3:00 PM - 4:00 PM
[S24-P-02] Repeated borehole temperature logs: climate or anthropogenic impact?
More than two decades of the activities of the Borehole Climate Observatory of the Institute for Geophysics in Prague clearly proved that the local urban climate gets substantially warmer by more than 2 K since 1993. A 150 m deep borehole, part of the observatory, has been repeatedly logged since then to trace the corresponding time changes in the subsurface temperature field. Transient components of the individual logs yielded by the functional space inversion (FSI) indicated a strong impact of the down penetrating (climate) warming. Its magnitude exceeded 1.3 deg.C at 20 m below the ground surface and reached 0.7 deg.C at 40 m and 0.15 deg.C at 80 m within years 1993 through 2017. The individual temperature logs were inverted into ground surface temperature (GST) histories, compared with the history yielded by a simultaneous inversion of all obtained logs. Their variations were confronted with the results of the surface air temperature monitoring as well as with the records of the nearby meteorological station. Special attention was paid to the analysis the surface temperature offset, the difference between the near surface air temperature and the “skin" surface temperature. The monitored ground surface temperature series were further used as the forcing function to model the corresponding temperature-depth distribution and the resulting time-variable geothermal models were compared with the measured data. It was proved that the observed warming must have been sizeably affected by the terrain alternations and by an effect of new building erected nearby. Some 30-40 per cent of the observed warming can be attributed to the human activities in the direct vicinity.