ONE-DIMENSIONAL STATISTICAL DYNAMIC REPRESENTATION OF SUBGRID SPATIALVARIABILITY OF PRECIPITATION IN THE 2-LAYER VARIABLE INFILTRATION CAPACITY MODEL

The two-layer variable infiltration capacity (VIC-2L) model is extende d to incorporate a representation of subgrid variability in precipitat ion, using an analytical one-dimensional statistical dynamic represent ation for partial area coverage of precipitation. The analytical appro ach allows the effects of subgrid-scale spatial variability of precipi tation on surface fluxes, runoff production, and soil moisture to be r epresented explicitly. With this method, spatially integrated represen tations of surface fluxes, runoff, and soil moisture due to subgrid-sc ale spatial variability in precipitation, infiltration, and vegetation cover are obtained. The results are compared with those obtained usin g an exhaustive pixel-based approach, and the results obtained by appl ying uniform precipitation over the precipitation-covered area. The pr ecipitation coverage over a grid cell is shown to play a primary role in estimating the surface fluxes, runoff, and soil moisture. In genera l, the spatial distribution of precipitation within the precipitation- covered area plays a secondary role, in part because VIC-2L represents the subgrid spatial variability of soil properties. While the analyti cal approach gives good approximations to the pixel-based approach, an d is superior to the uniform precipitation approach in general, the di fferences are not large.