Investigating the effect of seasonal plant growth and development in three-dimensional atmospheric simulations. Part I: Simulation of surface fluxes over the growing season

The authors examine the effect of seasonal crop development and growth on the warm-season mesoscale heat, moisture, and momentum fluxes over the central Great Plains region of North America. The effect of crop growth and development on the atmospheric boundary layer is addressed in a follow-up paper (Part II). Energy, moisture, and momentum fluxes are studied over a maize agroecosystem at the scale of a 90-km atmospheric grid cell. Daily plant development and growth functions incorporated into the surface flux calculations are based on a physiological crop growth model CERES-Maize version 3.0. CERES-Maize simulates daily plant growth and development as a function of both environmental conditions (temperature, precipitation, solar radiation, and soil moisture) and plant-specific genetic parameters. Plant growth and development functions from CERES were incorporated into the Biosphere-Atmosphere Transfer Scheme (BATS), and selected crop parameters [i.e., Leaf Area Index (LAI) and crop height] were validated against field data. The sensitivity of sensible (H) and latent (LE) heat fluxes, and momentum flux (τ) to interactively simulated LAI and canopy height was quantified. During the extremely dry season of 1988, 20%-35% changes in sensible heat and 30%-45% changes in latent heat occurred in response to LAI changes from 5 to 1 (the values simulated in the control and interactive experiments, respectively). These changes are statistically significant (at the 0.05 level) for all the locations and years under consideration. Relative contributions of evaporation and transpiration to the latent heat flux were also strongly affected by these LAI changes. This effect had a distinct diurnal pattern, with the strongest signal seen in midafternoon hours, and was more pronounced during the dry years (e.g., 1988 and 1989) compared to the favorably moist years (e.g., 1991, 1993).