Key points are not available for this paper at this time.
• Ground temperature is not constant due to groundwater flow. • Horizontal temperature gradients are less relevant than vertical ones. • Time evolution of geothermal heat flux in deep layers shows changes in direction. • Constant heat flux at the bottom of domain is appropriate for modelling BHE field. The actual thermal field of the ground is important for the design of systems that exchange thermal energy with the ground. This paper presents a characterisation of the thermal field and basal geothermal flow within the Sabatini volcanic succession, translating these into boundary conditions, and implementing site-specific monitoring with implications for the broader area. Geothermal flow is evaluated using direct temperature data from a one-year in situ monitoring, rather than relying on indirect or model-based estimates, thus addressing a gap in the literature for shallow volcanic geothermal systems. Heat conduction in the lithostratigraphic successions area is investigated through a Distributed Temperature Sensing system installed in five boreholes of varying depths. Vertical and horizontal thermal gradients are calculated to explore the spatial distribution of ground temperature and the relative contributions of conductive and advective transport. Even though seasonal fluctuations impact only surface layers, deeper layers exhibit a non-uniform temperature field due to lithological heterogeneity and groundwater flow. The geothermal heat flow is predominantly upward-directed, up to 55 m depth, while upper layers show downward or null values, suggesting a dominant influence of groundwater and surface conditions. These findings demonstrate that assuming isothermal lower boundaries is inaccurate in volcanic lithologies and support the use of dynamic, data-driven boundary conditions in geothermal system modelling.
Colacino et al. (Wed,) studied this question.