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Met Forecast Of Summer Downpours Ignores Evidence

June 2, 2014

By Paul Homewood 

 

image

http://www.bbc.co.uk/news/science-environment-27624478

 

The BBC report on the latest study by the Met Office & Newcastle University:

 

Global warming will lead to a significant increase in extreme summer downpours in the UK, a study suggests.

The Met Office and Newcastle University researchers say there could be five times the number of "extreme rainfall events" exceeding 28mm per hour, under extreme warming projections.

This would cause "really severe" flash flooding in many parts of the UK, according to the scientists.

However, they caution that this result is based on only one computer model.

Flash flooding in Britain has had devastating impacts on communities in recent years.

In Boscastle, north Cornwall, about 200mm (8in) of rain fell in four hours in August 2004 causing a 3m wall of water to sweep through the village.

In the summer of 2012, in Newcastle, the equivalent of a month’s rain fell in just two hours, causing widespread flooding in the city.

Super models

Researchers have struggled to work out how global warming might affect these types of events.

Until now, their climate models have not been good enough to work out the effect on extreme hourly rainfall in the warmer months.

To improve the resolution of their model, researchers in this latest experiment used 1.5km grid spacings instead of the normal 12km.

To gain this extra clarity, the Met Office supercomputer was employed for nine months to run the simulations. Even then, they could only model the southern half of the UK.

"Most people would be familiar with this model," Dr Lizzie Kendon, the report’s lead author told BBC News.

"It is the same one that is used for the weather forecasts on the BBC, so it is incredibly realistic and it represents these very intense convective-type storms that haven’t been captured before."

The researchers used both the low resolution and the high resolution models to examine the climate patterns that have occurred in recent years and to look ahead to what might happen at the end of this century.

They assessed the period up to the year 2100 using the most high-end climate projections from the Intergovernmental Panel on Climate Change.

When they looked at rainfall patterns for the winter months, they found that both the 12km and 1.5km grid models showed an increase in rainfall.

Both models found that summers in the future would be drier overall.

However, when it came to intense downpours, defined as more than 28mm per hour, the higher resolution model saw a significant increase.

 

The study suggests that flash flooding events in the summer could become much more common in the UK

It found that there could be up to five times the number of events per hour than we see currently.

"It is dry periods interspersed with these very intense downpours, and we are talking about thresholds of 30mm and above in an hour over quite a large area here, which would be associated with really severe flash flooding," said Dr Kendon.

The researchers stress that this is the result of just one model run and it is not a definitive forecast.

Temperatures may not rise at the level used in the model.

However, the scientists believe that their work shows that global warming will make downpours a more frequent event in British summers.

"From this model experiment and consistent with our theoretical understanding, we have quite a bit of confidence in this result."

Prof Hayley Fowler, from Newcastle University, who is another author of the paper, said the new study was an important step to understanding the flooding risks of the future.

She hopes that other research groups will try to replicate the study.

"The next steps are to see if these changes are consistent with observed trends in summer rainfall extremes and changes projected by climate models in other parts of the world," she added.

 

 

 

Despite the warnings in the study that this just the result of one, solitary model, and that the most high-end climate projections have been used, it is no surprise that the BBC use the alarmist headline “Global warming will lead to a significant increase in extreme summer downpours in the UK”.

 

 

I also note they give the example of Boscastle, which suffered from just such a flash flood in 2004. What they fail to mention is that a very similar flash flood, every bit as bad as Boscastle’s, occurred a few miles along the coast at Lynmouth in 1952 after 9” of rain fell. This tells us two things:

1) The Boscastle flood was not unprecedented.

2) Such floods are still very rare.

 

It is also probably worth pointing out that summer temperatures in England are hardly increasing in leaps and bounds!

 

image 

http://www.metoffice.gov.uk/climate/uk/summaries/actualmonthly

 

 

As stated, the study is based purely on one model, so how does it compare with recent trends and observations?

There is virtually no hourly rainfall data available, to use for long term comparisons. However, daily data is available, which should give us a good idea whether summer downpours are getting worse. It is, after all, reasonable to assume that, if “extreme rainfall events exceeding 28mm/hour” are becoming more common, then we should also expect to see a like increase in “extreme rainfall days”.

We can test this by having a look at a few sites, starting with Oxford, pretty representative of the area the study is looking at. Figure 1 plots the days with 30mm and over for summer months, available from Met Office data since 1930.

