Table 1 Thermogeological parameters of each location investigated in this study

Mean annual air temperature (°C)

4.51

3.38

0.89

Aalto et al., 2016

Mean annual ground temperature (°C)

6.1

5.3

3.6

Calculated from air temperatures using Eq. (1)

Rock type

Microcline granite

Granodiorite

Porphyritic granite

Digital geological map of Finland 5 M (GTK database)

Thermal conductivity of bedrock [W/(m∙K)]

3.30

3.19

3.30

Peltoniemi and Kukkonen, 1995

Radiogenic heat production (μW/m³)

2.96

1.33

2.56

Veikkolainen and Kukkonen, 2019

Geothermal heat flux (mW/m²)

44.5

44.0

42.8

See text for calculations

Geothermal gradient (K/km)

13.5

13.9

13.0

Calculated by dividing the geothermal heat flux density by the rock thermal conductivity