Multiple Equilibria and Soil Moisture‐Precipitation Feedbacks in Idealized Convection‐Permitting Simulations With an Open Hydrological Cycle

Abstract

Soil moisture‐precipitation feedbacks are influenced by both small‐scale land‐atmosphere coupling and large‐scale atmospheric circulations, and their sign has important implications for the stability of regional hydroclimate. However, the importance of both local and non‐local processes makes it difficult to model soil moisture‐precipitation feedbacks with high fidelity, limiting our ability to use models to understand controls on their sign. Here, we address this challenge by exploring a promising but seldom‐used approach to studying soil moisture‐precipitation feedbacks over tropical land: coupling small‐domain convection‐permitting simulations to a land‐like surface and a parameterization of large‐scale dynamics. The large‐scale dynamics parameterization, based on the weak temperature gradient (WTG) approximation, is a key component that produces an open hydrological cycle with interactive moisture convergence. We first show that WTG‐constrained simulations coupled to a freely‐evaporating land surface support both precipitating and non‐precipitating equilibria across a wide range of insolation. We then leverage this bistability to probe the influence of soil moisture feedbacks on dry spells by asking whether non‐precipitating equilibria remain stable as the underlying surface dries out. We find that surface drying can trigger transitions from dry equilibria back to precipitating equilibria—a negative soil moisture‐precipitation feedback—and attribute this transition to increasingly inefficient boundary layer ventilation by the parameterized large‐scale circulation. In sensitivity experiments, alternative versions of the WTG scheme modify the parameter space where the negative feedback occurs, but none eliminate it entirely. Our results provide a foundation for leveraging the rich behavior of WTG‐constrained simulations to probe controls on soil moisture‐precipitation feedbacks over tropical land.