 

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Figure 1

 

There is no evidence of any trend to heavy rainfall days becoming either more common or severe. The record for the wettest day was set in 1968, and extreme rainfall days were most common between 1950 and 1980, as Figure 2 illustrates.

 

image

Figure 2

 

We can repeat the exercise for Shawbury, in the West Midlands, and Heathrow.

 

image

Figure 3

 

image

Figure 4

 

 

Both show the same pattern, with the most extreme rainfall occurring between 1950 and 1980, suggesting that there is a pattern here. This is significant, because for most of that period, with the exception of the heatwaves of 1975/6, these decades experienced largely colder than normal summers.

There is therefore an implication here that extreme rainfall in summer is associated with cold, and not hot, conditions.

There is one more test we can do. Figure 5 shows the average rainfall/rainday, for the summer months in England South.

The Met Office only started keeping rainday data in 1961, so we have no figures prior to then. Nevertheless, the 1960’s and early 70’s show up as giving the wettest days. The purple trend line gives no evidence of any increase.

 

image

Figure 5

http://www.metoffice.gov.uk/climate/uk/summaries/datasets

 

 

 

Of course, we cannot automatically assume that hourly rainfall behaves in exactly the same fashion as daily rainfall. However, the data we do have suggests that when it did rain, in the summers of the 1950’s and 60’s, it tended to be heavier.

 

Two other things are worth mentioning.

 

1) The Met Office keep a page detailing record rainfall, etc.

The most recent record for any short duration was set 1989.

 

image

http://www.metoffice.gov.uk/public/weather/climate-extremes/#?tab=climateExtremes

 

2) In their Press Release, the Met Office mention winter rainfall:

In winter it is the daily or multi-day rainfall totals that are important, because we tend to get steady, long-lasting periods of rain from large scale weather systems – similar to those seen during the winter floods of 2013/14.

 

At the time, Julia Slingo was talking about intense rainfall, but this statement rather confirms what I have previously pointed out, that rainfall totals last winter were so high because of sheer persistence, and not intensity.

 

Conclusions

When forecasting the future effects of a warming climate, surely the first thing to look at is what effects a warmer climate has had in the past. Daily data will not necessarily provide the same results as hourly, but, nevertheless, that is the best information the Met Office have.

My analysis only covers three stations; I would like to use more, but the Met Office now operate a “fair usage policy”, which restricts the release of such data to small chunks. (The data I have used was sent to me last year, before this policy was put into effect). There is no reason, however, why a fuller coverage of sites could not have been used by the authors of this study.

While climate models have their uses, is it too much to expect researchers to spend a bit of time actually looking at the data as well?

 

 

Footnote

It was only back in March that another Met Office paper, “Drivers and impacts of seasonal weather in the UK”, stated on page 22,

There is no clear signal for how the wettest days in summer may change”

 

Sources

All the daily rainfall data used were supplied to me by the Met Office. 

27 Comments leave one →
  1. John Palmer permalink
    June 2, 2014 7:42 pm

    I, like I suspect, the majority of my age group, have been a fan and supporter of the BBC for nearly 50 years but I’m getting increasingly concerned at their knee-jerk, biased and unquestioning reporting of many major issues and particularly the climate change one.
    Just a simple one-liner at the end of this vacuous, verbatim report pointing out that this (single) model is the same one that cannot get the forecast right a week ahead more often than not – let alone breezily trying to predict up to 2100 would have injected a little bit of balance.
    What planet are these people on!

  2. Ron C. permalink
    June 2, 2014 8:04 pm

    Figure 2 suggests that at Oxford, at least, the warming decades had few extreme rainfall days. It is when temperatures are flat or cooling that the rain falls heavily.

    So maybe the Met is hedging here–more rain may be coming, consistent with lack of warming.

  3. June 2, 2014 8:18 pm

    To be fair, this is a prediction of what may happen in the future, so we wouldn’t necessarily expect to see any evidence in past data.

    That said, any heavy rain event in the future will doubtless be seen as vindication of the study, but there is so little data on hourly rainfall we won’t
    know if such events are increasing or not.

    The fact that they have used “the most high-end climate projections from the Intergovernmental Panel on Climate Change” when observed temperatures so far, are nothing like that indicates that they have deliberately attempted to produce the most extreme results, and then they say it’s only one model and not a definitive forecast.

