Effect of climate change on soil temperature and snow dynamics in Swedish boreal forests

Abstract: This thesis has investigated the possibility of improved soil temperature modeling using an updated version of an existing soil temperature model frequently used in catchment scale biogeochemical modeling. Future (2061-2090) snow dynamics and soil temperature was projected using ensemble of bias-corrected regional climate models (RCM). Effects over a north-south gradient of Sweden were analyzed using the four Swedish Integrated Monitoring (IM) catchments as study sites. Model calibration was applied on the study sites using daily observations of soil temperature for 1996-2008. The calibrated models were able to simulate soil temperature at different depths in the soil profile in a very accurate way in all IM sites. The lowest validation NS-value (objective criterion used for measuring goodness of fit) recorded in the study was 0.93. Even though the overall model performances were good, the simulations had problem of duplicating some of the winter temperatures at the northernmost site, Gammtratten. Whether the updated soil temperature model offered an improvement of the existing model is therefore debatable. The future simulations showed increasing soil temperatures at all study sites on annual basis, more in the south than in the north. Annual soil temperatures were projected to increase by 1.31 – 2.33 °C for the different study sites. Winter soil temperatures were clearly higher than during 1996-2008 for the two southernmost sites, whilst Gammtratten in the north, had colder winter soil temperatures. At the midmost catchment, winter soil temperatures were quite similar to that of the test period. Whether the cold winter soil temperatures at Gammtratten were a result of snow loss was ambiguous. The results from the future simulations showed the complexity of predicting soil temperature and strengthened the conclusion among scientists that any general assumptions of future soil temperature based on e.g. air temperature cannot be done.