Jil

Fig. 120. Penetration of the linear warming trend into the subsurface. Curves are labeled by the depth level. After 10-14 years the warming at 10 m depth will achieve about 70% of the value of the surface warming (k = 10"6m2/s).

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Fig. 121. One-year temperature monitoring record at 40m depth (Kocelovice hole).

observed at Sporilov. It had grown to 0.024 K/year in 2003. These rates, lower than those observed in Sporilov station, coincide well with the lower warming trend obtained for the Kocelovice location by the GST reconstructions as well as with SAT trends presented in Figure 82 (Chapter 3). On the other hand, similarly to the Sporilov site, data from the Kocelovice borehole have shown near 40% decadal increase in the warming rate. This hints that the increase of the amount of warming may represent essential feature on the recent climate change in the Czech Republic.

Similar to the results of the GST reconstructions mentioned above, monitoring experiments have revealed spatial dependence of observed recent warming rates, when the highest warming has occurred in the industrialized regions. For further examination of this conclusion, the next monitoring experiment was established at the site Potucky, the Czech Republic (50.43°N, 12.78°E, 864m a.s.l.). The choice was also inspired by the fact that it is this area where noticeable disagreement between warming trends calculated from the GST and SAT data was detected (Figures 82 and 83, Chapter 3). The borehole Potucky is situated in the western portion of the Ore Mts. (German Erzgebirge, Czech Krusne hory) forming the natural border between North Bohemia and Germany. For the long years, the Ore Mts. area has represented one of the most industrialized regions given by the rich mineral resources, especially the lignite coalfields and connected with them the power and chemical industries. Industrial activity was accompanied by extensive discharges of man-made pollutants into the environment. Acid rain resulting from sulfur dioxide emissions has damaged forests. The problem was particularly serious in North Bohemia during the 1980s due to pollution from the large amounts of fossil fuel used by the neighboring industries and brown coal (lignite) burned by power stations in the former East Germany and southern Poland. Only after 1991, emissions were stopped by the collapse of the emitting industries and by legal reductions of emissions from power plants. However, the long-term damages in the forests, caused by the acidification of the soils, are not yet repaired. High rates of the man-made climate warming may be expected in this territory.

The Potucky boreholes are situated in the highland region that is characterized by extensive forest cover of coniferous woods and mountain meadows with abundant peat bogs. However, natural woods are spoiled very much by emissions from foothill coal basins. Now intensive work on their recovery is being performed. The suite of shallow boreholes was drilled in Potucky site during 2002, and subsurface temperature monitoring at several shallow depths from 2 cm to 50 m began in 2003. Results of the temperature measurements at 40 and 50 m depth in Potucky borehole from October 2003 to June 2004 are shown in Figure 122. Because of the relatively high thermal conductivity of the subsurface strata in Potucky site (3.2W/(mK)) in comparison with approximately 2W/(mK) characteristic for the Sporilov and Kocelovice stations, an annual temperature wave penetrates deeper into the subsurface there. This is the reason that the warming trends detected in Potucky hole at both 40 and 50 m depths do not appear as linear as in Sporilov hole and can be inferred with little bit less significance. As shown in Figure 122, the warming rate calculated for the temperatures measured at 50m depth is quite high and equals to ~0.04K/year. It is still higher at the 40m depth where detected warming trend is approximately four times larger than that observed at the same depth at forested and less industrialized southwestern slope of the Bohemian Massif (Kocelovice hole) and approximately two times larger than that measured during the same period in the industrial region of Prague (Sporilov hole). Because the characteristic time of the penetration of the surface temperature signal into the subsurface is inversely proportional to the thermal conductivity of the medium, the warming trend detected in Potucky hole likely reflects more recent events. While the Sporilov and the

Fig. 122. Temperature monitoring at the depth of 40 and 50m (borehole Potucky, the Ore Mts., Czech Republic) from October 2003 to June 2004. Solid lines represent the estimated linear trends.

Kocelovice trends can be attributed to the strong warming that began in the area after the relatively cold 1940s, trends detected in Potucky site can be connected with climatic changes of the 1970s and the 1980s.

An interpretation of the enormous warming trend detected at Potucky site does not represent an easy task because of the still short observational period but mainly because of the complexity of the processes involved in the local climate changes. The high value of detected warming hints that at least part of it may reflect an influence of the human environmental pollution. However, detailed investigation of all possible forcings reveals the possibility of more complex interdependences. The warming trend observed at Potucky hole can be compared with the long-term SAT measurements at the nearby meteorological station at Fichtelberg, Germany (Figure 123). The Fichtelberg is one of the highest mountains in the German part of the Ore Mts. (50.43°N, 12.90°E, 1213 m a.s.l.). This region is characterized by harsh, cloudy weather with significant precipitation including both wet winters and summers. Long-time annual mean temperature on the Fichtelberg is only 3.2°C. The SAT record exists here from 1891. The local climate has experienced insignificant warming with the rate of 0.0077 K/year for the total observational period from 1891 to 2003. Time interval between 1950 and 1980 was relatively cold. Strong sudden temperature rise with more than 0.05 K/year rate began here since the 1980s. The main temperature increase occurred between 1987 and 1991. It was detected over the whole Central Europe and is known as the "Climate Jump II" (in comparison with the "Climate Jump I" that occurred between approximately 1920 and 1935; see, e.g., Figure 64, Chapter 2). During "Climate Jump II" the GST in Central Europe has

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