Differences in Kansas soil temperatures between the 1990s and 2000s

Near-surface soil temperatures are important because they have implications for climate change and agricultural productivity worldwide. Nonetheless, historic records of soil temperature are much less common than records of air temperature or precipitation. Those that exist do not indicate a predominant global trend in soil temperature over the last century, but suggest regional and seasonal differences that include both cooling and warming. In this paper, we compared the annual date at which near-surface soil temperatures in Kansas reached each of seven thresholds (five degree increments between 40 and 70° F) for each of two decades (the 1990s and 2000s) in order to see if soil temperatures warmed earlier in the year in one decade than in the other. Of the 13 stations tested, only Colby warmed more quickly in the 2000s than in the 1990s for all seven thresholds, and no station warmed more quickly in the 1990s across all thresholds. Typically lower thresholds that occur in the winter were reached earlier in the 1990s than in the 2000s, while higher temperature thresholds that occur in the spring were reached earlier in the 2000s than in the 1990s. These results generally reflect changes in temperature and precipitation during these two decades. Despite the relatively short duration of the data, these findings for Kansas show some similarities to those from studies in other parts of North America and the world. Most notably, areas with warming soil temperatures are often in areas with cooler climates.