Seasonal variation of surface fluxes and scalar roughness of suburban land covers

Flux observations above five different land covers over a year allowed evaluation and comparison of seasonal change of fluxes and roughness parameters. The selected land covers consist of a pine forest, a paddy field, short grass, tall grass and a building roof top which are typical surfaces one can find in a suburban area in a temperate humid region. It was found that the available energy was the largest through the year for the forest because of its small albedo and low surface temperature. The grass fields and the paddy field received a similarly large energy input, but only during midsummer. The ratio of the latent heat to the available energy fluxes was found to be the largest above the grassy surfaces during the growing season while above the forest it was the smallest. This reversed itself during the winter season when the pine trees still transpirated water while the grassy vegetation went into dormancy. Over the building, the lack of evaporation caused very large sensible heat fluxes during daytime, which often continued to be positive albeit smaller even after sunset. The momentum roughness length and the scalar roughness for sensible heat of the vegetated surfaces showed good correlation with vegetation growth, in general. However, the relation between the scalar roughness and vegetation growth was found to vary among the different sites. A comparison by means of model simulations has shown that this difference was probably caused not only by the difference of the LAI range of each site, but also by the difference of the roughness of the underlying soil surfaces. As expected, the apparent scalar roughness for latent heat depended not only on vegetation growth, but also on soil water availability.