The flow characteristics over inhomogeneous terrain differ significantly from those over homogeneous terrain. Changes in roughness and topographical features significantly affect the Prandtl layer, leading to notable changes in velocity profiles and turbulence parameters. Meteorological data show that complex topographies lead to greater standard deviations in wind direction and increased ratios of turbulence intensities to shear stress velocity. As terrain complexity increases, spectral densities shift to lower frequencies, with the maxima also moving toward lower dimensionless frequencies.
Wind load standards such as EN 1991-1-4:2005 primarily consider simple inhomogeneities, such as transitions between roughness categories in flat terrain or flows over isolated topographical features. These are addressed using topographical factors in relation to the velocity profile for flat terrain, distinguishing between windward and leeward areas. For slightly inhomogeneous terrain, these approaches can be modified to account for specific conditions. Additional literature, such as the works by Cook, provides ratios of local wind speeds to approach wind speed for various topographical scenarios.