Vulnerabilities - Overview

Cassar (1) presents a scoping study on climate change and the historic environment in the UK. According to Cassar little is published on conservation and directed adaptation of the historic environment in response to climate change. The publication by Cassar presents the best overview as far as is known.

Old buildings, archaeological sites, and historic parks and gardens are put at risk by the same dangers to the wider environment – flooding, coastal erosion, subsidence and possibly increased storminess – which have already been identified by other climate change studies. However, they present in addition a number of complexities that suggest they may be especially imperiled. Changes in rainfall patterns and temperatures, even where these may not be perceived as a major threat to modern buildings, are likely to have dramatic effects on buried or exposed archaeological sites (1).

Climate change effects are already being felt on all types of site (1,20). Some of these were:

• increased erosion, especially associated with increased storminess (Sutton Hoo);
• problems with local flooding (Audley End);
• problems with sustaining turf (Birkenhead Park, Furness Abbey);
• changing patterns of pests and diseases (such as the year-round presence of Canada geese at Birkenhead Park);
• problems with rainwater disposal (Audley End, Beeston Castle).

A major problem in assessing the impacts of climate change upon cultural heritage is a lack of clear empirical evidence (2).

Vulnerabilities - World heritage sites England and Scotland

Well-known examples of UK world heritage sites that are threatened by climate change are the Neolithic monuments of the Orkney Islands off the north coast of Scotland and at Stonehenge and Avebury in southern England. These are among the most remarkable Stone Age remains anywhere in the world (14). 

Stonehenge

Stonehenge is the most architecturally sophisticated stone circle on the planet, and Avebury, at just more than 300 metres in diameter, is the largest. Of most concern for Stonehenge are increasing rainfall amounts, more extreme rainfall events and worsening floods. Flash floods can result in damage through gullying and wetter conditions are also expected to increase the impact of visitors walking on the site. Thirty kilometres away, extreme rainfall recently led to the River Kennet overflowing its banks and causing floods at both Avebury and Silbury Hill (15). Besides, warmer winters are likely to bring higher populations of burrowing mammals including badgers, moles and rabbits, which may destabilize stonework and disturb buried archaeological deposits (14).

Heart of Neolithic Orkney (Scotland)

More than 1 000 kilometres north on Mainland, the biggest of the Orkney Islands, lies a group of archaeological sites that make up the Heart of Neolithic Orkney World Heritage property, pre-dating Stonehenge by at least 200 years. Orkney was for centuries an important maritime centre for trade and cultural exchange going back to around 3000 BC (16). Because of the importance of the sea in Neolithic life in Orkney, many archaeological sites are on the coast, and at least half are under threat from coastal erosion (16).

The sites comprise 5.000-year-old Skara Brae, the best preserved Neolithic settlement in northern Europe and one of the top ten visitor attractions for Historic Scotland. The ruins of Skara Brae are the best-preserved Stone Age dwelling complex in Western Europe, complete with stone houses, stone furniture including seats and shelves, and archaeologically rich middens or waste heaps (16). Together, the monuments of the Heart of Neolithic Orkney World Heritage site offer extraordinary testament to the living conditions, material culture, and burial and ritual practices of the Stone Age farmers who arrived in Britain about 6.000 years ago. Skara Brae is the highest-profile site at risk of eventual loss from coastal erosion. A sea wall was first constructed to protect Skara Brae from erosion in 1925
and periodic improvements have been made ever since, but the coast is eroding at either end of the wall.

In Orkney, sea-level rise, the increasing frequency of storms and accelerated coastal erosion present major threats (17). Sea-level rise, increased storm frequency and intensity, and coastal erosion are major threats to coastal heritage throughout the UK. Some
17% of the UK’s coast is eroding and storm damage is expected to increase (18). Scotland has northern Europe’s longest coastline aside from Norway, and conservative estimates suggest that 12% of it is eroding. Of 11.500 archaeological and historic sites surveyed between 1996 and 2011, nearly a third were assessed as needing some sort of action or protection (17). 

