Abstract
AbstractVersion 5 of the Community Land Model (CLM5) introduces the plant hydraulic stress (PHS) configuration of vegetation water use, which is described and compared with the corresponding parameterization from CLM4.5. PHS updates vegetation water stress and root water uptake to better reflect plant hydraulic theory, advancing the physical basis of the model. The new configuration introduces prognostic vegetation water potential, modeled at the root, stem, and leaf levels. Leaf water potential replaces soil potential as the basis for stomatal conductance water stress, and root water potential is used to implement hydraulic root water uptake, replacing a transpiration partitioning function. Point simulations of a tropical forest site (Caxiuanã, Brazil) under ambient conditions and partial precipitation exclusion highlight the differences between PHS and the previous CLM implementation. Model description and simulation results are contextualized with a list of benefits and limitations of the new model formulation, including hypotheses that were not testable in previous versions of the model. Key results include reductions in transpiration and soil moisture biases relative to a control model under both ambient and exclusion conditions, correcting excessive dry season soil moisture stress in the control model. PHS implements hydraulic gradient root water uptake, which allows hydraulic redistribution and compensatory root water uptake and results in PHS utilizing a larger portion of the soil column to buffer shortfalls in precipitation. The new model structure, which bases water stress on leaf water potential, could have significant implications for vegetation‐climate feedbacks, including increased sensitivity of photosynthesis to atmospheric vapor pressure deficit.
Highlights
Trees face emerging risk from climate change globally, which may lead to increases in mortality and decreases in the terrestrial carbon sink (Allen et al, 2010; Anderegg et al, 2013; McDowell et al, 2016)
The plant hydraulic stress (PHS) configuration of the CLM5 within the Community Earth System Model (CESM2) is, to our knowledge, the first land surface model within an ESM with a representation of vegetation water potential running in its default configuration
We have described the model implementation and illustrated a comparison of the model dynamics for a tropical rainforest site subjected to water limitation, given that prediction of rainforest responses to drought is one of the key uncertainties in the ESM predictions (Huntingford et al, 2013)
Summary
Trees face emerging risk from climate change globally, which may lead to increases in mortality and decreases in the terrestrial carbon sink (Allen et al, 2010; Anderegg et al, 2013; McDowell et al, 2016). Increases in vapor pressure deficit (VPD) are occurring with global warming (Ficklin & Novick, 2017; Seager et al, 2015) and are associated with impacts on vegetation, such as large-scale die-off Understanding vegetation response to environmental drivers is important both for discerning future climate impacts on forests and for modeling feedbacks to the carbon and hydrological cycles (Lemordant et al, 2018). Significant uncertainty remains in Earth System Model (ESM) predictions of the carbon cycle, partly attributed to the response of vegetation to changes in hydroclimate (De Kauwe et al, 2017; Friedlingstein et al, 2014; Trugman et al, 2018)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call