Land-atmosphere interaction during heat waves diagnosed using vapor pressure deficit dynamics

Vapor pressure deficit (VPD) plays an essential role in determining land-atmospheric interaction by proving a gradient for moisture transport and modulating the biophysical process of plants. Land-atmosphere interaction has been suggested to affect the evolution of heatwave, including its intensification and propagation. However, the role of VPD dynamics in this interaction during heat waves remains unclear. Here, we apply the Pearson correlation coefficient between VPD and energy fluxes to diagnose VPD-induced land-atmospheric interaction over different climate regions and ecosystems, and then evaluate key factors' contributions to this interaction through machine learning. The result shows a nonlinear coupling between VPD and sensible heat fluxes (H) or latent heat fluxes (LE) during heat waves with both strong positive and negative coupling. This coupling exhibits climate and species-dependent. there is a considerable positive coupling between VPD and LE in all climate regions. However, the coupling of VPD and H is more climate-sensitive which shows positive correlations in arid and cold regions and negative coupling in temperate region. Across various vegetation types, LE consistently demonstrates a positive correlation with VPD. In contrast, the coupling between VPD and H tends to be negative in short vegetation whereas positive in forests. In addition, we discovered that the coupling between VPD and LE or H is significantly influenced by the heat wave duration (HWD) at (p < 0.01). Specifically, the land- atmospheric interaction turns decoupling when the HWD extends beyond 8 days. Furthermore, the coupling direction between VPD and energy will change as heat waves evolve. The coupling direction between VPD and LE is considerably affected by maximum temperature. The direction of VPD and H coupling is intimately related to plant functional characteristics. Our research suggests that the VPD impacts should be imperative for accurately simulating land-atmospheric interaction during heat waves.