Improving Predictions of Forest Water Use

Data on plant responses to elevated CO₂ used to assess models.

The Science

Different ecosystem models vary widely in predicting the effect of elevated atmospheric carbon dioxide (CO₂) concentrations on transpiration, or the passage of water from a plant’s roots, through its vascular system, and then to the atmosphere. To better understand and constrain this variability, forest carbon and water flux data from the free-air CO₂ enrichment (FACE) experiments at Duke University and Oak Ridge National Laboratory were compared to simulations from 11 ecosystem models.

The Impact

This study yields a framework for analyzing and interpreting model predictions of transpiration responses to elevated CO₂. The results highlight important areas for immediate model improvement, hypotheses for experimental testing, and opportunities for data synthesis to significantly reduce discrepancies among models.

Summary

A primary objective of the study was to identify key underlying assumptions in model structure that cause differences in model predictions of transpiration and canopy water-use efficiency. Model-to-model and model-to-observations differences resulted from four main sets of assumptions: (1) the nature of stomatal response to elevated CO₂, (2) the roles of leaves and the atmospheric boundary layer, (3) treatment of canopy interception, and (4) impact of soil moisture stress. The degree of coupling between carbon and water fluxes and the way that coupling is calculated are key assumptions that determine how well the models compare with observations.

Contact

Martin G. De Kauwe
Macquarie University, Department of Biological Sciences
New South Wales 2109, Australia
[email protected]

Funding

Research was supported by the National Center for Ecological Analysis and Synthesis, a Center funded by the National Science Foundation (grant #EF-0553768); the University of California, Santa Barbara; and the state of California. The Oak Ridge and Duke FACE sites and additional synthesis activities were supported by the DOE Office of Science Biological and Environmental Research (BER) program. Duke FACE research was supported by BER’s Terrestrial Carbon Processes program (FACE, DE-FG02-95ER62083).

Publications

Kauwe, M.G., et al. “Forest water use and water use efficiency at elevated CO2: a model-data intercomparison at two contrasting temperate forest FACE sites.” Glob. Chang. Biol. 19(6), 1759–1779 (2013). [DOI: 10.1111/gcb.12164].

Highlight Categories

Program: BER , CESD

Performer: University , DOE Laboratory