- Research article
- Open Access
Preliminary results from a legacy indicator tool for measuring climate change related impacts on built heritage
© The Author(s) 2019
- Received: 4 February 2019
- Accepted: 6 May 2019
- Published: 17 May 2019
Gradual changes in weathering rates and mechanisms are the barely visible impacts of climate change on cultural heritage. Long-term monitoring of built and archaeological heritage is therefore necessary to ascertain the nature of loss due to slow onset effects. During research at the Dublin Institute of Technology in 2011 a Legacy Indicator Tool (LegIT) for measuring the weathering of stone surfaces into the far future was developed by the author and piloted at five National Monuments in Ireland. While it is too soon to evaluate the tool in relation to long term climate change trends, this article considers the data from 5 years of exposure and provides an early assessment of the pilot study’s design and implementation.
Measurements for colour, surface roughness, weight, and dimensions from the 5 year exposure of the LegIT were analysed. Comparisons between sites allows assessment of surface change under different atmospheric conditions. The indications for regional and localized weathering trends will aid managers in understanding risks and setting priorities—both for further monitoring and for conservation interventions.
Results from the 5 year pilot trial of the LegIT has allowed preliminary evaluation of its potential as a long term indicator for surface weathering. Recommendations have been made for modifications to the design, manufacture and implementation of the tool. The future aim is to compare results over time at each site, building a picture of surface weathering processes in relation to regional climatic change.
- Cultural heritage
- Climate change
The nature (dominant mechanisms, relative severity etc.) of surface weathering at the site, and
Whether those effects alter over time with changes in the climate.
It was intended that this information would inform decision making regarding the allocation of resources to monitoring and conservation campaigns. While it is too soon to evaluate the tool in relation to long term climate change trends, this article considers the data from 5 years of exposure and provides an early assessment of the pilot study.
Brimblecombe suggests that an embedded tool, capable of gathering and storing data without maintenance or management requirements would be ideal for monitoring climate change impacts on individual heritage sites . The LegIT is an attempt to create one such tool, in this case for the capture of surface and near surface effects such as physical and chemical surface recession and microbiological activity. These are the issues noted by Noah’s Ark  and others [7, 8] as being of primary concern for heritage in Western Europe under future climate projections.
During the pilot trial some data was lost from vandalism (1 cube stolen), accidental damage (1 cube broken), and miscommunication (steam cleaning of one plate). There was also a 3 year delay in the installation of the plates at Dublin Castle, resulting in an absence of data from the site. This occurred initially because of staff changes and failures in communication, but its continuation for such a long period (until 2016) was due to the fact that the project had not been integrated within the site management remit.
Measurement methods utilised for LegIT
Method and requirements
Digital camera, tripod
Digital colour photographs, of each exposed face. Change visually quantified using grid overlay
Financial: low—basic equipment. Human: low-medium—taking, assessing and archiving digital images. No expertise required
Low tech, comparison will be visual and somewhat subjective
Average surface roughness (Ra) surface characterization tool e.g. Diavite or Surtronic. Industry standard settings used = Lt 4.80 mm trace (sample length) and Lc 0.8 cut off filter (does not measure wavelengths > 0.8 mm)
The profile of the surface is measured using a stylus, magnified through software and quantified as roughness average (Ra) in µm, accurate to 0.01 mm
Average taken from 10 profiles on each exposed face
Financial: medium—equipment cost approx. €3000
Human: medium—taking 50 measurements/cube is time consuming however very little post-measurement processing is required, no expertise required
Highlights changes in surface characteristics, e.g. smoothing or roughening
Standard deviation in the Ra measurements can be used to indicate homogeneity of the surface
Cannot be used on very weathered stone or over large lichen growths
Ultra Scan Pro USP1577 Hunter Lab. Mode #3 RSEX or similar
Values for brightness (L*) redness (a +) and yellowness (b +) are taken. Average values are calculated from the five points by the spectrometer
Financial: medium–low—from €3000 to buy, the project initially used borrowed equipment at a food science lab.
