European Journal of Soil Science, 2017 doi: 10.1111/ejss.12489 Multi-year simulation and model calibration of soil moisture and temperature profles in till soil J. Okkonen a , P. Ala-Aho b , P. Hänninen c , M. Hayashi d , R. Sutinen e & P. Liwata e a Geological Survey of Finland, PO Box 97, Vaasantie 6, FIN-67101 Kokkola, Finland, b Water Resources and Environmental Engineering Research Group, Faculty of Technology, University of Oulu, PO Box 4300, Pentti Kaiteran katu 1, FI-90014 Oulu, Finland, c Geological Survey of Finland, PO Box 96, Betonimiehenkuja 4, FIN-02150 Espoo, Finland, d Department of Geoscience, University of Calgary, Calgary, Alberta T2N 1N4, Canada, and e Geological Survey of Finland, PO Box 77, Lähteentie 2, FIN-96101 Rovaniemi, Finland Summary In Nordic regions water infltration into soil is controlled by soil moisture content and frozen soil conditions, which are regulated by soil temperature. For long-term model predictions of the effects of climate change, models need to be tested with long-term data to assess model sensitivity to parameter uncertainties under both typical and exceptional conditions. Ten-year (2002–2011) daily soil moisture and temperature data at different depths in glacial till soils in central Finland were used to assess the sensitivity of a coupled heat and water transfer model, COUP, to model parameters. The model was most sensitive to the parameters controlling snow accumulation and melt, the thermal conductivity of frozen soil and soil water retention characteristics. Observed time series for soil temperature and moisture at different depths were matched reasonably well by model simulations, although the model performance with respect to moisture dynamics in the topsoil was relatively poor. The model was not able to simulate accurately exceptional winter conditions, such as mid-winter snowmelt events. This study showed that the main characteristics of long-term variation in soil temperature for till-derived soil in a cold climate can be resolved by a coupled water and heat transport model. Better characterization of infltration in cold climates would require measurement of water fuxes, and soil frost occurrence and penetration. Highlights • Ten-year soil temperature and moisture observations are predicted with coupled heat and water model. • Snow processes and soil thermal and water retention properties proved critical in our simulations. • Exceptional winter conditions pose a challenge in parameterization of the model. • Studies measuring water fuxes and soil frost occurrence are needed for advances in modelling. Introduction Soil moisture is one of the most important variables for understand- ing the hydrology of the vadose zone. It controls water fuxes at the land surface and affects the partitioning of rain and snowmelt water to surface runoff and infltration. Therefore, its accurate representa- tion in numerical land-surface models is important for climate and weather predictions. Soil moisture conditions in root zones provide information for assessing the risks of foods and droughts and fore- casting crop yields. In cold regions, understanding the soil mois- ture dynamics is also of practical importance because soil moisture and temperature affect the development of soil frost that controls Correspondence: J. Okkonen. Email: jarkko.okkonen@gtk.f Received 14 October 2015; revised version accepted 14 September 2017 snowmelt runoff and infltration (Kane & Stein, 1983; Bayard et al., 2005) and groundwater recharge during winter (Hayashi et al., 2003; Okkonen & Kløve, 2010, 2011). Snowmelt in spring replen- ishes both surface water and groundwater, and has a major effect on the hydrological cycle in cold environments. In addition, recent studies have shown that warm weather events during winter may increase soil water content and infltration capacity (Sutinen et al., 2007), and affect groundwater quantity and quality (Okkonen & Kløve, 2012). In cold regions, research interests are in the prediction of near-surface hydrological processes such as infltration, freeze–thaw cycles and surface runoff, and the variation in factors that affect model prediction (Wu et al., 2011; Hayashi, 2013). The factors affecting infltration are total (liquid and ice) water content, soil and ice structure, and rate and amount of snowmelt © 2017 British Society of Soil Science 1