    “It is the same one that is used for the weather forecasts on the BBC, so it is incredibly realistic and it represents these very intense convective-type storms that haven’t been captured before.”

    This model can’t forecast rain precisely, 24 hour ahead, so how can it forecast 90 years ahead?

    The MO website has a news item which includes the following paragraph:

    “These simulations looked at two 13-year periods, one based on current climate and one based on expected climate around 2100.”

    I haven’t worked out what this means yet. No doubt it’s made clear in the paper, but I’m not prepared to spend £22 to find out.

    http://www.metoffice.gov.uk/news/releases/archive/2014/extreme-summer-rainfall

    I think these people have become so obsessed by their models that they have lost track of reality.

    They call it “evidence” but it’s nothing of the sort.

  4. Retired Dave permalink
    June 2, 2014 8:18 pm

    Just another example of the appalling standard of reporting by the BBC. It is without doubt now totally lacking in any credibility, especially in the field of environmental coverage. They will publish any old Tat, just as long as it is extremist and alarmist. The BBC Environmental Correspondents are just the propaganda arm of the environmental activists.

    Christopher Booker’s report at the GWPF says it all and I found the comments of Antony Jay in the foreword quite illuminating. Like John Palmer above I had respect for the BBC for decades and didn’t realise how institutionally biased it was even 50 years ago, as he describes.

    • June 2, 2014 8:23 pm

      The BBC just assumes that anything the MO say is the literal truth.
      Aren’t journalists supposed to question what they are told?

  5. June 2, 2014 8:34 pm

    The MO forecasted 3 periods of “heavy rain” for Albermarle over the last 24 hours.
    None of them happened.

    • Green Sand permalink
      June 2, 2014 8:52 pm

      According to the MO there have been 2 incidents of heavy rain showers in the last 6 hours?

      “Albemarle hourly observations”

      http://www.metoffice.gov.uk/weather/uk/ne/albemarle_latest_weather.html

      • June 2, 2014 9:56 pm

        Heavy rain “showers”.
        The forecasts were for “heavy rain”.
        The actual observations were:
        15:00 (heavy shower)
        16:00 (overcast).
        22:00 (mist)

        Sorry I was premature on the third one, I thought it was 22:00 last night.
        I am not sure of the precise definition of “heavy rain”, but I imagine it should be a fairly sustained period of rain.

  6. mitigatedsceptic permalink
    June 2, 2014 11:03 pm

    Yes we are familiar with the `MO’s forecasts and we have to be proud that they are ~~NEVER WRONG! This because they are now expressed as probabilities and so whatever happens, MO can say we told you so! MO still expresses some forecasts using symbols and words such as heavy showers. These seem to be remarkably unreliable.

    As to comparing models with historical data – will someone please show me how models can be falsified?

  7. June 3, 2014 8:11 am

    I have noticed a propensity for the MO 5 day forecast to over forecast heavy rain.

    In April there were 48 hourly periods of heavy rain forecast in the first day of the 5 day
    forecast for Albemarle, of which only 12 were observed as “heavy rain”.

    That’s 25% accuracy, compared with 31% overall.

    On one day (25th) 14 hours of “heavy rain” were forecast, of which only 3 were observed
    as “heavy rain”.

    “Most people would be familiar with this model,” Dr Lizzie Kendon, the report’s lead author told BBC News.”

    “It is the same one that is used for the weather forecasts on the BBC, so it is incredibly realistic and it represents these very intense convective-type storms that haven’t been captured before.”

    The MO news item states:
    “The new study, from the joint Met Office and NERC funded CONVEX project, uses a state-of-the-art climate model providing the first evidence that hourly summer rainfall rates could increase.”

    “First evidence”

    Haven’t they been telling us for years that heavy rainfall would increase in summer due to “climate change”, without any evidence apparently.

  8. June 3, 2014 10:58 am

    From the “Carbon Brief” blog, to which there is a link on the “Nature Climate Change” site:

    “Global Climate Models (GCMs) have done a good job of predicting changes in global average temperatures and rainfall in recent decades.”

    Which models they been looking at?

    I take it they mean the IPCC “Commitment” scenario models.

  9. Black Pearl permalink
    June 3, 2014 3:23 pm

    Paul: “In the summer of 2012, in Newcastle, the equivalent of a month’s rain fell in just two hours, causing widespread flooding in the city.”
    *******
    Yes I remember that well
    Piers Corbyns forcast was only an incredible one day out on that one,– weeks in advance !
    How does he do that ?

