Abstract
Although affected by atmospheric circulations, variations in soil temperature result primarily from the radiation and sensible and latent heat exchanges at the surface and heat transfer in the soils of different thermal properties. Thus, soil temperature and its variation at various depths are unique parameters that are useful in understanding both the surface energy processes and regional environmental and climatic conditions. Yet, despite the importance, long-term quality data of soil temperatures are not available for the United States. The goal of this study is to fill this data gap and to develop a soil temperature dataset from the historical data of U.S. cooperative stations. Cooperative station soil temperatures at various depths from 1967 to 2002 are collected and examined by a set of quality checks, and erroneous data of extended periods are estimated using methods constructed in this study. After the quality control, the data are used to describe the climatic soil temperature as well as soil temperature change in the contiguous United States. The 35-yr climatological dataset shows that the annual soil temperature at 10-cm depth, at which most stations have soil temperature measurements, decreases gradually from 297 K in the coastal areas along the Gulf of Mexico to below 281 K on the United States–Canada border. In seasonal variation, the largest change occurs from spring to summer, during which time soil temperatures are adjusted from the cold season to the warm season, particularly in snow-cover regions. Mild changes are observed from autumn to winter, during which time the soil heat storage still dominates the soil temperature variations. An analysis of the soil temperature variation reveals a warming trend of soil temperatures in most of the stations in the northern and northwestern United States and a large cooling trend in some stations in the southeastern United States. Significant warming is found in the winter and spring season. Potential effects of these trends on regional agriculture are discussed.
Corresponding author address: Dr. Qi Hu, School of Natural Resource Sciences, 237 L.W. Chase Hall, University of Nebraska at Lincoln, Lincoln, NE 68583-0728. qhu2@unl.edu
