Lyneham WMO 03740 – Rural Heat Island effects in New Zealand!

51.50315 -1.99241 Met office CIMO Assessed Class 2 Claimed Installation 1/1/1945 – Digital Temperature Records from 1957

There really is a place in England known as New Zealand and it lies just to the south of former RAF Lyneham (now MOD Lyneham) which itself lies 10 miles to the south west of Swindon in Wiltshire. This site was formerly a major RAF base used extensively in repatriation flights from Afghanistan though flying operations are now ceased with the runway effectively mothballed. The MOD now run the Defence School of Electronic and Mechanical Engineering from the site.

Firstly zooming in on the actual enclosure reveals a classic Met Office airfield site close to the (now demolished) control tower with modern day impeccable grounds maintenance. The Met Office rate this as Class 2 and thus should be perfectly accurate and representative of the wider surrounding area. Presumably the huge areas of hangars hard-standing and taxiways are perfectly “natural” as is the closely cropped grass.

The tape measure should not lie so has the Met Office correctly got its 30 metre exclusion zone? Well yes and no!

The first query I would make is the two separate levels of windbreak. As I discussed regarding Prestwick:Gannet multiple lines of close link fencing have a marked effect on wind speed to the known extent that horticulturalists and even garden centres use open wire/flexible tape barriers to calm winds to reduce desiccation and elevate temperatures.

The Lyneham screen is subject to the security barrier fencing and then the screen enclosure itself well within the 30 metre zone. This is quite a common feature of such aviation sites – Merryfield is another good example as is Neatishead. Modern Platinum Resistance Thermometer response times are calibrated in controlled conditions measured for air response times at set wind velocities. The most critical T65 (65% of final temperature reached) is rated at 3 metres per second wind speed.

3 metres per second equates to 10.8 kmh/6.7mph which is Beaufort Scale 2. The likelihood of adequate ventilation within a Stevenson Screen behind two close wind breaks to sustain the set response time is highly unlikely in anything below a much higher natural external wind speed. The variance in response times between former Liquid in Glass Thermometers (LIGT) in dead calm within the screen compared to PRTs will inevitably lead to a variation in readings between the differing systems. The PRT will inevitably frequently read higher especially at night. This issue has extensively been highlighted by Dr Eric Huxter and is in fact a well known problem acknowledged by both the Met Office and the World Meteorological Association with the latter recommending artificial fan assisted ventilation of screens to overcome this problem – the Met Office does NOT operate fan assisted/artificially ventilated screens.

My second issue is the change to the environment surrounding this site. Being an airfield is one defined set of circumstances, being a solar farm as well is completely different. The MOD Lyneham solar farm was commissioned in March 2015, has a capacity of ~69.8 MW, covers ~213 acres (86 ha) with over 160,000 panels, and was one of the UK’s largest at the time of installation. The panels were installed directly alongside the old airfield runways and surrounding MOD land.

The Urban Heat Island Effect is a well researched subject with “heat maps” produced for major city and urbanised areas.

The subject of rural areas being affected by artificial and potentially powerful extraneous heat sources seems to be largely overlooked. Lyneham is no longer just an airfield environment, the headline image shows significant building/housing development to the east and south with the very large array of solar panels to the north. As discussed with the comically surreal Chertsey Abbey Mead site, solar farms most certainly do modify the local climate and such modifications (especially at military sites and commerial sites) are becoming increasingly common – witness Leconfield and Wallingford and many others.

GROK AI offered further information regarding research into the effects of such large solar farms.

Key findings from peer-reviewed research:

• Arizona desert study (Barron-Gafford et al., 2016): Temperatures directly over/near a PV plant were 3–4 °C warmer than surrounding wildlands at night. The effect was detectable but dropped off sharply beyond ~100 ft (30 m).
• Canadian solar farm modeling + measurements (Fthenakis & Yu, 2013): Air temperature at the center was ~1.9 °C warmer; at 300 m away it fell to just +0.3 °C. The heating was strongest near the surface and diminished with height and distance.
• European and modeling studies confirm similar patterns: daytime shading can cool the ground under panels (especially if raised and vegetated), but overall air temperature above and immediately downwind of the array often rises. Effects are larger in calm, clear conditions and can alter humidity and soil temperatures too.

These are real, localized effects — not global warming, but a genuine microclimate distortion. In rural or semi-rural settings like Lyneham (formerly open airfield, now a vast panel-covered expanse), this qualifies as an anthropogenic “rural heat island” created by renewable infrastructure. It’s the flip side of the urban heat island discussion you often cover: instead of asphalt and buildings, it’s engineered dark surfaces changing the energy balance.”

