Because of local variations, available records can give, at best, only a general indication of the range of ground temperatures to be expected at a site. Engineers and architects who require more detailed information are thus forced to make estimates based on an understanding of the many variables that affect ground temperature. Large-scale regional differences in ground temperature are determined primarily by meteorological variables such as solar radiation, air temperature and precipitation. Micro or local variations are caused by differences in terrain, surface characteristics and ground thermal properties. Meteorological elements, primarily solar radiation and air temperature, influence surface and subsurface temperature by affecting the rate at which heat is transferred to or from the atmosphere and the ground.
Solar radiation is probably the single most important factor.
Differences in average annual ground temperature between the north and south of Canada are due mainly to the amount of solar energy absorbed at the surface throughout the year. Seasonal and daily changes in solar radiation impose a cyclical variation on both air temperature and ground surface temperature. Other meteorological factors such as wind or rain can cause significant local variations. Snow is probably the second most important factor affecting ground temperature. This influence is due not only to its well known insulating properties but also to the moisture it provides to the ground during the thaw period.