The impact of snow cover on seasonal ground frost and freeze-thaw processes is not yet fully understood. The authors therefore examined how snow cover affects seasonal ground frost in a coastal setting in northern Sweden. Air and soil temperatures were recorded in a paired-plot experiment, both with and without snow cover, during the frost season 2012-2013. The frequency, duration, and intensity of the freeze-thaw cycles during the frost season were calculated. The results showed that the freeze-thaw frequency was 57% higher at the soil surface and the intensity 10 degrees C colder in the spring of 2013, when the ground lacked snow cover. Furthermore, the duration of the seasonal freeze-thaw cycle was 30 days longer on average in cases where there was natural snow accumulation. The correlation between air and ground surface temperatures weakened with increased snow-cover depth. The authors conclude that continued increases in air temperature and decreases in snow in coastal northern Sweden might alter freeze-thaw cycles and thus affect natural and human systems such as geomorphology, ecology, spatial planning, transport, and forestry.

Autumn-sown field crops have important agronomic advantages (e.g., reduction of soil erosion and nutrient leaching, maximizing the use of spring moisture) and have the potential to be highly productive even though adverse winter conditions can negatively affect crop viability and yield. In the face of the unpredictable weather patterns and the expected shifts in climate in the near future, there is an imperative to develop methods to quantify both the risk of winter damage and how it is affected by altered climatic conditions and crop variety. We propose a set of indices to characterize synthetically the risk of crop damage stemming from cold spells, extended periods at low temperature, frequent occurrence of freeze-thaw cycles, and prolonged snow cover. An existing model of crop hardening and dehardening is further developed to account in full for the variability of lethal threshold temperature among individual plants. This model is coupled to a simple yet realistic description of crop-sensed temperature, so that required inputs are limited to crop-specific responses to low temperature and standard meteorogical data (average daily temperature and snow depth). This framework is applied to winter wheat under the current climatic conditions for central and southern Sweden. The roles of variety-specific hardening ability, temperature, and snow are assessed separately, thus obtaining indications of the potential impacts of variety selection and future predicted changes in temperature and snow cover in the region. Variety-specific hardening ability and response to exposure to low temperature may drastically alter the extent of winter damage. The most prevalent damaging mechanism depends on the climatic regime, with crops in colder areas benefiting from extended snow cover. A tradeoff between temperature (and hence latitude) and snow emerges, with locations at intermediate latitudes subjected to the highest risk of crop damage from exposure to low temperature and frequent freeze-thaw cycles. The same locations are also characterized by the highest inter-annual variability in the extent of winter damage - a fact that has potential implications for yield reliability. (C) 2014 Elsevier B.V. All rights reserved.

Observations of active-layer thickness from nine sites with up to 29 years of gridded measurements located in the Tornetrask region, northernmost Sweden, were examined in relation to climatic trends. Mean annual air temperatures in this area have warmed and recently rose above 0 degrees C. Active layers at all sites have become thicker, at rates ranging from 0.7 to 1.3 cm per year. This trend has accelerated in the past decade, especially in the westernmost site where rates have reached 2 cm per year and permafrost has disappeared at 81 per cent of the sampling points. Increased active-layer thicknesses are correlated with increases in mean summer air temperature, thawing degree-days and, in five of the nine sites, with increases in snow depth. Copyright (C) 2008 John Wiley & Sons, Ltd.