THE INTRODUCTION OF MACROSCALE HYDROLOGICAL COMPLEXITY INTO LAND SURFACE-ATMOSPHERE TRANSFER MODELS AND THE EFFECT ON PLANETARY BOUNDARY-LAYER DEVELOPMENT

The importance of surface hydrological processes on land surface-atmospheric fluxes is currently a major topic of investigation. It has been shown that the division of available energy into latent and sensible heat is sensitive to the prevailing hydrological conditions. Planetary boundary layer development is indicative of the amount of sensible heat being supplied to the lower atmosphere. Feedback mechanisms imposed by the boundary layer on the evaporative potential near the surface are also important. This paper uses a simple slab planetary boundary layer (PBL) model to show how PBL development is affected under a range of hydrological model scenarios. The investigation commences using a one-dimensional, single soil moisture root zone store model, which will represent the hydrological representation seen in current SVAT (soil-vegetation-atmosphere transfer) models. This model is the benchmark against which more complex models are tested and is also used to show the sensitivity of the PBL model to antecedent soil moisture conditions. A further level of complexity is added using the topographically derived distribution function model TOPMODEL, TOPMODEL introduces a water table that interacts with the root zone stores. The role of laterally redistributed water within a catchment or grid cell on the PBL is demonstrated; under certain circumstances, a spatially varying water table can substantially change the development of the PBL, A distribution function structure model showing a hydrological structure that includes spatially varying available water capacity (AWC) is also described. It is shown that the PBL development is sensitive to the spatial variability of available water and so can be highly dependent on the hydrological scenario at the land surface.