THE MAINTENANCE OF THE SURFACES OF THE BUILT HERITAGE IN RELATION TO THE CLIMATE CHANGES IN THE VENETIAN AREA

The present contribution deals with the definition of the size/extent of major decay phenomena in the Venetian architectural surfaces caused by the impact of the local environment and its variation due to the effects of the climate changes occurred in the last years. Decay patterns observed on historical buildings and data related to the surrounding environment have been taken into account for evaluating the impact of climate changes on the built Cultural Heritage of Venice. This contribution aims to animate a network of Cultural Heritage stakeholders devoted to promote an effective and sustainable preservation policy. 1. Introduction The surfaces of built Cultural Heritage of Venice have been exposed in the last century to a particularly aggressive environment, not only related to the presence of brackish water and marine aerosol, but also due to the atmospheric pollution produced by the local industries and the extensive use of fossil-oils [1]. In recent years a better air quality has been assessed, however frequent and intense high tides and meteoric precipitations, enhanced by climate changes, and the lack of preservation and maintenance of the natural defences (e.g. barrier islands and coastal wetlands) make Venice Lagoon and its coasts progressively more vulnerable [1-4].. The impact of the climate changes on the historic architectonic surfaces in Venice is therefore of crucial importance for the development of a sustainable preservation plan for the Venetian Cultural Heritage. General models and data which relate climate changes and construction materials are available [5], but specific studies for more complex systems, such as historical centres, are still absent. Furthermore, the quantitative relationship between pollutant concentrations, meteorological variables and stone degradation is still difficult to clear out [6]. 2. Discussion: Effects of climate change on architectural surfaces in Venice Climate changes have exacerbated the well-known degradation factors present and intrinsic in the Venetian environment (e.g. the capillary rise of salt solution, the marine aerosol, etc.) and others related to the human overexploitation of the lagoon resources [6, 7]. The decay due to sulphatation, nitration and oxidation is expected to be reduced, thanks to the decrease of the associated pollutants [4], but erosion and washout processes - in particular for carbonatic materials - will continue and most probably increase due to the raise of CO 2 and acidic precipitations [1, 3, 5, 8]. In addition to air pollution, marine aerosol, often wrongly considered as a mere co-factor, is another important degradation factor since it induces surface roughness and crust formation [8]. The nowadays frequency and height of the tides are mainly responsible for enhancing the erosion effects due to water waves and rising damp within the buildings [1]. An emblematic situation is the SOCIETÀ CHIMICA ITALIANA Divisione di Chimica dell’Ambiente e dei Beni Culturali 11 narthex of St. Mark’s Basilica, flooded by tides ≥ +80cm SLM, which increased from an average of 43 times/year in 1983-1993 to 118 times/year in 2004-2014 [9]. 3. Final considerations For better understanding the peculiar situation in Venice in relation to the future climate changes, the integration and implementation of existing database are necessary. In this prospect, the selection of case studies and their monitoring over time should be promoted, together with an accurate research and standardization of old and ancient archive data, often not taken into consideration as not published or promoted by local stakeholders. This contribution will show some of the collected literature data and underline the difficulty of working with old and often not scientifically organised data. References [1] “Flooding and environmental challenges for Venice and its lagoon: state of knowledge", C.A., Fletcher, T. Spencer editors, Cambridge University Press, Cambridge, 2005. [2] G. Seminara, S. Lanzoni, G. Cecconi: “Coastal wetland at risk: learning from Venice and New Orleans”, Ecohydrol. Hydrobiol., 11, 3-4, 183-202, 2011. [3] A. Barbi, M. Monai, R. Racca, A.M. Rossa: “Recurring features of extreme autumnal rainfall events on the Veneto coastal area”, NHESS, 12, 2463–2477, 2012. [4] A.R.P.A.V.: ”Qualità dell'Aria Provincia di Venezia - Relazione Annuale 2012”, L. Vianello, S. Pistollato editors, Venezia, 2013 [5] A. Bonazza, P. Messina, C. Sabbioni, C.M., Grossi, P. Brimblecombe: “Mapping the impact of climate change on surface recession of carbonate buildings in Europe”, Sci. Total. Environ., 407, 2039-2050, 2009. [6] G. Biscontin, V. Fassina, E. Zendri: “Il comportamento dei materiali lapidei a Venezia in relazione all'ambiente”, in F. Zezza “La Conservazione dei monumenti nel bacino del Mediterraneo: influenza dell'ambiente costiero e dello spray marino sulla pietra calcarea e sul marmo”, 195-201, Editore Grafo, Brescia, 1990. [7] E. De Zordi: “Studio della morfologia e della composizione dei depositi su superfici lapidee in area portuale ed aeroportuale a Venezia”, Master Thesis in Scienze chimiche per la conservazione ed il restauro, Ca’ Foscari University, Venice, 2012. [8] P. Maravelaki, G. Biscontin: “Origin, characteristics and morphology of weathering crusts on Istria Stone in Venice”, Atmos. Environ., 33, 1699-1709, 1999. [9] Centro previsioni e segnalazioni maree (2014), Historic Archive of tides in Venice available at: http://www.comune.venezia.it/flex/cm/pages/ServeBLOB.php/L/IT/IDPagina/25419