Vulnerabilities - Northern Ireland

The impacts on the coastal heritage

The probable impacts of climate change on the National Trust’s three key coastal sites, the Giants’s Causeway, North East Strangford Lough and the Murlough National Nature Reserve are increased wetness, drier summers, more frequent and longer-lasting storms with associated storm surges, and as a part of the rising sea-level, higher reaching extreme flood levels. The increased erosion will cause the loss of existing foreshores, salt marshes, sand dunes and cause cliff instability and weaken existing sea defences (9).

Among the impacts, sand dune retreat can be considered one of the most worrying. Northern Ireland possesses some of the most archaeologically rich dune systems in Ireland. All these contain very important Neolithic, Bronze Age and later archaeological deposits which have been stable since their deposition but are now likely to be lost in the coming years. The effects of accelerated erosion on sites located on soft coastal edges are already dramatically apparent. ... The maritime built heritage as represented in the ports harbours and landing places face severe problems of survival and much is likely to be lost (10).

The impact on the fresh water and wetland heritage

Direct Natural Impacts . River erosion may potentially destroy or rework the built heritage, such as, in-channel structures (bridges, mill dams, fish weirs, revetments, causeways, platforms etc.) and artefacts (logboats, metalwork, fishing equipment etc.); adjacent built structures (such as lock keepers cottages, mills and settlements) will be subject to greater attrition and the archaeology of the floodplain and adjacent terraces (multi-period cropmarks, crannogs, earthworks, artefacts and buildings) including organic sediments preserved in palaeochannels and palaeo-land surfaces, will all be affected (11).

Indirect human impacts. Hard engineering solutions to climate change will destroy archaeology in-channel and will affect the setting of historic structures along the riparian corridor. Even soft engineering solutions will have to be properly managed if they are not to impact negatively on the historic environment (11).

The impact on the general built heritage

Flash flooding, intense periods of rainfall, and the spread of mould, pests and disease through milder, wetter winters pose the greatest threats to its buildings and their interior fixtures. ... Clay soils which are common in some parts of Northern Ireland can also be particularly susceptible to wetting/ drying cycles and may pose a particular area of concern in this region (11).

Vulnerabilities - Old buildings and contents

For old buildings and their preserved contents the problems are also likely to prove acute (1); it has long been understood that fluctuations in the local microclimate present the main danger to continued survival. Historic building materials are extremely permeable to the environment of air and soil; changes in moisture content can occur rapidly, and these can activate damaging cycles of salt crystallisation. Old rainwater goods may be unable to cope with changed patterns of rainfall, and acute events such as flooding have much worse and longer-term effects on historic than on modern buildings. Expensive protection and adaptation strategies may be necessary to cope with these greatly increased dangers, and these will therefore require careful planning based on a controlled assessment of risk.

Coastal loss, fluvial flooding, storminess and extreme winds and rain are the greatest threats to historic buildings and their contents from climate change. Flooding was rated by experts as the most important general issue. Experts judged extreme weather to be of great importance to the fabric of buildings, noting that in many cases downpours were already exceeding the capacity of historic rainwater goods. A more extensive list ofimportant concerns for old buildings and contents is (1):

• rainfall
• flooding and soil moisture content
• extreme weather
• temperature and relative humidity
• pests and diseases
• human comfort, health and safety
• water table chemistry
• solar radiation
• lightning
• plant physiology and distribution

Additional concerns are mentioned by others (2,4,5):

• some historic buildings were built on timber piles or rafts which are stable as long as they are kept wet. Structures such as timber framed and cob-walled buildings may behave differently under differing temperature and humidities, and their internal fittings could be vulnerable to building movement;
• increased risks of fire with dry summers;
• incidence of fungal and insect problems such as dry rot and house Longhorn beetle under a warmer climate;
• potential damage from mobilised contaminants attacking foundationsas higher ground temperatures lead to ground contaminants becoming more active;
• increased visitor pressures and increased revenue for historic buildings brought about by expansion of tourist season and increase in the number of short-break holidays predicted within a warmer climate;
• potential increased insurance costs for listed buildings and National Trust properties arising from climatic damage.

