The development and validation of the Inhomogeneous Wind Scheme for Urban Street (IWSUS-v1)

The layout of urban buildings shows significantheterogeneity, which leads to the significant spatial inhomogeneity of thewind field in and over the canopy of urban street canyons. However, most ofthe current urban canopy models do not fully consider the heterogeneity ofthe urban canopy. Large discrepancies thus exist between the wind speedssimulated by the current urban canopy models and those observed in thestreet canyon. In this study, a parameterization scheme for wind fields,Inhomogeneous Wind Scheme for Urban Street (IWSUS), is developed to bettercharacterize the heterogeneity of the urban canopy. We use a computationalfluid dynamics method to generate the IWSUS scheme and compare it withobservations of the wind profile and turbulent flux in and over the streetcanyon for validation. In IWSUS, the wind speed vertical profiles at sixrepresentative positions located in a typical street canyon (i.e., thewindward or leeward side of a long straight street or the inflow or outflowend) are parameterized separately. The wind profile by IWSUS thus can betterdescribe the horizontal heterogeneity of the urban near-surface wind field,e.g., the dynamic drag effect of buildings in the lower atmospheric layer overthe urbanized land use. The validation based on observations shows that theperformance of simulation results by IWSUS is better than that bythe exponential-logarithmic (exp-log) law widely used in the current urbanschemes. We consider typical building arrangement and specific streetorientations in IWSUS for wind field simulations, which can better match thedistribution characteristics of street canyons around the observation pointin the street canyon. The averaged wind profiles and turbulence energyfluxes in the model grids of urban areas by IWSUS are also nearer to theobservations than those by the exp-log law. The normalized mean errors (NMEs)between the simulated and the observed vertical average wind speed are49.0 % for IWSUS and 56.1 % for exp-log law in the range from the groundto 4 times the average height of the buildings and 70 % for IWSUS and285.8 % for exp-log law in the street canyon (range from the ground tobuilding top). This study proves that the accuracy of simulations of land surface processes and near-ground meteorological processes over the urban canopy can be improved by fully considering the heterogeneity of the urban canopy layout structures and the inhomogeneity of wind field distributions in andover the street canyon. IWSUS is expected to be coupled with mesoscaleatmospheric models to improve the accuracy of the wind field, land surfaceenergy budget, meteorological and atmospheric chemistry simulations.