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Modeling Soil Temperatures and the Mesic-Frigid Boundary in the Central Great Lakes Region, 1951–2000

^a Dep. of Geography, Michigan State Univ., 128 Geography Bldg., East Lansing, MI 48824-1117
^b Moscow Service Center, 220 East 5th St., Moscow, ID83843-2977
^c Dep. of Plant Pathology, 205 Buckhout Lab. Universtiy Park, PA 16802

View larger version (45K): [in a new window]   Fig. 1. Locations of data stations (three types) used in this study. 1. Stations where soil temperatures were recorded twice monthly from 1990 to 1994 (stars). Data from these stations were initially used to develop the soil temperature model. 2. Stations where soil temperatures were recorded 12 times daily 1997 to 2000 (22401 observations total) (triangles). Data from these stations (open squares) were used to determine the accuracy of the soil temperature model. 3. National Weather Service stations in Wisconsin and Michigan used as inputs for air temperature and precipitation (dots). The best estimate of the mesic-frigid (M-F) line in the central Great Lakes region, as determined by our study, is indicated.

View larger version (57K): [in a new window]   Fig. 2. Various estimates of the location of the mesic-frigid (M-F) boundary in Wisconsin and Michigan. A. Based on a USDA-NRCS map of the soil temperature regimes of the United States (USDA National Cartography and Geographic Information Systems Center 1993). B. Based on interpretations of the MLRA map of the USDA-NRCS, on-line at http://www.essc.psu.edu/soil_info/soil_lrr/. The dotted line in Wisconsin cuts across the center of a MLRA that is being mapped with both mesic and frigid soils. The dotted line in Michigan shows where, based on current soil mapping operations, the M-F line is assumed to exist by NRCS personnel; this line is not shown on published NRCS maps, which are, in turn, probably based on Agricultural Handbook 296 (USDA-SCS 1981). C. Mean location of the M-F line, on a digital elevation model (DEM) base, based on model output, using climatic data for the period 1951–2000 (see Fig. 3 for details). DEM class interval = 50 m. D. Traditionally, mean annual soil temperature (MAST) is often assumed to be equal to mean annual air temperature (MAAT) + 1°C. This map shows the location of the 8°C [MAAT plus 1°C] line, as well as the locations of our 218 NWS stations.

View larger version (60K): [in a new window]   Fig. 3. Variation in mean annual soil temperatures across the central Great Lakes region, based on model output, using climatic data for the period 1951–2000; climatic data stations used in the analysis are indicated by small circles. The shaded choropleth map indicates the number of years in which the modeled mean annual soil temperature (MAST) was < 8°C for the period 1951–2000. The line shown is the best estimate of the mesic-frigid (M-F) boundary, based on 50% of the years being greater than 8°C.

View larger version (58K): [in a new window]   Fig. 4. Maps of variation in soil mean temperatures spatially and temporally, across the study area. A. Mean wintertime (November–April) soil temperatures (C) at 50-cm depth. B. Mean summertime (May-Oct) soil temperatures (C) at 50-cm depth. C. Mean date of coldest soil temperature at 50-cm depth. D. Mean date of warmest soil temperature at 50-cm depth.

View larger version (43K): [in a new window]   Fig. 5. Maps of the variability in soil temperatures across the study area. A. Coefficient of variation in soil temperatures at 50-cm depth. B. Mean annual range in soil temperatures at 50-cm depth.