EFFECTS OF TOPOGRAPHY AND CLIMATIC CHANGES ON THE TEMPERATURE IN BOREHOLE GFU-1, PRAGUE

In October, 1992, a 150 m borehole was drilled on the ground of the Ge ophysical Institute, Prague, for purposes of long-term temperature obs ervations. Since the borehole is intended for a detailed study of the change during downward propagation of the ground surface temperature ( GST), an evaluation of the topographic effect and the unsteady-state c omponent is necessary. As a first step, the effect of topography was s tudied by solving the heat conduction equation in 2-D models. The GST model presumed a lapse rate of 5 mK/m, superposed on the GST dependenc e on the slope orientation, which raises the GST on the southern slope by 0.5 K and lowers it by the same amount on the northern one. As a s econd step, the model was subjected to 1 K warming of the surface 70 y r ago (which is in the range of expected changes) and the computed pro file was inverted by a 1-D algorithm to reconstruct the GST. Neglectin g the influence of topography, the reconstructed warming gives a value of 1.05 K 74 yr ago. In view of these results, the inversion of the m easured profile was made without applying the topographic correction. If a step change in the GST is presumed, a warming of 1.2 K 70 yr ago is most probable; an assumption of a linear change gives a warming of 1.1 K 120 yr ago. The meteorological data recorded at Praha-Klementinu m support the latter case.