Near‐surface soil thermal regime and land–air temperature coupling: A case study over Spain

Understanding the near‐surface soil thermal regime and its connection to the atmospheric state is important for the assessment of several climate‐related processes. However, the lack of in situ soil temperatures measurements limits the analysis of such processes. In this study, we have developed a quality‐controlled soil temperature database for Spain that consists of 39 sites spanning from 1987 to 2018. We have used this database to assess the near‐surface soil thermal regime. Likewise, we evaluate at seasonal to multidecadal timescales the land–air temperature coupling over Spain by analysing the structure of the surface air temperature (SAT) and the ground surface temperature (GST) covariance and also their long‐term evolution. In addition, we have employed the ERA5‐Land reanalysis to test the consistence between observations and reanalysis. The results show that the near‐surface soil thermal structure is dominated by conduction despite some influence of hydrology‐related processes. Regarding the land–air temperature coupling, we have found a strong connection between SAT and GST. However, in the summer months there is an offset in SAT–GST at some sites due to limited evaporation and enhanced sensible heat fluxes. Furthermore, multidecadal SAT–GST decoupling may exist over some sites as a response to decreasing precipitation. The ERA5‐Land represents the observations' climatology well, but it underestimates the summer soil temperature observations and the long‐term trends at some sites. We developed a soil temperature database for Spain that consists of 39 sites spanning from 1987 to 2018. This database can be used in assessments of air‐ground interactions and modelling evaluation, among other things. We found that in summer, the ground tends to be warmer than the air above. At some sites. Furthermore, multi‐decadal air‐ground temperature decoupling may exist at some sites. This may have implications for several climate related issues, including paleoclimate temperature reconstructions.