England and Wales rainfall trends

In the wake of the "more rain and more intense rain" story, Doug Keenan sends this graph of England & Wales rainfall records for 1766-2012 (click for larger; data here).

Let's just say the trend towards more rainfall is not obvious. (As indeed is any trend towards less rainfall, which is said to be more likely by the UK Climate Impacts Programme).

[Updated to show England and Wales, rather than UK]

Update on Jan 7, 2013 by Bishop Hill

Doug writes:

The plot shows the total precipitation for England and Wales in 2012 as 1070 mm. That was the amount in the file for seasonal precipitation that the Met Office had on its web site when I downloaded the file on January 4^th (at 20:31). The amount, however, is incorrect. The Met Office has since changed the file to specify the amount as 1245 mm. The other data points in the plot seem to be correct. An amended plot is included in the e-mail that I sent to Julia Slingo on January 7^th. As shown and discussed there, the obvious problems remain.

Comments

[Les Johnson]

UKCIP is still wrong, your worship.

From 1960, summer rain trend has increased about 10%. Winter rain increased only about 0.6% over the same period.

Over the entire database, summer rains have fallen slightly, winter has picked up slightly.

[Les Johnson]

Retired Dave: I just found it odd that BOTH rain and sunshine increased over the same period. Intuitively, one would think increasing one, decreases the other.

It does lend support to increasing severe rainfall, though. Short lived and mainly nocturnal thunderstorms would allow more sun, and more rain at the same time. But I don't buy it. Thunderstorms are very localized, and unlikely to cover the entire UK.

But again, the signal is so noisy, I don't put much stock in it.

[rhoda]

Why is it right to give rainfall figures in absolute units but temperatures in anomaly form? Just asking, having seen massive screeds desperately supporting anomalies in temperature and wondering why that would not apply elsewhere.

[Retired Dave]

Pharos - "Are the records the raw truth, the whole raw truth, and nothing but the raw truth? So help me God?"

That's why I made my comment earlier at 10:56am.

It was not completely flippant.

[Philip Richens]

Les: Yes agreed, increase only after 1800, but with considerable variability on multiple scales. I like your explanation for the increase. However, I would also be interested to hear if there were any changes in data collection methods over the period. I agree that the GW signal is weak at best in this data-set.

[Philip Richens]

Looking at Damian's most recent piece, I notice that Vicky Pope says, "We have already seen over the last 50 years that there are more extreme rain events now."

I wonder what she means? There is a page at the MO site that lists rainfall and other extreme weather events in the UK, and you can see that with the exception of a prolonged downpour in Seathwaite(!) in 2009, there is nothing much there to support her claim.

Any suggestion as to what prompted her comment?

[Stephen Richards]

there is nothing much there to support her claim.

Any suggestion as to what prompted her comment?

Jan 5, 2013 at 5:45 PM | Philip Richens

No Phillip, you misunderstand. There is plenty to support all claims coming from the UK met off. It's called money and manipulation. Ask Betts.

[Guy Leech]

Can anyone answer a probably naive question: why is rainfall reported for a given time period and land area (such as for 2012 in England & Wales) in length not volume? Potentilla says at Jan 5, 2013 at 2:26 PM, the "annual rainfall data are spatially aggregated point measurements" and these are presumably averaged as well as aggregated, so does a single figure in mm for rainfall in a year for a large area have any physical meaning?

Verity Jones and lapogus also raise the question of how these averaged point measurements can be compared for different dates when the number and location of rain guages used has changed over time.

Surely a rainfall volume estimate is required, rather than a linear measurement, in order to give physical meaning to rainfall data, other than for a specific point location?

[Kasuha]

Carefully selected graph type, I must say, good to avoid anything being seen in it.

My graph says there is a trend in there. Of course, statistical significance of that trend, or the rate of the rise (20 mm/century) are another story. No apparent recent trend changes as well.

http://i47.tinypic.com/11090r4.png

[Philip Richens]

Stephen Richards:

Thanks for your answer. Since I posted, I've done a little bit of searching to try to answer my question. Found this from 2002:

The results suggest that there have been trends towards more protracted high flows over the last 30–50 years, but that this could be accounted for as part of climatic variation rather than climate change. There is no statistical evidence of a long-term trend in flooding over the last 80–120 years.

I'm busy for rest of evening, so will look more tomorrow. But surely, there must be something tangible behind her claim?

[Philip Richens]

Kasuha:

Les Johnson and myself were discussing this trend in some of the earlier comments -- may interest you.