Human: low—spot readings can be taken rapidly and processed immediately by software, no expertise required
Digital Vernier callipers. Measurements taken in three dimensions (width, depth and height). Three measurements taken in each case.
Negligible—low cost equipment, low human resources—rapidly completed by non-expert
Produces quantifiable measurements but of low accuracy (± 0.1 mm) Margin for human error (established from repeat measurements) is ± 0.3 mm
Digital laboratory scales (measure to 0.00 g).
Demounted stones (including internally fixed nut) weighed in grams. Stones must be dry before weighing. Calibrate scales
Financial: low—scales from €250 to buy
Human: low—quick to take measurements, no expertise required
The requirement for drying the stones can delay this method of assessment for several weeks after demounting
3D profile scanning
Renishaw Cyclone Series 2 SP600 M machine or similar. Used Tracecut programme
NB this method was utilized in the initial phase but not for repeat measurements
Profiling done in Z plane in increments of 5–10 mm (i.e. profiles taken at 45, 40, 35, 30, 20 and 10 mm from base). Profiles stored as DXF lines and arcs in CAD
Financial: high—cost of equipment prohibitive unless can access within an institution
Human: high—time consuming to take measurements and to process and requires expertise
The measurements could be introduced into CAD software to compare profiles over time, quantify change and produce visual overlays that show the progression of loss
The data from the pilot exposure of the LegIT has been analysed for both the nature and scale of measured change and a selection of the results are considered here to illustrate trends. Prior to undertaking paired T tests the data was checked for normality and outliers using statistical analysis software (SPSS) (histograms, QQ plots and Box plots). Significant outliers (at 1QR ≥ 3) were identified and removed. While comparisons between sites allows assessment of surface change under different atmospheric conditions, the future aim is to compare results over time at each site, building a picture of surface weathering processes in relation to regional climatic change.
L*a*b* colour system
ΔL*= (L*pre-exposure − L*post exposure) = difference in lightness (+ = lighter/− = darker)
Δa*= (a*pre-exposure − a*post exposure) = difference in red and green (− = greener)
Δb*= (b*pre-exposure − b*post exposure) = difference in yellow and blue (+ = yellower)
ΔL* Δa*and Δb* values for Peakmoor cubes from 4 case study sites for exposures of 3–5 years
Bru na Boinne
Rock of Cashel
− − 12.5
The growth rate of lichens will vary according to species, crustose lichens tend to be slow growing (0.1 mm–2 mm/year) while foliose lichens will grow between 0.5 and 4 mm/year . For all species growth rate is dependent on the environment, ideal conditions being high moisture availability and mild temperatures. With this in mind the number of rain days (≥ 2 mm) for two of the exposure years (2014 and 2015) were compared across the LegIT sites (Fig. 4).2 Unfortunately neither of the World Heritage properties has on site recording of environmental climate therefore data has to be used from the closest available met stations. These are Valentia Observatory, Cahersiveen Co. Kerry, which is approx. 30 km NW of Skellig Michael, and Dunsany automatic weather station in Co Meath which is approx. 20 km SW of Brú na Bóinne . Precipitation data, without wind measurement, is available for the site of Clonmacnoise and for Ballinamona (3.5 km W of the rock of Cashel). During this period Clonmacnoise experienced 43–49 more wet days than Cashel or Brú na Bóinne, but 38 days less than Skellig. Temperature readings are not available from the stations at Cashel for this period but non-quality controlled readings were sourced for Clonmacnoise.3 The indication from this data is that Clonmacnoise may not only be wetter than the other rural sites, but also experiences milder temperatures. Regional variation in lichen growth cannot be explained solely in relation to mild temperatures and the availability of water however, otherwise Skellig Michael would have the highest growth rate.
