Further Development of the Vegetated Urban Canopy Model Including a Grass-Covered Surface Parametrization and Photosynthesis Effects |
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Authors: | Sang-Hyun Lee |
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Institution: | 1.School of Earth and Environmental Sciences,Seoul National University,Seoul,South Korea;2.Cooperative Institute for Research in Environmental Sciences,University of Colorado,Boulder,USA;3.NOAA Earth System Research Laboratory,Boulder,USA |
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Abstract: | The vegetated urban canopy model (VUCM), which includes parametrizations of urban physical processes for artificial surfaces
and vegetated areas in an integrated system, has been further developed by including physical processes associated with grass-covered
surfaces in urban pervious surfaces and the photosynthesis effects of urban vegetation. Using measurements made from three
urban/suburban sites during the BUBBLE field campaign in 2002, the model’s performance in modelling surface fluxes (momentum
flux, net radiation, sensible and latent heat fluxes and storage heat flux) and canopy air conditions (canopy air temperature
and specific humidity) was critically evaluated for the non-precipitation and the precipitation days. The observed surface
fluxes at the urban/suburban sites were significantly altered by precipitation as well as urban vegetation. Especially, the
storage heat at urban surfaces and underlying substrates varied drastically depending on weather conditions while having an
important role in the formation of a nocturnal urban surface layer. Unlike the nighttime canopy air temperature that was largely
affected by the storage-heat release, the daytime canopy air conditions were highly influenced by the vertical turbulent exchange
with the overlying atmosphere. The VUCM well reproduced these observed features in surface fluxes and canopy air conditions
at all sites while performing well for both the non-precipitation and the precipitation days. The newly implemented parametrizations
clearly improved the model’s performance in the simulation of sensible and latent heat fluxes at the sites, more noticeably
at the suburban site where the vegetated area fraction is the largest among the sites. Sensitivity analyses for model input
parameters in VUCM elucidated the relative importance of the morphological, aerodynamic, hydrological and radiative/thermal
properties in modelling urban surface fluxes and canopy air conditions for daytime and nighttime periods. These results suggest
that the VUCM has great potential for urban atmospheric numerical modelling for a range of cities and weather conditions in
addition to having a better physical basis in the representation of urban vegetated areas and associated physical processes. |
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