Improving a widely used land surface model to enhance representation of interactions from groundwater to the atmosphere
Plant roots act as critical pathways of moisture from subsurface sources to the atmosphere. Moreover, deep plant roots allow vegetation to meet water demand during dry periods by taking up moisture from areas near accessible groundwater. This is an important resilience mechanism in the Amazon, a hydrologically and ecologically significant region. However, most regional land-atmosphere computational models do not adequately capture this mechanism. This study details the implementation of a dynamic root water uptake (DRWU) scheme in the Noah-Multiparameterization (Noah-MP) land surface model, a widely used tool for studying exchanges of energy and moisture between the land and atmosphere. The DRWU scheme is a first-order representation of RWU and rooting depth based on the soil water profile and allows for representation of deep RWU. The scheme is scalable and ideal for regional or continental-scale climate simulations. It is used in conjunction with a groundwater scheme that adequately resolves spatial water table variations, allowing us to capture the critical influence of deep moisture on rooting depth. We perform 20-year simulations with and without the DRWU scheme for a region in the Amazon. We analyze time series of soil moisture, RWU, evapotranspiration, and other relevant variables at points with differing vegetation cover and elevation. We demonstrate functionality of the root scheme and ensure it is consistent with physical expectations. We also compare model output with observational products available for the region. Representation of deep RWU is key for realistic simulation of the soil-plant-atmosphere system. As the land surface is an important component of atmospheric predictability, inclusion of the DRWU scheme may contribute to improved simulation of variables such as precipitation in a coupled modeling framework.
