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uk.sci.weather (UK Weather) (uk.sci.weather) For the discussion of daily weather events, chiefly affecting the UK and adjacent parts of Europe, both past and predicted. The discussion is open to all, but contributions on a practical scientific level are encouraged. |
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#31
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On 29/10/2015 11:25, Eskimo Will wrote:
Hi Len, interesting stuff, but I have some questions about the graphs? 1. How consistent was the raingauge site over the years. My experience of looking at Dartmoor gauges has revealed that just a small change in location (even a few hundred metres) can make a statistically sig. difference to rainfall. Cowsic is a case in question, due to changes in aspect from one side of a valley to another. 2. In the 19th Century rainguage height was not consistent, in fact a lot of gauges were elevated. Scientifically this was proven to produce lower rainfalls than rainguages on the ground due to turbulence effects. In my Dartmoor study I have been very careful to only use data where the raingauge location has been consistent over the decades and where the height of the gauge above ground has been consistent. I think that is important. 3. Have you done a statistical Student's T test to measure significance of the changes, I suspect that they are very sig (esp. winter). but with the provisos of my points one and two above. Jim, you need to look at your local area rainfall over the decades too, if you can of course? Will Will. I've not been able to find anything from before 2000 anywhere. Seems all the local weather stations in the county suddenly woke up then, and records are pretty comprehensive after that date. All I can say is that we never had any weather here in Northamptonshire before 2000!!! jim |
#32
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On 30/10/2015 09:17, Eskimo Will wrote:
Hi Len, again! Having just read Jim's excellent response and queries in this thread, I'm getting interested now in my own hypothesis which I'd dearly like to test. If I gave you a list of "orographic enhancement days" (moist SW'ly winds), would you be able to extract the Plymouth rainfall (and wind) data for me? If we do this well it could end up as a super paper? What do you think? Could be a lot of work for me initially though to find the days, but that's science - hard work. Will Will. As I've stated elsewhere, I can't find anything before 2000, but since then, Pitsford have kept very comprehensive records which are all downloadable. This may or may not interest you, but they have a record of wind, various temperatures and rainfall at 15 minute intervals from 2001 onwards. It can be found at http://www.northantsweather.org.uk/archive/aws/ . They are .zip files for each year, base format .csv which open in MS Excel by default. "15 minute wind records" caught my eye bearing in mind how part of this conversation is unfolding. Being slap bang in the middle of the country, they could be fairly indicative of the rest of the country. (Home page at http://www.northantsweather.org.uk). Pitsford's AWS is situated on the roof of the Pitsford Hall Grammar School, about 5 miles north of Northampton. Ground level at the site is about 400ft asl. They have a page marked up "A review of 2011 and 2012 in the context of a changing climate". It includes the following paragraph: "However, there is every indication that not only is the timing of rainfall changing, but also the nature of rainfall itself. When it does rain, it is tending to rain harder and for longer. Again, this may be the result of an increase in number of depression ‘trains’ tracking across the UK – a product of the static position of the jet stream, but it may also be the result of more energy in the atmosphere which points to global warming as an ultimate cause. In Northampton, an analysis of temperature data in 2010, suggests the county has seen an overall increase in average temperatures of 0.1C since 1931. " "Tending to rain harder" accounts for the severe drop in ground water levels over the last few years, since most of that will result in surface water run off. Just found out Pitsford didn't start operating until 1998. That doesn't excuse the county's other stations for not posting older records. jim Today, a slightly damper Northampton! |
#33
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On Thursday, 29 October 2015 08:35:51 UTC, wrote:
"jbm" wrote in message ... I am absolutely and thoroughly stuck on something the local council has asked me to look into. Over the last seven years, the rainfall in this area has been well below normal for 5 of them. Currently, we are over 300mm short of what we would normally have expected in that time. Doesn't sound a lot, but it represents 6 months of normal rainfall. In 2011 we had just under 400mm, 60% of normal, and the following year, despite numerous thunderstorms, deluges and flood alerts along the River Nene, several springs in the area dried up, and have not flowed since. Result = steams with no water in them, local lakes well below level, with any pollution entering them not being diluted sufficiently not to cause problems. One lake lost all its waterfowl in July due to contamination from fuel oil from a local industrial estate. What I have found is enough evidence to prove that the ground water levels are severely depleted, with the water table at least 300mm below what it was 5 years ago. So I would appreciate it if some of you knowledgeable meteorologists out there would care to hazard a guess at the following. Having experienced so many dry years recently, what are the chances of getting some exceptionally wet ones, with steady and moderate rain to start replenishing the ground water, without the majority of it disappearing straight into the rivers as surface run-off? What we need is a lot of water, and I mean a lot, getting down to that water table as quickly as possible. Any ideas anyone? We have to make a decision shortly as to what to do with the lakes - leave them as they are, dredge out all the ****e and see what happens, or fill them in and be done with it. And a reasonably intelligent prediction on future rainfall might help in that decision. jim a very dry and rainless Northampton Hi Jim, I'm soon to give a public lecture on Dartmoor weather. As part of that I have been looking into climate change on Dartmoor. At Princetown in the 20th Century annual rainfall significantly (as revealed by an objective T test) decreased. In the 21st Century, evidence from Haytor would suggect that that drying trend has slowed but not reversed. My take on this is that our climate is slowly getting drier in terms of annual rainfall. Basically I think you're ****ed! Will -- http://www.lyneside.demon.co.uk/Hayt...antage_Pro.htm Will Hand (Haytor, Devon, 1017 feet asl) --------------------------------------------- Talking about liquid collection vessels "think you're ****ed!" Potty Mouth |
