Impacts of Spatial Resolution, Groundwater Parameterizations, and Vadose Zone Thickness on Land Surface Simulations

Abstract

Accurate kilometer-scale modeling of land processes is crucial for improving weather and climate forecasting. However, persistent biases, such as the well-documented warm temperature and dry bias in the central midlatitudes, continue to pose challenges. This study investigates the impacts of groundwater schemes, spatial resolution, and vadose zone thickness on simulated soil moisture, evapotranspiration, and ground temperature using the Noah-MP land surface model. We find that increasing spatial resolution reduces simulated median temperatures by 0.5 K over our domain of study. The groundwater scheme consistently increases soil moisture, evaporation, and transpiration, especially in wet, vegetated areas, resulting in cooling effects up to 1.5 K in the central midlatitudes from 2017 to 2019. The impact of vadose zone thickness is non-linear, and largely dependent on water table depth, and land cover categories, with the 8-m run showing higher magnitude changes compared to the 2-m run, while the 4-m run exhibits smaller changes. These findings underscore the critical role of spatial resolution, groundwater dynamics and vadose zone thickness in land surface models.

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