عنوان مقاله [English]
نویسنده [English]چکیده [English]
The trend of soil temperature is regarded as an important indicator of climate change which is scarcely discussed. Hence, considering the significance of climate change and soil temperature changes related to global warming on one hand, and the role of soil temperature on the other hand, the trend of different temperature changes having soil depths of (5, 10, 20, 30, 50, and 100 centimeters) in a period of 1994-2008 was studied in Iran in this study. Non-parametric Mann-Kendall test was applied in order to clarify and determine the trend. The results indicated that by increase in soil depth, the annual soil temperature at the depth of 20 centimeters decreases with a greater slope and then declines with a milder slope. The results of annual changes in temperature in different soil depths in the given stations showed that temperatures in different soil depths and in different regions do not follow the same trend. The trend of temperature changes in different soil depths in summer and winter revealed that shallow and deep soil layers show different contradictory behaviors. Most stations under study indicate an ascending trend. Based on the results of this study, the ascending and descending order of temperatures in the shallow soil layer (5cm) cannot be expressed with any degrees of certainty, but we can certainly say that the annual and seasonal temperatures in a deep soil layer (100 cm) have followed a clear ascending trend. In order to find out whether there is a relationship between soil temperature changes and mean air temperature changes or not, the trend of monthly mean temperature changes was considered in the given stations. As it was expected, the monthly mean temperatures during the statistical period in annual and seasonal scale have had an ascending trend. The annual results showed that the soil and air temperatures do not follow the same trend in the shallow and the deep soil layers.