    • June 3, 2014 3:56 pm

      He predicted Newcastle would be flooded?

  10. Black Pearl permalink
    June 3, 2014 4:10 pm

    QV His forecast was for “Thunder Floods” as he calls them in the area, for the Friday /Sat and the downpour happened on the Thursday

    • June 3, 2014 4:13 pm

      The area being Tyneside or just the North East?

      • Black Pearl permalink
        June 3, 2014 7:07 pm

        Just back checked on that forecast
        States 29th June to 1st July Very wet. Thundery deluges with large hail.Local flooding
        It all happened on Thursday 28th
        Not bad a month ahead I would say

      • Black Pearl permalink
        June 3, 2014 7:09 pm

        General area not specific to North East or Tyneside

  11. June 3, 2014 6:31 pm

    Reblogged this on the WeatherAction Blog and commented:
    Paul Homewood with ‘hard evidence’ that the Met Office’s, in ‘collusion’ with Newcastle University, latest projection/prediction of more floods is yet again total nonsense.
    They appear to be stuck in a feedback loop where a super computer filled with erroneous assumptions can predict angels on a pinhead and that this then becomes fact.

  12. tom0mason permalink
    June 3, 2014 7:40 pm

    As long as the Met Office staff are not being paid by the accuracy of the results this sort of nonsense will persist.
    How many (if any) would have published this if say it proves to be inaccurate by actual events, and they are all then paid at minimum wage!
    I have the strong notion that such alarmist reports would vanish overnight and the quite pursuit of accuracy and scientific probity would follow.

    • June 3, 2014 8:25 pm

      tom, prp would be a very good idea. Also be good if the cost to make these reports was made public. 9 months computer time must have an awful CO2 footprint and it’s not like electricity bills are going down anytime soon ;-)

      • tom0mason permalink
        June 3, 2014 8:56 pm

        I seem to be a one man campaign for PbR for the Met Office.
        I believe it would concentrate their tiny minds on actually getting the weather forecast correct, and stop faffing about with this sort of money wasting alarmist nonsense.

        Mandate them to perform, make daily, weekly and 3 monthly/seasonal forecasts. Every 6 months audit their performance on every forcast; rated by accuracy and timeliness, and the rating shall assist in determining their budget and wages.

        Do they understand how much waste they cause? No! do they care, No!
        Just take the UK Forestry Commission – wasted millions researching and planting forest with drought resistant trees (1990s-2000). Drought resistant! All because that shower at the Met Office said a drier climate was to come.

        Laughable if it were not stealing tax-payers money.

    • June 3, 2014 8:40 pm

      The trouble is, we won’t truly know how accurate it is until 2100!
      They can make predictions with impunity, knowing that they will have retired or be dead by then.

      • tom0mason permalink
        June 3, 2014 9:16 pm

        Which is why these ‘climate idiots scientist’ should be separated from the weather people and put in their own padded cell agency (the BCC Alarm>) and budgeted separately as and when it can be afforded. Their pension should depend on the accuacy of outcome. ( Your climate pension may go down as well up, seek professional advice before forecasting. )

        IMO forcasting for periods greater than 2 years is a nonsense with the state-of-the-art equipment and staff available at the moment. No long range forecast has been proved broadly correct in my lifetime. I doubt it will happen in my grandchildren’s time.

        And woe on them if the threated to leave for foreign pastures new, then spend the tax money wisely and buy them the ticket.

  13. June 4, 2014 8:32 am

    I think the problem at the MO is that they are all victims of “group think” and “confirmation bias”, and nobody is putting forward the alternative point of view, to keep them in the realms of reality.
    Even if I were a “warmist” I think that I would want some “sceptics” around to put the other side of the argument.
    All research seem to be intended to “prove” warming and it’s most extreme effects, and starts out on that basis.
    Nobody in the media really challenges them either (they apparently aren’t allowed to do so on the BBC) so I think we must expect more of the same.

  14. June 4, 2014 2:11 pm

    If 1955 to 1975 followed 2014, then I’d be worried; but it doesn’t and never will, so I’m not…
    Keep up the good work.

  15. June 5, 2014 6:10 pm

    The Met Office restricting the access to historic data, that we the taxpayers have paid for is outrageous.

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