The Role of Soil Hydro-physical Properties in Land-atmosphere Interactions and Regional Climate

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Soil hydro-physical properties are necessary components in weather and climate simulation; yet, the parameter inaccuracies introduce considerable uncertainty in the representation of surface water and energy fluxes. The surface fluxes not only affect the terrestrial water and energy budgets, but through land-atmosphere interactions, they can influence the boundary layer, atmospheric stability, moisture transports, and regional precipitation characteristics. This set of three experiments explores aspects of soil hydro-physical properties, and their impact on coupled regional climate simulations in the North American region.

In the first two experiments, two soil datasets are considered: State Soil Geographic dataset (STATSGO) and Global Soil Dataset for Earth System Modeling (GSDE). Each dataset’s dominant soil category allocations differ significantly at the model’s resolution. Large regional discrepancies exist in the assignments of soil category, such that, for instance, in the Midwestern United States, there is a systematic reduction in soil grain size. Because the soil grain size is regionally biased, it allows for analysis of the impact of soil hydro-physical properties projected onto regional scales.

In the first experiment, in areas of reduced soil grain size, there is also a reduction in latent heat flux and an increase in sensible heat flux following the physical understanding of soil properties. These differences in surface fluxes affected low-level thermodynamics, and PBLH. The second experiment analyzed soil-induced differences in the general circulation, emphasizing horizontal moisture transports, vertically-integrated moisture flux convergence, and regional precipitation. It found that soil-induced differences in surface fluxes influenced each term of the atmospheric water budget via both thermodynamic and dynamic means.

The third experiment assesses the impact of soil hydro-physical parameters on surface fluxes, and the atmospheric response. The default soil hydro-physical parameter table is replaced with a modernized soil parameter table. The findings indicate that the role of each soil hydro-physical parameter is sensitive to both climatic regimes (i.e., arid vs. temperate), and vegetation assignment.

Collectively, this series of experiments improves our understanding of the physical mechanisms that link the soil to the atmosphere in the coupled land-atmosphere system. The improved understanding will inform the development of the next generation of land surface models.