# Towards a Digital Twin Prototype of Alpine Glaciers: Proposal for a Possible Theoretical Framework
## 3 DT Theoretical Framework
### Enabling Different DT Outputs  
Within the theoretical framework of the proposed DT, the approach is certainly to be thought of as a scalable one; the DT of the single glacier (local) must somehow represent the element of a more comprehensive compartmental system (e.g., the entire Alpine sector) where local and regional conditions continuously interact, one determining the evolution of the other (Figure 6). For this reason, data collected by inventories should be harmonized, re-organized and processed using the orographic setting of the Alps (International Standardized Mountain Subdivision of the Alps, ISMA-SOIUSA, [78]) rather than local and regional administrative boundaries (regions and provinces). ISMA-SOIUSA refers to all the Alps by defining mountain ranges, sections and groups. As illustrated in Figure 6, in the proposed DT theoretical framework, the integration of digital replicas at the single (local) glacier level leads to obtaining a DT at regional scale, e.g., a DT of Eastern Alps, a DT of Western Alps, and so on. A further integration of the \"regional\" digital replicas of glacier systems is then expected to move the DT to an upper level corresponding to the Italian Alps Digital Twin. The possibility of having this type of DT enables a set of applications related to the two main aspects of glacier monitoring at the Italian level: spatial dynamics and health status. Applications can refer to different user's profiles, thus enabling different DT environments to generate the expected outputs. These \"environments\" are different in terms of the type of requirements from users and the type of outputs generated by DT. Three main DTenvironment types can be defined, starting from the best performing and scientifically based one: (i) Glacier Evolution Modelling (GEM), (ii) 4D Multi Glacier and (iii) Virtual Reality. All of them can be accessed at both single- or multi-glacier level. Glacier Evolution Modelling (GEM) is the most advanced and scientific approach for studying the behaviour of a single glacier or a system of glaciers. As previously mentioned, GEM relies on a computer-based simulation environment able to describe glacier behaviour under different past, present and forecasted climatic conditions. It can be therefore used to explore how glaciers could change and evolve over time, enabling predictions of, for example, their response to ongoing variations of thermal and pluviometric regimes. At the state of the art [81; 82], GEM is mainly devoted to simulating glacier balance and predicting its future evolution taking into account a combination of satellite, ground-based and climate data. Outputs of GEM are expected to describe the effects of glacier retreat on water resources, including changes in water stream, water availability and quality, with the aim of properly addressing future policies for water management. This involves a systemic approach to modelling, where all glaciers belonging to the same hydrological system, and jointly participate in the simulation, mutually interacting. The 4D Multi Glacier approach, conversely, can provide simulations of a single glacier or of a system of glaciers in a four-dimensional space that includes three spatial dimensions (x,y,z) and time. This approach [81] can provide detailed and accurate representations of glacier systems over time by integrating real-time data from various sources, such as satellite imagery, ground sensors and climate models. It entirely relies on recorded data, with no capability of entering simulated climatic data and generating future scenarios. The Virtual Reality (VR) approach is relatively new and represent the answer to dissemination instances. It is mostly thought to improve the geo-touristic experience by giving a more effective interpretation of environmental geographic features. VR can provide an interactive experience that engages visitors and helps them to understand geological and environmental processes by combining virtual elements with a live view of a place [82].