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Spring 2000

Modeling plant growth gives better results

by Carol Rasmussen and Zhenya Gallon

NCAR and Pennsylvania State University researchers modeling agricultural ecosystems have found that as a crop grows, its effects on temperature, precipitation, and water vapor change, and incorporating these changes into a regional climate model leads to a more realistic simulation.

Most land-surface schemes in climate models use highly simplified, static estimates to represent plant ecosystems. "We wanted to test the effect of having an interactive, growing canopy as opposed to a static canopy in a climate model," explained NCAR researcher Elena Tsvetsinskaya (Environmental and Societal Impacts Group). She, Linda Mearns (ESIG), and William Easterling (Penn State) began with a crop model known as CERES, which includes changes in growth stages, allocation of biomass among the different plant parts, leaf area, and canopy height. They coupled these parts of CERES to the NCAR Biosphere-Atmosphere Transfer Scheme, which simulates exchanges of heat, moisture, and energy with the atmosphere, and then coupled this modified version of BATS (dubbed BATS-GF) with the NCAR Regional Climate Model.

In the Great Plains, the drought of 1988 stunted crop growth, leading to plants with decreased leaf area. The scientists simulated that growing season using two versions of BATS-GF and two types of control runs with the standard BATS. They found that by including the wilted plants, they obtained a more realistic result--with more heat, less water vapor, and less precipitation over the region--than in the control cases.

The team also found that using the interactive plant simulation altered not only the patterns of temperature, water vapor, and precipitation during a single season, but also the annual variability in these factors. The results matched better with real-world observations of the same period than did the static vegetation case. Tsvetsinskaya said, "Our work adds to the evidence that growing agricultural ecosystems have a considerable effect on the warm- season climate of the Great Plains. For climate change studies, our results suggest that a potentially warmer climate could develop over the central U.S. than is currently simulated by climate models without interactive vegetation."

Tsvetsinskaya presented the team's results at the January meeting of the American Meteorological Society. Their research was funded by the University of Nebraska, the Environmental Protection Agency, and NSF.

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Edited by Carol Rasmussen, carolr@ucar.edu
Prepared for the Web by Jacque Marshall
Last revised: Thu May 4 14:53:14 MDT 2000