Evaluating the sensitivity of surface soil moisture dynamics to soil profile layering schemes

We utilize a number of soil profile layering schemes within the Noah and Noah-MP land surface models to quantify their influence on simulated surface soil moisture dynamics. Experiments are carried out over the continental U.S. with the model's top soil layer thickness set to: 10 cm (default), 5 cm, and 2 cm. Continent-wide, the simulated surface soil moistures are compared with SMAP retrievals, which are nominally sensitive to moisture between the surface and a depth of 5 cm. At seven USDA watersheds, the simulated soil moistures are also compared to basin-wide averages from in-situ probes placed at 5 cm.

The three layering schemes exhibit differences in their dynamic ranges: shallower layers have lower means and higher standard deviations. Agreement between models, SMAP observations, and in-situ probes depends on region, reflecting differences in hydrologic regimes and suggesting differences in effective SMAP sensing depth. Insights from this work will aid efforts to enhance the observability (i.e. consistency with in-situ estimates) of simulated soil moisture from models, which is necessary for improving the efficiency of soil moisture data assimilation environments.