Cristina Sabbioni

Cultural heritage is widely recognized to be at risk due to the impact of climate change and associated hazards, such as events of heavy rain, flooding, and drought. User-driven solutions are urgently required for sustainable management and protection of monumental complexes and related collections exposed to changes of extreme climate. With this purpose, maps of risk-prone areas in Europe and in the Mediterranean Basin have been produced by an accurate selection and analysis of climate variables (daily minimum and maximum temperature—Tn and Tx, daily cumulated precipitation—RR) and climate-extreme indices (R20mm, R95pTOT, Rx5 day, CCD, Tx90p) defined by Expert Team on Climate Change Detection Indices (ETCCDI). Maps are available to users via an interactive Web GIS (Geographic Information System) tool, which provides evaluations based on historical observations (high-resolution gridded data set of daily climate over Europe—E-OBS, 25 km) and climate projections (regional climate models—RCM, ~12 km) for the near and far future, under Representative Concentration Pathways (RCP) 4.5 and 8.5 scenarios. The tool aims to support public authorities and private organizations in the decision making process to safeguard at-risk cultural heritage. In this paper, maps of risk-prone areas of heavy rain in Central Europe (by using R20mm index) are presented and discussed as example of the outputs achievable by using the Web GIS tool. The results show that major future variations are always foreseen for the 30-year period 2071–2100 under the pessimistic scenario (RCP 8.5). In general, the coastal area of the Adriatic Sea, the Northern Italy, and the Alps are foreseen to experience the highest variations in Central Europe.

Calcium oxalate patinas have been sampled on architectural elements of two ancient churches located on Torcello Island (Venetian Lagoon) and subsequently analyzed. The site had been selected presenting patinas of exceptional amount and thickness, elsewhere generally found as thin alteration layers covering stone surfaces or within black crusts on monuments in urban environments. Optical and mineralogical analyses suggest that these patinas are not the result of a simple deposition process, but originate as surface “transformations” of the substrate, and are mainly composed of dihydrate calcium oxalate (weddellite) and gypsum. Among the experimental techniques, isotope analyses (C and S) have been specifically carried out aiming at achieving a better understanding of their origin and possible causes of formation. The observed carbon isotopic fingerprint reveals in fact a strong biological fractionation recorded in the oxalate patina (δ¹³C ranging from −22.3‰ to −28.0‰), almost exclusively attributable to C3 pathway photosynthesis processes. Slightly negative sulfur isotope ratio values seem to be inversely correlated with patina exposure to atmospheric agents and pollutants. The results obtained prove that calcium oxalate originates from a biomineralization process induced by lichen colonization in specific environmental conditions.

Black crusts are recognized to have been, up to now, one of the major deterioration forms affecting the built heritage in urban areas. Their formation is demonstrated to occur mainly on carbonate building materials, whose interaction with an SO₂-loaded atmosphere leads to the transformation of calcium carbonate (calcite) into calcium sulfate dihydrate (gypsum) which, together with embedded carbonaceous particles, consequently forms the black crusts on the stone surface. An analytical study was carried out on black crust samples collected from limestone monumental buildings and churches belonging to the European built Heritage, i.e., the Corner Palace in Venice (Italy), the Cathedral of St. Rombouts in Mechelen (Belgium), and the Church of St. Eustache in Paris (France). For a complete characterization of the black crusts, an approach integrating different and complementary techniques was used, including laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), Fourier transform infrared spectroscopy, optical and scanning electron microscopy. In particular, the application of LA-ICP-MS permitted to obtain a complete geochemical characterization in terms of trace elements of the black crusts from the inner parts to the external layers contributing to the identification of the major combustion sources responsible for the deterioration over time of the monuments under study. In addition, the obtained results revealed a relation between the height of sampling and the concentration of heavy metals and proved that the crust composition can be a marker to evaluate the variation of the fuels used over time.