engleski

Mean and Extreme Soil Temperature under Climate Change

The mean, maximum and minimum soil temperatures have been analyzed, at different depths 2, 5, 10, 20, 30, 50 and 100 cm, for selected meteorological stations in Croatia. The main goals were to study the impact of climate change on soil temperature by depth and identify vulnerable areas due to the high and low soil temperature. At most stations mean annual soil temperatures have 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 at the 0.05 significance level. A significant increase in soil temperature is observed, at the depth of 2 cm in particular, at all meteorological stations in the period 1961–2010. 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 (0.3–0.6 °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 because the surface layers are heated more quickly during the day and in the summer, and cooled more quickly during the night and in the winter. In the period 1961-2010 for almost all stations in all seasons and depths there are positive trends of maximum soil temperature. Annual trends of maximum values at 2 cm of depth are 2–4°C/decade and generally decrease with depth. However, there are not so many significant annual and seasonal trends of minimum soil temperature. Annual trends of minimum values are -0.5–0.3°C/decade in related to depth. Analysis of consecutive days with daily maximum soil temperatures above 35°C shows the longest extremely warm periods in the southern part of Croatia (Dubrovnik area). Soil temperatures above 45°C in the surface layer with duration above10 days appeared only in Dubrovnik in the period 1961–1990. Since 2000 year such warm period has began to occur along the Adriatic coast and islands, and in the eastern Croatia. Vulnerability of the warm/cold soil temperature in agriculture is defined by warm/cold period longer than 10 days which appeared in the six years out of the observed 30 years. Thus, the likelihood of the occurrence is above 20%. A soil temperature above 35°C for depth of 2 cm affected the entire Croatia according to available data of soil temperature. Vulnerability to heat stress is greater on the Adriatic coast and islands than in the Croatian inland up to 10 cm of depth. With increasing the critical soil temperature and the depth, the size of vulnerable areas decreases. The greatest vulnerability to cold stress (> 10 consecutive days with minimum soil temperature < 0°C) shows the stations in the mountainous and north-western Croatia in the surface layer. Freezing depth occurs between October and April, and absolute maximum freezing depth is 50 cm. Slight decrease in freezing depth is observed in the last 50 years. Thus, this analysis indicates the significant increase in soil temperature, particularly in maximum soil temperature, and increase in affected areas due to heat stress in the previous three decades.

heat and cold stress ; vulnerability of extreme soil temperatures ; linear trend

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