HR: 16:50h
AN: H34E-04 INVITED    [Abstracts]
TI: Temporal Dynamics of the Spatial Variance of Sub-Grid Soil Moisture: A Look at Scaling Implications
AU: * Albertson, J
EM: john.albertson@duke.edu
AF: Duke University, Department of Civil and Environmental Engineering, Pratt School of Engineering, Durham, NC 27708, United States
AU: Montaldo, N
EM: nmontaldo@unica.it
AF: Universita' di Cagliari, Dipartimento di Ingegneria del Territorio, Via Marengo, 3, Cagliari, 09121, Italy
AB: Experimental efforts to define the dynamics of sub-grid spatial variance of soil moisture have led to contradictory results. Moreover, most reports of soil moisture variability range from qualitative to descriptively quantitative, and are unsupported by a theoretical framework for moisture variance dynamics. In this talk we present a conservation equation for the spatial variance of sub-grid root-zone soil moisture, based on first principles of statistical fluid mechanics. We arrive at a variance budget in which explicit covariances between moisture fields and land surface flux fields act to produce or destroy variance through time (according to the sign of the correlation between the flux and state fields). A series of examples are used to explore how simple forms of soil, vegetation, precipitation, topography, and initial moisture variability lead to evolving covariances between spatial fields of soil moisture and particular land surface fluxes, and how these covariances relate to the temporal trajectory of the spatial variance of soil moisture. We isolate a set of processes and conditions that demonstrate spatial variance production through time and a set that demonstrate variance destruction. Of particular interest is the tendency for transpiration and infiltration-runoff processes to either produce or destroy variance, depending on the background wetness regime. Field data are also employed and shown to demonstrate a temporal behavior of the spatial variance that is readily described by the proposed approach. The implications of this theory for multi-scale analysis of soil moisture variability is explored and discussed. Ultimately, this work should aid field data interpretation and, when supplemented with a closure model for the variance budget, lead to improved land surface flux predictability over coarse grids.
DE: 1843 Land/atmosphere interactions (1218, 1631, 3322)
DE: 1866 Soil moisture
DE: 1875 Vadose zone
DE: 1878 Water/energy interactions (0495)
SC: Hydrology [H]
MN: 2007 Fall Meeting