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 t he warm- season mesoscale heat, moisture, and momentum fluxes over the cent ral Great Plains region of North America. The effect of crop growth and dev elopment on the atmospheric boundary layer is addressed in a follow- up pap er (Part II). Energy, moisture, and momentum fluxes are studied over a maiz e agroecosystem at the scale of a 90- km atmospheric grid cell. Daily plant development and growth functions incorporated into the surface flux calcul ations are based on a physiological crop growth model CERES- Maize version 3.0. CERES- Maize simulates daily plant growth and development as a functio n of both environmental conditions (temperature, precipitation, solar radia tion, and soil moisture) and plant- specific genetic parameters. Plant grow th and development functions from CERES were incorporated into the Biospher e- Atmosphere Transfer Scheme (BATS), and selected crop parameters [i. e., Leaf Area Index (LAI) and crop height] were validated against field data. T he sensitivity of sensible (H) and latent (LE) heat fluxes, and momentum fl ux (tau) 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 fro m 5 to 1 (the values simulated in the control and interactive experiments, respectively). These changes are statistically significant (at the 0.05 lev el) for all the locations and years under consideration. Relative contribut ions of evaporation and transpiration to the latent heat flux were also str ongly affected by these LAI changes. This effect had a distinct diurnal pat tern, with the strongest signal seen in midafternoon hours, and was more pr onounced during the dry years (e. g., 1988 and 1989) compared to the favora bly moist years (e. g., 1991, 1993).