The Internal Boundary Layer (IBL) developing downwind of a change in surface roughness in neutrally stratified surface boundary layer flow is quite well represented by the Panofsky-Dutton formula. An additional factor influencing the growth of an IBL is the vertical velocity associated with convergence or divergence caused by the roughness change. This can be introduced into "diffusion analogy" analysis. Continuity constraints in 2D then allow us to estimate a "characteristic value" of the vertical velocity in the local advection region.

A published set of wind-tunnel and atmospheric data has been used to investigate the influence of the roughness change on IBL height. An extension of the approach to non-neutral IBL heights and to evaporation from small lakes calculations was carried out. Numerical model calculations have been used to validate proposed assumptions.