A Soil - Vegetation - Atmosphere Model for Microclimatological Research in Arid Regions

A multi-layer one-dimensional vertical model of the upper soil, vegetation and lower atmosphere is developed and implemented. This model includes explicit representations of the heat and moisture diffusion both in the soil and in the atmosphere, and computations of various mass and energy fluxes at the soil-air, vegetation-air and soil-root interfaces. Four models are run in parallel to compute the fluxes and profiles both under clear and cloudy skies, and over bare and vegetated soil, with otherwise similar forcing. Under specific scaling conditions, environmental profiles are derived from a weighted average of these submodels, where the weights depend on the assumed cloud and vegetation covers. The model is specially designed to describe dry ecosystems where the vegetation cover is discontinuous. The vegetation component includes explicit parameterizations of the canopy (to intercept both radiation and precipitation), of a root system (able to pump soil water) and of the stomates (to control the transpiration rate). No biochemistry or photosynthesis is included in the current version. The sensitivity of the model to various parameters is assessed. The surface water and energy fluxes, and the profiles of temperature and specific humidity in the four submodels are compared. This model is currently better suited as a theoretical research tool for sensitivity analyses than for applied research on a specific crop, plant species or environment. Thesis Supervisors: Robert E. Dickinson (NCAR) and Reginald E. Newell (MIT)