A non-climatic influencing factor on biological growth on stone is air quality and although most lichens will not grow in a polluted environment, the presence of elevated levels of atmospheric nitrogen may act as a biofilm fertilizer . All of the case study sites are in Zone D of Ireland’s Environmental Protection Agency’s (EPA) air quality management plan (rural areas and towns < 15,000 population). While this suggests there should be little difference in the air quality between the sites, in reality this may not be the case—both Brú na Bóinne and Clonmacnoise are located in regions with fuel burning power stations (West Offaly peat burning station is approximately 8 km SW of Clonmacnoise and the Indaver waste to energy incinerator is approximately 6 km SE from Newgrange4) while the Rock of Cashel is within a town environ. In the case of Skellig Michael the exposed maritime environment, with high winds and air borne salts is also likely to be influencing biofilm growth.
Change in average surface roughness (Ra) of the cubes was examined in relation to both material type and site location. It is should be noted that the utilisation of the surface profilometer to measure Ra of the artificial cubes (concrete and brick) was unsuccessful due to the heterogeneity of these aggregated materials, therefore this analysis concentrates on the natural stone cubes. In some cases lichen growth had to be removed before measurement could be taken (this was done with the pad of a finger to minimise scratching to the surface). While this action was undertaken after photography and colour measurement, it does remove the ability to monitor cumulative patterns in biological growth. In addition as the lichens form a protective layer over the stone but are attached to the surface with hyphae strands, removal (however gently) may loosen and remove grains from the stone—artificially increasing the roughness. That biological growth may prevent surface roughness measurement (and vice versa) is significant for future implementation, essentially requiring the researcher to prioritise a specific data-set.
Weight and dimensional change
Rock of Cashel and Skellig Michael
Given projections for a shift towards shorter periods of heavy precipitation at the case study sites, it is expected that the recession rate caused by the physical action of rain will increase over the long term. The initial results from the LegIT show that roughening is being evidenced first on the softer and less dense stones (Peakmoor and Portland) and at the sites where rainfall volume is highest (Skellig Michael), suggesting that the tool will provide a good indication of this impact. The anticipated reduction in mass due to material loss has not manifested in the weight change results. Most cubes actually demonstrating a small gain in weight, possibly due to microbiological colonisation or accumulation of air/water borne pollutants such as soluble salts . While the dimensional change recorded with Vernier callipers also does not follow a linear pattern of loss—in some instances being due to an increase rather than reduction in dimensions—there appears to be a relationship in this data between degree of change and length of exposure. In relation to colour change as an indicator of biofilms, there is a notable difference in biological growth type and extent between the locations, due to variations in both regional and local (micro-climatic) environmental conditions.
Surface roughness measurements have proven very useful to date, but as the stones become more weathered they are starting to exceed the sensitivity of the stylus profilimeter. Alternative methods of undertaking surface roughness measurement were investigated and could be trialled during the next phase of the LegIT pilot. The growth of lichens also interfered with these measurements, requiring a choice to be made between the long term measurement of biological growth and of surface roughness.
Design and implementation
The LegIT was designed to be left to gather data without intervention over the long-term, with potential widespread application for unmanned heritage sites. Accidental and malicious interference has occurred in several instances however resulting in some data loss. In Brú na Bóinne one cube was stolen and others were loosened in situ, in the Rock of Cashel steam cleaning of one plate occurred, while the lacuna in the Dublin Castle data was the result of communication and organisational breakdown (a major challenge for projects that aim to operate over the long-term). Following the discovery of the steam cleaning at Rock of Cashel the plates were moved to an area accessible only to site staff and not external contractors.
The overall design and mounting system worked well during the pilot trial and was found to be practical for installation and demounting. Unfortunately the use of a hammer-drill to create the fixing holes proved problematic as stress cracks have subsequently appeared on some cubes. The inclusion of concrete and brick was intended to widen the application of the LegIT but these materials have proven hard to interpret, partly due to their heterogeneous nature (e.g. aggregate inclusions, air pockets). The act of cutting brick into cubes removed the fired face and therefore rendered it less representative of built fabric. The concrete also required a mould to make the cubes and was particularly difficult to drill.
