A simple framework linking tree water deficit dynamics to internal water status across scales

Internal tree water storage buffers demand–supply imbalances and is central to drought physiology, yet most ecosystem models omit this process or rely on complex hydraulic schemes. A simple representation of internal water pools and their depletion as physiologically interpretable drought stress signals therefore remains a key research gap.

We developed a parsimonious physiology-based module (TWIST) that simulates tree water deficit (TWD) and derives relative tree water content (RWCtree). Because TWIST only requires transpiration, relative soil water content and an estimate of available internal water storage as input, it can be readily integrated into a variety of forest models.

Coupled to LandscapeDNDC and evaluated against multi-year dendrometer observations, TWIST reproduced tree drought responses, including diurnal depletion–refilling cycles, reduced nocturnal rehydration with declining soil moisture, and progressive TWD accumulation. Simulated TWD trajectories agreed with the observed temporal dynamics, while RWCtree provided a physiologically interpretable proxy of internal dehydration.

The framework provides a practical basis for linking tree-level dendrometer signals with stand-level processes and, in principle, for comparison with remotely sensed indicators of canopy water status. By explicitly simulating TWD and RWCtree, it can also help to improve the representation of drought impacts in ecosystem models.