Rainfall

Of all the concerns mentioned above, the greatest concern for experts from the buildings sector is the predicted increases in heavy rainfall. Many of the historic rainwater goods are not capable of handling heavy rains, and are often difficult to access, maintain, and adjust. Although often rainwater goods have been over-designed, close monitoring is needed to ensure that they are successfully coping with the changing climate (1).

Flooding and soil moisture content

Fluvial flooding is a major problem, requiring directed repairs and upgrading to drainage. According to experts disaster plans should be reassessed and upgraded to cope with flood risks. Post-flood drying is critical, with buildings and excavated archaeology at great risk from subsidence. Experts identify ground heave and subsidence as water recedes as the major issues arising from projected changes in the water table height. Coastal flooding and storm surge are also considered as extremely worrying, at least for sites in high-risk areas (1).

Extreme weather

Ruined buildings and excavated archaeology in particular are considered to be in great danger of wind throw, indicating that more careful thought may have to be given to the stabilisation of such sites. As with extreme rainfall, it was noted that increases in high winds will rapidly reveal any problems with maintenance (1).

Temperature and relative humidity

Rising temperature is a risk for deterioration of materials and contents, since it might increase the rate of chemical reactions. According to the experts questioned by Cassar (1) the outcome of changes in relative humidity is unpredictable, and therefore requires close monitoring. Since climate change is a gradual process, it is hoped that vulnerable materials will accommodate to these changes.

Pests and diseases

Humidity and temperature have synergistic effects on pests and diseases: changes to relative humidity could result in new sorts of insect pests attacking collections. Current management regimes are probably adequate.

Human comfort, health and safety

Human comfort, health and safety issues would have implications for climate control. According to the experts questioned by Cassar (1) the introduction of intrusive climate control equipment should be resisted, preferring if possible to use passive or minimally intrusive methods.

Water table chemistry

If changes in water table chemistry result from a fall in water table height, or from seawater incursion, certain areas may see a change in the pattern of damage from rising damp. Monitoring was felt to be a necessity, especially for sites already known to suffer from rising damp problems (1).

Solar radiation

Experts consider current practices sufficient to cope with the impact of increased solar radiation on contents (rather than on the buildings themselves) (1).

Vulnerabilities - Buried archaeology

Experts expressed extreme concern about coastal loss, flooding and changes in the height of the water table. This last change was seen as more than a wetlands issue: it was pointed out that monitoring of the water table in York has shown seasonal fluctuations in the upper 2 metres, and any changes could have catastrophic results. The most important concerns for buried archaeology are (1):

• soil chemistry and moisture content
• flooding
• plant physiology and distribution
• human comfort, health and safety
• temperature
• wind
• pests and diseases

Additional concerns are mentioned by others (1,5,6):

• forest fires;
• impacts of increased tourism due to climate change upon historic sites;
• loss of pollen and other records by drying-up of archaeological sites;
• impacts of farm winter reservoir construction (a potential option for adapting to climate change) upon archaeological sites;
• the impact of changes in (agriculture) land use;
• damage to protected wrecks as a result of increased storminess;
• increased management tensions and conflicts between conservation agencies and local communities brought about by implementation of ‘managed retreat’ or ‘managed re-alignment’ of coastal and riparian margins.

Soil chemistry and moisture content

Archaeologists consider soil moisture and due chemistry a great concern due to the projected changes in equilibrium conditions which have preserved the sites until now (1).

For wetlands sites, archaeologists are expecting a very serious loss of certain data types which are only preserved in waterlogged/anaerobic/anoxic conditions. According to experts archaeology presently preserved close to the ground surface (i.e. especially in rural areas, or post-medieval archaeology in more urban situations) is likely to be destroyed before it is excavated and recorded (1).

Drying of the soil may disturb the archaeological record because the stratigraphic integrity will be lost if they crack and heave due to changes in sediment moisture. Strong changes between water levels for summers and winters will have a tremendous effect on those sites which are situated in the area of dry-wet cycles (1).

