth, drought and flood associated with the occurrences of blocking in middle latitudes.
I cannot leave this North v South topic without highlighting what the Met Office themselves have projected. In 2011, they published a report called “Climate: Observations,projections and impacts”, which was written by a team led by a certain J Slingo. This report is absolutely clear:-
Europe shows a strong contrast in projected precipitation changes, with large decreases in the south and large increases in the north. The UK falls towards the northern region with generally increasing precipitation, with projected increases of up to 10%, though some southern parts of the UK may experience decreases of up to 5%. There is generally good agreement between ensemble members over the north of UK, but moderate agreement further south, indicating uncertainty in the position of the transition zone between increasing and decreasing precipitation over Europe.
While the exact demarcation line is not certain, they are sure that the North will be wetter, and the South drier. This is the opposite of what has happened in 2012.
It would appear that the Met have very little idea as to what will actually happen.