Changes in the long-term soil temperature regime in Karelia

In the situation of warming climate, the variation of soil temperature at the surface and at different depths is important no less than that of air temperature. Based on long-term data collected by weather stations of the Russian Hydrometeorological Service network located in Republic of Karelia, this paper presents an analysis of changes in the soil temperature regime. Changes in annual and monthly mean soil temperatures at 20, 80 and 160 cm depths, the sums of daily mean temperatures above 10 °C during the warm period at 20 cm depth, and duration of the period with soil temperatures equal to or below 10 °C at 20 cm depth were estimated for the new baseline period 1991–2020. It is demonstrated that soil temperatures have risen since the beginning of the 21st century in all months of the year nearly throughout the study area; the dates of stable soil temperature transition across 10 °C have changed, and the sums of mean daily temperatures above 10 °C in the warm period have increased.