Alwen DCNN 7623 – A case study of changes over time.

53.06194 -3.55383 Met Office CIMO Assessed Class 5 Archived Temperatures records from 1/1/1959

Llyn Alwen Reservoir is certainly anthropogenic being constructed between 1911 and 1920. The CIMO regulations specifically state that weather stations should avoid large bodies of water unless typical of the region – being an artificial modification will mark down this site. The Met Office already rates the site as the lowest possible and effectively unregulated Class 5 but I doubt the reservoir was even considered. This site had a rain gauge fitted shortly after the dam and reservoir construction in 1928 but archived temperature records only run from 1/1/1959. The story with Alwen is one of significant change over time effectively rendering historic comparisons from this manaul “Climate Reporting” station effectively impossible.

The CEDA records for this site head up its current location and in the absence of any site renaming and/or renumbering it would be reasonable to assume it had always been at that location. However at the foot of the “Remarks” section there is a notification of a relocation in 1994. MET Office procedures indicate the following:

“Over time certain instruments, or the whole enclosure, may be relocated some distance away from the original site. Where the distance moved is small, the observations obtained from the new site may have exactly the same climatological characteristics as previously and it makes sense to regard them as coming from the same source or station distinguished by certain identifiers. Where the distance moved is large, or, where the exposure at the new site is sufficiently different that a detectable impact on the measured climatology is judged likely, it is appropriate that observations from the new site are labelled by a different set of identifiers.”

The lack of any change of “identifiers” suggests the relocation effects were minimal so firstly how far was this relocation and was it really so insignificant?

The old site was both 302 metres/ 990 feet away but also at a 10 metre/33 feet elevation difference. An indication of whether such a distance could make any substantial difference is given by the 58 metre differential between two separate official Met Office stations at Manston showing marked discrepancies so clearly, yes such a move definitely could. Below is an image of the original site from the given coordinates with a 100 metre radius circle

Whether or not the Met Office would consider the reservoir an issue is probably unlikely – they certainly are not concerned about proximity to Loch Shin at Cassley which they claim achieves Class 1 despite the majority of a Hydro Electricity generating plant within the 100 metre radius and a significant slope. In the case of the original Alwen reservoir site, I would not be surprised if the Met Office classed it similarly as Class 1 and class 2 would not seem unreasonable.

Both the original and current site are manual reporting units so it would not have been necessary for electricity or communication supplies for automation to have enforced relocation. Whatever the reason to move the site it certainly did not improve it though initially it was not as bad as the modern day site. Below is a close up of the site shortly after the move.

This new position is not as good as its original with buildings, hard-standing, roadways and parking encroaching, however, this only got much worse over further time as this water works site developed.

The 10 metre zone is now largely covered by new buildings rendering the weather station’s reading to junk status for the purposes of representing any area other than its own footprint. It will, however, no doubt read elevated temperatures from its enclosed “courtyard” location which raises the obvious question of why does the Met Office not now relocate it again to a much more representative open site? Or is the more likely case (in my personal opinion) that such inevitably elevated readings are a modern design feature that the Met Office finds necessary.

But then to add more poor management of this site we must add in the modern day inevitability of lack of readings being taken. In the last archived year (2023) the 365 daily requirements dropped to just 205 times the effort was actually made. On top of that, on no fewer than 28 occasions either the maximum or minimum daily reading was omitted making a daily mean figure an impossibility to derive. Under half the annual days averages could have been arrived at rendering any annual figure frankly an absurdity.

Overall these are an unacceptable standard from a taxpayer funded organisation.In any serious independent temperature reconstruction of the UK national historic record there is no possible justification for including any of the many sites, like Alwen, that the Met Office currently finds acceptable.

Source: https://tallbloke.wordpress.com/2025/03/31/alwen-dcnn-7623-a-case-study-of-changes-over-time/