Implementation and Evaluation of Plant Hydraulics and Hydraulic Redistribution in the Common Land Model (CoLM)

Plant hydraulic plays an important role in ecosystem resilience during ecosystem drought. Land surface model has recently introduced the plant hydraulic, but the performance is not fully evaluated yet. In this study, we implemented and evaluated plant hydraulic and hydraulic redistribution in Common Land Model (CoLM). The Community Land Model version 5 (CLM5) plant hydraulics model and Amenu-Kuma hydraulics redistribution model are implemented in Common Land Model (CoLM) to physically represent the water flow throughout the Soil-Plant-Atmosphere continuum (SPAC). In addition to CLM5 plant hydraulic model, Amenu-Kuma model represents root axial conductance at different soil levels, which is supposed to be weaker but more realistic than CLM5 plant hydraulic model. We set up CoLM simulations at site-level and use three configurations: a) Coupling plant hydraulic and Amenu-Kuma hydraulic redistribution model, b) plant hydraulic only, and c) no plant hydraulic and no hydraulic redistribution. We then compared CoLM results among configurations, with FLUXNET observation, and with CLM5 simulations. Model results with plant hydraulic deviate much less from observation. When coupling with Amenu-Kuma model, plant hydraulic models agree with observation slightly more. Both CoLM and CLM5 with plant hydraulic consistently simulated higher transpiration and productivity than those without plant hydraulic at extremely dry season. Those results further prove the assumption that hydraulic redistribution can reserve soil water for vegetation. Moreover, both CoLM and CLM5 with plant hydraulic models show strong correlation between the soil moisture stress and vapor pressure deficit (VPD) at wet condition, while default models do not. Such correlation is consistent with observation. Since more extreme event and higher VPD are widely predicated, implementing plant hydraulic and hydraulic redistribution model in land surface model is imperative to improve the simulation results, enhance our understanding of ecosystem water and carbon cycle, and provide suggestions to policy maker.