ABSTRACT:
Classic meteorological instruments for measuring soil temperature are mercury geothermometers. They are placed in the ground at prearranged depths (2, 5, 10, 20, 30, 50 and 100 cm), so that each station has standardized measurements. In this paper the annual and seasonal mean soil temperatures have been analyzed, at different depths for selected meteorological stations: Osijek, Vinkovci, Križevci, Zagreb-Maksimir, Ogulin, Gospić, Poreč, Rijeka, Rab, Knin and Dubrovnik, for which a long-term data series in the period 19612009 is available. The main aim of the paper is to study the impact of climate change on soil temperature by depth. A comparison of mean annual soil temperature between a more recent period 19812009 and the standard climate period 19611990 shows that at most stations soil temperature has increased by approximately 1°C at all depths in the last three decades. The analysis of the linear trend and the Mann-Kendall test confirm the existence of a significant positive trend of mean annual soil temperature. A significant increase in soil temperature is observed, at the depth of 2 cm in particular, at all meteorological stations in the period 19612009. In shallower soil layers, up to a depth of 10 cm, the positive trend is between 0.2 and 0.7°C/decade. In deeper layers, up to 100 cm, the trend is slightly less pronounced (0.30.6 °C/decade). Seasonal trends show the greatest contributor to the increase in mean annual soil temperature is their increase in the spring and summer. A more significant trend of temperature increase is in the upper layers. The shallower soil layers are heated more quickly during the day and cooled more quickly during the night, due to low heat conductivity. The surface layers are heated more quickly in the summer, and cooled more quickly in the winter over the period of a year. Due to low heat conductivity, the deeper layers are cooler during the summer and warmer during the winter than the surface layers.