The LegIT design is essentially modular, with 5 cubes on each plate, and can therefore be adapted to suit the requirements of any location. Similarly the measurement techniques can be tailored to specific conservation priorities, for example retaining biofilm growth where this is of more interest than surface roughness measurement, or if surface roughness is more important to partially or completely treat the cubes with biocides.
The pilot study has allowed the initial design to be evaluated. The recommendation for future applications is not to include concrete and brick, but to use two cubes each of Peakmoor and Portland as these produced the most useful comparative data sets, together with the site specific stone. Given the issues with stress cracks a low impact diamond core drill or similar should be used for embedding the fixing system in future.
The central concept of the LegIT is to have long-term continuous exposure of the same cubes, capturing cumulative deterioration. The possible alternative approach would be to periodically replace the cubes thereby building comparative datasets over time from consecutive short-term exposures of fresh stone. While this does not fit within the original Legacy concept it may be a useful approach for some sites to take if there are the resources required to maintain it.
The LegIT is currently utilizable as a practical management aid, an indicator for understanding deterioration and planning conservation treatments. Attribution of observed deterioration to individual environmental parameters, and subsequently to climate change, is not currently possible. Site specific environmental data (climate and air quality) would be necessary to determine the exact conditions that lead to specific mechanisms of surface change, such as biological colonization. Extending the study to locations where such data is available is one future possibility. To increase the robustness of the method and ultimately widen the application of results beyond individual sites, a more statistically relevant trial would need to be developed. This could be achieved by increasing the number of samples while simultaneously reducing the number of materials (maximum two stone types) and other variables (i.e. location and aspect). It is hoped that this pilot trial may serve as a jumping off point for those interested in further developing on the legacy indicator concept.
Consideration of the results from the 5 year pilot trial of the LegIT has allowed a preliminary evaluation of its potential as a long term indicator for surface weathering. Recommendations have been made for modifications to the design, manufacture and implementation of the tool. Experience from the Rock of Cashel and Dublin Castle illustrate the importance of transferring responsibility from external researchers to those permanently in place, and embedding the LegIT into local management systems. The careful choice of location for installing the plates is also essential to reduce the problem of human interference. The lack of site specific climate and air quality data is noted as a limitation in terms of being able to analyze causality. The methodological questions regarding how best to continue measuring the effects over time and how to interpret these in relation to climate change remain challenging. Nonetheless, the LegIT has provided a clear indication of regional and localized weathering trends, information which can already begin to aid managers in understanding risks and setting priorities—both for further monitoring and for conservation interventions.
Brú na Bóinne and Skellig Michael are also UNESCO designated World Heritage properties.
Values from Met Eireann (Irish meteorological services) online database of climate data at http://www.met.ie/climate-request/ (accessed 1/10/18). Clonmacnoise temperature data provided by Aidan Murphy, Climate Services, Met Eireann (15/10/18).
Obtained by Email from Aidan Murphy, Climate Services, Met Éireann, 15.10.2018.
The prevailing wind direction is from the South and West, likely to carry pollution from Shannonbridge over Clonmacnoise but should have the reverse effect with the exhaust from Indaver, as it lies to the SE of Brú na Bóinne.
I owe my thanks to the many people that helped with the design, manufacture, installation and evaluation of the LegIT and to Lynda Skipper for her comments on this article. Special thanks are due to the OPW staff working at the sites of Brú na Bóinne, Clonmacnoise, Dublin Castle, Rock of Cashel and Skellig Michael. I would also like to acknowledge the financial support of University of Lincoln’s Research Resources Allocation Fund, without which the 2016 fieldwork phase of the project would not have been possible. Lastly to the anonymous peer-reviewers whose comments helped to improve this article and whose suggestions for future research have been incorporated.
This research was partially funded by the University of Lincoln from the internal Research Resources Allocation Fund.
The author read and approved the final manuscript.
The author declares that they have no competing interests.
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