#34
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On Friday, October 30, 2015 at 12:56:51 AM UTC, jbm wrote:
Right, I'll try to pass comment on all the relevant answers in one go. Thank you all for your input. The best answer seems to be from Will: "Basically I think you're ****ed!". Which corresponds very closely to my assessment!!! I too (like Alastair) am a retired engineer of the civil and construction kind. I was asked to look into this because I am one of the few (if any) people in Northampton who has first hand knowledge of the local lakes, having been briefed very fully on their design and construction back in the 1970's. A lot of the work I have done on this concerns the geology and science behind ground water (N_Cook note - I have subsidiary qualifications in Geology and Soil Mechanics), though in a broad sense, not taking into account exact local conditions. While I was preparing my report for the council, I received a report from an adjacent local council on the flood assessment of a large housing development about to take place alongside the stream that feeds the lakes. I haven't been able to go through it in depth yet, but it appears to contain a lot of information along the lines I was pursuing. There are no figures available for the River Nene, which flows through the county, but at Wansford near Peterborough its level is as low as it has ever been. Flow rates earlier this year for the River Great Ouse in Cambridgeshire were about 30% of what would be expected at that time of year. One thing I did learn was that the rainfall pattern throughout the year was not what I expected. The summer months, Jul-Aug-Sep, are on average about 10-15mm wetter than the rest of the year. Also those 3 months have the least rain days, which means because of the heavier rate of rainfall less water manages to get down to the ground water because of its intensity forcing more in the way of surface run-off. What I have noticed over the last few years is the numbers of times I hear reports of torrential downpours to the west of here, whilst we get next to no or no rain at all. Same applies to the east of us, but not so noticeable. So it would appear that here in the East Midlands, and especially in Northamptonshire, all the rain is falling elsewhere before it gets to us. Never used to be like that - we always got more than our fair share, not not so these days. Any ideas why that may be so? Interesting, and somewhat puzzling, that Will is experiencing less rain up in the hills, whilst Graham reports a slight increase down at the seaside! Thought that would have been the other way round. Thanks for those graphs, Len. Although you are a couple of hundred miles away, they reflect very accurately what we had here in 2011, a very dry year (60%), and 2012, a very wet year (130%). Unfortunately, most of that 2012 total fell during thunderstorms, and I reckon sweet sod all got down to the ground water. Probably more got down there in 2011. As to water usage, the main reservoir in the area, Pitford, is in the next catchment area to the west, though it relies on water extraction from the River Nene to keep it going. Grafton Water is too far away to worry us. Sywell Reservoir, within our catchment area, was decommissioned some years ago, so no longer enters the equation. It is now used for purely recreational purposes (fishing). So far I have been unable to find any rainfall records for this area from before 2000. What I have got, however, is a full record of monthly rainfall since Jan 2006. Since then, by my reckoning, we are about 260mm = 4% short of what we should have had. Bernard in Wokingham, about 50 miles south of here, has had 20% more. Which sort of emphasises my belief that something is stopping the rain getting here. And finally, in answer to Alastair's "So what ever you decide will be wrong!", no I won't, because after receiving an email earlier this evening I won't be making any decision in the foreseeable future. I am stepping back from this for a while. One of our local councillors, much against the wishes of me and someone I am working with on this, is going to raise the matter at a full council meeting shortly, and from what we understand he is going to push for the first lake to be dredged out to remove the residual pollution and build up of silt. What he doesn't realise yet (because he has already been cut out of the loop by everybody concerned over his behaviour on a related matter - his only interest is in scoring political points over the other parties) it that silt is the result of a bank collapse alongside some houses, and if it is allowed to continue or accelerate, those houses will be at risk of falling down. Our other councillor has been made fully aware of the situation, as have the Chief Executive and Assets manager of the council. 2nd councillor has been instructed to shoot first councillor down by revealing these findings at the meeting and telling him to make sure of his facts before shouting his mouth off. I wish I could be there to see and hear it all! I hadn't wanted this to get political, but it is now out of my hands, for the time being at least. Well, the general consensus of opinion seems to be no one here has any bloody idea if we are going to get any rain. Fair enough I accept that, and is basically what I expected. Will's "Basically I think you're ****ed!" sums it up perfectly. jim Northampton-under-Desert Jim, I have just come across this paper which you might find interesting: https://www.researchgate.net/publica...gdom#full-text Cheers, Alastair. |
#35
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On 02/11/2015 09:40, Alastair wrote:
Jim, I have just come across this paper which you might find interesting: https://www.researchgate.net/publica...gdom#full-text Cheers, Alastair. Thanks for that Alastair. Looks interesting, more so because we were slap bang in the middle of the drought order issued in June 2011. Anyone else still reading this, since my last post I have managed to find the complete historical rain data (monthly rain totals) from 1880 to 1997 for the county. I already have a similar set for 2006-2015. If I scratch my way through the Pitsford site I should be able to fill in the gap, though they do have a tendency to put similar sets of data for different years in different sections. That's school kids for you! jim, Northampton |
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