A Simple Dynamic Root Model for Use in Earth System Models—Introducing a Mechanism for Plants to Survive Droughts

Dynamic leaf models have been implemented into Earth System models for decades. However, the modeled ecosystems may not be able to survive droughts for lack of root dynamics, resulting in unrealistically low gross primary productivity (GPP) and transpiration during droughts. In this study, we develop a simple dynamic root model that links the subsurface carbon and water processes (Figure 1). The model allocates more photosynthate (GPP) to roots in wetter soil layers while allowing less turnover than drier layers, resulting in more live root mass (C_R) and surface area (A_R) in wetter soil and hence more efficient root water uptake (Q_R) to meet the transpiration demand (E_T) during dry seasons or droughts. The model predicts plant water storage (M_q) as a residual of Q_R and E_T. Different from conventional models, the water availability factor (β) for stomatal conductance is parameterized as a function of M_q assuming the plants’ stomata would close if they lose 10% of the maximum plant water storage. We will present the modeling results of live root mass, GPP, latent heat, and terrestrial water storage anomaly compared to the results from a static, evenly distributed root profile over the contiguous United States with a focus on drought years.