Investigating the impact of different ground sealing types upon shallow subsurface temperatures

The monitoring of soil and groundwater temperatures is usually performed to estimate the environmental and economical sustainability of large scale shallow geothermal installations. The difference between the measured up- and downstream temperatures is mostly attributed to the impact of the shallow geothermal usage. However, especially in densely settled urban areas there are multiple other potential impacts on the subsurface temperature regime. The individual drivers are hard to distinguish and therefore mostly not considered when temperature monitoring data is evaluated.

In the presented study empirical temperature data in varying depths up to three meters has been collected below typical kinds of ground sealing in the urban environment, such as tarmac, different types of gravel and lawn. For that purpose, test sites have been installed artificially at a similar time and location. After a measurement period of 18 months, first results reveal clear effects on the very surface near underground temperatures. In a depth of 5 cm, measured temperatures show differences up to 8 K between different types of ground sealing. Depending on the degree and type of the ground sealing, temperature differences are measurable up to a depth of one meter.

The obtained data advance knowledge to quantify the impacts of different ground sealing types on underground and groundwater temperatures in urban areas. Furthermore, it contributes to a more reliable assessment of temperature monitoring data in the context of shallow geothermal applications as the effect of ground sealing on measured temperatures may be considered.