Numerical investigations on the influence of subgrid-scale surface heterogeneity on evapotranspiration and cloud processes

Abstract

Numerical experiments were performed with a meso-β-scale meteorological model to investigate the influence of subgrid-scale surface heterogeneity on the prediction of evapotranspiration, cloud, and precipitation formation. The results of simulations using different horizontal grid resolutions and assuming the dominant land-use type within a grid box as the representative surface type for the entire grid element are compared with those obtained from model runs considering subgrid-scale heterogeneity by separately determining the fluxes of the respective subgrid-scale land-use types. The same surface parameterization scheme was applied in both cases. All of these numerical experiments show that the surface characteristics and, hence, the subgrid-scale surface processes strongly affect the predicted microclimate close to the ground. Furthermore, the model results also provide evidence that in the case of applying dominant land-use types the grid resolution may strongly affect the calculated water and energy fluxes because a subgrid-scale land-use type on a coarse grid is of minor importance and may be dominant on a finer grid. Moreover, if surface heterogeneity was considered, the simulation with coarser-grid width also predicted many features provided by the run with a finer-grid resolution with a sufficient degree of accuracy. The results substantiate that the degree of heterogeneity especially affects evapotranspiration, clouds, precipitation, and soil wetness.