Global pattern of soil temperature exceeding air temperature and its linkages with surface energy fluxes

Abstract

Understanding the pattern of changes in extreme heat is crucial to developing climate change adaptation strategies. Existing studies mostly focus on changes in air temperature and tend to overlook soil temperature; however, changes in extreme heat in air and soil can be inconsistent under global change and water–carbon cycling may be more sensitive to soil condition. In this study, we examine the global pattern of long-term trends in the difference between air temperature and soil temperature (T_soil − T_2m) for the hottest month of the year during the period of 1961–2022. The results show that in certain hotspots, such as the middle and high latitudes of Eurasia, the Mediterranean, and the Western United States, the increasing trend in soil temperature has exceeded the increasing trend in 2 m air temperature during the warm season, implying that the land surface can contribute to the increase in air temperature extreme by releasing more heat than before. Our study suggest that the effect of soil temperature to air temperature is strongly related to the partitioning of surface latent heat, sensible heat (H) and soil heat flux (G). In the hot spots, T_soil − T_2m was significantly positively correlated with H and G while a significant negative correlation was found with evaporative fraction (EF) (p< 0.05), and the significant correlations with G and EF exhibit greater spatial heterogeneity. Moreover, the higher the degree of vegetation cover and soil moisture the smaller the difference between soil and air high temperatures. Therefore, changes in vegetation cover and land use management may play an important role in regulating the range of soil and air temperature differences as well as land-atmosphere coupling effects on heat extreme.