Models of Soil Hydraulic Properties with Adjustable Soil Structure and their Application in an Earth-system Model

Objective

The spatial arrangement of solids and pore spaces within soil (soil structure) is a major source of variability in the hydraulic properties of soils. It is through changes in soil structure that biological activity, land management, or the passage of time (including wet-dry and freeze-thaw cycles) affect the capacity of soil to retain and conduct moisture. Nevertheless, soil structure is at most tentatively represented in Earth-system models. As a result, we cannot quantify the effect of biological activity and management on soil water content and thus their full effect on the regional climate or the land carbon sink. This represents an important gap in our understanding of the natural environment, as well as a potential blind spot in our response to the climate emergency. Including soil structure in land-surface models is difficult, because its effect on the soil hydraulic properties cannot be reliably predicted based on a single, easy-to-measure quantity such as bulk density. At the same time, more detailed soil structure data and the methods to incorporate it are largely missing. MOSS will address these issues by 1)~developing a physics-based method of incorporating beyond-density soil structure information into the models of soil hydraulic properties, 2)~implementing this method in a state-of-the-art Earth-system model, and 3)~using the new model to quantify the impact of soil structure on the land carbon sink. By doing so, MOSS will likely demonstrate that soil structure must be included in numerical models and protected in the field. Moreover, the method developed by MOSS will be applicable to agronomical and hydrological models and thus will have a plausible impact on the socially and economically important policy decisions these models inform. Finally, because of the interdisciplinary background of the researcher, we expect that the high visibility and copious training program offered by the fellowship will have a defining impact on their scientific career.