The preservation of buried deposits is favoured by water-logging. Even small changes to these conditions may reduce the survival of remains. Waterlogged, anaerobic conditions can preserve a wide range of archaeological artefacts, including those made of leather, wood and other organic materials. These artefacts are rare and important. Crucial environmental evidence is also preserved, including ancient pollen, seeds, wood, insects, bone and molluscs. The survival of these remains is linked to the chemical composition of the deposits in which they are contained. Lowering or fluctuating water levels, or pH changes, may have a significant impact on preservation (7). A move towards a more ‘Mediterranean’ climate with wetter, milder winters and drier, hotter summers would result in significant changes in preservation regimes (6).

Climate change could have a significant impact on wetland and waterlogged habitats, including raised mires, blanket bog, fens, and reed-beds, all of which are potential areas of good archaeological preservation (6).

Flooding

Many sites will be endangered by sea level rise and storm surge: 600 to 1800 good sites are vulnerable to coastal erosion. Flood protection or managed retreat plans tend to consider only scheduled ancient monuments (1).

Sites vulnerable to erosion will also be at risk from increased storminess and tidal range. Increased flood frequency and inundation of river corridors resulting from high waters in estuarine areas, and from increased precipitation leading to greater river volume, may also have a significant impact (6)

Plant physiology and distribution

Changes in vegetation cover will greatly affect the survival of buried sediments and artefacts and ecofacts. Deep root penetration is very damaging to structures and sediment boundaries. There is also the problem of dewatering by transpiration, and loss of vegetation cover through drought could also exacerbate erosion (1).

Changes in (agriculture) land use

Farmland contains the vast majority of archaeological sites and agriculture is (often inadvertently) one of the greatest causes of their destruction (Farrar and Vaze, 2000). A shift towards a more ‘Mediterranean’ climate would result in longer growing and grazing seasons, and possibly, faster growth rates. Cultivation limits and patterns would also shift, with some new areas coming under plough. Deep ploughing is particularly destructive of buried archaeological remains.

Any change in land use away from unimproved or semi-improved grassland is likely to have a deleterious impact on the historic environment. The combination of wetter winters and warmer summers would make soils more vulnerable to poaching (damage to soil structure by grazing animals and from machinery), a major source of damage to vulnerable archaeological sites. Climate predictions suggest that new areas would be amenable to colonisation by woodland, or to commercial or private plantation. Tree growth can be very damaging to both above-ground and buried sites and features, through root growth and root-pull resulting from tree-blow (1).

Pests and diseases

Additional temperature-related effects relate to biological decay. Whilst the immediate termite threat to British buildings has arisen through the accidental introduction of the subterranean termite Reticulitermes lucifugus, the northward movement of R. santonensis is occurring unaided and would adapt to warmer conditions in southern Britain quite readily. The northern penetration of the oakbeam-eating deathwatch beetle (Xestofobium rufovillosum) into Scotland may occur directly as a result of warmer conditions (5).

Vulnerabilities - Historic parks, gardens and landscapes

According to experts historic parks and gardens will inevitably suffer badly. The most important concerns for historic parks, gardens and landscapes are (1):

• wind
• temperature
• plant physiology and distribution
• pests and diseases
• rainfall
• soil moisture content
• water table height and chemistry
• fluvial flooding
• coastal flooding

Wind

Mature important specimens are particularly susceptible to wind damage: storms can quickly destroy landscape designs.

Temperature

The predicted changes in temperature may be of some advantage in protecting tender plants, but less favourable impacts will be seen on species needing frost to germinate or set seed (such as daffodils and apples).

Pests and diseases

Warmer conditions may greatly increase the risks from pests and diseases: particularly for plant collections and structural planting. Historical integrity may prove difficult to maintain for this reason alone.

Rainfall

The projected changes in rainfall patterns are likely to give rise to many changes in parks and gardens. To cope with summer droughts some form of water storage is likely to prove necessary for many sites, particularly in the East of England; but this may be challenging to install invisibly. Drainage redesigned to cope with heavy autumn and winter rain may prove even more difficult to integrate with historic parks and gardens.

