Effects of winter weather conditions on soil freezing in southern Michigan

We examined climatic and (modelled) soil-temperature data from five winters in southern Michigan to ascertain the spatial variability in soil-freezing and freeze-thaw cycles at 5 cm. The five winters chosen for study (1951-1952, 1952-1953, 1953-1954, 1976-1977, and 1979-1980) represent the extremes of weather (e.g., cold and snowy, warm and dry) for the 1951-1980 period. We chose this study area because it lies on an ecotone between the cold, snowy climates of southern Canada and the warmer climates of the Ohio Valley where persistent snowpacks are rare, and because virtually no data on soil freezing exist for this area. Soil freezing in winter in southern Michigan is more dependent on snowpack persistence and thickness, especially in mid-winter, than on air temperatures. Here, even in warm winters, soils freeze to 5 cm, provided that snowpacks are thin or absent. Conversely, in even the coldest winters, soils rarely freeze where deep snows accumulate. Thus, freezing is least frequent, and in some years nonexistent, in the lake-effect snowbelt region, where deep, reliable snowpacks insulate the soil. Conversely, soil-freezing and freeze-thaw activity are most common in dry winters, almost regardless of temperature. On average, less than two freeze-thaw cycles a year can be expected in the snowbelt region; 3 to 5 cycles a year are typical in eastern and southeastern southern Michigan. Soil freezing is likely to increase in Michigan's lower peninsula, under a doubled-CO2 climate that is warmer and drier.