Heritage hydrology: a conceptual framework for understanding water fluxes and storage in built and rock-hewn heritage

Abstract

Water plays a vital role in the deterioration and conservation of built and rock-hewn heritage and it is generally agreed that climate change is significantly changing the environmental controls on stone decay. We here introduce the framework of heritage hydrology as a holistic way of conceptualising the flows and stores, processes and impacts of water interacting with building materials. We distinguish the basic types of stone-built buildings, ruins and free-standing walls, and rock-hewn sites. Analogous to catchment hydrology, heritage hydrology can be subdivided into water fluxes and water reservoirs, further subdivided into inputs (e.g. wind-driven rain, capillary rise), throughputs (e.g. runoff down façade), storages (moisture content) and outputs (evaporation and runoff). Spatial patterns of moisture are different between buildings and rock-hewn sites, both presenting hydrological complexities. The interaction between mean and short-term precipitation, wind, radiation and resulting evaporation may lead to very different impacts at different heritage sites. We here differentiate between the detail scale, the façade scale and the building or site scale. Patterns at different sites can be very variable on different scales due to the multitude of influencing parameters and it is not clear which scale of moisture variations is actually relevant for decay processes. Temporal patterns are equally scale-dependent and include short-term fluctuations in temperature and rainfall, high-magnitude episodic events such as floods and storms, and longer-term changes as a result of seasonality, interannual variability and secular trends or climate change. Based on the outlined framework we advocate a research agenda for heritage hydrology in the future. This should focus on (1) finding the best combinations of methods to measure and model spatio-temporal patterns in moisture; (2) researching the major factors controlling spatio-temporal patterns in moisture; (3) figuring out which spatio-temporal patterns are most important for driving deterioration and how their respective scales interact.