Fluvial flooding

A likely outcome of heavy rain is a significant increase in fluvial flooding. This is not only directly damaging, but also of concern for erosion.

Coastal flooding

Coastal properties may also be at risk from flooding associated with sea level rise and storm surges. For these sites, the after effects of floods are exacerbated by the salinity of the flood water; all these problems are currently seen in the National Trust gardens at Westbury Court, and a number of other sites around the country such as Fountains Abbey and Alfriston.

The cost of flood protection/drainage channel diversions onto surrounding land is likely to be very high. As for buildings and archaeology, coastal loss is generally considered to be unavoidable: it is against National Trust policy to protect land from coastal erosion.

Coastal sites are under the very highest level of threat: there is no management strategy at present, and it is unrealistic to expect that development funding will be available for investigation and recording. Developers, unsurprisingly, are not willing to purchase land that is about to be eroded away by the sea. Without a developer to take responsibility for the demise of an archaeological site, there is no one to call upon presently to pay for recording prior to destruction.

Benefits and opportunities

Climate change may bring benefits and opportunities for management, understanding and promotion of the historic environment (6).

Drier summers would provide improved conditions for the discovery of buried archaeological remains through aerial reconnaissance. Dry conditions produce marks visible from the air in crops as a result of differential growth over features like buried walls and ditches where moisture content varies considerably from the surrounding soil. The efficiency of both excavation and survey work depends partly on weather, and an ameliorating climate would be a potential benefit.

Tourism relies heavily on the beauty of the Welsh landscape. Historic features are an important part of this attractiveness. If conditions for tourism in Wales improve as a result of climate change, there may be increased opportunities for the heritage sector.

On balance the opportunities for heritage management would be significantly outweighed by negative impacts.

Adaptation strategy - General

An important focus of attention should be adaptation of drainage and rainwater goods, and the discreet provision of irrigation and water storage. The latter makes sense in any circumstances, as too much water is being drawn from aquifers and groundwater sources. Opportunities should be identified to roll out and integrate these issues into existing or planned projects in buildings, archaeology, parks and gardens (1).

English Heritage’s technical advice note on ‘Flooding and Historic Buildings’ (8) provides the most up-to-date advice on adaptation measures in response to flood events.

Options for adaptation are closely related to dilemmas for the historic environment (1):

• The biggest decision will probably be over which sites to ‘let go’. There will never be the money to save everything. Decisions on the value and significance of a site may need to be made upfront before money is spent on short-term or no-real-hope projects.
• The sector should be planning for climate change and not trying to hold the cultural heritage in stasis, and this should be communicated to the public.
• If climate change means that deposits begin to deteriorate if not excavated (and thus preserved by recording), the current strategy of preserving in situ may lead to the destruction rather than the preservation of the archaeological heritage. If this is the case, then preservation by record should be favoured wherever possible.
• Increases in rainfall intensity are already causing gutters to overflow and drainage pipes to back up. Invisible or non-invasive fixes may not be possible. What aspects of heritage are we prepared to sacrifice in order to save the rest?

Adaptation strategy - Risk assessment

Floods in England in the past, like the widespread flooding of Gloucestershire and Worcestershire in 2007, have impacted upon large numbers of historic structures. Increasing concern has been voiced on risks posed by flood events to historic buildings, due to varied weather patterns (13). Preservation of cultural heritage requires greater depth of understanding of the vulnerability of historic structures to flood inundation, and associated extreme rainfall events. Flood loss estimation methods that account for the highly specialised nature of historic buildings’ vulnerability to flooding are lacking, however (12).

The first step in a novel approach to assess the vulnerability of built cultural heritage with respect to flooding includes the assessment of a series of risk indicators of the intrinsic properties that contribute to the value of the asset, and the damage phenomena observed after such natural disasters occur. With this information, the vulnerability of a heritage building can be considered appropriately in the wider scheme of urban flood risk estimation. These risk indicators are: age, listed status, use, footprint, number of storeys, materials and structure, and condition. In the future this method could be applied to other European countries as well, providing that where appropriate the parameters are adjusted to account for local conditions, and that surveyors with strong knowledge of local heritage and hazard factors are used (12).

