Urban groundwater warming in Turin area (NW Italy)

This study investigated the thermal regime of shallow groundwater in the Turin area (NW Italy), where the large energy demand has driven a new interest for ground-source heat pumps (GSHPs). The strongest vertical variability of groundwater temperature is found within 10-20 m below ground surface. In spring, deeper temperatures are higher than shallow temperatures, while in autumn the trend is reversed. These variations are connected with the heating and cooling cycles of the ground surface due to seasonal air temperature oscillation, propagating into the aquifer. The areal temperature distribution shows an increase from the foothill sectors close to the Alps towards the central Po Plain, driven by the progressive warming along the flow path. In the Turin city aquifer temperatures are 0.6 ÷1.6 °C higher than rural sectors. This groundwater warming is linked to the urban heat island effect, mainly driven by the typical artificial land use. Sparse warmer outliers (16-20 °C) are in some cases connected to documented point heat sources, such as GSHP systems, industrial districts and landfills.