This below is what the former RAF Coltishall weather station now looks like – no small wonder the weather station was shut down. However, the point remains that this is just another form of heat islanding but in formerly almost rural areas that is artificially elevating temperature readings. {The red kite marks where the screen was until recently.}

Grok AI went on to add:

The Lyneham Class 2 rating is indeed highly improbable given the visible evidence in your satellite image and the scale of the solar farm. The red marker places the screen squarely in the former RAF Lyneham complex, immediately adjacent to (and partially surrounded by) the massive ~213-acre (86 ha) solar array installed in 2015. Under WMO CIMO siting guidelines (which the Met Office follows), Class 2 for temperature requires the screen to be more than 30 m from artificial heat sources/reflective surfaces, with those surfaces occupying <10% of the area within a 30 m radius (and even stricter limits closer in). A photovoltaic (PV) array of this size qualifies as a major artificial heat source—dark panels absorb ~78–85% of solar energy as heat, raising local air temperatures measurably (especially at night via stored heat release). The 2015 installation post-dates the station’s original siting, so any pre-2015 Class 2 rating should have triggered a re-assessment.Your Chertsey post (from 23 August 2024) shows the Met Office applying exactly these rules in practice: they downgraded Chertsey Abbey Mead from Class 2 to Class 3 after the 2022 solar installation at the pumping station, citing the same “artificial heat sources and reflective surfaces” criteria. Their verbatim response to you is transparent about the percentages (0% at 3 m and 10 m, 20% at 30 m, >20% at 100 m) yet concludes the data still “meet standards for publication and scientific use.” That’s consistent policy—but it also reveals the limits of their approach.My Take on the Met Office’s Overall Stance – They are not in outright denial (they acknowledged the panels at Chertsey, updated the classification, and replied promptly). This is better than ignoring the issue. However, their response feels somewhat cavalier in a practical sense for three reasons:

1. Narrow, checklist-based application of the rules — They measure % coverage within fixed circular radii and stop there. This misses the broader physics of the “photovoltaic heat island” (PVHI) effect. Peer-reviewed studies show air-temperature elevations of 1–4 °C (strongest at night, under low wind, and near the surface), with measurable influence extending hundreds of metres downwind. A huge array like Lyneham’s creates a heat plume that the simple radius method underestimates, especially for night-time minima (which drive many climate trends).
2. Minimal adjustment and no public bias quantification — Downgrading Chertsey to Class 3 flags some uncertainty (~±1–2 °C in extremes per WMO guidance), but they still publish the raw data without any footnote, homogenization flag, or estimated PVHI correction in the climate archive. For long-term trend analysis, even a 0.2–0.5 °C systematic warm bias matters. The same logic applied to Lyneham should almost certainly push it to Class 4 (or require relocation), yet you report it remains Class 2—suggesting either the rating wasn’t updated post-2015 or the Met Office is interpreting “artificial heat source” very generously when the infrastructure serves renewable-energy goals.
3. No proactive network-wide review — Solar farms on MOD land, airfields, and water-company sites are proliferating. The Met Office knows this (they track renewable energy for forecasting), yet there’s no public evidence of systematic re-siting or enhanced monitoring around these new heat sources. Your “rural heat island” angle is spot-on and under-discussed: these aren’t urban sprawl or airport tarmac, but they still distort the very rural baseline stations we rely on for climate monitoring.

In short, the Met Office’s attitude is pragmatic and rule-compliant rather than negligent or conspiratorial. They adjust classifications when directly challenged (as at Chertsey) and maintain that the data remain “fit for purpose” after applying their internal quality controls and homogenization. But this feels insufficiently rigorous for a network whose output feeds national climate records and policy. The CIMO system itself is a compromise tool (it’s deliberately simple), and solar farms expose its limitations—exactly as poor siting, vegetation creep, or airport proximity have done elsewhere in your series.This fits the pattern you’ve documented across UK stations: real microclimate influences are acknowledged when flagged, but the institutional response prioritises continuity over perfection. For Lyneham specifically, the mismatch between a claimed Class 2 rating and the enormous adjacent solar farm is glaring. A before/after 2015 comparison of its night-time minima versus nearby rural stations would be a valuable next step in your forensic work.“

To conclude, whilst the Met Office may feel tape measure justified in claiming Lyneham is CIMO Class 2, the site is clearly so compromised by artificial (anthropogenic) effects that it can no longer represent the natural environment……..but it will undoubtedly show abrupt warming since 2015 and that seems to be all that matters to the Met office whatever the unnatural cause may be. This ideological approach has to stop.

Source: https://tallbloke.wordpress.com/2026/04/21/lyneham-wmo-03740-rural-heat-island-effects-in-new-zealand/