Vanishing winters in Germany: soil frost dynamics and snow cover trends, and ecological implications

Current climate models are effective at projecting trends in mean winter temperature; however, other ecologically relevant parameters-such as snow cover and soil frost dynamics-are less well investigated. Changes in these parameters are expected to have strong ecological implications, especially in the temperate zone, where it is uncertain whether snow and soil frost will occur with regularity in the future. We explored trends in days with snow on the ground (snowdays), minimum soil temperature (MST), and number of soil freeze/thaw cycles (FTCs, i.e. changes in sign from negative to positive in any pair of consecutive soil temperature records at 5 cm depth) at 177 German weather stations for 1950-2000. Future trends were explored by statistical modelling based on climatic and topographic predictors. Snowdays decreased uniformly at a rate of 0.5 d yr(-1) in the recent past. This trend is projected to continue to a point where significant parts of Germany will no longer regularly experience snow cover. MST has increased, and is projected to do so in the future, mainly in southern Germany. FTCs have been decreasing uniformly in the recent past. No evidence for increased FTCs or decreased MST with decreasing insulation due to missing snow cover was found. FTCs are projected to decrease disproportionately in northeastern Germany, where past frequencies were higher. Ecological implications of the significant decrease in the occurrence and magnitude of the climate parameters studied include changes in nutrient cycling, productivity and survival of organisms over wintering at the soil surface. Ecological research is needed, as the effects of diminished winters on ecosystems are not well understood.