Adaptation strategy - Historic parks, gardens and landscapes

The projected changes in rainfall patterns are likely to give rise to many changes in parks and gardens. To cope with summer droughts some form of water storage is likely to prove necessary for many sites, particularly in the East of England; but this may be challenging to install invisibly. Drainage redesigned to cope with heavy autumn and winter rain may prove even more difficult to integrate with historic parks and gardens (1).

The opportunities for a more diverse choice of plants must be offset against losses of historical integrity, and likely increases in maintenance costs. ‘English Heritage is unlikely to support reconstruction of a historic park and garden.’ Monitoring and maintenance, evaluating priorities, and encouraging education and traditional skills are greatly important for preserving parks and gardens and landscapes in the face of a changing climate (1).

Parks, gardens and historic landscapes will be faced not only with changed climates, but very possibly with shortages of water and other resources that could make maintenance increasingly troublesome. It may become difficult to propagate even endemic species (1).

Adaptation strategy - Buried archaeology

There is a need for appropriate and feasible management/conservation plans for historic sites, and for these to address nationally standardised issues. Conservation plans need to focus on deterioration mechanisms, and monitoring and maintenance (1).

Restoring wetlands would assist in reducing vulnerability of sites and artefacts to drying-out (2).

The complexity and variability of the buried environment requires the development of a series of prediction maps that draw on a wide number of interrelated variables and not on single variables such as soil type. These maps which could emerge from staged studies characterising the heritage resource, field testing the characterization and defining a management model for the site or landscape based on qualitative values and vulnerability to climate change, would be used by resource managers (landowners, statutory bodies, local authorities) to inform management or conservation plans for archaeological landscapes or sites (1).  

Adaptation strategy - Old buildings and contents 

Responding to climate change may lead to an increase in maintenance costs. For example, rainwater disposal systems on buildings may need to be redesigned and updated, whilst storms may cause costly structural damage (4). Increased frequency of building inspections and attention to repair of defects in roof coverings will be increasingly essential (1).

There is a wealth of historic sites on the coast and these sites will be subject to increased coastal flood risk, whilst inland properties may be at increased risk of fluvial flooding. Such risks will be hard to respond to, as it may not always be appropriate to defend sites, and acceptance of some losses may be necessary (4). The National Heritage Protection Plan sets out how England’s landscapes, archaeological sites and historic buildings will be protected from the impacts of climate change. This includes actions such as the continuation of ‘Rapid Coastal Zone Assessment Surveys’ that record and assess the risk to heritage assets on the coast (19).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for the United Kingdom.

1. Cassar (2005)
2. Kersey et al. (2000)
3. West and Gawith (2005)
4. Land Use Consultants, CAG Consultants and SQW Limited (2003a)
5. C-CLIF and GEMRU (2003)
6. Farrar and Vaze (2000)
7. Castledine (1990),in: Farrar and Vaze(2000)
8. www.english-heritage.org.uk/filestore/conserving/advice/flooding%20tan.pdf
9. Orford et al. (2007), in: Northern Ireland Environment Agency (2009?)
10. National Trust (2008), in: Northern Ireland Environment Agency (2009?)
11. Northern Ireland Environment Agency (2009?)
12. Stephenson and D’Ayala (2014)
13. Cassar (2005); Sabbioni et al. (2006), in: Stephenson and D’Ayala (2014)
14. Markham et al. (2016)
15. UNESCO (2014), in: Markham et al. (2016)
16. Gibson (2014), in: Markham et al. (2016)
17. Dawson (2013), in: Markham et al. (2016)
18. Masselink and Russell (2013), in: Markham et al. (2016)
19. DEFRA (2013), in: Dronkers and Stojanovic (2016)
20. Howard (2013)