[diogenes]

Rhoda

As I see it, the use of temperature anomalies comes from having thermometers in different locations that have not been calibrated against each other, which in the case of a mercury thermometer (essentially a barometer with a different scale) can make a difference. In that case, it can make sense to talk in terms of a 2 degree rise at point a and a 2 degree rise at point b, rather than talking about the temperature that each piece of equipment actually showed.

However, rainfall is measured in a way that is not dependant on barometric pressure - how many inches/millimetres in a tube of standard diameter. So the standardisation worries should not apply.

[Rob]

The Victorian Floods in Windsor,

http://www.thamesweb.co.uk/windsor/windsorhistory/floods1875.html

[Capell]

The graph reminds me of spot-the-ball competitions (yes, don't ask, the treatment's going well). Perhaps Josh might oblige?

[jamspid]

Now that the BBC reputation for integrity and honesty has been devastated by the Savile /Lord McAlpine affair

Looks like Channel Four has been left to carry the torch for Climate Change.

Just watched C4 "Is our weather getting worse" More alarmist panic mongering propaganda.

Catch it now on C4+1 or 4OD

Better get your stop watches and your note books out

[Julian Flood]

Les Johnson wrote

quote
...both sunshine and rainfall have been increasing for about 50 years, on an annual basis.
unquote

Easily explained if the rainfall bursts are more violent. I think this was the gist of that MO paper mentioned recently. Is anyone looking for a reason, though? My guess is fewer aerosols -- lots of aerosols lead to many tiny droplets and drizzly rain, with increased albedo. Fewer give higher intra-cloud RH and, when it rains, bigger drops. I think. Perhaps there's an expert around to explain.

JF

[Philip Richens]

Thanks to musterfritz for these more pro-Pope references from Tim Osborn and co-authors:-

http://rsta.royalsocietypublishing.org/content/360/1796/1313.full.pdf

Daily precipitation in the UK has changed over the period 1961–2000, becoming on average more intense in winter and less intense in summer. Recent increases in total winter precipitation are shown to be mainly due to an increase in the amount of precipitation on wet days, with a smaller contribution in the western UK from a trend towards more wet days.

http://www.cru.uea.ac.uk/cru/info/ukrainfall/ukrainfall.pdf

Over the past 100 years the intensity of UK precipitation has increased during winter, and to a lesser extend also during spring and autumn. This has been accompanied by more
frequent spells of very wet weather and an increase in total precipitation, at least during the last 40 years.

Not sure these are saying anything more than what is in the data here, but need to read them more fully I think. From conclusions of second one (2008), the following:-

It is not yet possible to say whether these observed changes in UK rainfall characteristics can be attributed to man-made climate change, because (although they can have very significant impacts) the changes may not be outside the range of variation that could occur naturally. Nevertheless, it is possible to say that the changes are consistent with scenarios of man-made climate change, based on climate model simulations.

What a marvelous final sentence that is!

Thanks also to OPatrick for this one:

http://www.metoffice.gov.uk/news/releases/archive/2013/2012-weather-statistics

Looking at the figure, the data goes back only to 1960 when the rainfall was at a minimum, and so again don't think this adds anything.

[Bishop Hill]

Rob Wilson writes:

This paper might put some of the discussion in a longer term context

Wilson, R.J.S, Miles, D., Loader, N., Melvin, T.M., Cunningham, L., Cooper, R.J., Briffa, K.R. 2012. A millennial long March-July precipitation reconstruction for southern-central England. Climate Dynamics doi:10.1007/s00382-012-1318-z

http://www.st-andrews.ac.uk/~rjsw/all%20pdfs/Wilsonetal2012.pdf

[ThinkingScientist]

Bish,

I just scanned through that paper. Figure 10 is the most interesting, comparing the results to other published work. Lamb (1965) is shown in the graph, likely to be an unadulterated view in my opinion.

What do I see when I look at these results? Without doubt a very clear MWP, a Dalton minimum and in some of the comparisons what looks like the LIA.

[euge power]

thank god i am not alone in querying Met Office propaganda. I just fix roofs so I thought there was much more than 27% rainfall above average in 2012. And is that so far out of line in a 100 year series?
I am surprised that an extra 27% rain has been enough to refill reservoirs and aquifers after a couple of dry years.
Oh and if air is warmer(global warm) therefore can hold more moisture what diff does 1 degree make to the amount of precipitation? why arent we just warmer and more humid?

[jamspid]

Small question according to the UK Met a hotter climate means more rain because the Air holds more moisture.
So if its been hotter in Australia has there been more Rain in Australia then?