Spatiotemporal Patterns of the Vegetation‐Atmosphere Decoupling Coefficient Across the Contiguous United States

Abstract

The decoupling coefficient (Ω), a dimensionless metric that quantifies the balance between stomatal conductance (Gs) and aerodynamic conductance (Ga) in regulating evapotranspiration (ET), is key to understanding vegetation‐atmosphere interactions, which are fundamental to ecohydrological cycles and ecosystem functioning. However, the spatiotemporal patterns of Ω across different plant functional types (PFTs) and climatic gradients remain poorly understood, particularly in heterogeneous land surfaces under climate change. Here, we quantified Ω at 52 AmeriFlux sites across four PFTs in the contiguous U.S. (CONUS) from 2001 to 2024 and developed a high‐resolution Ω modeling framework that integrates eXtreme Gradient Boosting (XGBoost) with satellite observations and reanalysis data to produce spatially explicit 8‐day Ω maps at 0.1° resolution. This framework reveals a significant increasing trend in continental‐mean Ω (1.0 × 10−3 yr−1, p < 0.05), indicating progressively weaker vegetation‐atmosphere coupling, whereby ET becomes relatively insensitive to Gs and increasingly constrained by available energy. We also found that Ω in water‐limited regions show highly volatile and asymmetric responses to drought, shifting toward stronger coupling in dry periods and toward stronger decoupling in wet periods, whereas Ω in energy‐limited regions remain strongly buffered with a stable coupling state. Our study reveals the spatiotemporal variability of Ω in CONUS, shedding light on the pivotal role of vegetation in modulating water fluxes under shifting climatic regimes and drought stress.