Monitoring of air-ground temperature coupling and examples of shallow subsurface warming in Slovenia

Abstract

We have started with a long-term monitoring of the air-ground temperature coupling in three different climate provinces of Europe with the aim to explore the assumption on a long-term tracking of the mean annual surface air temperature and the ground surface temperature. Under the frame of a joint project the borehole climate stations have been established in three countries and the monitoring launched in Prague (Czech Republic) in 2002, near Kostanjevica (Slovenia) in November 2003, and near Evora (Portugal) in May 2005. The monitoring is vital for the climatic interpretation of the ground surface temperature history that is obtained from present-day temperature-depth profiles that are measured in deep boreholes. With temperature measurements every 30 minutes in the air, in the soil and in the bedrock down to 40 m depth we are able to observe a propagation of surface soil temperature changes into depth. Gathered data on the differences between mean air and soil temperatures and its inter-annual variability from the Slovene station are presented. The 2 year and 10 months long monitoring has given so far a rough estimation of the difference between mean annual soil and air temperatures to be around 1 °C. We present also examples of non-conductive features in the temperature time series both in the soil and in bedrock. Another method of checking the air-ground temperature coupling is based upon repeated temperature measurements in the boreholes. The present rate of surface warming is large enough, and therefore, allows a reliable detection of the underground temperature-time changes in the temperature-depth profiles that are acquired by repeated temperature logging with a time span of several years. We present the results of these repeated measurements in some chosen boreholes in Slovenia with the time span of measurements between 8 and 20 years.