Seminar: Sinikka Paulus

Soils take up water vapor from the atmosphere through processes that involve vapor diffusion and water retention. This can theoretically occur in any ecosystem under the preconditions of a humid atmosphere and dry soil pores. It can play a critical role in dry ecosystems because it can provide a substantial proportion of the total water inputs at the daily timescale. However, it remains insufficiently investigated in many regions, partly due to the absence of continuous, dedicated measurements.

In our previous work, we successfully showed for a Mediterranean ecosystem that EC data can be used to detect soil water vapor adsorption. In this study, we expand this analysis to a global Network of Eddy Covariance stations. Our results provide compelling evidence that negative latent heat fluxes are not just random occurrences, but are significantly influenced by specific conditions of VWC and RH, especially in arid regions. This supports our hypothesis and highlights the prevalence of the phenomenon of soil water vapor adsorption beyond the isolated case observed at Majadas de Tiétar in our previous study. By imposing physical constraints on our analysis, we were able to detect signals of soil water vapor adsorption at different sites, revealing an emergent ecosystem-scale behavior detectable by EC stations. This behavior is rooted in processes occurring at the soil pore scale, which are specifically influenced by the surface properties of the soil matric.

We also analyze the factors controlling the occurrence and dynamics of soil water vapor adsorption. In this way, our work extends our knowledge of the spatial extent and inter-annual dynamics of soil water vapor adsorption in natural ecosystems and, more generally, sheds light on a mostly overlooked aspect of land-atmosphere interactions.