Nuevas tecnologías geoespaciales aplicadas a la gestión de riesgos en entornos patrimonialesLa preservación de fortificaciones de tapia mediante teledetección, índices de vulnerabilidad y sistemas de información geográfica

Resumen

Abstract The conservation of earthen heritage poses many challenges. Today, the effects of anthropogenic climate change and its impact on natural environments and traditional sociodemographic models increase the levels of risk that affect the conservation of this type of heritage site. In this context, having tools that enable efficient risk management is a priority to provide a rapid response and to ensure the preservation of these unique resources. The hypothesis of this Doctoral Thesis is t he adaptation and improvement of traditional risk assessment models through recording climate and anthropogenic changes since that can help to more efficiently manage available resources and minimise damage to this type of heritage. Based on this hypothesis, the main objective is to develop a comprehensive and dynamic model that assesses the risk that affects rammed earth fortifications by exploring the possibilities that new geospatial analysis techniques offer to this line of research. The new comprehensive model developed in this research considers risk assessment as the result of 26 hazard and vulnerability factors that operate together. The threats are divided into 3 categories: meteorological, hydrological-geophysical and social; and vulnerability into 4 categories: conservation status, construction characteristics, use and surroundings. Meteorological and climatic threats have been assessed by implementing a workflow on Google Earth Engine (GEE) to statistically analyse large volumes of satellite imagery. The proposed method is based on the use of functions, statistical reducers, indices and map algebra. Its use has made possible to analyse the reliability of estimated satellite products, selecting those that exhibit better precision and accuracy. The design model has used the CHIRPS and PERSIANN climate reanalyses and the GSMAP, MODIS and LANDSAT satellite resources. The use thereof has been validated through the mapping of the climatic and meteorological threats that affect the conservation of rammed earth fortifications in the region of Andalusia (Spain). The geophysical and hydrological hazards have been modelled based on the mapping proposed in the Art-Risk 1 model (Ortiz et al., 2014; Moreno et al., 2022a); in the case of social hazards were analysed using an adaptation of the Art-Risk 3 model indicators (Prieto et al., 2020) and the use of images from historical flights and on-site inspection. Vulnerability has been assessed and mapped adapting Leopold matrix model and Art-Risk 1 simple and expanded vulnerability indices (Ortiz, 2014; Ortiz & Ortiz, 2016). The vulnerability associated with the composition of the rammed earth has been analysed through mineral characterisation by X-Ray Diffraction (XRD) in powder and oriented aggregates to identify the clays present in the fine fraction of the historical rammed earth walls. The use of multi-risk analysis techniques, Geographic Information Systems (GIS) and multi-criteria techniques such as the Analytical Hierarchy Process (AHP) has made it possible to assess and structure the joint evaluation of the 26 risk factors based on the perception and judgement of an interdisciplinary group of 14 experts. The main result of this Doctoral Thesis is the development of a workflow that enables the massive use of satellite time-series imagery and vulnerability indices to rank and map the exposure of rammed earth wall fortifications to risk. Among its advantages are that information can be updated rapidly and the ability to monitor changes occurred over large territories in climatic periods of more than 30 years. In order to obtain validation, this model has been applied to 31 Andalusian municipalities that preserve the remains of rammed earth fortifications. In total, 1405 rammed earth ramparts and wall towers belonging to 57 historical fortifications have been analysed. The results obtained have enabled: 1) the mapping of the meteorological, geophysical, hydrological, and social threats that rammed earth fortifications are exposed to within the Andalusian territory; and 2) the classification of the fortifications according to their vulnerability and level of exposure to hazards and risk with the aim of facilitating decision-making regarding their conservation. The assessment of threats through mapping reveals that the main hazard factors in Andalusia are drought and extreme precipitation. An elevated seismic threat has been recorded for rammed earth fortifications located in the provinces of Granada and Almería. In addition, there has been a general trend towards higher average and maximum temperatures during summer and autumn, as well as a prolongation of droughts and an increase in vegetation density in semi-natural areas. Using the tools developed to assess the vulnerability of rammed earth fortifications in Andalusia, it was obtained a ranking list of the vulnerability exhibited by the 57 fortifications analysed. In general terms, it has been recorded low to moderate vulnerability values related to the good state of conservation of the rammed earth and the existence of stone reinforcements within the walls. Highly vulnerable fortifications are those that are in a poor state of conservation, have lost their coverings, and that are exposed to moisture seeping inside the walls, which causes the development of pathologies and decreases their durability. In the restored areas, the onset of spalling and sandblasting is related to deficient bonds between the original core of the walls and the mortars used in their restoration. The results obtained by XRD show that the earthen walls with a lower proportion of phyllosilicates and calcite tend to exhibit spalling more frequently. The state of each of the analysed fortifications is visible thanks to the risk mapping and this makes it possible to prioritise the urgency of restoration from a spatial risk management perspective. In this way, the proposed comprehensive risk model makes it possible to include a standardised risk approach in the diagnosis of rammed earth fortifications in accordance with the European Standard EN 16096:2012 and the National Defensive Architecture Plan. In summary, the research of this Doctoral Thesis offers a method that can be replicated in other locations in order to model the level of risk. This method is based on the analysis of reliable satellite data andthe assessment of vulnerability factors through the use of indices to provide early warning for rammed earth fortifications exposed to high levels of risk.