A height scale for turbulent flow above an inhomogeneous surface, at which the influences of individual surface patches on vertical profiles or fluxes become horizontally blended. Below this height scale it is not permissible to treat the structure of turbulence as horizontally uniform. Some authors distinguish between 1) the physical blending height, where local perturbations become negligible due to turbulent mixing, and 2) the numerical blending height in numerical models, above which the horizontal average of locally variable profiles (e.g., wind speed) corresponds to a similarity profile. Both of these height scales are related to the length scale of horizontal surface variations and, typically, the physical blending height is an order of magnitude higher than the numerical blending height. See effective roughness length, flux aggregation.