Upscaling and Hysteresis in Models of Soil Moisture, Evaporation, and Transpiration

Tuesday, January 8, 2002 - 2:00pm - 2:25pm
Keller 3-180
Michael Celia (Princeton University)
Soil moisture dynamics are central to vegetation growth, ground-water recharge, and land surface-atmosphere interactions. While the basic equations of two-phase (air-water) flow may be applied to this system, the appropriate spatial scale over which to define averaged quantities is not always obvious. In some cases, detailed simulations using multi-dimensional flow equations are used, while in other cases simplified, spatially averaged models are used. A computational study involving upscaling from the highly spatially-resolved scale to a spatially averaged scale covering the entire root zone provides insights into how upscaled models relate to highly-resolved models. Analysis of computational results indicates that dimensionless groups can provide guidelines for conditions under which certain upscaled models may be appropriate. In addition, computational results indicate that upscaled evaporation and transpiration functions exhibit hysteresis, despite having no hysteresis at the small scale. This observation leads to the conjecture that hysteresis is caused by upscaling.