#L01 Soil-Plant-Atmosphere Continuum model for ALM

Abstract

The land-atmosphere exchange of water, energy, and carbon fluxes plays a critical role in the evolution of the terrestrial water cycle. Several recent studies have demonstrated the need for explicitly resolving the vertical light and thermal regimes within the vegetation canopies and the surrounding air space to accurately capture vegetation response to future climate perturbations. Additionally, estimation of the hydraulic gradients through the soil-root-plant system is crucial for estimating transpiration. The ACME Land Model version 1.0 (ALM-v1.0) uses big-leaf and diagnostic canopy air modules to simulate fluxes of water, energy, and carbon exchanged between land and atmosphere. Moreover, ALM-v1.0 directly links stomatal responses to soil moisture instead of accounting for the stem water potential.

The overall objective of this research is to develop a rigorously verified, vertically-resolved soil-plant-atmosphere continuum (SPAC) model to simulate transport of water, energy, and carbon along the soil-plant-atmosphere continuum. The SPAC model will include: (i) extension of the ALM-v1.0’s VSFM formulation to simulate transport of water across the soil-root-xylem system; (ii) inclusion of a roughness sublayer model to account for turbulence within canopies; (iii) development of a vertically resolved shortwave and longwave radiation scheme; and (iv) development of models for conservation of water, energy, and carbon within the SPAC. To deliver this new capability to ALM, we will use the Portable, Extensible Toolkit for Scientific Computation (PETSc) library for the numerical solution of the discretized equations. Automated Verification & Validation will be performed to build trust-worthiness of the high-fidelity SPAC model by comparing numerical solution for multiple benchmark problems with known and manufactured solutions.