Exploring deep root water uptake, soil moisture, and land surface fluxes in the Amazon

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 seasonally dry periods by taking up moisture from 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 the link between deep roots and groundwater. This study details the implementation of a dynamic rooting scheme in the Noah-Multiparameterization (Noah-MP) land surface model, a widely used tool for studying the exchange of energy and moisture between the land and atmosphere. The rooting scheme is a first-order representation of dynamic rooting depth based on the soil water profile and includes quantification of deep root water uptake (RWU). The scheme is easily scalable and ideal for regional or continental-scale climate simulations. It is used in conjunction with a groundwater scheme which captures high-resolution spatial groundwater variations, allowing us to capture the critical link between deep roots and groundwater. We perform 10-year simulations with and without the root scheme for a test region in the Amazon to validate the enhanced model. We analyze time series of soil moisture, RWU, and evapotranspiration for points with differing vegetation cover and elevation. This allows us to demonstrate functionality of the root scheme and ensure it behaves properly for varying conditions. Representation of deep RWU is critical for realistic simulation of the soil-plant-atmosphere system. As the land surface is an important component of atmospheric predictability, inclusion of deep RWU can contribute to improved prediction of atmospheric variables such as precipitation.